Patent Publication Number: US-9890101-B2

Title: Methods of producing para-xylene and terephthalic acid

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. application Ser. No. 14/345,216 filed Sep. 14, 2012 (Int&#39;l), now issued as U.S. Pat. No. 9,260,359, which is a national phase patent application of PCT/US2012/055651, filed on Sep. 14, 2012, which claims priority to U.S. Provisional Patent Applications Nos. 61/535,853, filed Sep. 16, 2011, 61/606,824, filed Mar. 5, 2012, 61/611,114, filed Mar. 15, 2012, and 61/651,594, filed May 25, 2012, which are incorporated herein by reference in their entireties. 
    
    
     FIELD 
     The present disclosure relates generally to the production of para-xylene and terephthalic acid, and more specifically to the production of para-xylene and terephthalic acid from renewable biomass resources (e.g., cellulose, hemicellulose) and ethylene. 
     BACKGROUND 
     There exists a high demand to produce para-xylene and terephthalic acid from renewable biomass resources for use in the manufacture of clothing and plastics. Terephthalic acid is a precursor of polyethylene terephthalate (PET), which may be used to manufacture polyester fabrics. Terephthalic acid may be produced by oxidation of para-xylene. Commercial production of para-xylene is typically accomplished by catalytic reforming of petroleum derivatives; however, the use of petroleum-based feedstocks to commercially produce para-xylene (and hence terephthalic acid) generates greenhouse gas emissions and perpetuates reliance on petroleum resources. Alternative methods to produce para-xylene from renewable biomass resources have been under investigation. Biomass containing cellulose and/or hemicellulose can be converted into DMF. Then, DMF may be converted into para-xylene by cycloaddition of ethylene. Specifically, DMF and ethylene may be reacted in the presence of activated carbon to produce para-xylene; however, this reaction produce para-xylene in low yields, making these conditions commercially impracticable. Thus, what is needed in the art is a method to produce para-xylene and terephthalic acid in higher yields. 
     BRIEF SUMMARY 
     The present disclosure addresses this need by providing methods to produce para-xylene from 2,5-dimethylfuran (DMF) in higher yields than what is currently known in the art. The methods provided herein use Lewis acids to convert DMF into para-xylene. Without wishing to be bound by any theory, higher yields for producing para-xylene may be achieved by reducing the amount of 2,5-hexanedione formed from DMF or by converting any 2,5-hexanedione formed into para-xylene. The para-xylene produced can be oxidized to produce terephthalic acid. 
     One aspect of the disclosure provides a method A for producing a compound of formula I, wherein formula I has the structure: 
                         
in which each R 1  and R 2  is independently an optionally substituted member chosen from alkyl, cycloalkyl, heterocycloalkyl, carboxyl, aryl, heteroaryl, hydrido, and arylalkyl; in which the method includes: a) providing a compound of formula II, wherein formula II has the structure:
 
                         
b) providing ethylene; and c) combining the compound of formula II and ethylene in the presence of an acid, a desiccant, or an acid and a desiccant to produce a reaction mixture that includes the compound of formula I, wherein less than 10% of the reaction mixture is a compound of formula III, wherein formula III has the structure,
 
     
       
         
         
             
             
         
       
     
     In some embodiments of method A, each R 1  and R 2  is independently an optionally substituted alkyl or carboxyl. In one embodiment, R 1  and R 2  is methyl. In another embodiment, R 1  and R 2  is carboxyl. In yet another embodiment, the compound of formula I is para-xylene, the compound of formula II is 2,5-dimethylfuran (DMF), and the compound of formula III is 2,5-hexanedione. In yet another embodiment, the compound of formula I is terephthalic acid, the compound of formula II is 2,5-furandicarboxylic acid (FDCA), and the compound of formula III is 2,5-dioxohexanedioic acid. 
     In some embodiments that may be combined with any of the preceding embodiments of method A, the method further includes producing one or more plastics or fuels from the compound of formula I. 
     In some embodiments that may be combined with any of the preceding embodiments of method A, the acid is a Lewis acid. In some embodiments of method A, the acid is a Lewis acid that reacts with water. In certain embodiments of method A, the acid is chosen from acetic acid, trichloroacetic acid, trifluoroacetic acid, phosphorus pentoxide, titanium chloride, boron trifluoride, boron trichloride, tin chloride, tin bromide, iron chloride, iron bromide, lanthanum triflate, aluminum triflate, and a combination thereof. In some embodiments that may be combined with any of the preceding embodiments of method A, the desiccant is a Lewis acid. In some embodiments, the desiccant is a Lewis acid that reacts with water. In some embodiments of method A, the desiccant is chosen from acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, hexafluoroacetic anhydride, aluminum trichloride, tin chloride, iron chloride, boron trifluoride, lanthanum trichloride, tantalum chloride, activated alumina, aerogel, bentonite clay, calcium chloride, calcium hydride, calcium sulfate, cobalt chloride, copper sulfate, lithium chloride, lithium hydride, lithium bromide, magnesium sulfate, magnesium perchlorate, molecular sieve, phosphorus pentachloride, phosphorus pentoxide, potassium carbonate, silica gel, sodium chlorate, sodium chloride, sodium sulfate, and sucrose. In certain embodiments, the desiccant is acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, phosphorus pentoxide, calcium chloride, a 4 Å molecular sieve, or silica gel. In one embodiment of method A, the acid acts as a desiccant. 
     In yet other embodiments that may be combined with the preceding embodiments of method A, the method further includes adding one or more molecular sieves to the reaction mixture. In some embodiments of method A, the one or more molecular sieves has a pore size of 3 Å to 100 Å. In another embodiment, the one or more molecular sieves has a pore size between 4 Å to 10 Å. In yet another embodiment, the one or more molecular sieves has a pore size of 3 Å to 5 Å. In one embodiment, the one or more molecular sieves has a pore size of 3 Å, 4 Å, or 5 Å. In yet other embodiments, the one or more molecular sieves are two molecular sieves, wherein the two molecular sieves independent have a pore size of 3 Å to 100 Å, 4 Å to 10 Å, or 3 Å to 5 Å. In one embodiment, the first molecular sieve has a pore size of 3 Å to 100 Å, and the second molecular sieve has a pore size of 3 Å to 5 Å. 
     In some embodiments that may be combined with the preceding embodiments of method A, the method further includes heating the reaction mixture to a temperature sufficient to form the compound of formula I. In some embodiments of method A, the reaction mixture is heated to a temperature between 0° C. and 400° C. In other embodiments that may be combined with the preceding embodiments of method A, the method is performed at a pressure sufficient to form the compound of formula I. In some embodiments of method A, the ethylene is provided at a pressure from about 20 barg to about 1000 barg. In other embodiments of method A, the method is performed at a supercritical temperature and a supercritical pressure. In one embodiment of method A, the method is performed at a temperature of about 147-152° C. (i.e., 420-425 K) and a pressure of about 40-60 barg. 
     In other embodiments that may be combined with the preceding embodiments of method A, wherein the compound of formula I is obtained from cellulose, hemicellulose, or a combination thereof 
     Provided is also the use of the compound of formula I produced by method A for the manufacture of a plastic or fuel. 
     One aspect of the disclosure provides a method B for producing para-xylene by: a) providing 2,5-dimethylfuran (DMF); b) providing ethylene; and c) combining the DMF and the ethylene in the presence of an acid, a desiccant, or an acid and a desiccant to produce a reaction mixture comprising para-xylene, wherein less than 10% of the reaction mixture is 2,5-hexanedione. In some embodiments of method B, the method further includes oxidizing the para-xylene to produce terephthalic acid. In some embodiments that may be combined with the preceding embodiments of method B, the method further includes producing one or more plastics or fuels from the para-xylene. 
     In some embodiments that may be combined with any of the preceding embodiments of method B, the acid is a Lewis acid. In some embodiments of method B, the acid is a Lewis acid that reacts with water. In certain embodiments of method B, the acid is chosen from acetic acid, trichloroacetic acid, trifluoroacetic acid, phosphorus pentoxide, titanium chloride, boron trifluoride, boron trichloride, tin chloride, tin bromide, iron chloride, iron bromide, lanthanum triflate, aluminum triflate, and a combination thereof. In some embodiments that may be combined with any of the preceding embodiments of method B, the desiccant is a Lewis acid. In some embodiments, the desiccant is a Lewis acid that reacts with water. In some embodiments of method B, the desiccant is chosen from acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, hexafluoroacetic anhydride, aluminum trichloride, tin chloride, iron chloride, boron trifluoride, lanthanum trichloride, tantalum chloride, activated alumina, aerogel, bentonite clay, calcium chloride, calcium hydride, calcium sulfate, cobalt chloride, copper sulfate, lithium chloride, lithium hydride, lithium bromide, magnesium sulfate, magnesium perchlorate, molecular sieve, phosphorus pentachloride, phosphorus pentoxide, potassium carbonate, silica gel, sodium chlorate, sodium chloride, sodium sulfate, and sucrose. In certain embodiments, the desiccant is acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, phosphorus pentoxide, calcium chloride, a 4 Å molecular sieve, or silica gel. In one embodiment of method B, the acid acts as a desiccant. 
     In yet other embodiments that may be combined with the preceding embodiments of method B, the method further includes adding one or more molecular sieves to the reaction mixture. In some embodiments, the one or more molecular sieves has a pore size of 3 Å to 100 Å. In another embodiment, the one or more molecular sieves has a pore size between 4 Å to 10 Å. In yet another embodiment, the one or more molecular sieves has a pore size of 3 Å to 5 Å. In one embodiment, the one or more molecular sieves has a pore size of 3 Å, 4 Å, or 5 Å. In yet other embodiments, the one or more molecular sieves are two molecular sieves, wherein the two molecular sieves independent have a pore size of 3 Å to 100 Å, 4 Å to 10 Å, or 3 Å to 5 Å. In one embodiment, the first molecular sieve has a pore size of 3 Å to 100 Å, and the second molecular sieve has a pore size of 3 Å to 5 Å. 
     In some embodiments that may be combined with the preceding embodiments of method B, the method further includes heating the reaction mixture to a temperature sufficient to form the para-xylene. In some embodiments of method B, the reaction mixture is heated to a temperature between 0° C. and 400° C. In other embodiments that may be combined with the preceding embodiments of method B, the method is performed at a pressure sufficient to form the para-xylene. In some embodiments of method B, the ethylene is provided at a pressure from about 20 barg to about 1000 barg. In other embodiments of method B, the method is performed at a supercritical temperature and a supercritical pressure. In one embodiment of method B, the method is performed at a temperature of about 147-152° C. (i.e., 420-425 K) and a pressure of about 40-60 barg. 
     In other embodiments that may be combined with the preceding embodiments of method B, wherein the DMF is obtained from cellulose, hemicellulose, or a combination thereof 
     Provided is also the use of the para-xylene produced by method B for the manufacture of a plastic or a fuel. 
     Another aspect of the disclosure provides a method C for producing terephthalic acid by: a) providing 2,5-furandicarboxylic acid (FDCA); b) providing ethylene; and c) combining the FDCA and ethylene in the presence of an acid, a desiccant, or an acid and a desiccant to produce a reaction mixture comprising terephthalic acid. In some embodiments of method C, less than 10% of the reaction mixture is one or more byproducts of FDCA. In some embodiments that may be combined with the preceding embodiments of method C, the method further includes producing one or more plastics or fuels from the terephthalic acid. 
     In some embodiments that may be combined with any of the preceding embodiments of method C, the acid is a Lewis acid. In some embodiments of method C, the acid is a Lewis acid that reacts with water. In certain embodiments, the acid is chosen from acetic acid, trichloroacetic acid, trifluoroacetic acid, phosphorus pentoxide, titanium chloride, boron trifluoride, boron trichloride, tin chloride, tin bromide, iron chloride, iron bromide, lanthanum triflate, aluminum triflate, and a combination thereof. In some embodiments that may be combined with any of the preceding embodiments of method C, the desiccant is a Lewis acid. In some embodiments, the desiccant is a Lewis acid that reacts with water. In some embodiments of method C, the desiccant is chosen from acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, hexafluoroacetic anhydride, aluminum trichloride, tin chloride, iron chloride, boron trifluoride, lanthanum trichloride, tantalum chloride, activated alumina, aerogel, bentonite clay, calcium chloride, calcium hydride, calcium sulfate, cobalt chloride, copper sulfate, lithium chloride, lithium hydride, lithium bromide, magnesium sulfate, magnesium perchlorate, molecular sieve, phosphorus pentachloride, phosphorus pentoxide, potassium carbonate, silica gel, sodium chlorate, sodium chloride, sodium sulfate, and sucrose. In certain embodiments, the desiccant is acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, phosphorus pentoxide, calcium chloride, a 4 Å molecular sieve, or silica gel. In one embodiment of method C, the acid acts as a desiccant. 
     In yet other embodiments that may be combined with the preceding embodiments of method C, the method further includes adding one or more molecular sieves to the reaction mixture. In some embodiments, the one or more molecular sieves has a pore size of 3 Å to 100 Å. In another embodiment, the one or more molecular sieves has a pore size between 4 Å to 10 Å. In yet another embodiment, the one or more molecular sieves has a pore size of 3 Å to 5 Å. In one embodiment, the one or more molecular sieves has a pore size of 3 Å, 4 Å, or 5 Å. In yet other embodiments, the one or more molecular sieves are two molecular sieves, wherein the two molecular sieves independent have a pore size of 3 Å to 100 Å, 4 Å to 10 Å, or 3 Å to 5 Å. In one embodiment, the first molecular sieve has a pore size of 3 Å to 100 Å, and the second molecular sieve has a pore size of 3 Å to 5 Å. 
     In some embodiments that may be combined with the preceding embodiments of method C, the method further includes heating the reaction mixture to a temperature sufficient to form the terephthalic acid. In some embodiments of method C, the reaction mixture is heated to a temperature between 0° C. and 400° C. In other embodiments that may be combined with the preceding embodiments of method C, the method is performed at a pressure sufficient to form the terephthalic acid. In some embodiments of method C, the ethylene is provided at a pressure from about 20 barg to about 1000 barg. In other embodiments of method C, the method is performed at a supercritical temperature and a supercritical pressure. In one embodiment of method C, the method is performed at a temperature of about 147-152° C. (i.e., 420-425 K) and a pressure of about 40-60 barg. 
     In other embodiments that may be combined with the preceding embodiments of method C, wherein the FDCA is obtained from cellulose, hemicellulose, or a combination thereof 
     Provided is also the use of the terephthalic acid produced by method C for the manufacture of a plastic or fuel. 
     Yet another aspect of the disclosure provides a method D for producing terephthalic acid by: a) producing para-xylene according to the method described herein; and b) oxidizing the para-xylene to produce terephthalic acid. In some embodiments of method D, the method further includes producing one or more plastics or fuels from the terephthalic acid. 
     Provided is also the use of the terephthalic acid produced by method D for the manufacture of a plastic or fuel. 
     Yet another aspect of the disclosure provides a method E for producing para-xylene by reacting 2,5-dimethylfuran and ethylene, in a suitable solvent such that the concentration of the 2,5-dimethylfuran is from about 1 to about 75% by weight in the suitable solvent, with a catalyst selected from the group consisting of Lewis acids such as aluminum chloride, zinc chloride, indium chloride, divalent transition metal ions of copper, nickel or cobalt or mixtures thereof, triflates such as the triflate of indium, copper, gadolinium, yttrium, and trivalent metal ions from the lanthanide series of elements, H—Y zeolite, copper on mordenite, mordenites, activated carbon, and molecular sieves, at a temperature greater than 150° C., at a pressure greater than 100 psig, and with a desiccant. 
     In some embodiments of method E, the suitable solvent is tetrahydrofuran, dimethylsulfoxide, dioxane, C 1  to C 10  alcohol, C 2  to C 6  ketone, C 2  to C 10  ester, C 2  to C 10  ether, chlorinated solvent, ethyl acetate, ethyl lactate, triacetin, dibutylphthalate, C 1  to C 10  aliphatic hydrocarbon solvent, or C 6  to C 12  aromatic hydrocarbon solvent. In one embodiment of method E, the suitable solvent is dioxane. In some embodiments that may be combined with the preceding embodiments of method E, the concentration of the 2,5-dimethylfuran is from about 3 to about 50% by weight in the suitable solvent. 
     In some embodiments that may be combined with the preceding embodiments of method E, the catalyst is aluminum chloride, copper triflate, indium triflate or gadolinium triflate. In other embodiments that may be combined with the preceding embodiments of method E, the desiccant is calcium sulfate, magnesium sulfate, molecular sieves, metal chloride or anhydride. 
     In some embodiments that may be combined with the preceding embodiments of method E, the 2,5-dimethylfuran is recovered and recycled in the reaction. In other embodiments that may be combined with the preceding embodiments of method E, upon completion of the reaction, the reaction mixture is filtered. In yet other embodiments that may be combined with the preceding embodiments of method E, the para-xylene is isolated from the reaction mixture by distillation. In yet other embodiments that may be combined with the preceding embodiments of method E, the yield of para-xylene is greater than 75% by weight after isolation. In yet other embodiments that may be combined with the preceding embodiments of method E, the temperature is from about 150° C. to about 300° C. 
     Provided is also the use of the para-xylene produced by method E for the manufacture of a plastic or fuel. 
     Yet another aspect of the disclosure provides a method F for producing para-xylene by reacting 2,5-dimethylfuran and ethylene, in a suitable solvent such that the concentration of the 2,5-dimethylfuran is from about 1 to about 75% by weight in the suitable solvent, with a catalyst selected from Lewis acids such as aluminum chloride, zinc chloride, indium chloride, divalent transition metal ions of copper, nickel or cobalt or mixtures thereof, triflates such as the triflate of indium, copper, gadolinium or yttrium, trivalent metal ions from the lanthanide series of elements, H—Y zeolite, copper on mordenite, mordenites, activated carbon, and molecular sieves, at a temperature greater than 150° C., at a pressure greater than 100 psig, and with a desiccant. 
     In some embodiments of method F, the suitable solvent is tetrahydrofuran, dimethylsulfoxide, dioxane, C 1  to C 10  alcohol, C 2  to C 6  ketone, C 2  to C 10  ester, C 2  to C 10  ether, chlorinated solvent, ethyl acetate, ethyl lactate, triacetin, dibutylphthalate, C 1  to C 10  aliphatic hydrocarbon solvent, or C 6  to C 12  aromatic hydrocarbon solvent. In one embodiment of method F, the suitable solvent is dioxane. In some embodiments that may be combined with the preceding embodiments of method F, the concentration of the 2,5-dimethylfuran is from about 3 to about 50% by weight in the suitable solvent. 
     In some embodiments that may be combined with the preceding embodiments of method F, the catalyst is aluminum chloride, copper triflate, indium triflate or gadolinium triflate. In other embodiments that may be combined with the preceding embodiments of method F, the desiccant is calcium sulfate, magnesium sulfate, molecular sieves, metal chloride or anhydride. 
     In some embodiments that may be combined with the preceding embodiments of method F, the 2,5-dimethylfuran is recovered and recycled in the reaction. In other embodiments that may be combined with the preceding embodiments of method F, upon completion of the reaction, the reaction mixture is filtered. In yet other embodiments that may be combined with the preceding embodiments of method F, the para-xylene is isolated from the reaction mixture by distillation. In yet other embodiments that may be combined with the preceding embodiments of method F, the yield of para-xylene is greater than 75% by weight after isolation. In yet other embodiments that may be combined with the preceding embodiments of method F, the catalyst is recovered and recycled in the reaction. In yet other embodiments that may be combined with the preceding embodiments of method F, the temperature is from about 150° C. to about 300° C. 
     Provided is also the use of the para-xylene produced by method F for the manufacture of a plastic or fuel. 
     Yet another aspect of the disclosure provides a method G for producing para-xylene by: reacting 2,5-dimethylfuran and ethylene, in a suitable solvent such that the concentration of the 2,5-dimethylfuran is from about 1 to about 75% by weight in the suitable solvent, with a metal containing catalyst selected from the group consisting essentially of Lewis acids, at a temperature greater than about 150° C., at a pressure greater than about 100 psig, and wherein the yield of para-xylene is greater than about 75% by weight. The Lewis acids may include aluminum chloride, zinc chloride, indium chloride, divalent transition metal ions of copper, nickel or cobalt or mixtures thereof such as CuCl 2  or CoCl 2 , triflates such as the triflate of indium, copper, gadolinium or yttrium, trivalent metal ions from the lanthanide series of elements or mixtures thereof, wherein the metal catalyst is used alone or supported, such as on silica, alumina, mordenite, carbon, or other known supports. 
     In some embodiments of method G, the suitable solvent is tetrahydrofuran, dimethylsulfoxide, dioxane, C 1  to C 10  alcohol, C 2  to C 6  ketone, C 2  to C 10  ester, C 2  to C 10  ether, chlorinated solvent, ethyl acetate, ethyl lactate, triacetin, dibutylphthalate, C 1  to C 10  aliphatic hydrocarbon solvent, or C 6  to C 12  aromatic hydrocarbon solvent. In one embodiment of method G, the suitable solvent is dioxane. In certain embodiments that may be combined with the preceding embodiments of method G, the concentration of the 2,5-dimethylfuran is from about 3 to about 50% by weight in the suitable solvent. 
     In other embodiments that may be combined with the preceding embodiments of method G, the catalyst is aluminum chloride, copper triflate, indium triflate or gadolinium triflate. In yet other embodiments that may be combined with the preceding embodiments of method G, a desiccant is present. In one embodiment, the desiccant is calcium sulfate, magnesium sulfate, molecular sieves, metal chloride or anhydride. 
     In some embodiments that may be combined with the preceding embodiments of method G, the 2,5-dimethylfuran is recovered and recycled in the reaction. In other embodiments that may be combined with the preceding embodiments of method G, upon completion of the reaction, the reaction mixture is filtered. In yet other embodiments that may be combined with the preceding embodiments of method G, the para-xylene is isolated from the reaction mixture by distillation. In yet other embodiments that may be combined with the preceding embodiments of method G, the catalyst is recovered and recycled in the reaction. In certain embodiments that may be combined with the preceding embodiments of method G, the temperature is from about 200° C. to about 400° C. In yet other embodiments that may be combined with the preceding embodiments of method G, the yield of para-xylene is greater than about 85% by weight as shown either after isolation or by NMR analysis prior to isolation. 
     Provided is also the use of the para-xylene by method G for the manufacture of a plastic or fuel. 
     Yet another aspect of the disclosure provides a method H for producing para-xylene by: a) providing 2,5-dimethylfuran (DMF); b) providing ethylene; c) providing a Lewis acid; d) providing a solvent; e) combining the DMF, the ethylene, the Lewis acid, and the solvent to form a reaction mixture; and f) producing para-xylene from at least a portion of the DMF in the reaction mixture. In some embodiments of method H, the method further includes isolating the para-xylene from the reaction mixture. 
     In some embodiments of method H, the solvent is an aprotic solvent. In one embodiment, the aprotic solvent has a dipole moment above 0.1. In certain embodiments of the method H, the solvent is an ether. In one embodiment of method H, the solvent is selected from the group consisting of dioxane, glyme, diglyme, triglyme, and tetrahydrofuran. In a particular embodiment, the solvent is 1,4-dioxane. 
     In some embodiments that may be combined with the preceding embodiments of method H, the Lewis acid has a metal cation. In certain embodiments of method H, the Lewis acid may have a Group 3 metal cation, a Group 9 metal cation, a Group 10 metal cation, a Group 11 metal cation, or a metal cation from the lanthanide series. In other embodiments of method H, the Lewis acid has a divalent metal cation or a trivalent metal cation. The divalent metal cation may, for example, be selected from Zn 2+ , Cu 2+ , Ni 2+ , and Co 2+ . The trivalent metal cation may, for example, be selected from Al 3+ , In 3+ , Fe 3+ , La 3+ , Gd 3+ , and Y 3+ . In other embodiments of method H, the Lewis acid is water-stable. In certain embodiments of method H, the Lewis acid is selected from AlCl 3 , Bi(OTf) 3 , CuCl 2 , Cu(OTf) 2 , CoCl 2 , CrCl 3 , Fe(OTf) 2 , Gd(OTf) 3 , InCl 3 , In(OTf) 3 , NiCl 2 , Ni(OTf) 2 , MnCl 2 , SnCl 2 , TiCl 4 , VCl 2 , Y(OTf) 3 , acetic acid, chloroacetic acid, and P 2 O 5 . In one embodiment, the Lewis acid CuCl 2  or Cu(OTf) 2 . In another embodiment, the Lewis acid is Y(OTf) 3 . 
     In some embodiments that may be combined with the preceding embodiments of method H, less than 10% of the reaction mixture is 2,5-hexanedione. In other embodiments of method H, at least a portion of the DMF is converted to para-xylene at a temperature of at least 150° C. In one embodiment of method H, at least a portion of the DMF is converted to para-xylene at a temperature of between 150° C. and 300° C. 
     In other embodiments that may be combined with the preceding embodiments of method H, the method further includes adding one or more molecular sieves to the reaction mixture. In one embodiment, the one or more molecular sieves has a pore size of 3 Å to 100 Å. 
     In some embodiments, the method for producing para-xylene, includes: a) providing 2,5-dimethylfuran (DMF); b) providing ethylene; c) providing a water-stable Lewis acid; d) providing a solvent; e) combining the DMF, the ethylene, the water-stable Lewis acid, and the solvent to form a reaction mixture; and f) producing para-xylene from at least a portion of the DMF in the reaction mixture. 
     In other embodiments, the method for producing para-xylene, includes: a) providing 2,5-dimethylfuran (DMF); b) providing ethylene; c) providing a Lewis acid; d) providing a solvent, wherein the solvent is an ether; e) combining the DMF, the ethylene, the Lewis acid, and the solvent to form a reaction mixture; and f) producing para-xylene from at least a portion of the DMF in the reaction mixture. 
     Provided is also the use of the para-xylene produced by method H for the manufacture of a plastic or a fuel. 
     Yet another aspect of the disclosure provides a method I for producing para-xylene, by: a) providing 2,5-dimethylfuran (DMF); b) providing ethylene; c) providing a Lewis acid, wherein the Lewis acid is selected from the group consisting of acetic acid, AlCl 3 , CuCl 2 , Cu(OTf) 2 , GdCl 3 , Gd(OTf) 3 , InCl 3 , In(OTf) 3 , YCl 3 , and Y(OTf) 3 ; d) combining the DMF, the ethylene, and the Lewis acid to form a reaction mixture; and e) producing para-xylene from at least a portion of the DMF in the reaction mixture. In certain embodiments of method H, the Lewis acid is CuCl 2 , Cu(OTf) 2 , or Y(OTf) 3 . 
     Provided is also the use of the para-xylene produced by method I for the manufacture of a plastic or a fuel. 
     Provided is also a method for producing terephthalic acid, by: a) producing para-xylene according to any of the methods described above; and b) oxidizing the para-xylene to produce terephthalic acid. 
     Yet another aspect of the disclosure provides a method J for producing a compound of formula I, wherein formula I has the structure: 
                         
wherein each R 1  and R 2  is independently hydrogen or alkyl, and wherein the method includes:
 
     a) providing a compound of formula II, wherein formula II has the structure: 
     
       
         
         
             
             
         
       
     
     b) providing ethylene; 
     c) providing a Lewis acid; 
     d) combining the compound of formula II, the ethylene and the Lewis acid to form a reaction mixture; and 
     e) producing a compound of formula I from at least a portion of the compound of formula II in the reaction mixture. 
     In some embodiments of method J, the method further includes providing a solvent and combining the compound of formula II, the ethylene, the Lewis acid and the solvent to form a reaction mixture. 
     In some embodiment of method J, each R 1  and R 2  is independently hydrogen or a C 1-10  alkyl. In one embodiment, R 1  and R 2  are each methyl. In another embodiment of method J, R 1  is H and R 2  is methyl. 
     In some embodiments that may be combined with the preceding embodiments of method J, the solvent is an ether. In certain embodiments, the solvent is a C 1-10  ether. In other embodiments, the solvent may be selected from dioxane, tetrahydrofuran, triglyme, and sulfolane. In one embodiment of method J, the solvent is 14-dioxane. 
     In some embodiments that may be combined with the preceding embodiments of method J, the Lewis acid has a transition metal cation. In other embodiments of method J, the Lewis acid is water-stable. In certain embodiments of method J, the Lewis acid is selected from AlCl 3 , Bi(OTf) 3 , CuCl 2 , Cu(OTf) 2 , CoCl 2 , CrCl 3 , Fe(OTf) 2 , Gd(OTf) 3 , InCl 3 , In(OTf) 3 , NiCl 2 , Ni(OTf) 2 , MnCl 2 , SnCl 2 , TiCl 4 , VCl 2 , Y(OTf) 3 , acetic acid, chloroacetic acid, and P 2 O 5 . In one embodiment of method J, the Lewis acid is CuCl 2  or Cu(OTf) 2 . In another embodiment of method J, the Lewis acid is Y(OTf) 3 . 
     In some embodiments that may be combined with the preceding embodiments of method J, at least a portion of the DMF is converted to para-xylene at a temperature of at least 150° C. In other embodiments that may be combined with the preceding embodiments of method J, the method further includes adding one or more molecular sieves to the reaction mixture. 
     In some embodiments that may be combined with the preceding embodiments of method J, less than 10% of the reaction mixture is a compound of formula III, wherein formula III has the structure, 
                         
wherein R 1  and R 2  are the same as for formula I.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present application can be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals: 
         FIG. 1  depicts an exemplary reaction to produce a compound of formula I by cycloaddition of ethylene to a compound of formula II; 
         FIG. 2  depicts an exemplary side reaction, in which a compound of formula I decomposes in the presence of water to form a compound of formula III; and 
         FIG. 3  depicts exemplary reaction pathways to produce DMF and FDCA from cellulosic materials. 
     
    
    
     DETAILED DESCRIPTION 
     The following description sets forth numerous exemplary configurations, methods, parameters, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure, but is instead provided as a description of exemplary embodiments. 
     The following description relates to methods of producing commodity chemicals, such as para-xylene and terephthalic acid. For example, the methods described herein can produce para-xylene from 2,5-dimethylfuran (DMF) via a Diels-Alder reaction using ethylene as the dienophile. The ethylene used in the Diels-Alder reaction is unsubstituted. In some embodiments, para-xylene can be produced by: a) providing 2,5-dimethylfuran (DMF) and ethylene; b) combining the DMF and the ethylene in the presence of a Lewis acid and optionally a solvent to form a reaction mixture; and c) converting at least a portion of the DMF to para-xylene in the reaction mixture. Under certain conditions, the methods described herein may reduce the amount of byproducts formed from side reactions (e.g., decomposition of starting materials) and improve the yield of para-xylene produced from DMF. 
     With reference to  FIG. 1 , reaction 100 is an exemplary embodiment for producing a compound of formula I (compound 110), which has the structure: 
                         
in which each R 1  and R 2  is independently hydrogen or alkyl. R 1  and R 2  may be the same or different substituents. For example, in one embodiment, R 1  and R 2  are both methyl. In another embodiment, R 1  is methyl, whereas R 2  is hydrogen. In yet another embodiment, R 1  is methyl, whereas R 2  is ethyl. In certain embodiments, at least one of R 1  and R 2  is other than hydrogen.
 
     As used herein, “alkyl” encompasses straight chain and branched chain. Examples include methyl, ethyl, propyl, isopropyl, and butyl. The total number of carbon atoms in each such group is sometimes described herein, e.g., when the group can contain up to ten carbon atoms it can be represented as 1-10C or as C1-C10, C1-10 or C 1-10 . 
     For example, when R 1  and R 2  are both methyl, the compound of formula I is para-xylene (or “p-xylene” or “PX”), which has the structure: 
     
       
         
         
             
             
         
       
     
     When R 1  is methyl and R 2  is hydrogen, the compound of formula I is toluene, which has the structure: 
     
       
         
         
             
             
         
       
     
     With reference again to  FIG. 1 , the method described herein employs various components, including a compound of formula II (compound 102), ethylene 104, an acid 106 and/or a desiccant, and optionally one or more solid catalysts (e.g., molecular sieves). 
     The compound of formula II has the structure: 
                         
in which R 1  and R 2  are the same as in the compound of formula I.
 
     When R 1  and R 2  are both methyl, the compound of formula II is 2,5-dimethylfuran (DMF), which has the structure: 
     
       
         
         
             
             
         
       
     
     When R 1  is methyl and R 2  is hydrogen, the compound of formula II is 2-methylfuran, which has the structure: 
     
       
         
         
             
             
         
       
     
     When the compound of formula I is para-xylene, the compound of formula II is 2,5-dimethylfuran (DMF). When the compound of formula I is toluene, the compound of formula II is 2-methylfuran. The compound of formula I may be obtained from carbonaceous materials. One of skill in the art would know suitable methods to obtain DMF and 2-methylfuran from biomass. For example, with reference to  FIG. 3 , cellulose (and hemicellulose, if present) or other C 6  sugars (e.g., glucose, fructose) may be converted into halomethylfurfurals, such as 5-chloromethylfurfural (CMF), which may be converted into DMF either directly or via 5-hydroxymethylfurfural (HMF). It is also well known in the art that 2-methylfuran can be obtained from hemicellulose or other C 5  sugars (e.g., xylose), which can be converted to furfural and then reduced to 2-methylfuran. Examples of suitable carbonaceous materials from which the compound of formula I, such as DMF and 2-methylfuran, can be derived include agricultural materials (e.g., corn stover, rice hulls, peanut hulls, spent grains), processing waste (e.g., paper sludge), recycled cellulosic materials (e.g., cardboard, old corrugated containers (OCC), mixed paper, old newspaper (ONP)), as well as fructose (e.g., high fructose corn syrup), sucrose or glucose. 
     With reference to  FIG. 2 , certain embodiments are directed to the production of para-xylene by reacting DMF with ethylene under cycloaddition reaction conditions in the presence of an acid, a desiccant, or an acid and a desiccant to reduce the formation of a compound of formula III (compound 202), which has the structure: 
                         
in which R 1  and R 2  are the same as in the compound of formula I.
 
     In one embodiment, when the compound of formula I is para-xylene, the compound of formula III is 2,5-hexanedione: 
     
       
         
         
             
             
         
       
     
     In another embodiment, when the compound of formula I is toluene, the compound of formula III is 4-oxopentanal: 
     
       
         
         
             
             
         
       
     
     The methods described herein to convert a compound of formula II into a compound of formula I employ various catalysts, solvents, desiccants, and reaction conditions, each of which are described in further detail below. 
     Acid 
     With reference again to  FIG. 1 , in an exemplary embodiment, acid 106 is a Lewis acid. Without wishing to be bound by any theory, the acid may be catalyzing the ring opening and subsequent dehydration of the Diels-Alder cycloaddition adduct (intermediate 108). 
     In some embodiments, the Lewis acid may have a metal cation. In certain embodiments, the metal cation is a transition metal cation. For example, the metal cation may be selected from Group 3, Group 9, Group 10, Group 11, or the lanthanide series. In certain embodiments, the metal cation may be selected from Group 3, Group 9, Group 11, or the lanthanide series. It should be understood that the group number used for these metals follow the IUPAC or long-form nomenclature, which is well-known to one of ordinary skill in the art. 
     In other embodiments, the Lewis acid may have a divalent metal cation or a trivalent metal cation. For example, in certain embodiments, the divalent metal cation may be selected from Zn 2+ , Cu 2+ , Ni 2+ , and Co 2+ . In one embodiment, the divalent metal cation may be selected from Zn 2+ , Cu 2+ , and Co 2+ . In certain embodiments, the trivalent metal cation may be selected from Al 3+ , In 3+ , Fe 3+ , La 3+ , Gd 3+ , and Y 3+ . In one embodiment, the trivalent metal cation may be selected from Al 3+ , In 3+ , La 3+ , Gd 3+ , and Y 3± . The divalent or trivalent metal cation of the Lewis acid may coordinate two or three counterions, respectively. The counterions may include, for example, halides, triflates (-OTf), or any combination thereof. 
     In some embodiments, the Lewis acid is selected from aluminum chloride, bismuth triflate, copper chloride, copper triflate, cobalt chloride, chromium chloride, iron triflate, gadolinium triflate, indium chloride, indium triflate, nickel chloride, manganese chloride, tin chloride, titanium chloride, vanadium chloride, yttrium triflate, zinc chloride, acetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, fluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, and phosphorus pentoxide. In certain embodiments, the Lewis acid is selected from aluminum chloride, copper triflate, copper chloride, and yttrium triflate. In one embodiment, the Lewis acid is copper triflate or copper chloride. In other embodiments, the Lewis acid is acetic acid, chloroacetic acid, or phosphorus pentoxide. 
     In some embodiments, the Lewis acid is selected from AlCl 3 , acetic acid, chloroacetic acid, BiCl 3 , Bi(OTf) 3 , CuCl 2 , Cu(OTf) 2 , Cu(II) on mordenite, CuCl 2 /alumina, CuCl 2 /HY zeolite, CoCl 2 , CO(OTf) 2 , CrCl 3 , Cr(OTf) 3 , FeCl 2 , Fe(OTf) 2 , CdCl 2 , Cd(OTf) 2 , H—Y-Zeolite, InCl 3 , In(OTf) 3 , NiCl 2 , Ni(OTf) 2 , MnCl 2 , Mn(OTf) 2 , P 2 O 5 , SnCl 2 , Sn(OTf) 2 , TiCl 4 , Ti(OTf) 4 , VCl 2 , V(OTf) 2 , YCl 3 , Y(OTf) 3 , ZnCl 2 , Zn(OTf) 2 , GdCl 3 , Gd(OTf) 3 , VCl 5 , V(OTf) 5 . In certain embodiments, the Lewis acid is selected from AlCl 3 , Cu(OTf) 2 , CuCl 2 , and Y(OTf) 3 . In one embodiment, the Lewis acid is Cu(OTf) 2  or CuCl 2 . 
     In some embodiments, the Lewis acid may be used alone or supported, for example, on silica, alumina, mordenite, carbon, zeolites, or other suitable supports known in the art. In certain embodiments, the Lewis acid is Cu (II) on mordenite, CuCl 2 /alumina, or CuCl 2 /HY zeolite. Solid supported acid catalysts can more easily be recovered, recycled, and used in a continuous process. 
     In other embodiments, the Lewis acid is selected from acetic acid, trichloroacetic acid, trifluoroacetic acid, phosphorus pentoxide, titanium chloride (e.g., TiCl 4 ), boron trifluoride (BF 3 ), boron trichloride (BCl 3 ), tin chloride (e.g., SnCl 2 ), tin bromide (e.g., SnBr 2 ), iron chloride (e.g., FeCl 2 ), iron bromide (e.g., FeBr 2 ), and various triflate metals (e.g., lanthanum triflate, and aluminum triflate). 
     In yet other embodiments, the Lewis acid is a water-stable Lewis acid. As used herein, “a water-stable Lewis acid” refers to a Lewis acid that is not deactivated by the presence of water in a given reaction. It should be understood, however, that a particular Lewis acid may show water stability for the purposes of one reaction, but not toward another. Water-stable acid catalysts can improve recyclability of the catalyst used in the reaction on industrial scale, since water can often be produced as a by-product in the reaction. In some embodiments, the water-stable Lewis acid may have a pK h  between 4.3 and 10.08. K h  is the hydrolysis constant. pK h  is defined as follows: 
                 p   ⁢           ⁢     K   h       =       -   log     ⁢           ⁢     K     x   ⁢           ⁢   y           ,     
     ⁢   where                   K   ⁢           ⁢   x   ⁢           ⁢   y     =             [         M   x     ⁡     (   OH   )       y       (       x   ⁢           ⁢   z     -   y     )     +       ]     ⁡     [     H   +     ]       y         [     M     z   +       ]     x       +         g     x   ⁢           ⁢   y       ⁢     g     H   +     y           g     M     z   +       y     ⁢     a       H   2     ⁢   O     y             ,         
based on the following reaction: x M 2+ +y H 2 O M x (OH) y   (xx−y)+ +y H + , where M is the metal cation. In other embodiments, the water-stable Lewis acid may have a water exchange rate constant of at least 3.2×10 6  M −1 s −1 . See generally Kobayashi et al.,  J. Am. Chem. Soc.  1998, 120, 8287-8288.
 
     Examples of water-stable Lewis acids may include those with a metal cation selected from Sc(III), Y(III), Ln(III), Fe(II), Cu(II), Zn(II), Cd(II), Pb(II), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III). In certain embodiments, the Lewis acid may include Fe(II), Cu(II), Zn(II), Cd(II), Pb(II) Sc(III), Y(III), Ln(III), Mn(II), or Ag(I). Water-stable Lewis acids may include, for example, ScCl 3 , Sc(ClO 4 ) 3 , Mn(ClO 4 ) 2 , FeCl 2 , Fe(ClO 4 ) 2 , FeCl 3 , Fe(ClO 4 ) 3 , Co(ClO 4 ) 2 , Ni(ClO 4 ) 2 , CuCl 2 , Cu(ClO 4 ) 2 , ZnCl 2 , Zn(ClO 4 ) 2 , YCl 3 , Y(ClO 4 ) 3 , AgClO 4 , CdCl 2 , Cd(ClO 4 ) 2 , InCl 3 , In(ClO 4 ) 3 , SnCl 2 , La(OTf) 3 , Ce(OTf) 3 , Pr(OTf) 3 , Nd(OTf) 3 , Sm(OTf) 3 , Eu(OTf) 3 , Gd(OTf) 3 , Tb(OTf) 3 , Dy(OTf) 3 , Ho(OTf) 3 , Er(OTf) 3 , Tm(OTf) 3 , YbCl 3 , Yb(ClO 4 ) 3 , Yb(OTf) 3 , Lu(OTf) 3 , PbCl 2 , and Pb(ClO 4 ) 2 . 
     In certain embodiments, the Lewis acid used in the reaction may be obtained from an anhydride that hydrolyzes into its corresponding acid form in the presence of water. For example, in one embodiment, acetic anhydride may be combined with DMF and ethylene, in which the acetic anhydride may contain a small percentage of acetic acid, which acts as a Lewis acid that catalyzes the reaction. Additionally, the acetic anhydride in the reaction mixture may further convert into acetic acid during the course of the reaction. 
     In other embodiments, the acids may also act as a desiccant (“acid desiccants”), and remove at least a portion of the water present in the reaction mixture. In certain embodiments, the acid desiccant may be a Lewis acid that is reactive with water. In one embodiment, the acid desiccant may be phosphorus pentoxide (P 2 O 5 ). Other suitable acid desiccants may include, for example, aluminum trichloride, tin chloride, iron chloride, and boron trifluoride. A combination of acids may be used, as well as a combination of acids, acid desiccants and desiccants (described in further detail below) may be used. 
     It should be understood that a combination of acids described herein may also be used. The amount of acid used in the reaction may also vary depending on the type and amount of starting material, the type and amount of solvent (if present), and the reaction conditions used. In some embodiments, the acid is used in a catalytic amount. For example with respect to the reaction to convert DMF into para-xylene, in some embodiments, the acid is present at a concentration of between 0.5 wt % and 10 wt %, or between 0.5 wt % and 5 wt % of DMF. 
     Molecular Sieves 
     Furthermore, a solid catalyst such as a molecular sieve may optionally be added to the reaction mixture. Suitable molecular sieves may include, for example, aluminosilicate minerals, clays, porous glasses, microporous charcoals, zeolites, and activated carbons. Without wishing to be bound by theory, it is believed that the addition of a molecular sieve with a pore size of 4 Å to 10 Å will both catalyze the Diels-Alder reaction, as well as selectively remove water. In certain embodiments, the solid catalyst added to the reaction mixture has a pore size of 3 Å to 100 Å. Solid catalysts with pore sizes of 3 Å to 100 Å may be useful to catalyze the Diels-Alder reaction. In other embodiments, the solid catalyst added to the reaction mixture has a pore size of 3 Å to 5 Å, or 3 Å to 4 Å. Solid catalysts with pore sizes of 3 Å to 5 Å may be useful to remove water from the reaction. It should also be understood that two or more solid catalysts with different pore sizes may be used. For example, in some embodiments, a first solid catalyst and a second solid catalyst may be used, in which the first solid catalyst has a pore size between 3 Å to 100 Å, and the second solid catalyst has a pore size between 3 Å to 5 Å. 
     Solvent 
     A solvent may also be optionally added to the reaction mixture. In some embodiments, a solvent is added to the reaction mixture. A combination of solvents may also be used. The solvent can help dissolve and dilute the DMF, and lessen the bimolecular reaction of DMF with itself to form a polymer, which can be a side reaction that lowers the yield of para-xylene. 
     The solvent used typically has good solubility for ethylene and DMF, which can help to enhance the solvation effect and improve the reaction rate. Additionally, the solvent used is typically stable to the process conditions, and preferably can be recycled for use again in the reaction. The recyclability of the solvent is particularly useful for performing the methods described herein on a commercial scale. 
     Certain solvents may lead to high product yields under certain reaction conditions. For example, in some embodiments, the solvent is an aprotic solvent. In particular embodiments, the aprotic solvent may have a dipole moment above 0.1. One of skill in the art would understand that the dipole moment is a measure of polarity of a solvent. The dipole moment of a liquid can be measured with a dipole meter. Suitable aprotic solvents may include, for example, dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide, dioxane, polyethers (including, for example, glyme, diglyme, triglyme, etc.), acetonitrile, sulfolane, ethers (including, for example, tetrahydrofuran, diethylether, dialkylether), nitromethane, anisole, nitrobenzene, and bromobenzene. 
     In certain embodiments, the solvent is an ether. For example, the solvent can be a C 2  to C 10  ether, which refers to an ether having 2 to 10 carbon atoms. It should be understood, however, that the ether can be an alkyl ether or a cycloalkyl ether. An alkyl ether may include, for example, diethyl ether, glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), or triethylene glycol dimethyl ether (triglyme). A cycloalkyl ether may include, for example, dioxane (e.g., 1,4-dioxane) and tetrahydrofuran. The ether may, in certain embodiments, be a polyether with two or more oxygen atoms. Suitable polyethers may include, for example, glyme, diglyme, triglyme, or tetraglyme. 
     In other embodiments, the ether solvent may have additional functional groups, such as alcohols. In one embodiment, the solvent is polyethylene glycol. 
     In particular embodiments, the solvent may be selected from dioxane, THF, DMSO, C 1  to C 10  alcohols, diglyme, C 2  to C 10  ethers, C 2  to C 6  ketones, chlorinated solvents, C 2  to C 10  esters, triacetin, dibutylphthalate, C 1  to C 10  aliphatic solvents, and C 6  to C 12  aromatic solvents, and mixtures thereof. C 1  to C 10  alcohols may include, for example, ethanol and propanol. C 2  to C 10  ethers may include, for example, dioxane, diethyl ether, triethylene glycol dimethyl ether (triglyme), and other glycol ethers. Chlorinated solvents may include, for example, carbon tetrachloride, chloroform and methylene chloride. C 2  to C 10  esters may include, for example, ethyl acetate, and ethyl lactate. C 1  to C 10  aliphatic solvents may include, for example, hexane and cyclohexane. C 6  to C 12  aromatic solvents may include, for example, toluene and octane. 
     In certain embodiments, the solvent is selected from dioxane, tetrahydrofuran, sulfolane, and triglyme. In one preferred embodiment, the solvent is 1,4-dioxane. The use of 1,4-dioxane may help with minimizing the self-condensation of DMF. Additionally, DMF and ethylene are soluble in dioxane at room temperature and ambient pressure based on NMR observations of the reaction products. Also dioxane is stable under the reaction conditions specified herein, such that no solvent by-products were observed by NMR. Any of the above indicated solvents which have these same properties as dioxane are suitable and considered to be suitable solvents. 
     The amount of solvent used may vary. For example, in some embodiments, the concentration of the DMF in the reaction mixture is from about 1 to about 75% by weight in the solvent, preferably from about 3 to about 50% by weight in the solvent. 
     Desiccant 
     In some embodiments, the method described herein may optionally include the addition of a desiccant. As discussed above, some of the Lewis acids may be an acid desiccant. In other embodiments, the desiccant described herein may not be a Lewis acid. A combination of desiccants may be used, including a combination of desiccants and acid desiccants. 
     In some embodiments, suitable desiccants that may be added to the reaction mixture include, for example, acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, hexafluoroacetic anhydride, aluminum trichloride, tin chloride, iron chloride, boron trifluoride, activated alumina, aerogel, bentonite clay, calcium chloride, calcium hydride, calcium sulfate, cobalt chloride, copper sulfate, lithium chloride, lithium hydride, lithium bromide, magnesium sulfate, magnesium perchlorate, molecular sieve, phosphorus pentachloride, phosphorus pentoxide, potassium carbonate, silica gel, sodium chlorate, sodium chloride, sodium sulfate, and sucrose. In certain embodiments, the desiccant is acetic anhydride, trichloroacetic anhydride, trifluoroacetic anhydride, phosphorus pentoxide, calcium chloride, a 4 Å molecular sieve, or silica gel. 
     In other embodiments, the desiccant may be selected from calcium sulfate, magnesium sulfate, molecular sieves, metal chlorides and anhydrides. Metal chlorides may include, for example, calcium chloride, barium chloride, or zinc chloride. Anhydrides may include, for example, acetic anhydride, chloroacetic anhydride, or the anhydride of phosphoric acid (P 2 O 5 ). One skilled in the art would recognize that the anhydride may contain a small percentage of hydrolyzed anhydride, which is an acid. For example, less than 1% acetic acid may be present in acetic anhydride that is commercially purchased. Additionally, when anhydrides are used in the methods described herein, the presence of water in the reaction may cause the anhydride to convert into its hydrolyzed form, which is a Lewis acid. 
     Reaction Conditions 
     The reaction of the compound of formula II with ethylene proceeds in the presence of an acid, and optionally a desiccant and/or a solid catalyst, under suitable cycloaddition reaction conditions. The reaction temperature and/or pressure may affect the rate of the reaction, including the amount of the compound of formula I produced in the reaction, as well as the amount of byproducts produced (e.g., 2,5-hexanedione). 
     In some embodiments, the reaction proceeds at a temperature between 0° C. and 400° C., and a pressure between 10 barg to 1000 barg. In certain embodiments, the reaction temperature is between room temperature (e.g., 18° C.-22° C.) and 300° C. 
     In certain embodiments, the reaction temperature is at least 150° C., or at least 200° C. In other embodiments, the reaction temperature is between 100° C. and 300° C., between 150° C. and 400° C., between 150° C. and 300° C., between 125° C. and 175° C., between 200° C. to 350° C., between 200° C. to 250° C., between 200° C. and 400° C., between 220° C. to 230° C., or between 150° C. and 220° C. Higher temperatures can be used so long as the suitable solvent is stable. 
     In certain embodiments, the reaction pressure is between 20 barg to 1000 barg, between 50 barg to 1000 barg, between 100 barg to 1000 barg, between 150 barg to 500 barg, or between 35 and 38 barg. 
     In other embodiments, the reaction pressure may reflect the pressure at which ethylene is added to the reactor. The ethylene may be added at a pressure such that the concentration of this reactant is sufficiently high in the solvent for optimal reaction rates. In some embodiments, the ethylene pressure is at least 10 psig, 50 psig, or 100 psig. 
     It should be understood and clearly conveyed herein that the reaction temperature and reaction pressure may be the same as if each and every combination were individually listed. For example, in one variation, the method is carried out at a temperature of about 225° C. and a pressure of about 34 barg (equivalent to about 500 psig). 
     The method may also be carried out under supercritical conditions (e.g., supercritical pressures and/or supercritical temperatures). For example, in one embodiment, supercritical conditions may be used if a solvent is not used in the reaction. In one embodiment, the method is carried out at or above 49.7 barg and/or at or above 9° C. (i.e., 282 K). It should be understood that temperature may be expressed as degrees Celcius or degrees Kelvin. One of ordinary skill in the art would be able to convert the temperature described herein from one unit to another. Pressure may also be expressed as gauge pressure (barg), which refers to the pressure in bars above ambient or atmospheric pressure. Pressure may also be expressed as bar, atmosphere (atm), pascal (Pa) or pound-force per square inch (psi). One of ordinary skill in the art would be able to convert the pressure described herein from one unit to another. 
     The method may be carried out batch-wise or continuously. The time of the reaction will also vary with the reaction conditions and desired yield, but is generally about 1 to 72 hours. In some of the foregoing embodiments, the reaction time is determined by the rate of conversion of the starting material. In some of the foregoing embodiments, the reaction mixture is heated for 1 to 24 hours. In some of the foregoing embodiments, the reaction mixture is heated for 1 to 10 hours. In some of the foregoing embodiments, the reaction mixture is heated for 1 to 5 hours. In some of the foregoing embodiments, the reaction mixture is heated for 1 to 3 hours. In some of the foregoing embodiments, the reaction mixture is heated for less than 2 hours. 
     Isolation and Purification 
     The methods described herein may further include isolating the compound of formula I from the reaction mixture. Any methods known in the art may be employed to isolate the product. For example, the products may be isolated by distillation. 
     In one exemplary embodiment, to isolate para-xylene from the reaction mixture, the reaction mixture can be first filtered to remove any catalyst and desiccants (if present). The filtered mixture may then be transferred to a distillation column One of skill in the art would know how to recovery para-xylene by distillation since the boiling points of the various components of the reaction mixture are known, including the boiling points of the solvents used (e.g., 1,4-dioxane has a boiling point of 101° C.), para-xylene has a boiling point of 138° C., 2,5-hexanedione has a boiling point of 191° C., and DMF has a boiling point of 94° C. The solvent and DMF recovered can be recycled. The catalysts can be covered and recycled. Byproducts such as 2,5-hexanedione can also be recovered. 
     The methods described herein may also include purifying the isolated compound of formula I. Any suitable methods known in the art may be employed to purify the isolated compound, including for example column chromatography or recrystallization. 
     Yield, Conversion and Selectivity 
     The yield of a product takes into account the conversion of the starting materials into the product, and the selectivity for the product over other byproducts that may be formed. 
     The difference between yield, conversion and selectivity is explained in the example provided below. The exemplary reaction for converting DMF into para-xylene can be generalized as follows, where “A” represents the moles of DMF; “B” represents the mole of ethylene; “C” represents the mole of para-xylene; and “a”, “b”, “c” are stoichiometric coefficients.
 
 aA+bB→cC,  
 
     Conversion is the percentage of reactant A that has been consumed during the reaction shown above, as expressed by the following equation: 
                 %   ⁢           ⁢   Conversion     =           A   ⁢           ⁢   o     -     A   ⁢           ⁢   f         A   ⁢           ⁢   o       *   100   ⁢   %       ,         
where A o  is the initial number of moles of reactant A; and A f  is the final number of moles of reactant A.
 
     Selectivity is the percentage of product C produced from the converted amount of reactant A, as expressed by the following equation: 
                 Selectivity   ⁢           ⁢     (   %   )       =         C   ⁢           ⁢   f   *         a           c               A   ⁢           ⁢   o     -     A   ⁢           ⁢   f         *   100   ⁢   %       ,         
where A o  is the starting moles of reactant A; A f  is the final number of moles of reactant A; and C f  is the number of moles of product C. In some embodiments where “a” and “c”=1, and the equation can be simplified to:
 
     
       
         
           
             
               
                 Selectivity 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   % 
                   ) 
                 
               
               = 
               
                 
                   
                     C 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     f 
                   
                   
                     
                       A 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       o 
                     
                     - 
                     
                       A 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       f 
                     
                   
                 
                 * 
                 100 
                 ⁢ 
                 % 
               
             
             , 
           
         
       
     
     The yield of product C is the percentage of reactant A that is converted into product C, as expressed by the following equation: 
     
       
         
           
             
               Yield 
               ⁢ 
               
                   
               
               ⁢ 
               
                 ( 
                 % 
                 ) 
               
             
             = 
             
               
                 ( 
                 
                   Conversion 
                   * 
                   Selectivity 
                 
                 ) 
               
               100 
             
           
         
       
     
     In certain embodiments, the methods described herein have a yield of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, or 99% by weight. In other embodiments, the yield is between 10% to 90%, 20% to 80%, 30% to 80%, 40% to 80%, 50%-80%, or 60%-80% by weight. 
     In certain embodiments, the methods described herein have a selectivity of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 99%. In other embodiments, the selectivity is between 40% to 99%, 40% to 95%, 40% to 90%, 40% to 80%, 50% to 99%, 50% to 95%, 50% to 90%, 50% to 80%, 60% to 99%, 60% to 95%, 60% to 90%, 60% to 80%, 70% to 99%, 70% to 95%, 70% to 90%, or 70% to 80%. 
     In certain embodiments, with reference to  FIG. 2 , the reaction conditions described herein for producing a compound of formula I (compound 110) reduces the amount of a compound of formula III (compound 202) produced. The amount of byproducts (compound 202) present in the reaction mixture is described relative to the amount of starting materials (compound 102). For example, in one embodiment where a compound of formula I is para-xylene, the reaction conditions described herein reduces the amount of 2,5-hexanedione produced as a byproduct. The amount of 2,5-hexanedione present in the reaction mixture is described relative to DMF used in the reaction. In one embodiment, the reaction mixture has less than 10% of 2,5-hexanedione. In other embodiments, the reaction mixture has less than 5%, 2.5%, 1%, 0.05%, or 0.01% of 2,5-hexanedione. In other embodiments, the reaction mixture has between 1-10%, 1-5%, or 0.01-1% of 2,5-hexanedione. 
     In some embodiments, a compound of formula I is suitable for manufacture of one or more plastics. In other embodiments, a compound of formula I is suitable for manufacture of one or more fuels. In some embodiments where para-xylene is produced, the methods include further oxidizing the para-xylene to produce terephthalic acid. In other embodiments, the terephthalic acid is further processed to manufacture one or more plastics. 
     As used herein, the term “about” refers to an approximation of a stated value within an acceptable range. Preferably, the range is +/−10% of the stated value. 
     EXAMPLES 
     The following Examples are merely illustrative and are not meant to limit any aspects of the present disclosure in any way. 
     Example 1 
     Preparation of Para-Xylene from DMF 
     
       
         
         
             
             
         
       
     
     This example demonstrates the conversion of DMF into para-xylene. Dimethylfuran (DMF, 0.25 mL), and acetic anhydride (0.010 mL) were added to a hastelloy reactor (1 L) under an argon atmosphere. An inert compound, such as tetradecane (0.25 mL), was added to the reaction only to serve as an internal standard to quantify the product produced. The reactor was sealed and charged with ethylene gas (50 barg). The reactor was heated (175° C.) and mechanically stirred for 15 hours. The reactor was cooled to room temperature, and vented into a trap containing dichloromethane (DCM, 250 mL). Dichloromethane (100 mL) was used to extract the remaining organics from the reactor. 
     An aliquot was taken from the DCM trap and from the DCM extraction solution, and analyzed by gas chromatography mass spectrum (GCMS). The following GCMS protocol was used. Initial oven temp: 45° C. for 3 minutes then 15° C./min to 220° C. (14.67 min run time); inlet temperature: 300° C.; column type: HP-5MS 5% phenyl methyl siloxane. A peak at retention time 4.802 was observed, corresponding to para-xylene. A peak at retention time 2.251 was also observed, corresponding to DMF. 
     Example 2 
     Effect of Temperature on Synthesis of Para-Xylene from DMF 
     This example demonstrates the impact of temperature on the synthesis of para-xylene from DMF. Three different catalysts were tested, including AlCl 3 , Cu(OTf) 2  and CuCl 2 , at various temperature between 150° C. and 220° C. 
     For each catalyst and temperature set forth in Table 1 below, the following general procedure was used: 2,5-dimethylfuran (10 g, 0.10 mole), 1,4-dioxane (200 g), 4 Å sieves (2 g), and the catalyst set forth in Table 1 below (1 g) were added into a hastelloy autoclave reactor, which was equipped with a gas impeller. The contents in the reactor were stirred at room temperature. The reactor was charged with ethylene gas until the pressure stabilized to 450 psig. The reactor was heated to the temperature as set forth in Table 1 below, and allowed to react for 24 hours. The reactor was then cooled and depressurized. A sample was taken from the reactor, and the sample was analyzed by  1 H-NMR. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Effect of temperature on the synthesis of para-xylene from DMF 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Temperature 
                   
                 Conversion 
                 Selectivity 
                 HD 
               
               
                 Entry 
                 (° C.) 
                 Catalyst 
                 (%) 
                 (%) 
                 (mol %) 
               
               
                   
               
               
                 1 
                 150 
                 AlCl 3   
                 22 
                 40 
                 2.9 
               
               
                 2 
                 190 
                 AlCl 3   
                 73 
                 79 
                 5.8 
               
               
                 3 
                 220 
                 AlCl 3   
                 98 
                 89 
                 3.5 
               
               
                 4 
                 190 
                 Cu(OTf) 2   
                 68 
                 88 
                 9.1 
               
               
                 5 
                 220 
                 Cu(OTf) 2   
                 99 
                 96 
                 1.8 
               
               
                 6 
                 190 
                 CuCl 2   
                 64 
                 87 
                 4.6 
               
               
                 7 
                 220 
                 CuCl 2   
                 93 
                 92 
                 3.6 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Effect of Catalyst on Synthesis of Para-Xylene from DMF 
     This example demonstrates the impact of the catalyst on the synthesis of para-xylene from DMF. Various different Lewis acid were tested. 
     For each catalyst, temperature, reaction time and pressure of ethylene added set forth in Table 2 below, the following general procedure was used, unless as otherwise noted in Table 2: 2,5-dimethylfuran (10 g, 0.10 mole), 1,4-dioxane (200 g), 4 Å sieves (2 g), and catalyst (1 g) was added into a hastelloy autoclave reactor and was stirred at room temperature. The reactor was charged with ethylene gas until the pressure stabilized to the pressure set forth in Table 2 below. The reactor was heated to the temperature set forth in Table 2 below, and allowed to react for 24 hours. The reactor was then cooled and depressurized. A sample was taken from the reactor, and the sample was analyzed by  1 H-NMR or GC-FID. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Effect of catalyst on the synthesis of para-Xylene from DMF 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Temperature 
                 Reaction 
                 Ethylene 
                 Conversion 
                 Selectivity 
                 HD 
               
               
                 Entry 
                 Acid 
                 (° C.) 
                 time (h) 
                 (psig) 
                 (%) 
                 (%) 
                 (mole %) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 AlCl 3   
                 220 
                 24 
                 490 
                 98 
                 89 
                 3.5 
               
               
                 2 
                 acetic anhydride a, d   
                 225 
                 65 
                 140 
                 42 
                 61 
                 — 
               
               
                 3 
                 acetic acid a   
                 225 
                 65 
                 780 
                 64 
                 60 
                 — 
               
               
                 4 
                 chloroacetic 
                 225 
                 15 
                 140 
                 19 
                 21 
                 — 
               
               
                   
                 anhydride a, d   
                   
                   
                   
                   
                   
                   
               
               
                 5 
                 chloroacetic acid a   
                 225 
                 15 
                 140 
                 9 
                 10 
                 — 
               
               
                 7 
                 CuCl 2   
                 220 
                 24 
                 490 
                 92 
                 92 
                 3.6 
               
               
                 8 
                 Cu(OTf) 2   
                 220 
                 24 
                 490 
                 99 
                 96 
                 1.8 
               
               
                 9 
                 Cu (II)/Mordenite 
                 220 
                 24 
                 490 
                 8 
                 18 
                 6.3 
               
               
                 10 
                 CuCl 2 /Alumina b   
                 250 
                 7 
                 500 
                 52 
                 70 
                 1.3 
               
               
                 11 
                 CuCl 2 /HY Zeolite b   
                 250 
                 7 
                 500 
                 77 
                 82 
                 1.3 
               
               
                 12 
                 CoCl 2   
                 190 
                 24 
                 490 
                 40 
                 76 
                 9.1 
               
               
                 15 
                 Gd(OTf) 3   
                 190 
                 24 
                 490 
                 72 
                 75 
                 2.7 
               
               
                 16 
                 H-Y-Zeolite 
                 190 
                 24 
                 490 
                 56 
                 49 
                 4.6 
               
               
                 17 
                 InCl 3   
                 190 
                 24 
                 490 
                 73 
                 75 
                 1.4 
               
               
                 18 
                 In(OTf) 3   
                 190 
                 24 
                 490 
                 79 
                 80 
                 7.6 
               
               
                 19 
                 NiCl 2   
                 190 
                 24 
                 490 
                 10 
                 56 
                 1 
               
               
                 20 
                 Norit (steam 
                 190 
                 24 
                 490 
                 5 
                 20 
                 1.1 
               
               
                   
                 treated) 
                   
                   
                   
                   
                   
                   
               
               
                 21 
                 Norit (H 3 PO 4  acid 
                 220 
                 24 
                 490 
                 11 
                 73 
                 0.9 
               
               
                   
                 treated) 
                   
                   
                   
                   
                   
                   
               
               
                 23 
                 P 2 O 5   c   
                 225 
                 4 
                 260 
                 100 
                 17 
                 — 
               
               
                 27 
                 Y(OTf) 3   
                 250 
                 7 
                 550 
                 97 
                 91 
                 0 
               
               
                 28 
                 ZnCl 2   
                 190 
                 24 
                 500 
                 26 
                 79 
                 0 
               
               
                 29 
                 control (no acid 
                 225 
                 14 
                 500 
                 18 
                 6 
                 0 
               
               
                   
                 catalyst) 
               
               
                   
               
               
                   a Reaction was performed without a solvent 
               
               
                   b Reaction was performed without 4 Å sieves 
               
               
                   c Reaction was performed with hexane as the solvent 
               
               
                   d Anhydrides were undistilled, and had a small percentage of hydrolyzed anhydride 
               
            
           
         
       
     
     Example 4 
     Effect of Catalyst on Synthesis of Para-Xylene from DMF 
     This example describes experiments testing various additional Lewis acids in the synthesis of para-xylene from DMF. The Lewis acids include Bi(OTf) 3 , CrCl 3 , Fe(OTf) 2 , MnCl 2 , SnCl 2 , TiCl 4 , and VCl 2 . For each of these catalysts, 2,5-dimethylfuran (10 g, 0.10 mole), 1,4-dioxane (200 g), 4 Å sieves (2 g), and catalyst (1 g) are added into a hastelloy autoclave reactor and are stirred at room temperature. The reactor is charged with ethylene gas until the pressure stabilizes to 500 psig. The reactor is heated to 225° C. The reaction is monitored. Once the reaction reaches a threshold conversion percentage, the reactor is cooled and depressurized. A sample is taken from the reactor, and is analyzed by  1 H-NMR or GC-FID. 
     Example 5 
     Effect of Solvent on Synthesis of Para-Xylene from DMF 
     This example demonstrates the impact of the solvent on the synthesis of para-xylene from DMF. Five different solvents were tested. 
     For solvents #1-4 in Table 3 below, the following general procedure was used: 2,5-dimethylfuran (10 g, 0.10 mole), solvent (200 g), and yttrium triflate (0.5 g) were added into a hastelloy autoclave reactor, which was equipped with a gas impeller. The contents of the reactor were stirred at room temperature. The reactor was charged with ethylene gas until the pressure stabilized to 500 psig. The reactor was heated to about 250° C., and allowed to react for 7 hours. The reactor was then cooled and depressurized. A sample was taken from the reactor, and the sample was analyzed by  1 H-NMR. 
     For solvent #5 in Table 3 below, the following procedure was used: 2,5-dimethylfuran (44.5 g, 0.46 mole), tetrahydrofuran (250 mL), ethylene (450 psig), calcium sulfate (13.7 g) and aluminum chloride (2.0 g) were added into a hastelloy autoclave reactor. The contents of the reactor were stirred at room temperature. The reactor was charged with ethylene gas until the pressure stabilized to 500 psig. The reactor was heated to about 220° C. and allowed to react for 24 hours. The reactor was then cooled and depressurized. A sample was taken from the reactor, and the sample was analyzed by  1 H-NMR. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Effect of solvent on the synthesis of para-xylene from DMF 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Conversion 
                 Selectivity 
               
               
                 Entry 
                 Solvent 
                 (%) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 1,4-dioxane 
                 99 
                 84 
               
               
                 2 
                 tetraethylene glycol 
                 100 
                 27 
               
               
                 3 
                 sulfolane 
                 88 
                 41 
               
               
                 4 
                 triglyme 
                 99 
                 81 
               
               
                 5 
                 tetrahydrofuran 
                 95 
                 71 
               
               
                   
               
            
           
         
       
     
     Example 6 
     Effect of Catalyst Loading on Synthesis of Para-Xylene from DMF 
     This example demonstrates the impact of the amount of catalyst used on the synthesis of para-xylene from DMF. 
     For each reaction set forth in Table 4 below, the following general procedure was used: 2,5-dimethylfuran (amount specified in Table 4), dioxane (amount specified in Table 4), and copper triflate (amount specified in Table 4) were added into a hastelloy autoclave reactor, which was equipped with a gas impeller, and was stirred at room temperature. The reactor was charged with ethylene gas until the pressure stabilized to 500 psig. The reactor was heated to 250° C. and allowed to react for 7 hours. The reactor was then cooled and depressurized. A sample was taken from the reactor, and the sample was analyzed by  1 H-NMR. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Effect of copper triflate loading on the synthesis of 
               
               
                 para-xylene from DMF 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 Time 
               
               
                   
                   
                   
                   
                   
                   
                 to reach 50% 
               
               
                   
                 Catalyst 
                 DMF 
                 Dioxane 
                 Conversion 
                 Selectivity 
                 conversion 
               
               
                 Entry 
                 (g) 
                 (g) 
                 (g) 
                 (%) 
                 (%) 
                 (h) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 0.025 
                 5 
                 100 
                 99 
                 100 
                 0.3 
               
               
                 2 
                 0.10 
                 10 
                 200 
                 100 
                 95 
                 1.0 
               
               
                 3 
                 0.50 
                 10 
                 200 
                 100 
                 86 
                 1.3 
               
               
                   
               
            
           
         
       
     
     Example 7 
     Synthesis of Toluene from Methylfuran and Ethylene 
     
       
         
         
             
             
         
       
     
     2-Methylfuran (4.113 g, 0.05 mole), calcium sulfate (3.25 g), and acetic acid (1.06 g) was added into a hastelloy autoclave reactor and was stirred at room temperature. The reactor was charged with ethylene gas until the pressure stabilized to 780 psig. The reactor was heated to 175° C. and allowed to react for 65 hours. The reactor was then cooled, depressurized, and the solution was analyzed by GC-FID, GC-MS giving toluene (586.2 mg).