Abstract:
A process for preparing carbonate compounds having the following formula: ##STR1## wherein R and R&#39; are, the same or different, C 1  -C 6  alkyl group, a C 3  -C 6  cycloalkyl group, an optionally substituted C 6  -C 14  aryl group, an alkylaryl group, or an arylalkyl group is proposed; the process comprises reacting urea or derivatives thereof with appropriate alcohols or phenols and preparing the carbonate compounds via a multiple-step synthesis process.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for preparing carbonate compounds via a multiple-step synthesis process. 
     2. Description of Prior Art 
     Conventionally, a phosgene process and a non-phosgene process are used for producing carbonate compounds. In the phosgene process, phosgene is reacted with alcohols in the absence of catalyst at a low temperature to produce carbonate compounds; the phosgene process, however, has problems such as highly toxic phosgene is used as a starting compound, and a special manufacturing facility required to cope with the highly corrosive by-product (hydrochloric acid) generated by the process; such facility is very costly. Furthermore, extremely high amount of chlorine is often contained in the resulting carbonate products. 
     The non-phosgene process can be roughly divided into alcohols/carbon monooxide oxidation process, alkyl nitrite process and transesterification process. These processes will be described in detail as follows: 
     The alcohols/carbon monooxide oxidation process can be further divided into a liquid phase process and a gas phase process; for the liquid phase process as described in the U.S. Pat. No. 4,218,391, a high reaction pressure and a corrosive catalyst are required; therefore, special facilities are in need and such facilities are very costly for the process. In addition, the resulting carbonate products always contain a large amount of water and a great deal of energy is wasted in purification process for removing the water from the carbonate products. The gas phase process as described in the U.S. Pat. No. 3,114,762 avoids the need of high reaction pressure in the liquid phase process; however, because heterogeneous catalyst is used the yield of product is low, and the catalyst used in the process is toxic. 
     The alkyl nitrite process also includes a liquid phase process and a gas phase process. The liquid phase process as described in the U.S. Pat. No. 4,229,589 relates to the reaction of carbon monooxide with alkyl nitrite in the presence of metallic palladium as catalyst under a high pressure to obtain carbonate compounds. Nevertheless, there are problems in this process such that the yield is, low and a costly facility is needed. The gas phase process as described in the U.S. Pat. No. 4,229,591 employs the catalytic reaction of carbon monooxide with alkyl nitrite, which reaction is carried out under a low pressure and gas phase. The disadvantage with the above process is that the cost for recycling the alkyl nitrite from the resulting products is high. 
     The transesterification process can be further divided into the following two processes according to the starting materials used: one is the process (see U.S. Pat. No. 4,434,105) which involves the catalytic reaction of alcohols, ethylene oxide and carbon dioxide in liquid phase; and another one is the process (see U.S. Pat. No. 4,062,884) which involves the catalytic reaction of alcohols and ethylene carbonate in liquid phase. The disadvantages of these processes are such that the cost of the preparation of ethylene oxide or ethylene carbonate, to be used as the starting material, is high and, in order to obtain a high selectivity, the use of a large amount of alcohols is required with a high reflux ratio as a result the operating cost increases. 
     Under the circumstances mentioned above, attempts had been made in order to overcome the disadvantages described above through the inventors&#39; extensive and intensive studies, and the present invention was thus completed. 
     SUMMARY OF THE INVENTION 
     It is the main object of the present invention to provide an improved process for preparing alkyl carbonates, which comprises reacting urea or derivatives thereof with appropriate alcohols or phenols to produce carbonate compounds via a multiple step synthesis process. While compared with the conventional processes for preparing alkyl carbonates, the process of the present invention provides the following advantages: 
     1. By using the urea derivatives as starting material, the cost of raw material is reduced; 
     2. The use of noble metal as catalyst is optional such that the cost of catalyst is reduced when non-noble metal is employed as catalyst; 
     3. Homogeneous catalysts are used in this invention which results in a high selectivity for the reaction; the catalysts are not corrosive, and can be recovered for re-use; 
     4. The reaction is carried out under low pressure and liquid phase, therefore, problems existing in a high pressure reaction such as high degree of danger and high cost in facility as well as in operation are eliminated; and 
     5. No water is produced throughout the process reactions of the present invention, so the catalyst will be free from being poisoned by the combination of water and the catalyst, and side reactions which adversely affect the cost of the purification of the resulting alkyl carbonates can be avoided. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a process for preparing carbonate compounds represented by the following formula [I]: ##STR2## wherein R and R&#39; are, the same or different, a C 1  -C 6  alkyl group, a C 3  -C 6  cycloalkyl group, an optionally substituted C 6  -C 14  aryl group, an alkylaryl group, or an arylalkyl group; the carbonate compounds can be prepared according to the following reaction scheme A: ##STR3## wherein R and R&#39; are defined as above, and R 1 , R 2 , R 3  and R 4  are, the same or different, hydrogen, a C 1  -C 6  alkyl group, a C 3  -C 6  cycloalkyl group, an option-ally substituted C 6  -C 14  aryl group, an alkylaryl group, or an arylalkyl group; or R 1 , and R 2 , or R 3  and R 4  may be bonded together with the nitrogen atom adjacent thereto to form an optionally substituted nitrogen-containing five- or six- member heterocyclic ring. The term &#34;C 1  -C 6  alkyl group&#34; described herein includes a straight- or branched- alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, butyl, n-pentyl, neo-pentyl, isopentyl and n-hexyl. 
     Examples of the &#34;C 3  -C 6  cycloalkyl group&#34; include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like. 
     Examples of the &#34;C 6  -C 14  aryl group&#34; include phenyl, naphthyl and anthryl, and the like. 
     Examples of the &#34;arylalkyl group&#34; include phenylmethyl, phenylethyl, phenyl propyl, and the like. 
     Examples of the &#34;alkylaryl group&#34; include methylphenyl, ethylphenyl, and the like. 
     Examples of the &#34;nitrogen-containing heterocyclic ring&#34;, which can be formed by the linking of R 1  and R 2 , or R 3  and R 4  with the nitrogen atom adjacent thereto, include pyrrolidyl, pyrazolidinyl, imidazolidinyl, piperidinyl, piperazinyl, and the like. 
     Examples of the substituents for the aryl, arylalkyl, alkylaryl, and the nitrogen-containing heterocyclic ring include hydroxyl, C 1  -C 4  alkyl, C 1  -C 4  alkoxyl, hydroxyl-(C 1  -C 4 )alkyl, amino, C 1  -C 4  alkoxylcarbonyl, N-monosubstituted amino, N,N-disubstituted amino, nitro, halogen, C 1  -C 4  alkylthio, thiol groups, and the like. 
     The starting material [II] in the reaction scheme A can be the compounds examplied as follows: 
     The process of the present invention according to reaction scheme A is composed of reactions represented by the following reaction schemes A1, A2 and A3. These reactions will be described in detail, accompanied with the following reaction schemes, as follows: ##STR4## wherein R 1 , R 2 , R 3  and R 4  are defined as above; and R 5 , R 6 , R 7  and R 8  are, the same or different, hydrogen, a C 1  -C 6  alkyl group, a C 1  -C 6  alkoxyl group, a C 1  -C 6  alkoxycarbonyl group, a substituted or unsubstituted phenyl group, provided that at least one of R 5  and R 6  is a substituted or unsubstituted phenyl group, and that at least one of R 7  and R 8  is a substituted or unsubstituted phenyl group 
     Examples of the substituents on the substituted phenyl group are a C 1  -C 6  alkyl group, a nitro group, an amino group, a halogen, a hydroxyl group, a C 1  -C 4  alkoxyl group, a C 1  -C 4  alkylthio group, a thiol group, and the like; the number of the substituents is from 1 to 4, preferably 1 to 2. 
     The reaction according to the reaction scheme A1 is carried out in the presence or absence of catalyst under atmospheric pressure at a temperature from 100° to 300° C., preferably 120°to 180° C., for a period from 1 to 4 hours (see U.S. Pat. No. 2,729,677). 
     According to the following reaction scheme A2, the resulting product [III] from the reaction of scheme A1 is further reacted with alcohols or phenols. ##STR5## wherein the symbols have the same meaning as above. 
     The reaction according to reaction scheme A2 is carried out in the presence or absence of catalyst at a temperature from 100° to 300° C., preferably from 140° to 200° C., in a pressurized reactor whose pressure is self-provided (see U.S. Pat. 2,409,712) 
     According to the following reaction scheme A3, the resulting products [IV] to [VII] from the reaction of scheme A2 may be further subject to either independently versatile decomposition or replacement reaction between products [IV] and [V] or products [VI] and [VII] to give the compounds represented by formula [I]. The reaction scheme is shown as follows: ##STR6## The reaction according to reaction scheme A3 is carried out in the presence of catalyst at a temperature from 100° to 300° C., preferably 140° to 200° C., under atmospheric pressure, reduced pressure or pressurized condition. 
     The amount of catalyst used is in the range between 0.001 and 10% by weight, preferably between 0.01 and 5% by weight based on the total weight of reactants. 
     The catalyst used in the present invention, which can be used alone or in combination with others, is selected from the group consisting of the following compounds (A) through (H): 
     (A) hydroxides, oxides, hydrides, alcoholates and halides of alkali metal or alkali earth metal, and alkali metal or alkali earth metal salts of organic and inorganic acid, such as LiOH, NaOH, KOH, Mg(OH) 2 , Ca(OH) 2  ; Li 2  CO 3 , Na 2  CO 3 , Na 2  CO 3 , K 2  CO 3  MgCO 3 , CaCO 3 , BaCO 3  ; LiBH 4 , NaBH 4 , KBH 4 , Mg(BH 4 ) 2 , Ca(BH 4 ) 2  ; Li 2  HPO 4 , Na 2  HPO 4 , K 2  HPO 4 , MgHPO 4 , CaHPO 4  ; LiCl, NaCl, KCl, MgCl 2 , CaCl 2  ; Li(CH 3  COO), Na(CH 3  COO), K(CH 3  COO), Mg(CH 3  COO) 2 , Ca(CH 3  COO) 2 , lithium, sodium or potassium phenolate, and lithium, sodium or potassium bisphenol A; 
     (B) titanium- and zirconium-containing compounds such as TiCl 4 , Ti(OR) 4 , ZrCl 4 , Zr(OR) 4 , etc.; 
     (C) iron-, cobalt- and nickel-containing compounds, especially the complexes thereof, etc.; 
     (D) zinc-, cadmium-, gallium-, tin-, lead-, antimony- and bismuth-containing compounds, preferably zinc-, tin-, lead- and antimony-containing complexes and oxides, such as R 2  SnO wherein R is alkyl, aryl, arylalkyl or alkylaryl group, or Sb 2  O 3  , etc. 
     (E) borates such as B(OR) n  (OH) 3-n  wherein n is 1, 2 or 3, for example, B(OMe) 3 , B(OMe) 2  OH; B(OMe)(OH) 2 , B(OPh) 3 , etc. 
     (F) amino compounds including primary, secondary, tertiary amine and quaternary ammonium salt, for example, RNH 2 , R 2  NH, R 3  N and R 4  N +  X -   wherein R is alkyl, aryl, arylalkyl or alkylaryl group, such as (CH 3 ) 4  N+Cl-, (CH 3 ) 4  N +  Br - , (CH 3 ) 4  N +  OH - , etc. electron-donating nitrogen-containing heterocyclic compounds: 
     (a) pyridines such as 4-aminopyridine, 2-aminopyridine, 4-dimethylaminopyridine, 4-hydroxypridine, 2-hydroxypyridine, 4-methoxypyridine, and 4-mercapto-pyridine; 
     (b) imidazoles such as imidazole, 2-methylimidazole, 4-methylimidazole, 2-dimethylaminoimidazole, 2-methoxyimidazole, and 2-thioimidazole. 
     (c) others such as picoline, pyrimidine, pyrazole, aminoquinoline, pyrrolidine, morpholine, piperidine, piperazine, and pyrrole. 
     (H) electron-donating phosphorus-containing compounds, for example, phosphines and phosphites, such as trimethyl phosphine, triphenyl phosphine, trimethyl phosphite, triphenyl phosphite and tris(tolyl) phosphite. 
     The process according to this invention will now be described in detail with reference to the following examples; however, the invention is not limited thereto. 
     EXAMPLE 1 
     To at three-liter reactor were added 180 grams of urea and 2,232 grams of aniline. The mixture was heated to 160° C. and subjected to reaction for 4 hours under stirring. The mixture was then cooled to a temperature below 20° C. and sampled for the analysis of HPLC. The product N,N&#39;-diphenylurea (abbreviated as DPU; chemical formula: ##STR7## was obtained at a yield of 99.5% 
     EXAMPLE 2 
     To a two-liter reactor were added 424 grams of DPU obtained from Example 1 and 800 grams of methanol. The mixture was heated to 160° C. and subjected to reaction for 3 hours under stirring. The mixture was then cooled to, a temperature below 20° C. and sampled for the analysis of HPLC. A conversion of 99.6% for DPU and a selectivity of 99.4% for the resulting product methyl N-phenylcarbamate (abbreviated as MNPC; chemical formula: ##STR8## were found. 
     EXAMPLE 3 
     To a two-liter reactor were added 424 grams of DPU obtained from Example 1 and 1,150 grams of ethanol. The mixture was heated to 170° C. and subjected to reaction for 3 hours under stirring. The mixture was then cooled to a temperature below 20° C. and sampled for the analysis of HPLC. A conversion of 98.4% for DPU and a selectivity of 99.0% for the resulting product ethyl N-phenylcarbamate (abbreviated as ENPC; chemical formula: ##STR9## were found. 
     EXAMPLE 4 
     To a two-liter reactor were added 318 grams of DPU obtained from Example 1 and 1,388 grams of n-butylalcohol. The mixture was heated to 180° C. and subjected to reaction for 3 hours under stirring. The mixture was then cooled to a temperature below 20° C. and sampled for the analysis of HPLC. A conversion of resulting 96.2% for DPU., and a selectivity of 98.1% for the resulting product n-butyl N-phenylcarbamate (abbreviated as BNPC; chemical formula: ##STR10## were found. 
     EXAMPLE 5 
     To two-liter reactor were added 318 grams of DPU obtained from Example 1 and 2,350 grams of phenol. The mixture was heated to 180° C. and subjected to reaction for 4 hours under stirring. The mixture was then cooled to a temperature below 20° C. and sampled for the analysis of HPLC. A conversion of 91.2% for DPU and a selectivity of 88% for the resulting product phenyl N-phenylcarbamate (abbreviated as PNPC; chemical formula: ##STR11## were found. 
     EXAMPLE 6 
     To a one-liter reactor were added 500 grams of MNPC obtained from Example 2 and 5 grams of Pb(OAC) 2 .3H 2  O. The mixture was heated to 180° C. and subjected to reaction for 3.5 hours with stirring. After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 87.3% for MNPC and a selectivity of 85.2% for the resulting product dimethyl carbonate (abbreviated as DMC; chemical formula: H 3  C--O--CO--O--CH 3 ) were found. 
     EXAMPLE 7 
     To a one-liter reactor were added 500 grams of MNPC obtained from Example 2 and 10 grams of Mg(OAC) 2 .2 H 2  O. The mixture was heated to 170° C. and subjected to reaction for 4 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 75.4% for MNPC and a selectivity of 77.6% for DMC were found. 
     EXAMPLE 8 
     To a one-liter reactor were added 500 grams of MNPC obtained from Example 2 and 1 gram of KI. The mixture was heated to 160° C. and subjected to reaction for 6 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 81.8% for MNPC and a selectivity of 80.1% for DMC were found. 
     EXAMPLE 9 
     To a one-liter reactor were added 500 grams ENPC obtained from Example 3 and 5 grams of Ti(OPr) 4 . The mixture was heated to 180° C. and subjected to reaction for 5 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 75.0% for ENPC and a selectivity of 69.7% for the resulting product diethyl carbonate (abbreviated as DEC; chemical formula: H 5  C 2  --O--CO--C 2  H 5 ) were found. 
     EXAMPLE 10 
     To a one liter reactor were added 500 grams of ENPC obtained form Example 3 and 10 grams of Na 2  CO 3 . The mixture was heated to 180° C. and subjected to reaction for 6 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 68.2% for ENPC and a selectivity of 53.2% for DEC were found. 
     EXAMPLE 11 
     To a one-liter reactor were added 500 grams of BNPC obtained from Example 4 and 1 gram of N,N-dimethyltolylamine. The mixture was heated to 160° C. and subjected to reaction for 6 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 60.1% for BNPC and a selectivity of 45.5% for the resulting product di-n-butyl carbonate (abbreviated as DBC; chemical formula: H 9  C 4  --O--CO--O--C 4  H 9 ) were found. 
     EXAMPLE 12 
     To a one, liter reactor were added 500 grams of BNPC obtained from Example 4 and, 1 gram of Pb(OAC) 2 .3H 2  O and 1 gram of NaOCH 3 . The mixture was heated to 160° C. and subjected to reaction for 6 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 82.5% for BNPC and a selectivity of 76.7% for DBC were found. 
     EXAMPLE 13 
     To a one-liter, reactor were added 250 grams of MNPC obtained from example 2 and 250 grams of ENPC obtained from Example 3 and 1 gram of Zr(NO 3 ) 4 . The mixture was heated to 180° C. and subjected to reaction for 5 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 80.4% for (MNPC+ENPC) and selectivities of 26.1%, 8.8%and 36.5% for DMC, DEC and the resulting product ethyl methyl carbonate (abbreviated as EMC; chemical formula: H 5  C 2  --O--CO--O--CH 3 ), respectively, were found. 
     EXAMPLE 14 
     To a one-liter reactor were added 500 grams of PNPC obtained from Example 5 and 3 grams of LiCl . The mixture was heated to 180° C. and subjected to reaction for 6 hours under stirring. 
     After the reaction was completed, the mixture was cooled to a temperature below 20° C. and sampled for the analysis of HPLC and GC. A conversion of 75.2% for PNPC and a selectivity of 36.4% for the resulting product diphenyl carbonate (abbreviated as DPC; chemical formula: ##STR12## were found.