THE USE OF PERFLUOROSULFONIC ACID RESINS AS CATALYSTS FOR PREPARING ESTERS

Abstract: Esters can be made from the addition of carboxylic acids to olefins in the presence of perfluorosulfonic acid resins.

Description: THE USE OF PERFLUOROSULFONIC ACID RESINS AS CATALYSTS FOR PREPATING ESTERS Technical Field This invention pertains to the preparation of es¬ ters via the addition of carboxylic acids to olefini- cally unsat rated hydrocarbons and in particular to the use of perfluorosulfonic acid resins as catalysts. Background Art Esters in general are highly useful chemicals which have found application in a diversity of uses. Acetate esters are used in large quantities as solvents for coatings. Acrylate and ethacrylate esters have been used for the synthesis of latex paints, photocurable resins, powder coatings and many other useful products. Esters are conventionally made by the reaction of alcohols with carboxylic acids in the presence of a strong acid catalyst to form ester and water. Although the yield of this reaction is normally high, the forma- tion of water represents an inefficiency in the con¬ version of raw materials into useful products. Further¬ more, the water formed must be purified before it can be discharged into the environment. These limitations have a negative effect on the economics of ester pro- duction. There is therefore a need for a more effici¬ ent means of producing esters. The addition of acids to olefins to form esters is known. It is taught in U.S. 3,102,905 that sulfonic acids such as benzenesulfonic acids are effective for the addition of acetic acid to isobutylene at 75°C. using a mole ratio of 1.5/1 of acid to olefin. In U.S. 3,053,887, a sulfonated polystyrene- divinylbenezene crosslinked macroreticular resin was used for the addition of acetic acid to isobutylene at 0°C. In U.S. 3,037,052, a catalyst much like the one in the preceding paragraph was used to add a variety of acids to various olefins " . In U.S. 3,678,099, the production of t-butyl acetate from isobutylene and acetic acid using a resin¬ ous sulfonated polystyrene-divinylbenezene copolymer at a temperature of 38 to 93°C. was described. Disclosure of Invention It is an object of this invention to provide a catalyst system for the preparation of esters which affords high yields at a minimum of by-products. It is another object of this invention to provide a catalyst for ester production which is temperature stable up to 200 to 220°C. It is a further object of this invention to provide a catalyst for the production of esters which is chemically stable. It is still further object of this invention to provide a catalyst for the production of esters which is stronger than those hitherto known. It is yet another object of this invention to provide a catalyst for the production of esters which resists physical deterioration during use. Detailed Description A method of preparing esters satisfying the above requirements has been found which comprises contacting an organic carboxylic acid having 1 to 18 carbon atoms with an ethylenically unsaturated hydrocarbon having 2 to 16 carbon atoms in a mole ratio of carboxylic acid to unsaturated hydrocarbon of from 10:1 to 1:20 at ' BU a temperature of 0°C. to 220°C. at a pressure of 0 psig to 5000 psig in the presence of a catalytic amount of a perfluorosulfonic acid resin which is a copolymer of tetrafluoroethylene and a sulfonyl fluoride vinyl ether that has been saponified with caustic and then converted to the acid form. Although the reaction temperature " may vary widely from 0°C. to 220°C, preferred temperature ranges depend upon the particular ethylenically un- saturated hydrocarbon being used. Thus for example, with isobutylene the reaction temperature is preferably between 0°C. and 25°C. With other ethylenically un¬ saturated hydrocarbons, such as, ethylene, propylene, 1-butene, 2-butene, t-butylene, norbornylene, or cyclo¬ hexene higher temperatures may be used. The particular temperature required for the optimum reaction conditions varies with the reaction temperature. As a rule of thumb, it is preferable to have the pressure high enough to keep the ethylenically unsaturated hydrocarbon dissolved in the acid or acid ester solution. The ethylenically unsaturated hydrocarbons used in the method of this invention are preferably monoun- saturated but do not have to be single components and so may be used as mixtures. A practical use of this observation is demonstrated by the use of BAV gas. BAV gas is a convention used in the refining and gas in¬ dustry for butadiene absorber vent gas which generally contains from 40% to 20% isobutylene mixed with 40 to 60% normal butenes, principally 1- and 2-butene. The difference in optimum reaction temperatures can be put to advantage with gas mixtures, such as, BAV gas, by running the esterification reaction first at 25°C. where isobutylene is readily esterified and then at 100°C. where the esterification with 1- and 2-butene readily takes place. The acids which are most suitable for this reaction are formic, acetic, propionic, and higher saturated aliphatic acids; diprotic acids, such as, oxalic, malonic, succinic, glutaric, or adipic, as well as unsaturated acids, such as, acrylic acid, methacrylic acid and crotonic acid. Aromatic acids can also be used, such as, benzoic or phthalic. The perfluorosulfonic acid resins used as cata- lysts in this invention are commercially available under the Trademark Nafion from the duPont de Nemours Company of Wilmington, Delaware. Suitable variations of these resins are described in U.S. 4,065,512 and in duPont "Innovation", Volume 4, No. 3, Spring 1973. The term "catalytic amount of perfluorosulfonic acid resin" is meant to mean concentrations, based on the total reaction mixture, of 0.001%, to 5% by weight. It was surprising to find that the perfluoro¬ sulfonic acid resins were more active, giving higher yields and less by-products, than conventional ion ex¬ change resins, such as those provided by Dow, e.g., Dowex 50W-X8, and those from Rohm and Haas, such as the Amberlyst series of resins. These are strong acid cation exchange resins composed of sulfonated styrene-divinylbenezene beads in macroreticular form. These prior art macroreticular resins are rigid, break down under agitation encountered during their use as catalysts and eventually deteriorate in physical form to a powder. The Nafion resins on the other hand are extremely resilient. No signs of wear or tear have been observed in these catalysts after many hours of use in making esters. Furthermore, because of this great durability, the Nafion catalysts are ideally suited for use as esterification catalysts in a fluidi- zed bed type of reactor. As polymer supported catalysts, Nafion is also well suited for use in packed bed reactors. No special equipment is required for carrying out the preparation of esters under this invention and so conventional reactors, stirrers, heating sources, and installation apparatus can be employed. This in¬ vention may be practiced as either a batch or continuous process. The esters available from unsaturated acids through this invention are polymerizable monomers easily convertible to polymers which are particularly useful in industrial coating and adhesive applications. The invention is further described in the examples which follow. All parts and percentages are by weight unless otherwise specified. Example 1 To a steam heated reactor equipped with a stirrer and thermocouple there were added 8.60 grams of 1-decene, 5.65 grams of formic acid, and 0.282 grams of Nafion 501 powder which had been saponified and then ion ex¬ changed into the acid form. The reaction mixture was heated to 100°C. for six hours. Analysis of the reactor contents showed: 37.8% Formic acid 8 8..77%% 1-Decene 51.3% 2-Decyl formate Example 2 To a pressure reactor equipped with a stirrer and thermocouple there was added 100 grams of acetic acid, 100 grams of tetrahydrofuran, 100 grams of isobutylene, and 5 grams of Nafion 501 catalyst which had previously been ion exchanged to the acid form. The temperature was maintained at 25°C. for six hours. Analysis of the reaction mixture showed a 57% conversion of the acetic acid to t-butyl acetate. Example 3 A small reactor equipped with a stirrer and thermocouple, was charged with 6.25 grams of acrylic acid, 8.15 grams of norbornylene and 0.31 grams of Amberlyst XN-1005 ion exchange resin (a sulfonated styrene-divinylbenezene copolymer sold by Rohm and Haas. It is a macroreticular resin.). The reactor was heat¬ ed to 102°C. for 1 hour. Samples were taken and analyz¬ ed as follows : Time (Minutes) Percent Norbornyl Aerylate 10 46.1 30 83.6 60 95.3 Example 4 Example 3 was repeated with the exception that the reactor was charged with 16 grams of an equimolar norbornylene/acrylic acid solution and 0.31 grams of Nafion 811 resin instead of the Amberlyst XN-1005. The temperature was raised to 102°C. After 15 minutes the solution was analyzed and indicated a 97% content of norbornyl acrylate. This demonstrates the superiority of the Nafion catalyst over that of an Amberlyst type catalyst. Example 5 Reactor used in Example 3 was charged with 16 grams of an equi olar norbornylene/acrylic acid solution and 0.31 grams of dried Dowex 50W-X8 ion exchange resin (a sulfonated styrene-divinylbenezene copolymer obtained from Dow Chemical Company. It is a macroreticular resin.). The temperature was raised to 102°C. Samples were taken and analyzed as follows: \ Time (Minutes) Percent Norbornyl Acrylate 5 27 15 63 25 80 35 91 45 91 These results when compared with Examples 3 and 4 indicate that for this esterification reaction the Amberlyst and Dowex resins are comparable to each other but inferior to Nafion. Example 6 The reactor used in Example 2 was charged with 100 grams of propionic acid, 100 grams of tetrahydro¬ furan, 132 grams of isobutylene, and 5.0 grams of Nafion 501 catalyst which had previously been ion ex¬ changed to the acid form. The temperature was main¬ tained at 25°C. for six hours. Analysis of the re¬ action mixture showed 51% conversion of the propionic acid to t-butyl propionate. These results when compared with Example 2 show Nafion as a more than adequate catalyst for this reaction. Increasing the size of the reactant acid slows the esterification reaction rate. This is believed due to unfavorable steric interactions with the cata¬ lyst. Example 7 The reactor used in Example 2 was charged with 120.0 grams of methacrylic acid, 100.0 grams of tetra¬ hydrofuran, 5.0 grams of Nafion 501 exchanged to the acid form, and 125.0 grams of isobutylene, the reaction was stirred and maintained at 25°C. for 24 hours. Samples were taken and analyzed as follows: Percent Acid Converted Time (Hours) t-butyl methacrylate 3 5.7 5 16.4 7 — 23.2 24 44.3

Claims: CLAIMS : 1. Method of preparing esters which comprises contacting an organic carboxylic acid having 1 to 18 carbon atoms with an ethylenically unsaturated hydro- carbon having 2 to 16 carbon atoms in a mole ratio of carboxylic acid to unsaturated hydrocarbon of from 10:1 to 1:20 at a temperature of 0°C. to 220°C. at a pressure of 0 psig to 5000 psig in the presence of a catalytic amount of a perfluorosulfonic acid resin which is a copolymer of tetrafluoroethylene and a sulfonyl fluoride vinyl ether that has been saponi¬ fied with caustic and then converted to the acid form. 2. Method claimed in claim 1 wherein the mole ratio of carboxylic acid to unsaturated hydrocarbon is 1:10 to 1:20. 3. Method claimed in claim 1 wherein the unsaturated hydrocarbon is isobutylene, the car¬ boxylic acid is acrylic acid and the temperature is 4. Method claimed in claim 1 wherein the carboxylic acid is acrylic acid and the unsaturated hydrocarbon is ethylene. 5. Method claimed in claim 1 wherein the car- boxylic acid is acrylic acid and the unsaturated hydrocarbon is propylene. 6. Method claimed in claim 1 wherein the car¬ boxylic acid is acrylic acid and the unsaturated hydrocarbon is t-butylene. ** 7. Method claimed in claim 1 wherein the car¬ boxylic acid is acrylic acid and the unsaturated hydrocarbon is 1-butene. 8. Method claimed in claim .1 wherein the car¬ boxylic acid is acrylic acid and the unsaturated hydrocarbon is 2-butene. 9. Method claimed in claim 1 wherein the car¬ boxylic acid is acrylic acid and the unsaturated hydrocarbon is a mixture of 1-butene and 2-butene. 10. Method claimed in claim 1 wherein the car¬ boxylic acid is acrylic acid and the unsaturated hydrocarbon is norbornylene. 11. Method claimed in claim 1 wherein the car¬ boxylic acid is acrylic acid and the unsaturated hydrocarbon is cyclohexene. 12. Method claimed in claim 1 wherein the car- boxylic acid is acrylic acid and the unsaturated hydrocarbon is 2-hexene. 13. Method claimed in claim 1 wherein the car¬ boxylic acid is methacrylic acid and the unsaturated hydrocarbon is t-butylene. 14. Method claimed in claim 1 wherein the car¬ boxylic acid is methacrylic acid and the unsaturated hydrocarbon is norbornylene. 15. Method claimed in claim 1 wherein the car¬ boxylic acid is formic acid. 16. Method claimed in claim 1 wherein the car¬ boxylic acid is acetic acid. 17. Method claimed in claim 1 wherein the car¬ boxylic acid is oxalic acid. 18. Method claimed in claim 1 wherein the car- boxylic acid is benzoic acid.

Inventors: SCHRECK D
Applicants: UNION CARBIDE CORP
Application year: 1980
Main classification: C07C67
IPC codes: C07C67