Preparation of carboxylic acid esters with BF3 complex catalyst

Abstract

In a process wherein ethylene or propylene is carbonylated with carbon monoxide to form carboxylic acid esters in the presence of a catalyst complex of one mole of BF 3 and one mole of alcohol, the invention concerns a technique wherein the catalyst is recovered from the reaction product and recycled. The carbonylation is carried out until approximately one-half of the alcohol is consumed, to form a reaction mass containing the BF 3 , the alcohol, and the carboxylic acid ester in a 2:1:1 molar ratio. In the first step, the one mole of the free BF 3 is vaporized from the reaction mass. The remaining admixture is a 1:1:1 mixture of the three aforesaid compounds. To this mixture additional alcohol is added and the mixture is subjected to distillation. A carboxylic acid ester/alcohol azeotrope and residual alcohol are removed by the distillation, to leave a residue containing a 1:2 BF 3 /alcohol complex. This complex is combined with an additional mole of BF 3 to form the 1:1 catalyst complex used in the carbonylation. The additional mole of BF 3 is preferably that initially separated from the reaction mass; however, it may be obtained from an external source. The carboxylic acid ester/alcohol mixture may be separated by azeotropic distillation using an azeotroping agent, such as octane, to recover the alcohol-octane as overhead product and the carboxylic acid ester as bottoms product.

Having thus described my invention, what I claim and desire to protect by Letters Patent is: 
     
       1. A process for the carbonylation of an olefin selected from the group consisting of ethylene and propylene which comprises reacting the olefin with carbon monoxide in the presence of a catalyst complex containing equimolar amounts of BF 3  and alcohol at a temperature of from 0° C. to 100° C., carrying out said reaction with an internal molar ratio of carbon monoxide to olefin of at least 5:1 until about 50% of the alcohol in said catalyst is consumed, thereby forming a carboxylic acid ester and liberating free BF 3  ; separating sufficient BF 3  from the reaction mass by stripping to leave a first residue containing equimolar amounts of the BF 3 , the alcohol and the carboxylic acid ester; admixing the first residue with additional alcohol; thereafter distilling said admixture to separate overhead an azeotrope of said alcohol and said carboxylic acid ester .[.and additional uncomplexed alcohol.]. until a second residue containing BF 3  to alcohol in a molar ratio of 1:2 remains; and thereafter combining said second residue with additional BF 3  to form the catalyst complex. 
     
     
       2. The process of claim 1 wherein the additional BF 3  added to the second residue is that BF 3  initially removed from the reaction mass. 
     
     
       3. The process of claim 1 wherein the olefin is propylene, the catalyst is BF 3 .CH 3  OH, and the product obtained is methyl isobutyrate. 
     
     
       4. The process of claim 1 wherein the olefin is ethylene, the catalyst is BF 3 .CH 3  OH, and the product obtained is methyl propionate. 
     
     
       5. The process of claim 1 wherein the carboxylic acid ester and alcohol stream is combined with an azeotroping solvent and said combination is subjected to further distillation wherein a low boiling azeotrope comprised of solvent and alcohol is removed from the carboxylic acid ester. 
     
     
       6. The process of claim 5 wherein the azeotroping solvent is a paraffin having a boiling point of from 30° C. to 150° C. 
     
     
       7. The process of claim 6 wherein the paraffin is octane. .Iadd. 8. The process of claim 1 wherein additional uncomplexed alcohol is distilled from the admixture of the first residue and additional alcohol, after the azeotrope of said alcohol and said carboxylic acid ester is separated overhead. .Iaddend.