Preparation of carboxylic acid esters with bf.sub.3 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.sub.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.sub.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.sub.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.sub.3 /alcohol complex. This complex is combined with an additional mole of BF.sub.3 to form the 1:1 catalyst complex used in the carbonylation. The additional mole of BF.sub.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.