Acid accelerated hydrocarboxylation

A process for the hydrocarboxylation of an olefinically unsaturated straight chain compound selected from the class consisting of linear olefinically unsaturated esters having the formula:

• ##STR2## wherein n is 0 to 5, R.sub.1 is H, CH.sub.3 or C.sub.2 H.sub.5 and R.sub.2 is alkyl, and terminally unsaturated alkenes having 4 to 16 carbon atoms to form a mixture containing an increased amount of linear carboxylate acid, which comprises dissolving said compound in a solvent selected from the class consisting of methylene chloride;
• 1,2-dichloroethane and aromatic solvents having 6 to 9 carbon atoms, mixing the thus formed solution with carbon monoxide, water, rhodium catalyst, iodide promoter and an accelerator selected from the class consisting of aliphatic and aromatic acids having a pKa in the range of 4.2 to 5.2 in an amount at least equal, on a molar basis, to the amount of olefinically unsaturated straight chain compound, and reacting the mixture at temperature of from 50.degree. to 300.degree. C. to form linear carboxylic acid.