Process for the production of isobutyric acid anhydride

In a process for carbonylating propylene in the presence of a substantial excess of liquid anhydrous hydrogen fluoride to effect the formation of isobutyroyl fluoride followed by hydrolysis;

• the improvement of hydrolyzing the isobutyroyl fluoride to effect the formation of isobutyric acid anhydride and recycle anhydrous hydrogen fluoride comprising the steps:
• (1) fractionating the carbonylation reaction mixture to provide unreacted anhydrous hydrogen fluoride for recycle and isobutyroyl fluoride;
• (2) partially hydrolyzing the isobutyroyl fluoride at a temperature between about 0.degree. and 100.degree. C. in the presence of a hydrogen fluoride acceptor and from 0.05 to 0.5 mole of water per mole of the isobutyroyl fluoride whereby the water is used to extinction in the hydrolysis reaction thereby providing an equilibrium hydrolysis reaction mixture including a liquid phase consisting essentially of isobutyroyl fluoride and isobutyric acid anhydride and a solid phase consisting of a hydrogen fluoride complex of said acceptor;
• (3) fractionally distilling said liquid phase of the hydrolysis reaction mixture to provide an overhead fraction of isobutyroyl fluoride for recycle to said hydrolysis step (2) and an isobutyric acid anhydride product fraction.