Patent ID: 8097756

Claim:
A process for producing carboxylic acid anhydrides by the carbonylation reaction of a carboxylic acid ester with carbon monoxide containing a small amount of hydrogen in a liquid reaction medium in the presence of a Group VIII B catalyst to produce a carboxylic acid anhydride, the carboxylic acid ester being derived from an alcohol and a carboxylic acid, and the reaction medium comprising the Group VIII B catalyst, an organic halide, the carboxylic acid ester, an alkali metal salt, at least one ionic liquid promoter, the carboxylic acid anhydride and the carboxylic acid; wherein the ionic liquid promoter is selected from: the group consisting of 5-amino-1,3-dimethyl-1-phenylpyrazolium iodide, 2-amino-1-methylbenzimidazolium iodide, 1,2-dimethylbenzimidazolium iodide, N-methylquinolinium iodide, N-methyl-4-di(methylamino)pyridinium iodide, 1,4-dimethylquinolinium iodide, 4-amino-1,2-dimethylquinolinium iodide and 5-amino-1-methylisoquinolinium iodide.