Abstract: A process for the production of acetic acid comprising carbonylating with carbon monoxide methanol and/or a reactive derivative thereof in the substantial absence of a metal promoter and/or ionic iodide co-promoter in a carbonylation reactor containing a liquid reaction composition comprising an iridium carbonylation catalyst, methyl iodide co-catalyst, water, acetic acid and methyl acetate wherein there is maintained (i) in the liquid reaction composition:(a) water at a concentration of less than 5.0% by weight and(b) methyl iodide at a concentration greater than 12% by weight and (ii) in the carbonylation reactor a total pressure of less than 50 barg.

Abstract: A process for the production of a carboxylic acid by carbonylation of an alkyl alcohol or its reactive derivative comprises contacting the reactant with carbon monoxide in a liquid reaction composition comprising: (a) an iridium catalyst or rhodium catalyst, (b) alkyl halide, (c) at least a finite concentration of water and (d) rhenium as promoter.

Abstract: A process or the liquid phase carbonylation of methanol or a reactive derivative thereof comprises contacting carbon monoxide with a liquid reaction composition comprising methanol or a reactive derivative thereof, a halogen promoter and a rhodium catalyst system comprising a rhodium component and a bidentate phosphorus-sulphur ligand, the ligand comprising a phosphorus dative center linked to a sulphur dative or anionic center by a substantially unreactive backbone structure comprising two connecting carbon atoms or a connecting carbon and a connecting phosphorus atom. Novel rhodium ligand complexes of formula [Rh(CO)L].sub.m and Rh(CO)LY] wherein Y is a halogen, m is a number less than 10 and L is ##STR1## wherein the R groups are independently selected from C.sub.1 to C.sub.20 alkyl, cycloalkyl, aryl, substituted aryl and optionally substituted aralkyl; the R.sup.5 groups are selected from hydrogen, C.sub.1 to C.sub.

Abstract: A process for the production of a carboxylic acid anhydride comprises contacting a reaction composition comprising a carboxylic acid ester, a hydrocarbyl halide and/or a hydrocarbyl ether reactant and a hydrocarbyl halide promoter with carbon monoxide in the presence of a catalyst comprising an insoluble polymer support having pendant quaternised N-base or alkylated N-oxide pyridine groups supporting a rhodium species in which process the rhodium species is prevented from leaching from the polymer support by maintaining throughout the process a finite concentration of carboxylic acid anhydride in the reaction composition.