Process for producing carboxylic acids

A process for producing a carboxylic acid having (n+1) carbon atoms, comprising:

• carbonylating an alcohol having n carbon atoms, and/or an ester of said alcohol and said carboxylic acid with carbon monoxide in the presence of a catalytic system containing a rhodium catalyst, said process using a reaction medium for the carbonylation which comprises:
• (1) a rhodium catalyst;
• (2) an organic halide corresponding to said alcohol;
• (3) an ester of said alcohol and said carboxylic acid;
• (4) said carboxylic acid;
• optionally
• (5) water, a haloid acid, an inorganic halogen salt or an acetate;
• and
• (6) a cocatalyst selected from the group consisting of arginine, N-acetyl alanine, nitrogen- and oxygen-containing organic compounds represented by the following formula:
• wherein R1, R2 and R3 are identical or different, and each represents:
• wherein
• R4 represents H, an aliphatic group having 1 to 6 carbon atoms, or an arylaliphatic or aromatic group having 6 to 10 carbon atoms;
• U represents H, an aliphatic group having 1 to 6 carbon atoms or an arylaliphatic group or aromatic group having from 6 to 10 carbon atoms;
• V and W each represents a covalent bond, an aliphatic group having from 1 to 6 carbon atoms or an arylaliphatic group or aromatic group having 6 to 10 atoms;
• and
• X, Y and Z each represents H, metal ion or an aliphatic group having 1 to 6 carbon atoms,
• with the proviso that at least one of R1, R2 and R3 is a group other than R4.