Process for producing diol compounds

A process for producing diol compounds comprising the steps of;

• esterifying a carboxylic acid mixture collected from a reaction product mixture liquid obtained by a liquid phase oxidation reaction of cyclohexane with air, with an alcohol, and
• hydrogenate-decomposing the resultant esterification product with hydrogen,
• wherein the hydrogenate-decomposition of the esterification product with hydrogen is carried out in the presence of a combined catalyst comprising:
• a catalyst (A) comprising, as principal components, copper oxide and zinc oxide in the form of particles passed through a 200 mesh sieve and having an average size of 1 to 50 .mu.m,
• and a catalyst (B) comprising copper oxide and iron oxide carried on aluminum oxide in the form of particles having an average size of 5 to 15 .mu.m,
• the catalyst (A) and the catalyst (B) are present in a weight ratio of 1:0.5 to 1:10.