Process for preparing 1, 6-hexanediol

A process for preparing 1,6-hexanediol comprising feeding (A) a starting material recovered from a reaction mixture resulting from liquid phase oxidization of cyclohexane for the production of cyclohexanol and cyclohexanone, (B) an alkali salt of a carboxylic acid selected from the group consisting of adipic acid and .epsilon.-hydroxycaproic acid, and (C) hydrogen to a reaction zone having a solid catalyst containing ruthenium and tin and carrying out hydrogenation in an aqueous medium containing sodium sulfate in a concentration of 1000 ppm or higher at a temperature of 100 to 260.degree. C. under a pressure of 1 to 25 MPa, said starting material (A) being prepared by extracting carboxylic acids dissolved in said reaction mixture with an aqueous alkali solution, neutralizing the resulting extract containing an alkali salt of carboxylic acids with a mineral acid, extracting the carboxylic acids contained in the solution with an organic solvent to obtain an extract containing the carboxylic acids, evaporating the organic solvent of the extract to remove the organic solvent, and concentrating the residue to increase the total content of adipic acid, .epsilon.-hydroxycaproic acid, .epsilon.-caprolactone and oligomers of .epsilon.-caprolactone to 45 to 80% by weight, the concentrations of the .epsilon.-caprolactone and its oligomers being calculated as converted to .epsilon.-hydroxycaproic acid.