Abstract: Disclosed is a process for preparing .epsilon.-caprolactone comprising using a percarboxylic acid solution obtained by oxidizing organic carboxylic acid in an organic solvent in the presence of hydrogen peroxide and a boric acid catalyst, and cyclohexanone, supplying 1 to 1.5 mole of percarboxylic acid, 0.012 mole or less of hydrogen peroxide and 0.04 mole or less of the boric acid catalyst per mole of cyclohexanone in a reaction system, and reacting said cyclohexanone with said percarboxylic acid to form .epsilon.-caprolactone.

Abstract: A process for preparing perpropionic acid solution comprising reacting propionic acid with hydrogen peroxide in the presence of a boric acid catalyst wherein the reaction is carried out by using an ethyl propionate as a reaction solvent, and water in the reaction solution is removed continuously by azeotropic distillation with the reaction solvent. Since the reaction is carried out while the concentration of the peroxide in an aqueous phase separated from the distillate by the azeotropic distillation is maintained at not more than 0.1% by weight, a perpropionic acid solution containing almost no unreacted hydrogen peroxide can be prepared.