PURPOSE: To obtain the subject substance with extremely high reaction speed and wherein compsn. of the product can be selective and formation of tar is little by performing hydrogenation of acetic anhydride in the presence of an Ru compd. and CH3I or CH3I and LiI in liq. phase.

CONSTITUTION: When the objective substance is obtd. by hydrogenation of acetic anhydride, the reaction is performed in the presence of an Ru compd. and CH3I or CH3I and LiI in liq. phase at 18-21C under 1,000-2,000 psig. As the Ru compd., RuCl3.3H2O, RuO2, Ru salts of org. acids, etc., are pref. and they are used by a concn. of 500-1,000 ppm (in terms of Ru metal) to the substance to be hydrogenated. The amt. of use of CH3I is 0.25-15 wt.% per the substance to be hydrogenated and it is varied by a required hydrogenated product. In addition, formation speed of ethylidene diacetate is increased by using LiI of 0.5-1.5 wt.% of acetic anhydride.