KINETICS OF HYDROLYSIS OF p-NITROPHENYL ACETATE IN FROZEN SUSPENSIONS OF SILICA GEL.

The influence of silica gel on the hydrolysis of p-nitrophenylacetate in frozen aqueous solutions of Na//2HPO//4 was studied in the 273-233 degree K range. It was shown that at 268. 5 degree K, in frozen 13% suspensions, the increase in the reaction rate is more than 100 fold. It was found that the reason for the acceleration of the reaction is increase in the volume of the mobile phase in the frozen system due to the presence of nonfreezing water near the surface of the solid material, preventing the crystallization of p-nitrophenyl acetate on freezing, and thus promoting the retention of the substrate in a reactive soluble state, at temperatures tens of degrees lower than the cryohydrate point of the Na//2HPO//4-water system.