Studies on the hydrolysis reaction of model substances of cellulose in the presence of polymer catalyst, 2. Effect of inorganic salts on the hydrolysis rate of dextrin catalyzed by poly(vinyl alcohol-co-vinylsulfonic acid)

The effect of inorganic salts on the hydrolysis rate of dextrin catalyzed by poly(vinyl alcohol-co-vinylsulfonic acid) was studied. The reaction is enhanced by addition of sodium chloride and potassium nitrate, and retarded with sodium sulfate and potassium sulfate. It may be presumed that in the presence of large amounts of salts the acidity is a predominant factor for the hydrolysis rate of dextrin in the present system, since it was found that the rate shows a linear relationship with the pH of the reaction mixture, and that the logarithm of the reaction rate was proportional to the ionic strength at values > 0,5 moll^?1. The difference in the reaction rates catalyzed by the copolymer or sulfuric acid was diminished with addition of salt, having no relation to whether the reaction rate was enhanced or retarded. Activation parameters of these reactions in the presence of salt were investigated, and it was found that the rate acceleration obtained by addition of salt was due to the increase in entropy of activation, although the enthalpy of activation was also increased. These effects are quite different from that observed in the rate acceleration by introducing hydroxyethyl units into the copolymer, suggesting that the reaction mechanisms for both rate acceleration effects are quite different, as can be inferred from the isokinetic relationships.