Studies on the Derivatives of Pectic Substances Part III

The formation of ester derivatives of pectic acid was studied with the reaction mixture composed of alcohol, concentrated hydrochloric acid and water. With saturated aliphatic alcohols, ethylene glycol and glycerol, the esterification proceeded readily. Fully esterified derivatives, however, were not obtained in this reaction. Ethanol showed less reactivity than that of two alcohols described above. Among unsaturated alcohols, allyl alcohol effected esterification in the degree which was approximately the same as that of propyl alcohol. The reactivity of alcohols in esterification reaction of pectic acid may be determined by the proportion of the number of C atom and OH group in the molecule of alcohols rather than by the molecular weight. The degrees of esterification in the derivatives decreased with the increase of number of C atom with respect to the number of OH group. The viscosity decreased markedly as the ester content of the derivative increased, and, at 80% or over, the viscosity of esterified pectic acid was close to that of water. The reactions of pectin esterase and of an endo-polygalacturonase on synthesized ester derivatives of pectic acid are discussed.