The effects of structure and of ring-size upon some properties of mono- and di-alkoxybenzoic acids

Abstract

The pK_a values of methylenedioxy-, ethylenedioxy-, and trimethylenedioxy-benzoic acid (II; n = 1, 2, and 3; R = CO₂H) and the rates of alkaline hydrolysis of the corresponding ethyl esters have been determined. Dissociation of the acids (II) varies in the order, n= 1 < n= 2 < n= 3, whereas the order of reactivity for ester hydrolysis is n= 2 < n= 1 < n= 3. The effect of variation in n upon the reactivity of the esters provides further evidence for the operation of an inductive interaction between the oxygen atoms, which is relayed through the methylene chain which links them. For the corresponding carboxylic acids, this inductive interaction appears to have little significance. No additivity in the cumulative effects of the oxygen atoms has been observed.