Comparison of the proton-transfer behaviour of 4-(2,4-dihydroxyphenylazo)- and 4-(2-hydroxy-1-naphthylazo)-benzenesulphonates

Abstract

A linear dependence of rate on hydroxide ion concentration has been observed for removal of the intramolecularly hydrogen-bonded proton from 4-(2-hydroxy-1-naphthylazo)benzenesulphonate (2), in contrast to the complex rate dependence found for 4-(2,4-dihydroxyphenylazo)benzenesulphonate (1). Possible explanations are considered. The magnitude of the kinetic solvent isotope effect and the observation of general base catalysis in proton removal from (2) are discussed.