Nucleophilic Aromatic Substitutions. Part XIV.. Investigation of the mechanism of hydroxy‐denitration of 4,2‐and 2,4‐chloronitrobenzenediazonium ions as a function of pH

Abstract

Summary4,2-Chloronitrobenzenediazonium ions in aqueous buffer solutions between pH 2.9 and 7.9 do not hydrolyze by dediazoniation as previous authors have assumed, but by denitration. The isomeric 2,4-compound reacts by denitration (ca. 70%) and dechlorination (ca. 30%). The reactions are general base catalyzed. The products and kinetics are consistent with an S,Ar-mechanism in which the general base-catalyzed addition of a hydroxyl group at the reacting C-atom is rate-limiting. The rate maxima at or near the pH-values corresponding to (pK, + pK2)/2 of the diazonium cis-diazotate equilibria can be rationalized on the assumption that the diazonium ion is the only equilibrium form of the diazo compound which enters the substitution proper, and the superposition of rate term ;,k, [B] of all nucleophiles involved (HzO, OH-and buffer bases).