Polymerisation and related reactions involving nucleophilic aromatic substitution. Part 1. The rates of reaction of substituted 4-halogenobenzophenones with the potassium salts of substituted 4-hydroxybenzophenones

Abstract

The rate of displacement of fluorine from 4′-X,4-fluorobenzophenones by the potassium salts of 4′-X,4-hydroxybenzophenones (X = CF₃, Cl, F, H, OPh, and OMe) has been studied at 175–225 °C in diphenyl sulphone as solvent. Comparison with the corresponding rate of displacement of chlorine indicates that the reaction is a bimolecular nucleophilic aromatic substitution. The reaction obeys the Hammett equation using normal σ values for substitution in both the substrate (ρ 1.19) and the phenolate (ρ–0.53). There is also a marked salt effect on the reaction rate and this has been included with the substituent constants in a general equation for the calculation of rate coefficients. The effect of an O^– substituent is more marked than would have been expected from the previous range of σ values ascribed to this substituent.