A kinetic and mechanistic study of the cyclisation of 2′-carboxy-4-bromocarbanilide

Abstract

The cyclisation of 2′-carboxy-4-bromocarbanilide to 3-(4-bromophenyl)-1,2,3,4-tetrahydro-2,4-dioxoquinazoline goes exclusively to product except at high pH. However, when both compounds are ionised the reaction is an equilibrium process, and is complicated by decomposition to anthranilic acid and p-bromoaniline. A common mechanism for these two reactions is suggested. The equilibrium constant in aqueous ethanol varies in a serpentine manner with solvent composition; its changes are shown to reflect solute activity. The overall reaction rate falls with increasing ethanol content, but γ‡ unexpectedly exhibits extremum behaviour. Possible reasons for this are discussed. A more thorough study of the cyclisation than that reported was precluded by the severe errors introduced by the superimposed decomposition process.