Some aspects of the halogenation of phenols aromatic amines and their derivatives

Abstract

This thesis is divided into three main sections, as follows: 1. In "Section A" are outlined some of the features and broad concepts of the theory of electrophilic aromatic substitution with special reference to topics that are relevant to the present work. 2. In "Section B" are presented the results obtainedfor the rates of molecular chlorination in acetic acid at 25° of N-acetyldiphenylamine, N-acetylcarbazole, 2-chloro- and 3-chloro-N-acetylcarbazole. The isomer distribution has also been assessed, and partial rate factors have been calculated for the first two compounds. Results for competitive chlorination of carbazole and diphenylamine are also furnished. The reactivity of the various positions, as well as the overall relative reactivities of these systems are discussed in the context of the theory of aromatic substitution reactions, but with special reference to earlier work on these compounds. 3. In "Section C" the results are recorded for the bromination of phenol and of anisole at 25°, in presence of initially added bromide ion, with molecular bromine in either acetic acid or deuteroacetic acid as solvent. The ionic strength of the reaction medium has been kept constant (0.2M) by adding lithium perchlorate whenever necessary. The rate (apparent; app.) of bromination of the two compounds in both solvents were obtained; and from these the rate constants for bromination by free bromine (k) were evaluated by graphical means. It has been necessary also to obtain the equilibrium constant for tribromide ion formation in both solvents. The kinetics and mechanism of these reactions are discussed. Attempts are made to explain the observed isotope effects. The earlier suggestion by Robertson and de la Mare, that the greater reactivity of phenol as compared with anisole can in part be ascribed to OH hyperconjugation, is revived.