Reactions of Nucleogenic Chlorine Atoms with Simple Aromatic Compounds

Abstract

Summary Reactions of recoil chlorine resulting from the 37Cl(n, γ)38Cl-process have been studied in liquid aromatic compounds of the type C6H5X [X = F, Cl, I, CH3, CF3, NO2], using both binary CCl4/C6H5X-systems and 2 mole % Cl2-containing pure aromatic substrates. No pronounced orientation effects for the o-, m-, p-distribution of the monochloro isomers are observed at high ArH concentration. The functional group has little or no influence on the reactivity of the aromatic compound towards hydrogen substitution. The lack of selectivity- and reactivity effects indicates the absence of electrophilic substitution processes. It is suggested that recoil chlorination largely proceeds via hot, neutral chlorine atoms. Comparison with results obtained from the γ-radiolysis of the corresponding systems show that deviations from purely non-discriminating reactions can be ascribed to caged thermal radical reactions. The yield for heavy atom- and group displacement at high ArX concentration increases in the following sequence of the displaced group X:CH3 < CF3 < F < I < NO2 < CI. The mass of the displaced atom or group and cross sectional effects, rather than bond energies are shown to be yield-determining factors the lack of bond energy effects and the almost complete retention of the original isomeric form after chlorine replacement in o- and m-dichlorobenzene rules out an addition-type reaction followed by a decomposition of the excited intermediate. Both hot replacement reactions and caged thermal radical reactions are assumed to be responsible for the formation of C6H5 38Cl from C6H5X.