AROMATIC NUCLEOPHILIC-SUBSTITUTION REACTION OF 2,4-DINITROHALOGENOBENZENE AND ETHYL ALPHA-CYANO-PHENYLACETATE BENZYL ANION

The aromatic nucleophilic substitution reaction of 2,4-dinitrohalogeno benzene (DNHB; halogeno = F, Cl, Br) with ethyl alpha-cyanophenylaceta te (ECPA) benzyl anion has been studied by means of UV and IR spectrop hotometry as well as gas chromatography. The rates of intermediate for mation and product formation were determined respectively. In contrast with common SNAr reactions, the formation rate constant of the interm ediates, substituted cyclohexadienates, was in the order of halogen = F>Br>Cl, whereas the rate constant of product formation was in the ord er F>Cl>Br, which revealed that the departure of the halogen atom was the rate-limiting step for the overall reaction in the presence of a s terically hindered nucleophile. These reactions could be catalyzed by the solvated electrons. The corresponding reaction intermediates, radi cal species, were detected by ESR and the reactions were proved to pro ceed mainly by a solvated-electron induced radical chain reaction mech anism.