Thiol Anions in Nucleiphilic Aromatic Substitution Reactions with Activated Aryl Halides. Attack on Carbon vs Attack on Halogen

Article abstract of DOI:10.1021/jo00073a020

The reaction of o-iodonitrobenzene with thiol anions (RSNa, R = Me, 2-Pr, t-Bu) in 2-propanol solution produces the o-nitrophenyl thioether and nitrobenzene in relative proportions and with rates which depend on R.The results of kinetic analysis and of D-incorporation experiments are inconsistent with a radical chain mechanism as proposed earlier for the alkoxide-promoted hydro-de-halogenation of aryl halides.The data clearly indicate the involvement of a carbanionic intermediate (the o-nitrophenyl anion) and are consistent with a stepwise mechanism in which the first step is nucleophilic attack on iodine to form a sulphenyl halide and the o-nitrophenyl anion (a halogenophilic reaction).In contrast, the reaction of the other o-halonitrobenzenes (F, Cl, Br) produces exclusively the product of alkylthio-de-halogenation according to the addition/elimination (S_NAr) mechanism.The fact that in these systems the reactivity of thiol anions results from their ability as bielectronic nucleophiles rather than as reducing agents is discussed.