SOLVOLYSIS AND ABNORMAL MECHANISM OF CHLORINATION OF 2-NITROBENZENESULFENYL CHLORIDES .17.

The kinetics of the chlorination of various para-substituted o-nitrobenzenesulfenyl chlorides in solvolytic media such as aqueous acetic acid have been studied in detail. The stoichiometry of these reactions has been established. Chlorine-dependent and -independent terms in the rate equation appear to correspond to electrophilic and nucleophilic reactions at bivalent sulfur. Electron-releasing para substituents enhance the electrophilic reaction which has a Hammett p value equal to that of the corresponding reaction of substrates without the 2-nitro group.1a The chlorine-independent term in the rate equation, on the other hand, shows no rate response with change of the para substituent of the 2-nitro substrate. Dependence on methanol and/or water concentration in the rate equation is uniformly fourth order. In the aqueous acetic acid medium dependence of the rate on acetate and/or dihydrogen phosphate anion has been determined to be first order with specific catalytic constants of nearly the same magnitude. A strong normal salt effect19 was observed for the electrophilic reaction b = 24.5) for added lithium perchlorate. The chlorine-independent reaction, however, showed no rate change with neutral salt whereas the hydrolysis reaction showed moderate acceleration characteristic of the normal salt effect. Neither lithium chloride nor hydrochloric acid added to the reaction medium had any influence on rate. The unusual pattern of reactivity observed for these substrates has been explained by invoking reaction intermediates possessing a trigonal-bipyramid structure of sulfur valencies in which the o-nitro oxygen atom and a chlorine occupy apical positions. © 1968, American Chemical Society. All rights reserved.