Additional Evidence for Kinetic Salt Effects upon Chlorinations in Acetic Acid

Abstract

In the preceding report data were presented which demonstrated an ionic strength influence upon the room temperature chlorination of both alkene double bonds and arenesulfenyl chlorides in anhydrous acetic acid as the solvent (4). The observed kinetic acceleration exerted by the diverse electrolyte was assigIled to the activities of the free (dissociated) ions from the electrolyte and not to the ion pairs. The present communication cites very recent kinetic results involving the chlorination of aromatic hydrocarbons (2) which exhibit electrolytic effects like those found in the arenesulfenyl chlorides. Phenanthrene and biphenyl undergo chlorination in anhydrous acetic acid at 25°C to yield dichloro and acetoxychloro products (2). These second order processes have been interpreted by de la Mare, et v1., to require a sis-addition to the carbon-carbon bond and an ion pair transition state. Qualitative support for an ionic or strongly polar mechanism comes from the increased reaction rate in the presence of the added electrolytes: LiCl; LiC104; NaOAc; and HC104. Two instances for which sufficient data are available for the reaction in the presence of low concentrations of added electrolytes are biphenyl with perchloric acid and phenanthrene with lithium perchlorate. The rate