Possible nucleophilic addition accompanying electrophilic addition in the reaction of hypochlorous acid with 2,3-dichloropropene

Abstract

2,3-Dichloropropene reacts in water in the presence of mineral acid with hypochlorous acid to give the expected products of electrophilic addition, 1,3-dichloroacetone (76%), 1,2,3-trichloropropene (22%), and 2,2,3-trichloropropanol (ca. 2%). In the presence of silver ions (which prevents reaction via the chlorine molecule) the yields of these products are decreased and 1-chloro-3-hydroxyacetone is also formed. When the starting olefin is labelled with 36Cl in the 3 position, 1-chloro-3-hydroxyacetone is recovered with the full activity of the starting material. Kinetic measurements carried out in the presence of excess of olefin and silver ion show that an autocatalytic reaction sets in at some time during the course of the normal reaction. The position and extent of this autocatalysis vary markedly as the initial concentrations of hypochlorous acid, mineral acid, silver ion, and olefin are changed; It is most favoured at relatively high concentrations of hypochlorous acid, silver ion, and olefin and at low concentration of (or better in the absence of) mineral acid. Product analyses under kinetically controlled conditions showed that the autocatalytic reaction was associated with the formation of the ketol product. The results seem best discussed in terms of a silver-catalysed nucleophilic process superimposed upon the normal electrophilic reaction.