Halogen substitution in ethylenic hydrocarbons

Abstract

It has long been known that in the addition of halogens to acylic ethylenic compounds some substitution occurs simultaneously, as evidenced by the formation of halogen hydracid. In investigations of the kinetics of halogen addition to such compounds little attention has usually been paid to either the amount or the mechanism of this substitution. Recently, however, Taft (J.A.C.S. 1948, 70, 3364) has put forward a mechanism to explain the simultaneous occurrence of and to predict the relative amounts of addition and substitution in the chlorination of aliphatic olefines and chloro-olefines at low temperatures. This mechanism is based on the results of quantitative investigations by Groll, Hearne, Rust and Vaughan (Ind. Eng.Chem.1939, 31, 1239) and of Tishchenko (J.Gen.Chem.U.S.S.R.1938, 8, 1232-1245; Chem.Abstr.1939, 33, 4190). These investigators both chlorinated a large number of olefines and chloro-olefines in presence of a liquid phase at temperatures not greater than 70 ° C. The reaction products resulting from 100% absorption of chlorine by an excess of compound were quantitatively separated into their components and the percentage of each recorded. 15 of the compounds thus chlorinated are selected by Taft to illustrate his theory.