The kinetics and mechanisms of chlorohydrin formation.

The reaction between a halogen or hydrogen halide and an olefinic substance is one of the fundamental reactions of organic chemistry. It is not surprising, therefore, that considerable attention has been given to the kinetics of the electrophilic and nucleophilic addition of halogens or hydrogen halides to olefins under the influence of both thermal and photochemical activation (1-6). The factors most likely to influence the rate of the reaction viz., the nature of the olefin and its substituent groups, the particular halogen or hydrogen halide employed, the temperature, the influence of catalysts and the powerful solvent effects have all been investigated in detail with the result that this seemingly straightforward class of reactions has been shown to possess considerable complexity. On the other hand, the kinetics of the reactions of hypohalous acids, and in particular hypochlorous acid, with olefins has received rather scant attention. In some ways this is remarkable in view of the fact that the formation of chlorohydrins by this reaction has been known for at least seventy years when Erlenmeyer and Muller (7) and Melikov (8.9) investigated the addition of hypochlorous acid to the isomeric crotonic acids. Perhaps the most important contribution to our knowledge of reactions of this kind is due to Bloomfield and co-workers (10,11) who, while investigating the addition of olefinic acids and esters towards hypochlorous acid and ethyl hypochlorite, isolated, identified and estimated the relative amounts of the isomeric chlorohydrins formed in this reaction. At about the same time, Shilov and collaborators began an investigation of the kinetics of the reactions involving the addition of hypochlorous acid to olefinic compounds and during the past eighteen years, a series of papers from this source have been published Ca- 30. It is unfortunate that these investigators should have studied the catalytic effect of added\ud chloride ion, usually from hydrochloric acid, in the majority of their reaction systems as the intervention of molecular chlorine formed in this way would seriously interfere with the true nature of hypochlorous acid additions. The results of early work by Shilov et al. (14) on the addition to ethene, indicated that the addition of chlorine to the double bond was about 100,000 times greater than that of hypochlorous acid, yet it was only in later papers (10.- 22) that this complicating factor seemed to be fully appreciated. However, during their early work they concluded that the addition reaction was a complex one and could not be described by a simple bimolecular or termolecular process. It seemed, therefore, that a detailed investigation of the kinetics of chlorohydrin formation was desirable and would prove a profitable and useful subject for research