Free Radical Reductive Degradation of vic-Dibromoalkanes and Reaction of Bromine Atoms with Polyunsaturated Fatty Acids: Possible Involvement of Br. in the 1,2-Dibromoethane-Induced Lipid-Peroxidation

Bromine atoms generated upon reductive degradation of 1,2-dibromoethane and various other vic-dibromoalkanes have been shown to react with polyunsaturated fatty acids via both abstraction of bisallylic hydrogen and addition to the double bonds. The abstraction process occurs with 53, 68, and 77% efficiency from linoleic (18:2), linolenic (18:3), and arachidonic acid (20:4), respectively. The corresponding absolute rate constants have been evaluated to be 1.2 × 109, 1.8 × 109, and 5.1 × 109 M−1 s−1 for these three polyunsaturated fatty acids (PUFAs). The rate constants for the bromine atom addition reaction appear to be very similar for all PUFAs and have been determined to (1.2 ± 0.3) × 109 M−1 s−1. Absolute rate constants in the order of 105-106 s−1 have also been measured for the bromine atom elimination from various β-bromoalkyl radicals. The results render bromine atoms a potential initiator for lipid peroxidation, and their reactions may well provide an important chemical basis for the overall toxic action of 1,2-dibromoethane and related substrates.