An investigation of the photodecomposition of N-bromosuccinimide; the generation and reactivity of succinimidyl radical

The photolysis of acetonitrile solutions of N-bromosuccinimide (NBS) in the presence of ethylene oxide and an excess of olefins or benzene in the −30 ∼ 20 °C range was shown to generate the succinimidyl radical in competition with the bromine atom reactions. The succinimidyl radical preferentially attacked a π bond to give 1-succinimidyl-2-bromoalkanes, rather than abstracting alkyl hydrogens. Allylic bromination also occurred and competed with the 1,2-addition. Formation of 3-bromocyclohexene in the presence of cyclohexene at 10–20 °C could be effectively reduced at lower temperatures or in the presence of a high concentration of ethylene oxide; the 1,2-addition process was favored at low temperature but surprisingly not facilitated significantly in the presence of ethylene oxide. The primary adducts from benzene readily eliminate HBr to give N-phenylsuccinimide. The attack of a bromine atom on a carbon–carbon double bond may become an important step in the 0 ∼ −30 °C range. The ease of the addition reaction suggests that this succinimidyl radical may have a Σ electronic configuration.