A reinvestigation of the vapor phase bromination of 2-bromobutane

Abstract

The solution phase photobromination of 2-bromobutane yields 2,2-dibromobutane, meso-2,3-dibromobutane, dl-2,3-dibromobutane, small amounts of 1,2-dibromobutane, and 2,2,3-tribromobutane. However, in the corresponding vapor phase bromination these products appear along with other polybrominated products. The yield of these polybromides increases with temperature. The increase in yield of the polyhalogenated materials is rationalized by considering the thermal instability of the β-bromoalkyl radical, which eliminates a bromine atom to form the corresponding alkene. It is demonstrated that in the vapor phase allylic bromination competes successfully with bromine addition. Reaction schemes are suggested to explain the formation of polybromides. An explanation is also offered for the discrepancy between these results and those of previously reported vapor phase work.