Bromination of butyl rubber in the presence of electrophilic solvents and oxidizing agents

Bromination of 1,4-isoprene units in butyl rubber proceeds by substitution leading to the formation of hydrogen bromide as byproduct. In-situ conversi on of HBr back to bromine is possible by the use of oxidizing agents but th e reaction is very slow and oxidation of the polymer may occur. The reactio n is complex and is typically conducted in a two-phase system. It has been found that the rate-controlling step is the bromination of the 1,4-isoprene unit in the organic phase, and not the oxidation of HBr to Br-2 in the wat er phase or the mass transfer of HBr or Br-2 between phases. Increasing the electrophilicity of the organic phase dramatically increased the overall r ate. A 90-95 wt % conversion of bromine was achieved in one minute. Side or consecutive reactions (oxidation of the polymer, hydrobromination of the u nsaturation, rearrangement or dehydrohalogenation of the main product) coul d be avoided, allowing the synthesis of a highly uniform material.