The diamine reagent 1,2-bis(2-aminophenylthio)ethane is no longer commercially available but is still required for the synthesis of the bismaleimide resin, APO-BMI, used in syntactic foams. In this work, we examined the hydrolysis of benzothiazole followed by reaction with dichloroethane or dibromoethane. The deprotonation of 2-aminothiophenol followed by reaction with dibromoethane was also investigated and later optimized for scale-up by scrutinizing all aspects of the reaction conditions, work-up, and recrystallization. On bench-scale, the optimized procedure consistently produced a 75-80% overall yield of finely divided, high purity product (>95%). The material was also produced on both a 100 lb scale and a 200 lb scale using the optimized process, giving high quality material in excellent yield.

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