Densmore, C.G., H. Wheeler, R. Cohenour, T.W. Robison, D. Hasam, B.J. Cordova, P.C. Stark, E. Fuller, C. Cook and H. Weber, “Development of a Scaleable Synthesis for 1 Bismaleimide Resin 2-bis(2-aminophenylthio) ethane (APO-Link) used in the Production of Bismaleimide Resin”, Organic Process Research and Development, Vol. 11(6), pp. 996-1003, 2007. DOI: 10.1021/op700122q
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.