Regioselectivity of methoxydebromination of substituted pentabromobenzenes C6Br5X in pyridine

The kinetics and regioselectivity of methoxydebromination of some substituted pentabromobenzenes C₆Br₅X (X = NO₂, CN, NH₂, MeNH, and MeO) were studied in pyridine at 115°C. The partial rate factors (k_f) were calculated for different positions of the polybrominated ring in these compounds. The effect of substituents X on methoxydebromination at themeta- andpara-positions is satisfactorily described only by the Hammett substituent constants ( = 2.22,r = 0.96). This allows one to conclude that direct polar conjugation of the substituents contributes only slightly to the transition state of the reaction. Theorthobromine atoms have a significant steric effect.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1784–1788, September, 1995.