Design, Synthesis and Study of Catalysts for Organophosphate Ester Hydrolysis

摘要

The hydrolyses of tris-p-nitrophenylphosphate (5), tris-2-pyridylphosphate (6) and ethyl-p-nitrophenylphosphonate (7) catalyzed by two tris-imidazol-yl-phosphine: cobalt 2+ complexes (Co2+:3 and Co2+:4) were studied as a function of pH. In the hydrolyses of both 6 and 7, Co2+:3 (which contains no hydroxyethyl pendant) appears to act as its anionic form, generated by ionization of a Co(2+)- bound water having a pka approx. 8 at 37 C in 80% ethanol-water. On the other hand, (which possesses a hydroxyethyl pendant) catalyzes the hydrolyses of 6 and 7 with an activity that increases linearly with pH up to at least pH 8.3. Above this pH, precipitation of Co2+ (OH-) x becomes a problem. In the latter case, the active form of Co2+:4 has a pKa in excess of 8.3 that apparently obtains from ionization of the Co2+-associated hydroxyethyl group. Evidence is presented that Co2+:4 functions as a general base catalyst in the hydrolysis of 6.