Design, Synthesis and Study of Catalysts for Organophosphate Ester Hydrolysis.
Annual rept. 15 Mar 83-14 Mar 84,
ALBERTA UNIV EDMONTON DEPT OF CHEMISTRY
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We have prepared several tris-imidazol-2-yl phosphines 9-12 and evaluated their Co2 and Zn2 complexes as catalysts for the hydrolysis of p-nitrophenyl-picolinate 13 and ethyl-p-nitrophenyl methyl phosphonate 14. For the hydrolysis of 13, the Co2 complexes of bis4,5-diisoproylimidazol-2-yl-imidazol-2-yl phosphine 12 appear to act by a common mechanism. Plots of K sub obs the observed pseudo-first order rate constant for the hydrolysis of 13 catalysed by 11Coco2 or 12Co2 as a function of pH show two regions, suggestive of formation of an active LCo2-OH-unit. The pKas of the LCo2-OH2 speciesw of both 11 and 12 are also found to be 7.6-7.8. Kinetic analysis reveals that the basic forms of the complexes are acting as bimolecular nucleophiles toward 13. Hydrolysis of the phosphonate ester 14 is promoted by 12Co2, the reaction rate increasing in a first order way with OH- from pH 7.4-8.3. Since there is no signoidal titration behavior of the rate at pH 7.6-7.8 suggestive of active 12Co2-OH- form, the mechanism of hydrolysis of 14 by 12Co2 must be different from that found for the hydrolysis of 13. Complex 12Co2 is at least 5-fold more active than is 11Co2, although the latter precipitates from the reaction mixtures, which makes comparison difficult.
- Organic Chemistry