67771-45-3Relevant academic research and scientific papers
Equilibrium Constants and Rate Constants for the Transformations in Aqueous Solution of a Spirocyclic Hydroxyphosphorane
McClelland, Robert A.,Cramm, David A.,McGall, Glenn H.
, p. 2416 - 2420 (2007/10/02)
A quantitative study is reported for the reactions in water of the hydroxyphosphorane RvOH (Granoth and Martin, J.Am.Chem.Soc. 1978, 100, 5229; 1979, 101, 4618).This species equilibrates with the isomeric phosphinate RivOH (K1 = vOH>/ivOH>).Addition of base results in the phosphoranoxide RvO-, the conjugate base of RvOH (K2 = vO->+>/vOH>).This interconversion occurs with an apparent acidity constant K1K2/(1+K1) of 1.6E-10. With estimates of K1, pK2 is calculated to lie in the range 9-10.Base solutions of this system are not stable; a slower transformation produces the phosphinate anion RO2-, the hydrolysis product of RivOH.RO2- is converted back to RivOH/RvOH in acid solutions.The overall equilibrum (RvOH + RivOH) RO2- has an apparent acidity constant of 1.8E-8..At equilibrium the ratio of the concentrations of the two anions ->:vO-> is 1.3E3.Kinetics of the overall equilibrium have been studied as a function of pH.An analysis is presented in terms of hydronium ion and hydroxide ion catalyzed interconversion of RivOH and RO2H, the latter conjugate the acid of RO2-.The equilibration of RivOH and RvOH or RvO- is too rapid to be studied by stopped-flow spectroscopy at all pH.Comparison to analogous carbonyl group systems suggests that pentavalent intermediates of phosphoryl transfer reactions may be kinetically less stable than tetrahedral intermediates of acyl transfer reactions.
