Mechanism of the hydrolysis of N-aryliminotriphenylphosphoranes
Tóm tắt
Hydrolysis reactions of N-aryliminotriphenylphosphoranes (I) at varying pH have been investigated kinetically. The reactions produced aniline derivatives and triphenylphosphine oxide as the products. The reactions are first-order, and the Hammett ρ values are -0.29 and -0.63 at pH 3.0 and 8.0, respectively. The reaction rate increased linearly with acetate ion concentration at [AcO−] < 0.05 M and approached a limiting value at higher base concentration. The plot of logk
t versus pH shows that there are two different regions in the rate profile; one part in which logk
t increases with hydronium ion concentration and the other where k
t is a constant regardless of pH. On the basis of these results, a plausible hydrolysis mechanism is proposed. At pH < 8.0, the reaction proceeds by protonation of the iminophosphorane nitrogen atom, followed by the addition of a water molecule. At pH > 8.0, the proton transfer from water to α-nitrogen of the iminophosphorane becomes the rate limiting step.
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