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Why do hydrolysis reaction rates typically increase at higher pH?


bentleyt@expert.cc.purdue.edu

Hydrolysis reactions are a large and diverse set. Here is a very simple example. Methyl halides undergo hydrolysis according to

CH3X + H2O CH3OH + H+ + X- (rate constant k1)

but they also react with hydroxide in a reaction very familiar to first semester organic students:

CH3X + OH- CH3OH + X- (rate constant k2)

The first reaction is known to be first order, and the second is second order, so the rate law is

dx/dt = k1(CH3X) + k2(CH3X)(OH-)

where x is the concentration of methyl halide reacted at time t. You can use a similar explanation for many other substances that react with both water and hydroxide.

For a review of the kinetics of typical hydrolysis reactions, see H. Wendt, Chimia, 27, 575 (1973).

Author: Fred Senese senese@antoine.frostburg.edu



General Chemistry Online! Why do hydrolysis reaction rates typically increase at higher pH?

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/kinetics/faq/hydrolysis-rate-and-pH.shtml