Reactions of very weakly basic acids and esters

4 Reactions of very weakly basic acids and esters 

Oxalate and trifluoroacetate esters are reactive compounds, which are hydrolyzed in aqueous acid at rates which are not a great deal faster than the rates in neutral solution. Moffat and Hunt170, for example, studied the hydrolysis of a series of alkyl trifluoroacetates in 70% acetone-water, and found that the 

All these reactions involve acyl-oxygen cleavage. This has been demon- 

For the three reactions represented in Fig. 12 the maximum rate of hydrolysis in acid represents only a mpdest acceleration, compared with the rate in initially neutral solution. Bunton and Hadwick89,90 explained the maximum for methyl and phenyl trifluoroacetate in terms of negative salt effects on both acid-catalyzed and neutral reactions. Consistent with this interpretation, it was demonstrated directly that the rate of neutral hydrolysis is decreased by added salts. The effect of added salt should be to decrease the activity of water, and perhaps also to salt in the ester. 

The addition of LiCl to the solutions of o-nitrophenyl hydrogen and ethyl oxalates at pH 2.0 causes a progressive decrease in the rate of hydrolysis of each ester, and the rate depression, about tenfold over the range 1.0-6.0 M LiCl, is very similar to that observed when HCI is added91. This makes it clear that the decrease in rate is no more than an effect of changing, ionic strength. When the ionic strength is maintained constant, at 8.0, with LiCl, 

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