Pressure Dependences of Rates of Nucleophilic Attack by Water in Aqueous Solution. Hydrolyses of Methyl p-Nitrobenzenesulfonate and Ethyl Trichloroacetate

Article abstract of DOI:10.1021/j100231a032

The pressure dependences of the rates of two formally uncatalyzed reactions of water in aqueous solution have been measured in the range 0-2 kbar at 25 deg C.A plot of ln k vs.P for the hydrolysis of ethyl trichloroacetate (water-catalyzed water addition, followed by ethanol elimination) is smoothly and gently curved with ΔV^<*> = -33 +/- 3 cm³ mol^-1 near P = 0.The corresponding plot for the hydrolysis of methyl p-nitrobenzenesulfonate (direct methyl transfer from ArSO3^-1 to H2O) shows an abrupt change in slope near 0.1 kbar, the slope between 0 and 0.07 kbar corresponds to ΔV ^<*> = -24 +/- 5 cm³ mol^-1, while that between 0.14 and 2.07 kbar corresponds to ΔV^<*> = -6.3 +/- 0.1 cm³ mol^-1.Comparison to the data of Baliga and Whalley for CH3Br hydrolysis at higher temperatures suggests that the pressure dependences of rates of methyl transfer to water may commonly show such changes in slope and that increasing temperature shifts the slope change to higher pressure and decreases its sharpness.