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The decarboxylation kinetics of 2,4-dihydroxybenzoic acid have been studied in 0.1–8 N aqueous HCl at 50°. At low HCl concentrations, the observed first order rate constant, k, increases with increasing acidity of the solution. In solutions with 3.5–6 N HCl, k remains constant. The D2O solvent isotope effect decreases from kH2O/kD2O = 2.0 in 1N HCl to 1.3 in 5 N HCl, and it remains unchanged at 1.3 if the HCl concentration is increased further to 8 N. It is concluded that an increase of the acidity of the solution causes a change of the rate determining step from slow proton transfer to rate limiting C? C bond cleavage. 相似文献