Carbon-13 kinetic isotope effect and its temperature dependence in the decarboxylation of lactic acid of natural isotopic composition with aqueous sulphuric acid

Carbon-13 kinetic isotope effect in the decarboxylation of lactic acid of natural isotopic composition in sulphuric acid diluted with water in M(H2O)/M(H2SO4) molar ratio equal to 2.2 has been studied in the temperature range 80-130 C and found to be normal. The absolute values and the temperature dependence of the experimental 13C-K.I.E. are in agreement with the absolute values and the temperature dependence of the theoretical 13C-K.I.E. calculated under the assumption that one frequency corresponding to the carbon-oxygen bound broken in the decarboxylation reaction is lost in the course of activation of lactic acid molecules. The chemical side reactions leading to the abnormal temperature dependence of the carbon-13 and carbon-14 isotope fractionation, observed in the course of decarboxylation of lactic acid in concentrated sulphuric acid, have been suggested. (author). 11 refs, 1 fig., 1 tab