Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition

Abstract

Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition above and below its melting temperature have been studied and compared with the primary (PKIE) and secondary kinetic isotope effects (SKIE) of 13C and 180, respectively, in the decarboxylation of other heterocyclic acids. The temperature dependence of the secondary oxygen-18 isotope effects is negative in the total 221~55 ~ temperature interval investigated initially. The 13C KIE measured above melting point of N.A. (temperature interval 235 270 ~ are located in the range 1.007 1.009. Below melting point of nicotinic acid the 13C KIE are larger and reveal the negative temperature dependence (13C KIE decreases with decreasing the reaction temperature from 1.013/at 230 ~ to 1.0114/at 221 ~ A discussion of the above isotopic results is presented.