Carbon-13 fractionation observed in thermal decarboxylation of pure phenylpropiolic acid (PPA) dissolved in phenylacetylene

The determination of the C-13 fractionation in the decarboxylation of pure phenylpropiolic acid (PPA) above its melting point has been extended to higher degrees of decomposition of PPA by carrying out two-step decarboxylations to establish the maximum possible yield of carbon dioxide in the temperature interval of 423-475 K (58%). The result was compared with the yields of CO2 for decarboxylation of PPA in phenylacetylene solvent (PA) (much smaller, temperature dependent, and equal to 11% at 406 K). The ratios of carbon isotope ratios, R-so/R-pf, all smaller than 1.009 in the temperature interval 405-475 K, have been analyzed formally within the branched decomposition scheme of PPA, providing carbon dioxide and a decarboxylation resistant solid chemical compound enriched in C-13 with respect to CO2. A general discussion of the C-13 fractionation in the decarboxylation of pure PPA and PPA dissolved in PA is supplemented by the model calculation of the maximized skeletal C-13 KlEs, in the linear chain propagation of the acetylene polymerization process. Further studies of the C-13 fractionation in condensed phases and in different hydrogen defficient and hydrogen rich media have been suggested.