C-13 kinetic isotope effects in the decarboxylation of phenylpropiolic acid (PPA) assisted with formic acid and C-13 KIE in the decarbonylation of formic acid in the presence of PPA

Carbon-13 kinetic isotope effects,C-13-KIE, in the decarboxylation of pheny lpropiolic acid (carboxyl C-13) in formic acid medium and C-13 KIE in the d ecarbonylation of liquid formic acid assisted with PPA and acetophenone hav e been studied in the 70-100 degrees C temperature interval. The kinetic an d isotope results have been discussed and interpreted as indicating that th e formation of C alpha-H bond, preceded by the protonation of acetylenic bo nd of PPA, is the rate determining step followed by carbon dioxide splittin g. The (CO)-C-13-KIE in the carbon monoxide generation assisted with PPA is much larger than the (CO)-C-13-KIE observed in the generation of CO in the presence of phenylacetylene. Thus the decarboxylation of PPA and decarbony lation of formic acid are interrelated processes proceeding in the reaction cage.