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

Carbon-13 kinetic isotope effects,C-13-KIE, in the decarboxylation of phenylpropiolic acid (carboxyl C-13) in formic acid medium and C-13 KIE in the decarbonylation of liquid formic acid assisted with PPA and acetophenone have been studied in the 70-100 degrees C temperature interval. The kinetic and isotope results have been discussed and interpreted as indicating that the formation of C alpha-H bond, preceded by the protonation of acetylenic bond of PPA, is the rate determining step followed by carbon dioxide splitting. 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 decarbonylation of formic acid are interrelated processes proceeding in the reaction cage.