C-13 isotope effects in the decarboxylation of phenylpropiolic acid (PPA) in water solution of formic acid (FA), in pure water and the related C-13 kinetic isotope effect in the decarbonylation of formic acid in water solution of formic acid and phenylpropiolic acid

Kinetics and the carbon-13 kinetic isotope effects in the decarboxylation o f phenylpropiolic acid in HCOOH/H2O, 1:1/V:V, solution have been examined b etween 80-140.13 degrees C. C-13 KIE in the decarbonylation of formic acid, proceeding with measurable rate in this medium between 130-150 degrees C, has been determined also and compared with corresponding values found in th e pure HCOOH/H2O solution. Kinetics and C-13 KIE in the decarboxylation of phenylpropiolic acid in pure water have been investigated subsequently betw een 100-143 degrees C in all glass reaction vessels sealed under vacuum. Th e enthalpy of activation of decarboxylation of PPA in pure water, 30.20 kca l/mol, and the entropy of activation, Delta S-not equal = -3.7 e.u., are by 6.7 kcal/mol and 12.5 e.u., respectively, higher than the Delta H-# and De lta S-# values found in the decarboxylation of PPA in pure formic acid. The C-13 KIE equal to 1.004-1.005 between 70-100 degrees C in the pure HCOOH m edium increased to C-13 KIE of 1.020 in the case of decarboxylation of PPA at 133.7 degrees C in the initially pure water.