C13 ISOTOPE EFFECT IN THE DECARBOXYLATION OF NORMAL MALONIC ACID

Abstract

An investigation has been made of the relative rates of decarboxylation of two isotopic species of malonic acid, one containing only C12 carbon atoms and the other containing a C13 in a carboxyl position. Two effects were observed using malonic acid containing a normal abundance of C13—(1) a 3.3% faster rate of reaction for the molecule containing only C12 carbon atoms; (2) a 2% greater probability of rupture of a C12–C12 bond than a C12–C13 bond in the molecule containing a C13 carbon. The latter effect was found to be independent of temperature. The magnitude of the isotope effect is in reasonable agreement with theoretical predictions.