Temperature Dependence of the Carbon Isotope Effect in the Dehydration of Formic Acid by Concentrated Sulfuric Acid

Abstract

The C13 kinetic isotope fractionation in the dehydration of formic acid by concentrated sulfuric acid was studied over the range --30.0 to 0.0 . The observed temperature dependence was examined by the gamma-barl' method of Bigeleisen and Wolfsberg (both with and without consideration of the effects of loss of bending frequencies) and by the semi-empirical method of Yankwich, Weber, and Ikeda. Calculated values of the temperature-independent factor in the isotopic rate constant ratio lie within 1% of unity; the calculated sums of the differences upon activation of the diagonal cantesian force constants correspond especially well with the value expected for C- O bond rupture when bending frequency losses are taken into account, being near 7 md.A.-I.