Temperature Dependence of the Carbon-13 Isotope Effect in the Decarbonylation of Concentrated Formic Acid Solutions of Sodium Chloride and of Metaphosphoric Acid Reagent

Abstract

Abstract The temperature dependence of the carbon-13 kinetic isotope effect (13C KIE) in the decarbonylation of concentrated formic acid solutions of NaCl and of metaphosphoric acid reagent has been determined in the temperature interval 50–110°C and compared with the 13C KIE observed in the decarbonylation of pure liquid formic acid. The (k 12/k 13 ) values lay in the range 1.058–1.047, expected assuming that the C[sbnd]O vibration is lost in the course of activation of formic acid molecules leading to decarbonylation. Metaphosphoric acid reagent present in liquid formic acid at saturation concentrations eliminates all side “minor” processes of physical and chemical nature which caused the slight decrease of the experimental 13C kinetic fractionation observed in the course of decarbonylation of pure formic acid from the expected values of 13C KIE. Sodium chloride is a less effective breaker of the structure of liquid formic acid than the metaphosphoric acid reagent.