Carbon-13 Kinetic Isotope Effect for the Decarbonylation of Liquid Formic Acid Assisted with Uranium Trioxide, Uranium Peroxide and Uranyl Formate

13C KIE’s in the decarbonylation of liquid formic acid (FA) in the presence of uranium trioxide, UO3, uranium peroxide, UO4, and in the presence of uranyl formate, UO2(HCOO)2, produced in the reaction of the above two uranium oxides with FA have been investigated between 90–120°C. Decarbonylation of HCOOH assisted with uranium trioxide proceeds with normal 13C KIE, expected assuming that 13C–16O bond is broken in the transition state, (k12/k13) KIE = 1.0496/at 100°C. The decarbonylation of liquid formic acid in the presence of uranium peroxide and uranyl formate is accompanied with 13C KIE of intermediate value, which is higher than the 13C KIE observed in the decarbonylation of pure FA, but smaller than the maximum 13C KIE expected for complete rupture of the single carbon–oxygen bond in the decarbonylation T.S. of the protonated formic acid. A mechanism of decomposition of formic acid in the presence of uranium oxides is proposed.