Kinetics and mechanisms of the catalytic reactions of formaldehyde with copper oxides and a copper ion complex in aqueous alkali |
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Authors: | O A Demchenko D I Belkin |
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Institution: | 1.Institute of Chemical Technologies,East Ukrainian National University,Rubezhnoe, Lugansk oblast,Ukraine |
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Abstract: | The kinetics of the autocatalytic reactions of formaldehyde with copper(II) and copper(I) oxides and with the Cu2+ ion of the copper EDTA complex, as well as formaldehyde disproportionation in the presence of copper metal, have been investigated
in aqueous solutions of sodium hydroxide. Two likely reaction mechanisms are presented. The difference between these mechanisms
does not alter the observed kinetics of the processes, whose rate is determined by their first, slow step, namely, the oxidation
of the methylene glycol anion adsorbed on the copper surface into formic acid. In the slow step of the first mechanism, a
hydride ion is abstracted from the methylene glycol anion and is transferred to copper. In the slow step of the second mechanism,
the methylene glycol anion undergoes anodic oxidation, releasing a hydrogen atom and an electron. In the rapid steps of the
first mechanism, the hydride ion undergoes anodic oxidation to hydrogen, the copper compound undergoes cathodic reduction
to copper metal, and, simultaneously, the electron and hydrogen are transferred to a nonionized formaldehyde molecule to yield
methanol. Mathematical models are suggested for the reactions. The effective rate constants and activation energies of the
slow steps of the reactions have been determined. The effective rate constants of the noncatalytic reduction reactions of
the copper compounds and the ratios of the rates of the rapid hydrogen and methanol formation reactions have been estimated. |
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