Investigation of Isotope Effects with the Aid of Kinetic and Catalytic Polarographic Currents

Two types of chemical reactions, used to investigate isotope effects, are considered: reactions preceding the electrochemical stage proper and reactions accompanying this stage. The results of studies on the dehydration of formaldehyde are presented as examples of reactions of the first type and those on the oxidation of titanium(lll) to titanium(IV) by hydroxylamine and the decomposition of hydrogen peroxide by catalase are presented as reactions of the second type. The results of a polarographic determination of the rate constants for reactions involving isotopic molecules, on the basis of which it is possible to determine the isotope effect for the corresponding reaction, are described together with the results of the determination of the equilibrium constants with the aid of both classical polarography and oscillographic polarography with rapid potential scanning. The equilibrium constants of the acid dissociation and dehydration reactions involving formaldehyde were determined and were employed to determine the corresponding thermodynamic isotope effects. It is shown that a direct isotope effect obtains in the acid dissociation reaction and the inverse effect obtains in the dehydration reaction.
The possibility of using the results of the study of isotope substitution in relation to catalytic currents in the cobalt–sodium nitrohydroxylaminate–cysteine system in an ammonia buffer for the determination of the isotopic composition of water is demonstrated. It is concluded that the polarographic method has many possibilities for the investigation of both kinetic and thermodynamic isotope effects and the isotope effects of the solvent.
The bibliography includes 44 references.