THIO- AND SELENO-AMIDO GROUPS AS REDUCING AGENTS TOWARDS OsO4. A KINETIC STUDY WITH SOME IMIDAZOLIDINE-2-SELONES

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Abstract
OsO4 reacts with imidazolidine-2-selone and its N-methyl and N-ethyl-substituted derivatives in H2O/EtOH (1:1 vol) in presence of perchloric acid to give [OsL6]3+. The infrared spectroscopy shows that the imidazolidines bind the metal ion through the selenium in the same way as the imidazolidine-2-thiones use the thioketonic sulfur. By spectrophotometric measurements, the formation of [OsL6)3+ has been followed in time, recording the increase of absorbance at the wavelengths of the maxima of absorption of the complex. The pseudo-first order rate constants are linear both with respect to the acid and the ligand concentrations, indicating that the rate determining step involves one proton and one molecule of the ligand. The reaction has also been followed with selenourea only at 6°C. The activation parameters for the sulfur and selenium compounds have been comparatively discussed.