Polarographic Study of the Reaction of Vitamin K3 with Thiol Compounds in Aqueous Ethanol

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Abstract
The reaction of vitamin K3 (I) with some thiol compounds was studied by polarography in 80% ethanol containing acetate buffer and sodium perchlorate. In the absence of O2 in solution, thiol compounds react with I to form naphthohydroquinones having a thioether linkage as the result of the addition of the SH group at the 3-position of the naphthoquinone ring in I. The reaction products changed to quinone-thioether compounds by air oxidation with the formation of H2O2. The reaction mechanisms were confirmed by electrochemical and spectrophometric measurements of I in the presence of various thiol compounds. The effect of pH on the reaction rate was examined by following the change in the diffusion current of I with time at various pH''s. In the case of the L-cysteine reaction system, the polarograms were somwhat complicated compared with those obtained with thiol compounds. The results suggest that the subsequent reaction must be taken into account after the formation of hydroquinone-thioether compound between I and L-cysteine.

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