Reaction Products between Methyl-substituted p-Benzoquinones and Sodium Sulfite in Neutral and Alkaline Buffer Solution

Abstract

Methyl-substituted p-benzoquinones are known to undergo the two type reactions with Na₂SO₃ -the redox reactions (Eq. (1) and (2)) and the reaction via 1, 4-addition (Eq. (3)).
MPQ + HSO₂^- + H₂O=MH₂Q + SO₄^2- + H⁺ (1)
MPQ + 2HSO₃^-=MH₂Q + S₂O₆^2- (2)
MPQ + HSO₂^-=MH₂QS^- (3)
where MPQ, MH₂Q and MH₂QS^- represent methyl-substituted p-benzoquinones, methylhydroquinones and methylhydroquinonesulfonates, respectively.
The progress of those two type reactions have been investigated from the standpoint of the difference ΔE(=E_MPQ-E_SS) between the redox potential of methyl-substituted p-benzoquinones (E_MPQ) and that of Na₂SO₃ (E_SS), and it was described in the preceding paper that those two type reactions mainly proceeded in the case of ΔE>0. In this paper, it was confirmed by the identification of the reaction products at by means of the polarographic method and the spectrophotometric measurement that the reaction different from Eq. (1), (2) and (3) proceeded mainly in the case of ΔE<0. The product in the trimethyl-p-benzoquinone-Na₂SO₃ system is, for example, 3, 4, 6-trimethyl-2, 5-dioxo-3-cyclohexene-1-sulfonate. In the methylsubstituted p-benzoquinone-Na₂SO₃ and the p-benzoquinone-Na₂SO₃ systems, a small amount of other products which were easily oxidized by the electrolytic oxidation were detected by polarographic method.