Reactions of 1,4-benzoquinones with s2 reducing centers

Abstract

Aqueous solutions of Sn(II) and Ge(II) (in chloride media) and In(I) (in perchlorate media) react quantitatively with 1,4-benzoquinone and its 2,5-(OH)₂ and 2,5-Cl₂-3,6-(OH)₂ derivatives, reducing the oxo-functions to 1,4-(OH)₂. For Sn(II) and Ge(II), reaction is accelerated by incorporation of 2,5-(OH)₂ substituents and by chloroanation of the s² center. The most reactive reducing Sn(II) species are SnCl₃⁻ for benzoquinone and dihydroxyquinone but SnCl₂(aq)_x for the dichloroquinone. Reductions by Ge(II) proceed mainly through a species (probably GeCl₄²⁻) having one more chloride than the predominant form. The activated complex for the (OH)₂bzq–Ge(II) reaction features two germanium centers, only one of which is involved in the reduction act. Reductions of these quinones by In(I) proceed 10²–10³ times as rapidly as those by Sn(II) and Ge(II) and are not accelerated by hydroxylation of the quinone ring.