Initial adduct formation by 1,4-benzoquinones in liquid ammonia to give 4-amino-4-hydroxycyclohexa-2,5-dienones and 3,6-diamino-3,6-dihydroxycyclohexa-1,4-dienes

Abstract

N.m.r. spectra (¹H and ¹³C) of fresh solutions of 1,4-benzoquinone and substituted (mainly chloro-and methyl-)1,4-benzoquinones in liquid ammonia at 240 K correspond to adduct formed by nucleophilic addition to the carbon of the carbonyl group (4-amino-4-hydroxycyclohexa-2,5-dienones). In quinones where the two carbonyl group are not equivalent (namely mono-, 2,6-di-, and tri-chloro and the corresponding methyl-substituted 1,4-benzoquinones) this attack is always at the carbonyl which has the greater number of ortho-substituents. Solutions of 2,3-di-,2,5-di, and tri-chloro-1,4-benzoquinone also show other absorptions which correspond to smaller concentrations of the corresponding diadducts (3,6-diamino-3,6-dihydroxycyclohexa-1,4-dienes).On cooling from 240 to 220 K these latter absorptions intensify at the expense of those due to the monoadducts.

The adducts are relatively stable at 220K, persisting for many hours and, in the case of 1,4-benzoquinone itself, for several days. From fresh solutions the initial quinone may be recovered in all cases.