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il careful re-examination of the arylation (P. Brassard and P. ~' f i c u y e r .Can. J. Chem. 36, 814 (1958)) reaction with chlorobenzoquinone3 has revealed in its products the presence of all the three possible disubstituted isomeric quinones. Arylation using diazotized p-nitroaniline has resulted in the isolation of the three new isomeric quinones, whose structures are assigned, based on chemical and spectral evidences. RiIechanistic implications in the arylation and halogenation of benzoquinones are discussed.'I'lie A/Ieerwein reaction (2) provides a general method of arylation of activated double bonds, using aryl diazonium salts, in the presence of copper salts a s catalysts. Arylation of benzoquinone by diazotized aniline using typical Meerwein conditions (80% acetone-water solvent system, cupric chloride catalyst, and acetate buffer) is found to give crude phenylbenzoquinone in poor yield ( < l o % of crude product). Modified Meerwein conditions4 (variation of the solvent system or the type of buffer) have been used for the arylation of benzoquinones. I t has been recently (3) demonstrated that excellent yields of monoaryl benzoquinones are obtained by coilducting the reaction in a completely aqueous medium, in the presence of a n acetate buffer, and without the copper catalyst. An application of the procedure to the arylation of the moilosubstituted benzoquinones has also been described (1, 4). 14olvever, the latter reactions are complicated by the fact that theoretically three isomers call be formed. The substituent present in the starting quinone and the stability of the diazoniuin salt are the inajor factors responsible for influencing the yields of these isomers. The arylation of toluquinone and phenylbenzoquiilone with ArNZfC1-(Ar = I!-chlorophenyl) yields a single isolable disubstitutecl benzoquinone in reasonable yield (86% and 4370 respectively) as against that of chlorobei~zoq~iinone (I.) which gives two isomeric chloro-p-chlorophenylbenzoquinoiles (IIIa and IIIc). The last inentioned result strongly suggests the possibility of the forination of all three isomers in the course of this reaction.The investigation of the arylation of cl~lorobenzoquino~~e was therefore resumed with a view to the preparatioil of these isomers using benzene, p-cl~lorobenzei~e, and p-nitrobenzene diazonium chlorides as the arylating agents.I11 the previous studies (1, 4) and in synthetic studies with benzoquinones in general little or no attempt has been made t o use chroinatography as a ineans of separation of the products. The use of ordinary aluillina is impeded by the ease 1vit11 which a inolecule of benzoquinone call accept two electrons from a nucleophile t o go over t o the dianion of the corresponding hydroquinone. We found t h a t such a conversion on acid alumina is slow but nevertheless unavoidable. Silica gel has proved to be a satisfactory adsorbent for the separatioil of substituted benzoquinones with complete inhibition of reduction on the colun~n. I t is of interest to note that the order of e...

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