Une etude de la reaction cles sels de diazouium avec la p-benzoquinone a etd laite. Es6c~ltee selon des conditions bien dCtcrmin6cs quant B la n;lture d i~ solrant, la concentration tlc la solution tampon e t la temp6r;lture d u milieu, cctte rdnctioi~ constituc Line ezcellentc mGthode g6nerale de syi~thhse des m o n o a r y l -p -b e n z o q~~i~~o~~e s .
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...
SommaireEn faisant r6agir la solution aqueuse des sels de diazonium monosubstitu6s avec des solutions d'acides cinnamiclues substitu6s selon les conditions publi6es par Nleerwein, il a 6t6 possible de sl,nth6tiser un certain nombre de d6riv6s du stilbdne avec un groupement substituant dans chacun des anneaux benz6niques.De cette fagon ont 6t6 synth6tis6s pour la premidre fois les con.rpos6s suivants: 4nr6thode ont aussi 6t6 pr6par6s les compos6s suivants dont la synthdse selon une autre nr6thoclc a d6ji 6t6 rapport6e: 2-chloro-4'-m6thoxystilbdne,2,2'-dim6thoxystilbdne,2,l'-dirn6thox-vstilbdne,4,4'-dinitrostilbdne, -1-nr€tlrll-l'-nitrostilbine,2-rnetlroxl-l'-nitro'tilbene.t +-nr6thoxy-4'-nitrostil-tJCne. fait I'essence de la r6action. Il en r6sulte que la solubilit6 trds variable des acides cinnamiques substitu6s dans ce solvant nous empeche d'op6rer dans des conditions de milieu absolument identiques. C'est sans doute pour cette t Manuscrit regu le 17 septembre 1917, Contribution du Ddpartement de Chi.mie de la Faculti d,es Sciences, Uniaersitt Lawl', Qu6.bec. Can. J. Res. Downloaded from www.nrcresearchpress.com by MICHIGAN STATE UNIVERSITY on 02/20/15 For personal use only. Can. J. Res. Downloaded from www.nrcresearchpress.com by MICHIGAN STATE UNIVERSITY on 02/20/15 For personal use only.
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