1911 Encyclopædia Britannica/Quinones

QUINONES, in organic chemistry, a group of compounds in which two hydrogen atoms of a benzene nucleus are replaced by two oxygen atoms. This replacement may take place either in the ortho or para positions, giving rise to orthoquinones or to paraquinones; metaquinones do not appear to have been isolated. The para or true quinones are obtained by the oxidation of hydrocarbons with chromic acid or of various para di-derivatives of benzene with chromic acid mixture, such, for example, as para-aminophenol, para-phenylene diamine, para-aminoazobenzene, &c. H. v. Pechmann (Ber., 1888, 21, p. 1417) has shown that α-diketones are converted into paraquinones by the action of warm solutions of the caustic alkalis, diacetyl yielding para-xyloquinone:

CH₃CO·CO·CH·₃⁠CH₃·C·CO·CH

⁠ →  ||⁠E ||

⁠CH₃CO·CO·CH·₃⁠HC·CO·C·CH₃;

whilst P. H. Bayrac (Bull. soc. chim., 1894 (3) II, p. 1129) obtained anilino-derivatives of the paraquinones by the action of an aqueous solution of potassium chromate on an acetic acid solution of para-aminodimethylaniline and phenol:
C₆H₅OH+H₂N·C₆H₄·N (CH₃)₂→O:C→₆H₄:N·C₆H₄·N(CH₃)₂; these compounds yield the quinone when heated with mineral acids.

The paraquinones are generally crystalline solids of a yellowish colour, having a characteristic sharp odour and being volatile in steam. They are readily reduced to the corresponding hydroquinones or para-dihydroxy-benzenes, and also combine with hydroxylamine hydrochloride to form nitrosophenols, ON·C₆H₄·OH, which can further yield quinone dioximes, HON:C₆H₄:NOH. Paraquinones also combine with ammonia and with amines yielding amino-derivatives and hydroquinones. The orthoquinones more resemble the α-diketones; they are crystalline solids of a red or yellow colour, but differ from the paraquinones in being devoid of smell and not volatile in a current of steam.

Benzoquinone (para) or ordinary quinone, C₆H₄O₂, is formed by the oxidation of aniline with sodium bichromate and sulphuric acid. It sublimes in golden yellow needles. Hot concentrated nitric acid oxidizes it to picric acid and oxalic acid, whilst on treatment with hydrochloric acid and potassium chlorate it yields chloranil (tetrachloroquinone). It combines directly with two and four atoms of bromine. Free hydroxylamine reduces it to hydroquinone. It combines directly with aniline to form dianilidoquinone, dianilidoquinone-anil and dianilidoquinone-dianil or azophenine. Two alternative structural formulae have been given to benzoquinone, namely:

The former, due to C. Graebe (Zeit. f. Chemie, 1867, 3, p. 39), ascribes to the molecule a peroxide configuration which accounts for its oxidizing powers but not for the fact that each oxygen atom is capable of replacement by one atom of chlorine. The second formula, due to R. Fittig (Ann., 1876, 180, p. 23) readily explains the formation of the mono- and di-oximes of quinone and also that it readily combines with bromine.

Quinone-chlorimide, ClN:C₆H₄:O, is obtained when para-aminophenol is oxidized with bleaching powder. It is a yellow crystalline solid readily volatile in steam. The dichlorimide, ClN: C₆H₄: NCl, is formed in a similar manner from paraphenylene diamine. It is a strong oxidizing agent. Quinone-dioxime, HON: C₆H₄: NOH, crystallizes in colourless or yellow needles, which decompose when heated to about 240° C. Potassium ferrocyanide in alkaline solution oxidizes it to dinitrosobenzene, whilst cold concentrated nitric acid oxidizes it to para-dinitrobenzene. Quinhydrone, C₆H₄O₂⋅C₆H₄(OH)₂, is formed by the direct union of quinone and hydroquinone or by careful oxidation of hydroquinone with ferric chloride solution. On boiling with water it decomposes into quinone and hydroquinone.

Benzoquinone (ortho).—C. L. Jackson (Amer. Chem. Jour., 1901, 26, p. 10) attempted to prepare this compound by the action of iodine on the lead salt of pyrocatechin suspended in chloroform. A deep red solution was obtained but the free quinone was not isolated since the solution on stand ling deposits nearly black crystals of dihydroxyphenylhydroxybenzoquinone (HO)₂C₆H₃⋅C₆H₂O₂⋅OH. R. Willstätter (Ben, 1904, 37, p. 4744), by dissolving pyrocatechin in absolute ether containing ignited sodium sulphate and then adding dry silver oxide, obtained the quinone in dark red crystalline plates which decompose between 60° and 70° C. For naphthalene quinones see Napthalene; for anthracene quinone see Anthraquinone; and for phenanthrene quinone see Phenanthrene.

Quinoles.—The quinoles are a series of compounds of the type R
HO==
__O, obtained by the oxidation of para-alkylated phenols with nitric acid, Caro’s acid or bromine (Auwers, Ber., 1897–1903; E. Bamberger, ib., 1903, 36, p. 2028; Th. Zincke, ib., 1895, 28, p. 3121); by the action of sulphuric acid on para-substituted phenylhydroxylamines (E. Bamberger), and by the action of the Grignard reagent on quinones (Bamberger). They are crystalline solids which are readily converted into para-alkylated phenols by reducing agents. They possess a weak acid and also an alcoholic character.