Hydro quinol

Hydro-quinol, 1-4-Di-hydroxy Benzene.—The third isomeric dihydroxy benzene, viz., the para compound, i-4-di-hydroxy benzene, is known as hydro-quino or hydro-quinone. The latter name is derived from its relation to quinone (p. 636) from which it is obtained on reduction and which it yields on oxidation. Both hydro-quinol and quinone derive their names from the fact that they are obtained by the oxidation of quinic acid, an acid derived from the alkaloid quinine. The phenol is found in various plants or may be obtained from them by the hydrolysis of glucosides present, e.g., arbutin, which is a glucoside hydrolyzing into glucose and hydro-quinol. 

Hydro-quinol may be synthesized by any of the general methods. Of special interest is its synthesis by the electrolytic oxidation of benzene. It crystallizes in colorless prisms, m.p. 170°. With ferric chloride it gives no color reaction, but is oxidized to quinone, the same oxidation occurring in the air in alkaline solutions. It reduces Fehling s solution and its important use is as a reducing agent in photography. 

Only two of these will be considered in detail. Hydroxy hydro-quinol, so named because it is the only possible tri-hydroxyl compound derived from hydro-quinol, is not of special importance. 

It will be recalled that when para-di-hydroxy benzene, hydro-quinol, and also other para di-substitution products of benzene are oxidized there is obtained the compound known as quinone or benzo-quinone (p. 636). In a similar way para di-suhstituied naphthalenesy especially hydroxyl and amino compounds, and in fact naphthalene itself when oxidized with chromic acid, yield a quinone analogous to benzoquinone and which is known as alpha-naphthoquinone. 

Reduction, (a) By sulphurous acid. Benzoquinone, /> toluquinone, 1,2-naphthoquinone are readily reduced by SOj ultimately to the dihydroxy-compound. Thus benzoquinone gives colourless hydro-quinone or quinol, />-C2H4fOH)2. 

Quinol and Derivatives. See under Hydro-quinone and Derivatives in Vol 7, H227-R to H228-R... 

Lead dioxide hydro gen chloride Quinones from quinols... 

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