Inorganic chemistry,dihydroxybenzenes (benzenediols) areorganic compounds in which twohydroxyl groups (−OH) aresubstituted onto abenzene ring (C6H6). Thesearomatic compounds are classed asphenols. There are threestructural isomers: 1,2-dihydroxybenzene (theortho isomer) is commonly known ascatechol, 1,3-dihydroxybenzene (themeta isomer) is commonly known asresorcinol, and 1,4-dihydroxybenzene (thepara isomer) is commonly known ashydroquinone.[1]
| Isomer | ortho | meta | para |
|---|---|---|---|
| Trivial name | Catechol | Resorcinol | Hydroquinone |
| IUPAC name | benzene-1,2-diol | benzene-1,3-diol | benzene-1,4-diol |
| Other names | pyrocatechol 1,2-dihydroxybenzene o-dihydroxybenzene o-benzenediol | resorcin 1,3-dihydroxybenzene m-dihydroxybenzene m-benzenediol | 1,4-dihydroxybenzene p-dihydroxybenzene p-benzenediol |
| Structure |  |  |  |
All three of these compounds are colorless to white granularsolids at roomtemperature andpressure, but upon exposure to oxygen they may darken. All three isomers have thechemical formulaC6H6O2.
Similar to other phenols, the hydroxyl groups on the aromatic ring of a benzenediol are weaklyacidic. Each benzenediol can lose anH+ from one of the hydroxyls to form a type ofphenolate ion.
TheDakin oxidation is an organicredox reaction in which anortho- orpara-hydroxylated phenylaldehyde (−CH=O) orketone (>C=O) reacts withhydrogen peroxide in base to form a benzenediol and acarboxylate. Overall, thecarbonyl group (C=O) is oxidized, and the hydrogen peroxide is reduced.
