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, paraaminoazobenzene, &c . H. v . Pechmann (Ber., 1888, 21, p .