Colouring matters of the aphididae. Part XXXVIII. Methylation of erythroaphin. Cationic species derived from aphins in acidic media

Abstract

Methylation of erythroaphin-fb gives two isomeric dimethyl ethers, derivatives of perylene-3,9- and -3,10-quinones. Their visible absorption suggests that, in neutral organic solvents, erythroaphins occur principally as perylene-3,10-quinone tautomers. The dimethyl ethers together with other erythroaphin derivatives undergo striking colour changes in certain acidic media. It is suggested that these changes frequently involve formation of oxonium cations which may proceed by isomerisation, oxidation, or dehydration. In some cases comparatively stable radicals may be formed as well. Acid-catalysed reactions of naphthaquinone derivatives related to the protophins are also discussed.