PURPOSE: 2-( 1'-Acetoxy-4'-oxy-4'-methylbenzyl )-5, 8-diacetoxy-1,4-naphthoquinone is used as a starting substance to effect dehydration, treatment with an alkali hydroxide and acidification to give easily the titled substance as a violet dye.

CONSTITUTION: 2-(1'-acetoxy-4'-oxy-4'-methyl-3'-methylbenzyl)-5, 8-diacetoxy-1, 4- naphthoquinone of formula I is dehydrated with phosphorus pentoxide, thionyl chloride or the like to give a mixture of 2-(1'-acetoxy-4'-methyl-3'-pentenyl)- 5,8-diacetoxy-1,4-naphthoquinone of formula II and a compound of formula III. Then, the compound of formula II is separated, dissolved in an alkali hydroxide, then acidified to give a compound of formula IV. The compound of formula I is obtained from 2-formyl-1,4,5,8-tetramethoxynaphthalene of formula V via 4-step procedures.