Dyes Many natural and artificial coloring substances (dyes and pigments) are quinone derivatives, for instance lawsone is the active dye compound in henna. They are second only to azo dyes in importance as dyestuffs, with particular emphasis on blue colors. Alizarin (1,2-dihydroxy-9,10-anthraquinone), extracted from the madder plant, was the first natural dye to be synthesized from coal tar. Photography A commercial application of quinones is in black-and-white photography. Black-and-white film is covered with an emulsion containing silver bromide or silver iodide crystals, which exposure to light activates. Hydroquinone is used to reduce the activated silver ions to metallic silver. During this process, hydroquinone is oxidized to quinone. All silver halide not activated by light or reduced by hydroquinone is removed, leaving a negative by deposited silver where the film had been struck by light. Nomenclature Quinones are commonly named with a prefix that indicates the parent aromatic hydrocarbon ("benzo-" for benzene, "naphtho-" for naphthalene, "anthra-" for anthracene, etc.) and the "-quinone" suffix. Infix multipliers "-di-", "-tri-", "-tetra-" (etc.) are used when there are 4, 6, 8 (etc.) carbonyls. The position of the carbonyl groups can be indicated before the prefix (as in "1,4,5,8-naphthodiquinone") or after it ("anthra-1,4-quinone"). Structural analogues of quinones Quinone methide - where one O is replaced by C Xylylene - where both O's are replaced by C's Quinone imine - where one O is replaced by N, illustrated by NAPQI Quinone diimine – where both O's are replaced by N's, illustrated by the antiseptic Ambazone Azaxylylene - where both O's are replaced by one N and one C, illustrated by various fuchsine dyes like pararosaniline References External links Enones