Leuco Compounds - Leuco Compounds

Leuco- is a prefix derived from the Greek word meaning "colorless" or "white". Colorless or pale-colored compounds derived from colored organic compounds by reduction are generally called leuco compounds, and are often used for vat dyes. Vat dyes are insoluble in water, but when reduced with an alkaline solution of hydrosulfite Na ₂ S ₂ O ₄ , a colorless or pale-colored leuco compound is produced, which becomes water-soluble. Generally, a dye in the diketone form (a) is reduced to the leuco form with a dienol structure (b), and becomes soluble in water as an enolate (c).

For example, the leuco compound (leuco salt) obtained from indigo is called indigo white. When a fiber is immersed in a solution of the leuco salt and exposed to air, it is oxidized, regenerating the original dye and dyeing the fiber.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

ロイコ(leuco-)は，“無色”または“白色”を意味するギリシア語に由来する接頭語．有色の有機化合物から還元によって導かれる無色または淡色の化合物を，一般にロイコ化合物というが，建染め染料に使われる場合が多い．建染め染料は水に不溶性であるが，ハイドロサルファイトNa₂S₂O₄のアルカリ溶液で還元すると，無色または淡色のロイコ化合物を生じ，水溶性となる．一般に，ジケトン形(a)の染料がジエノール構造(b)のロイコ形に還元され，エノラート(c)として水に溶けるようになる．

たとえば，インジゴから得られるロイコ化合物(ロイコ塩)は，白藍(あい)(indigo white)とよばれる．ロイコ塩の溶液に繊維を浸し，空気中にさらすと酸化されて原染料が再生し，繊維が染色される．

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