Factors affecting yields of indigo and indirubin produced by acid hydrolysis of indican

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  • インジカンの酸加水分解により生じるインジゴ・インジルビンの量比に影響を及ぼす因子

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Various fabrics can be dyed reddish purple shade by using the precipitate from indican which is contained in indigo-bearing plants when the precipitate contains a significant amount of indirubin in addition to indigo. Such precipitate can be obtained from the solution of indican in the presence of citric acid at elevated temperatures. The yield of indirubin changes depending on the hydrolysis conditions. Effective conditions to yield much indirubin were investigated by using indican of commercial origin. These conditions were the effect of additives (hydrochloric acid, sodium chloride, surfactants or ethanol), indican concentration (0.075～2.4g/l) and the kind of acid to hydrolyze indican. The yield of indirubin increased when hydrochloric acid (0.02mol/l) was added to the citric acid solution (1mol/l) of indican and when the concentration of indican was about 0.3～0.6g/l which corresponds to the amount of fresh leaves of Polygonum tinctorium being 25～50g per liter. Citric acid was preferable as an acid to hydrolyze indican to other acids such as tartaric acid, malonic acid, maleic acid, malic acid, monochloroacetic acid, etc.

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