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The red crystalline colorant obtained from the alkanet root, Alkanna tinctoria. Alkannin is an indicator appearing red at pH 6.1, purple at pH 8.8, and blue at pH 10.0. Alkannin pH indicator paper is similar to litmus paper. It is prepared by dying white paper with a 1% dye solution. When used, alkalis turn the paper green or blue and acids appear red. Alkannin is also used as a red colorant in food stuffs and cosmetics.
Synonyms and Related Terms
alkannin paper; anchusa acid; anchusin; alkanna red; alkanet extract; Natural Red 20; CI 75530
Physical and Chemical Properties
Alkannin is soluble in alcohols, oils and other organic solvents. Alkannin is slightly soluble in water.
Alkannin forms a deep blue solution with alkalis and a purple precipitate with bichloride of tin.
|Melting Point||149 C|
Resources and Citations
- G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 184
- The Merck Index, Susan Budavari (ed.), Merck Research Labs, Whitehouse Station, NJ, 12th Edition, 1996 Comment: entry 238