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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.

See Alkanet.

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.

Composition C16H16O5
Melting Point 149 C
Molecular Weight 288.29

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

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