What molecule am I?
Carminic acid is a naturally occurring organic molecule whose structure consists of 9,10-anthraquinone-2-carboxylic acid “decorated” with a methyl group, a glucopyranose, and four hydroxyls. It is found in several species of scale insects known as cochineals, including Dactylopius coccus (Western Hemisphere), Porphyrophora hamelii (Armenia), and Porphyrophora polonica (north-central Europe).
In 1894, noted British dye chemist Henry Edward Schunk, working in Germany, isolated carminic acid from cochineals. German chemist Otto Dimroth reported its structure in 1920; and Indian chemists S. B. Bhatia and K. Venkataraman corrected the placement of the carboxyl group in Dimroth’s structure in 1965.
Cochineal insects use carminic acid to repel other insects. But for centuries, cochineals have been valuable to humans for providing carminic acid to use on its own or to make cochineal dyes. When carminic acid is treated with with aluminum and/or calcium salts, it forms complexes that are familiarly called carmine, carmine lake, crimson lake, or even the eponymous cochineal1. The dye is used for textiles and as a US Food and Drug Administration–approved food, cosmetic, and drug colorant, although some people exhibit allergic reactions to it.
Free carminic acid has been used as a bacteriological stain, an ingredient for artists’ paints, and a pigment for inks. In its cochineal dye form, you can even use it to make your own colored paper for cards and envelopes for Valentine’s Day!
1. CAS Reg. No. 1343-78-8.
Originally the Molecule of the Week for February 5, 2007
Carminic acid hazard information*
|Hazard class**||GHS code and hazard statement|
|Acute toxicity, oral, category 4||H302—Harmful if swallowed|
|Serious eye damage/eye irritation, category 2A||H319—Causes serious eye irritation|
Specific target organ toxicity, single exposure, respiratory tract irritation, category 3
|H335—May cause respiratory irritation|
*Most safety data sheets state that carminic acid is not a hazardous substance or mixture. The information given here was found in only one SDS.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
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|CAS Reg. No.||1260-17-9|
|2-Anthracene-carboxylic acid, 7-β-D-glucopyranosyl-9,10-dihydro-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-|
|Molar mass||492.39 g/mol|
|Appearance||Red crystals; bright red to dark purple powder|
|Melting point||136 °C (dec.)|
|Water solubility||1.3 g/L|
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