Carminic Acid
Title: Carminic Acid
CAS Registry Number: 1260-17-9
CAS Name: 7-a-D-Glucopyranosyl-9,10-dihydro-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-2-anthracenecarboxylic acid
Additional Names: C.I. Natural Red 4; C.I. 75470
Molecular Formula: C22H20O13
Molecular Weight: 492.39
Percent Composition: C 53.66%, H 4.09%, O 42.24%
Literature References: Glucosidal coloring matter from the scale insect Coccus cacti L., Homoptera (cochineal). The essential constituent of carmine. Isoln: Schunk, Marchlewski, Ber. 27, 2979 (1894); Dimroth, Scheuer, Ann. 399, 43 (1913). Structure: Dimroth, Kammerer, Ber. 53, 471 (1920); Ali, Haynes, J. Chem. Soc. 1959, 1033; revised structure: Bhatia, Venkataraman, Indian J. Chem. 3 (2), 92 (1965). See also Colour Index vol. 4 (3rd ed., 1971) p 4632.
Properties: Red prisms from alc, no distinct melting point, darkens at 120°. Has a deep red color in water and is yellow to violet in acid solns. uv max (water): 500 nm (e 6800); (0.02N HCl): 490-500 nm (e 5800); (0.0001N NaOH): 540 nm (e 3450). [a]15654 +51.6° (water). Sol in water, alc, concd H2SO4; slightly sol in ether. Practically insol in petr ether, benzene, chloroform.
Optical Rotation: [a]15654 +51.6° (water)
Absorption maximum: uv max (water): 500 nm (e 6800); (0.02N HCl): 490-500 nm (e 5800); (0.0001N NaOH): 540 nm (e 3450)
 
Derivative Type: Methyl tetra-O-methylcarminate
Molecular Formula: C27H30O13
Molecular Weight: 562.52
Percent Composition: C 57.65%, H 5.38%, O 36.98%
Properties: Yellow needles from benzene + petr ether, mp 185-188°.
Melting point: mp 185-188°
 
Derivative Type: Aluminum calcium lake
Additional Names: Carmine
Properties: Bright-red, light pieces; easily reduced to powder. Practically insol in cold water or dil acids. Partly sol in hot water; sol in solns of alkali hydroxides or their carbonates giving deep red solns; also sol in borax.
 
Use: Free acid in color photography; pigment for artists' paints; as bacteriol. stain; rarely now as acid-base indicator or as oxidimetric indicator; as a reagent for aluminum; as a complexing agent for cations. Aluminum calcium lake as dye; in inks; coloring foods, drugs and galenicals; in microscopy for making various stains.

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