4944. Indigo Carmine

Nomenclature

CAS number: 860-22-0
2-(1,3-Dihydro-3-oxo-5-sulfo-2H-indol-2-ylidene)-2,3-dihydro-3-oxo-1H-indole-5-sulfonic acid sodium salt (1:2); 3,3′-dioxo-[Δ2,2′-biindoline]-5,5′-disulfonic acid disodium salt; disodium 5,5′-indigotin disulfonate; sodium indigotin disulfonate; soluble indigo blue; indigotine; Acid Blue 74; C.I. Acid Blue 74; C.I. Food Blue 1; FD & C Blue No. 2; C.I. 73015.
C16H8N2Na2O8S2; mol wt 466.35.
C 41.21%, H 1.73%, N 6.01%, Na 9.86%, O 27.45%, S 13.75%.

Description and references

Synthesis and structure determination: Vorlander, Schubart, Ber. 34, 1860 (1901). Prepn and properties: Matthews, Color Trade J. 6, 96 (1920). See also Colour Index vol. 4 (3rd ed., 1971) p 4597.

Chemical structure

Properties

Dark-blue powder with coppery luster. Sensitive to light. Its solns have a blue or bluish-purple color. Changes color from blue to yellow between pH 11.5-14. One gram dissolves in about 100 ml water at 25°. Slightly sol in alcohol. Practically insol in most other organic solvents. It is also marketed as a paste with water, the dye contents varying according to specification or requirements of the user. It almost always contains sodium chloride or sulfate used for “salting” it out. Indigo carmine is very sensitive to oxidizing agents. The color is readily discharged by nitric acid, chlorates, etc. The color of the aq soln fades on standing.

Use

Colorant for nylon, surgical sutures, foods and ingested drugs. Histological stain used for collagen, plant cell nuclei, and fluorescent staining of eosinophil granules. In vivo stain for endoscopic diagnosis; detection of sentinel lymph nodes; angiographic tracer. As a reagent for functional kidney tests, for detection of nitrates, chlorates and in testing milk.