INDIGOTINE

EC / List no.: 212-728-8
CAS no.: 860-22-0

Indigotine, or 5,5′-indigodisulfonic acid sodium salt, is an organic salt derived from indigo by aromatic sulfonation, which renders the compound soluble in water. 
Indigotine is approved for use as a food colorant in the U.S and E.U.
Indigotine has the E number E132. 
Indigotine is also a pH indicator.

Uses:
Indigotine in a 0.2% aqueous solution is blue at pH 11.4 and yellow at 13.0. 
Indigotine is also a redox indicator, turning yellow upon reduction. 
Another use is as a dissolved ozone indicator through the conversion to isatin-5-sulfonic acid.
This reaction has been shown not to be specific to ozone, however: 
Indigotine also detects superoxide, an important distinction in cell physiology.
Indigotine is also used as a dye in the manufacturing of capsules.

In obstetric surgery, indigo carmine solutions are sometimes employed to detect amniotic fluid leaks. 
In urologic surgery, intravenous injection of indigo carmine is often used to highlight portions of the urinary tract. 
The dye is filtered rapidly by the kidneys from the blood, and colors the urine blue. 
This enables structures of the urinary tract to be seen in the surgical field, and demonstrate if there is a leak. 
However, the dye can cause a potentially dangerous increase in blood pressure in some cases.

Although not absorbed by the cells, indigo carmine stain, sprayed onto regions of interest, highlights the topography of the mucosal surface with its blue coloring. 
Generally used at a concentration around 0.2%, indigo carmine stain is useful as a screening method for diagnosing minute lesions, to differentiate between benign and malignant lesions, as well as to facilitate application of ME to observe and analyze the surface structure of a lesion, delineate boundaries of early stage malignant lesions and estimate the invasion depth of cancer. 
Indigotine has been used to diagnose Barrett’s esophagus, evaluate villous atrophy, diagnose and discriminate polypoid and non-polypoid lesions in the colon, and diagnose gastric adenoma and cancer.

Indolesulfonic acid used as a dye in renal function testing for the detection of nitrates and chlorates, and in the testing of milk.

Identifiers
Indigo Carmine
INS No. 132
FD&C Blue No. 2
E 132
CI No. 73015
CAS 860-22-0

Physical Description
Indigotine occurs as a blue-brown to red-brown powder or as granule. 
It is an indigoid dye, consisting of a mixture of disodium 3,3′-dioxo-[delta2,2′-biindoline]-5,5′-disulfonate (the principal component), disodium 3,3′-dioxo-[delta2,2′-biindoline]-5,7′-disulfonate (an isomer) and subsidiary coloring matters and may be converted to the corresponding aluminum lake.

Common Uses
Indigotine is distinguished by its rich royal blue color, and can be used for coloring foods and drugs, including dietary supplements, blueberry bagels, breakfast cereals, cakes and cupcakes, candies including chocolate, chewing gum, dairy products, decorations for baking, frozen treats, and sauces and seasonings.

Indigotine is an organic compound commonly used as a reddish blue food dye. 
It can also be referred to using the names:

Indigo Carmine
FD&C Blue #2
CI Food Blue 1
CI (1975) No. 73015

Description
The chemical formula for indigotine is C16H8N2Na2O8S2.

Historically, indigo was produced from natural products. 
The ancient Phoenicians first began to produce indigo dyes from the excrement of sea snails. 
As you might expect, each snail would only produce a very small amount of dye. 
This meant that the dye was very rare, and materials coloured with it were very expensive.

Later discoveries allowed the dyes to be produced from a variety of plants. 
Most plants used to produce indigo are shrubs of species Indigofera.

Synthetic Production of Indigotine
Indigo (or indigo paste) is synthetically produced by first using aniline (which is produced from benzene) and formaldehyde to create molecules called N -phenylglycine. 
These molecules are then fused in a molten mixture of sodamide and sodium and potassium hydroxides under ammonia pressure. 
The indigo is then isolated and purified.
Once the indigo has been produced, it is heated in the presence of sulphuric acid. 
Indigotine is then isolated and subjected to purification procedures.

Common Uses
Indigotine is currently approved for use in the U.S.1, Canada2 and the E.U.3.
There aren’t that many foods that need to be dyed blue.
 The common use cases are just what you might expect: confectionaries (candies), cereal, and other “junk” food. 

Two examples are:
- Froot Loops
- Skittles

Non-Food Uses
- It is used as a pH indicator. It is blue at pH 11.4 and yellow at 13.0.
- It is used in obstetrics to help detect amniotic fluid leaks.
- It is used during surgery to highlight the urinary tract and help to detect leaks.

Indigotine is an organic compound that is a reddish-blue food additive. 
Naturally, the compound is derived from sea snails and plants belonging to the genus Indigofera (Boer 2014). 
Production from organisms is not cost-effective because thousands of sea snails or plants are required to produce a pound of indigotine. 
Hence, the synthetic process of producing indigotine though benzene ammonification and aniline sulfonation is cost-effective (Preparation of indigo 2018). 
Thus, this assessment of the indigotine focuses on chemical structure, synthesis, applications, regulations, toxicology, the theoretical maximum daily intake, the estimated daily intake, and risk analysis.

The chemical (IUPAC) name of indigotine is 3,3′-dioxo-2,2′-bisindolyden-5,5′-disulfonic acid disodium salt. 
Other synonyms of indigotine are brilliant indigo, indigo carmine, FD&C-blue-2, CI food blue 1, and sicovit indigotin 85 (Food and Agricultural Organization 2010). 

 Physical properties show that the indigotine is a blue or purple powder that is soluble in water with a melting point of 3000C. 
It is classified as a food colorant and assigned a code number 132 in the range of blue and violet colors (Federal Register of Legislation 2018).

Manufacture and Specifications
Raw materials required for the synthesis of indigotine are benzene, formaldehyde, ammonia, sodium hydroxide, sodamide, potassium hydroxide, and sulfuric acid (Preparation of indigo 2018). 
The synthesis of indigotine occurs in five stages, which entail the formation of phenylglycine, the fusion of molten mixture, the oxidation of indigo, the acidification of indigo, and the purification of indigotine. 
The formation of phenylglycine is the first stage involves the combination of benzene, ammonia, and formaldehyde. 
In the second stage, which is the fusion stage, sodamide, phenylglycine, sodium hydroxide, and potassium hydroxide reacts in high temperatures of 5000C to form indoxylate salts (Preparation of indigo 2018). 
In the third stage of oxidation, indoxylate salts convert into indigo under alkaline conditions, 700C, and ammonia pressure. 
Subsequently, acidification with 30% sulfuric acid to form indigotine occurs in the fourth stage. 
To remove contaminants, which are mainly alkali salts, ammonium salts, and sulfuric acid, indigotine is boiled with pyridine and hydrochloric acid.

Food Use and Applications
Indigotine is a food additive that has been approved in the United States, Europe, and Australia. 
The joint committee of the World Health Organization and the Food and Agricultural Organization has established an acceptable daily level of indigotine intake as a food additive. 
The common foods colored with indigotine are cereals, candies, and cakes (Saltmarsh 2013).
Since indigotine is soluble in water, it is an appropriate food colorant, which provides a uniform coloring in diverse foods. 
In addition to coloring food, indigotine has numerous uses. 
In medicine, indigotine is an analytic agent used in the diagnosis of renal function by detecting orifices through cystoscopy and catheterization (Saltmarsh 2013). 
In the laboratory, indigotine is used as a pH indicator for it turns yellow at a pH of 13 and blue at a pH of 11.4.
Although heat does not influence the color of indigotine, oxygen and light decolorize it, whereas pH influences its color.

About Indigotine 
Helpful information
Indigotine is registered under the REACH Regulation and is manufactured in and / or imported to the European Economic Area, at ≥ 1 to < 10 tonnes per annum.

Indigotine is used by consumers, by professional workers (widespread uses), in formulation or re-packing, at industrial sites and in manufacturing.

Consumer Uses
Indigotine is used in the following products: biocides (e.g. disinfectants, pest control products), fertilisers, plant protection products, cosmetics and personal care products, air care products, coating products, fillers, putties, plasters, modelling clay, inks and toners, laboratory chemicals, perfumes and fragrances and polishes and waxes.
Other release to the environment of Indigotine is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Article service life
ECHA has no public registered data on the routes by which Indigotine is most likely to be released to the environment. ECHA has no public registered data indicating whether or into which articles the substance might have been processed.

Widespread uses by professional workers
Indigotine is used in the following products: biocides (e.g. disinfectants, pest control products), fertilisers, plant protection products, air care products, coating products, fillers, putties, plasters, modelling clay, inks and toners, laboratory chemicals, perfumes and fragrances, polishes and waxes, washing & cleaning products and cosmetics and personal care products.
Indigotine is used in the following areas: agriculture, forestry and fishing.
Other release to the environment of Indigotine is likely to occur from: outdoor use and indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners).

Formulation or re-packing
Indigotine is used in the following products: biocides (e.g. disinfectants, pest control products), fertilisers, plant protection products, cosmetics and personal care products, air care products, coating products, fillers, putties, plasters, modelling clay, finger paints, inks and toners, laboratory chemicals, perfumes and fragrances, polishes and waxes and washing & cleaning products.
Release to the environment of Indigotine can occur from industrial use: formulation of mixtures and formulation in materials.
Uses at industrial sites
Indigotine is used in the following products: laboratory chemicals.
Indigotine has an industrial use resulting in manufacture of another substance (use of intermediates).
Indigotine is used in the following areas: formulation of mixtures and/or re-packaging.
Indigotine is used for the manufacture of: chemicals.
Release to the environment of Indigotine can occur from industrial use: as an intermediate step in further manufacturing of another substance (use of intermediates), in processing aids at industrial sites, as processing aid and in the production of articles.
Manufacture
Release to the environment of Indigotine can occur from industrial use: manufacturing of the substance.

IUPAC NAMES:
1H-Indole-5-sulfonic acid, 2-(1,3-dihydro-3-oxo-5-sulfo-2H-indol-2-ylidene)-2,3-dihydro-3-oxo-, disodium salt
2-(1,3-dihydro-3-oxo-5-sulfo-2H-indol-2-ylidene)-2,3-dihydro-3-oxo-1H-Indole-5-sulfonic acid, disodium salt
3,3'-dioxo-2,2'-bis-indolyden-5,5'-disulfonic acid disodium salt
disodium (2E)-3-oxo-2-(3-oxo-5-sulfonato-1H-indol-2-ylidene)-1H-indole-5-sulfonate
disodium 3,3'-dioxo-1,1',3,3'-tetrahydro-2,2'-biindole-5,5'-disulfonate
disodium 3-oxo-2-(3-oxo-5-sulfonato-2,3-dihydro-1H-indol-2-ylidene)-2,3-dihydro-1H-indole-5-sulfonate
Disodium 5,5'-(2-(1,3-dihydro-3-oxo-2H-indazol-2-ylidene)-1,2-dihydro-3H-indol-3-one)disulphonate
disodium 5,5'-(2-(1,3-dihydro-3-oxo-2H-indazol-2-ylidene)-1,2-dihydro-3H-indol-3-one)disulphonate
disodium;(2E)-3-oxo-2-(3-oxo-5-sulfonato-1H-indol-2-ylidene)-1H-indole-5-sulfonate
FD+C Blue No. 2 powder
Indigo Carmine
Indigo carmine

SYNONYMS:
Sachsischblau
Indigotine
Murabba
Indigo Extract
Indigotine Lake
Soluble Indigo
Indocarmine F
Indigotine B
Indigotine I
Indigotine N
Intense Blue
Indigotin I
Indigotine IA
Cilefa Blue R
Indigo Carmine A
Indigo Carmine X
Grape Blue A
Airedale Blue IN
Acid Blue W
HD Indigo Carmine
Indigo Carmine AC
Indigo Carmine BP
Food Blue 2
Indigotine Blue LZ
Atul Indigo Carmine
Soluble Indigo Blue
Bucacid indigotine B
Grape Blue A Geigy
Maple Indigo Carmine
Edicol Supra Blue X
Amacid Brilliant Blue
Indigo Carmine Powder
Mitsui Indigo Carmine
FD and C Blue 2
Aniline Carmine powder
Acid Leather Blue IC
Dolkwal Indigo Carmine
San-ei Indigo Carmin
Usacert Blue No. 2
Canacert Indigo Carmine
Hexacert Blue No. 2
C.I. Food Blue 1
Indigotine disodium salt
Indigotine Conc. Powder
Indigotine Extra Pure A
Sumitomo Wool Blue SBC
C.I. Natural Blue 2
HD Indigo Carmine Supra
Indigo Carmine Conc. FQ
A.F. Blue No. 2
Sodium indigotindisulfonate
1311 Blue
FD & C blue no. 2
L Blue Z 5010
12070 Blue
Hexacol Indigo Carmine Supra
Indigo Carmine Disodium Salt
Carmine Blue (biological stain)
Disodium indigo-5,5-disulfonate
NSC8646
Sodium 5,5'-indigotindisulfonate
Indigo Carmine (Biological Stain)
C.I. Food Blue 1, disodium salt
NSC-8646
Disodium 5,5'-indigotin disulfonate
Indigo disulfonate (Biological Stain)
CI 73015
Disodium salt of 1-indigotin-S,S'-disulfonic aci
FD&C Blue 2
Sodium 5,5'-indigodisulfonate
Disodium 5,5'-indigodisulfonate
WLN: T56 BMYVJ GSWO CU- CT56 BMYVJ GSWO &-NA- 2
[.DELTA.2,5'-disulfonic acid, 3,3'-dioxo-, disodium salt
[.delta.(sup2,5'-disulfonic acid, 3,3'-dioxo-, disodium salt
1H-Indole-5-sulfonic acid,3-dihydro-3-oxo-5-sulfo-2H-indol-2-ylidene)-2,3-dihydro-3-oxo-, disodium salt
1H-Indole-5-sulfonic acid,3-dihydro-3-oxo-5-sulfo-2H-indol-2-ylidine)-2,3-dihydro-3-oxo-, disodium salt