Indigo carmine () is a disodium salt, synthetic blue dye also called Acid Blue 74, Indigotine and others. It is produced by the condensation of 2-formylbenzenesulphonic acid and aniline with a subsequent oxidation process. Mixed with tartrazine (E102) it can produce various shades of green.

Chemical Industrial Synthesis Process

• Preparation of reagents. The main raw materials include indigo and sulfuric acid.
• Synthesis of intermediate. The production of CI 73000 begins with the sulfonation of indigo by reacting it with concentrated sulfuric acid, forming a sulfonated indigo intermediate.
• Neutralization. The sulfonated intermediate is neutralized with a base, such as sodium hydroxide, to form the sulfonated indigo salt.
• Oxidation. The sulfonated structure is oxidized to form the indigoid chromophore, which is responsible for the coloring properties of CI 73000.
• Purification. The crude CI 73000 product is purified using techniques such as crystallization, filtration, and chromatography to remove impurities and achieve a high-purity colorant.
• Stabilization. The purified CI 73000 is stabilized to ensure its stability during transportation and storage, preventing degradation and oxidation.
• Quality control. The CI 73000 undergoes rigorous quality testing to ensure it meets standards for purity, color intensity, and safety. These tests include chemical analysis, spectroscopy, and microbiological testing.

It appears as a blue powder

A cosa serve e dove si usa

Food

According to EFSA, food experts believe that Indigo Carmine is poorly absorbed by the human body and does not raise genotoxicity concerns. No adverse effects were identified in subacute, chronic, reproductive and developmental toxicity studies, and no changes in haematological and biological parameters were identified in chronic toxicity studies at doses less than or equal to 500 mg/kg body weight/day (1).

An ADI (Acceptable Daily Intake) is established.

Medical

It is used in medicine in intravenous administration to examine sections of the human body to be explored with endoscopic probes, is usually biologically safe and inert and can rarely cause adverse reactions, except in rare exceptions (2).

Cosmetics

Restricted cosmetic ingredient as IV/98  a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported:

• 2-(1,3-Dihydro-3-oxo-2H-indazol-2-ylidene)-1,2-dihydro-3H-indol-3-one

Cosmetics - INCI Functions

Colorant. This ingredient has the function of colouring the solution in which it is inserted in a temporary, semi-permanent or permanent manner, either alone or in the presence of the complementary components added for colouring.

For more information:   

Indigotine studies

Appearance	Blu powder
Melting Point	>300°C
Density	1.01 g/mL at 20°C
PSA	189.36000
LogP	3.06060
Refraction Index	n20/D 1.335
Water Solubility	1 g/100 mL (25 ºC)
Safety

• Molecular Formula  C₁₆H₈N₂Na₂O₈S₂
• Molecular Weight    466,346
• Exact Mass   465.951752
• CAS   860-22-0
• UNII    D3741U8K7L
• EC Number   212-728-8
• DSSTox Substance ID  DTXSID1020190    DTXSID0044288    DTXSID6044224
• IUPAC  disodium;2-(3-hydroxy-5-sulfonato-1H-indol-2-yl)-3-oxoindole-5-sulfonate
• InChI=1S/C16H10N2O8S2.2Na/c19-15-9-5-7(27(21,22)23)1-3-11(9)17-13(15)14-16(20)10-6-8(28(24,25)26)2-4-12(10)18-14;;/h1-6,17,19H,(H,21,22,23)(H,24,25,26);;/q;2*+1/p-2  
• InChl Key      JFVXEJADITYJHK-UHFFFAOYSA-L
• SMILES   C1=CC2=C(C=C1S(=O)(=O)[O-])C(=C(N2)C3=NC4=C(C3=O)C=C(C=C4)S(=O)(=O)[O-])O.[Na+].[Na+]
• MDL number  MFCD00005723
• PubChem Substance ID    24847997
• ChEBI  31695
• Colour Index Number   73015    
• Beilstein      4103904
• RTECS   DU3000000
• NACRES   NA.47   
• NCI   C83799

Synonyms :

• Sodium indigotindisulfonate
• disodium;2-(3-hydroxy-5-sulfonato-1H-indol-2-yl)-3-oxoindole-5-sulfonate
• (delta(sup 2,2')-Biindoline)-5,5'-disulfonic acid, 3,3'-dioxo-, disodium salt
• FD C Blue 2
• Sachsischblau
• Murabba
• Indigotine Lake
• Indigo Extract
• Indigo carmine
• Acid Blue 74
• CI 73000
• Indigocarmin
• Indigotine
• C.I. ACID BLUE 74
• Indigotindisulfonate sodium
• FD&C Blue No. 2
• Food Blue No. 2
• C.I. Food Blue 1
• C.I. Natural Blue 2
• Amacid Brilliant Blue

References_____________________________________________________________________

(1) Scientific Opinion on the re-evaluation of Indigo Carmine (E 132) as a food additive - First published in the EFSA Journal: 25 July 2014

(2) Nandate K, Voelzke BB. Severe Hypotension, Hypoxia, and Subcutaneous Erythema Induced by Indigo Carmine Administration during Open Prostatectomy. Case Rep Urol. 2016;2016:5237387. doi: 10.1155/2016/5237387.