E127 is a chemical compound containing iodine, an ingredient included in the list of European food additives as a colouring agent. Its chemical name is Erythrosine.

The name describes the structure of the molecule:

• 'Erythro-' comes from the Greek word 'erythros', meaning red, and refers to the colour of the dye.
• "-sine" is a suffix commonly used in chemical names.

The raw materials for the production of Erythrosine are:

• Fluorescein - This is a bright yellow-green organic compound known for its fluorescence properties. It is a xanthene dye that is often used in biochemistry and medicine, for example, to stain cells under a microscope or to trace blood flow in the eyes.
• Iodine - Iodine is a chemical element with the symbol I and atomic number 53. It is a member of the halogen family and appears as a lustrous purple-black solid at room temperature. Iodine has many applications, including use as a disinfectant, as a contrast component in radiography, and as an essential nutrient for the thyroid.

The synthesis process takes place in different steps:

• Preparation of reagents - Fluorescein and iodine are prepared for the reaction. This may include cleaning and accurately weighing the reagents.
• Iodination - Fluorescein is reacted with iodine in a suitable solvent. This process is known as iodination and leads to the formation of erythrosine. The reaction is exothermic, which means it releases heat.
• Product isolation - After the reaction is complete, the erythrosine is isolated from the reaction mixture. This can be done through a series of techniques such as filtration or centrifugation.
• Purification - The isolated erythrosine is then purified to remove any impurities. This may include techniques such as crystallization, distillation, or chromatography.
• Drying and packaging - Finally, the purified erythrosine is dried and packaged for distribution.

It appears in the form of a red powder. 

Food

E127 in the European Food Additives List and CI 45430 in the Colour Index International.

Cosmetics

It is a restricted ingredient as a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009 IV/80 (CI 45430) and II/1337 (Acid Red 51; CI 45430) and its aluminium salt (Pigment Red 172 Aluminium lake) when used as a substance in hair dye products  

Used in toothpastes, it is considered safe for health if the maximum concentration does not exceed 0.0025% (25 ppm).

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

Safety

Has an effect on the thyroid gland and is considered by the scientific literature to be a secondary tumorigenic agent (1).

• Molecular Formula:   C₂₀H₆I₄Na₂O₅   C₂₀H₆I₄Na₂O₅H₂O
• Molecular Weight:  879.86 g/mol
• CAS:   16423-68-0
• UNII    8TL7LH93FM
• EC number:   240-474-8

Synonyms:

• FD & C Red No. 3
• Erythrosin B
• 2-(2,4,5,7-Tetraiodo-6-hydroxy-3-oxo-3H-xanthene-9-yl)benzoic acid
• Sodium 2',4',5',7'-tetraiodo-3-oxo-3H-spiro[isobenzofuran-1,9'-xanthene]-3',6'-bis(olate)
• 2',4',5',7'-Tetraiodofluorescein, disodium salt
• Disodium 2-(2,4,5,7-tetraiodo-6-oxido-3-oxoxanthen-9-yl)benzoate
• 9-(o-Carboxyphenyl)-6-hydroxy-2,4,5,7-tetraiodo-3H-xanthene-3-one disodium salt monohydrate
• Disodium 9-(O-carboxyphenyl)-6-hydroxy-2,4,5,7-tetraiodo-3H-xanthen-3-one monohydrate
• Disodium 3',6'-dihydroxy-2',4',5',7'-tetraiodospiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3-one
• C.I.Solvent Red 140
• Erythrosinic acid

References_____________________________________________________________________

(1) Poulsen E. Case study: erythrosine. Food Addit Contam. 1993 May-Jun;10(3):315-23. doi: 10.1080/02652039309374154.