Erythrosine is a chemical compound containing iodine, also known as Red No. 3 or E127, is a cherry-pink synthetic dye derived from coal tar. It is primarily used as a food coloring agent to give products a pink or red hue.

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. 

Cosmetics

It is a restricted ingredient IV/80 (CI 45430) a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009 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.

Food

Erythrosine is used in a variety of food products, including candies, cake decorating gels, and popsicles, to impart a pink or red color. E127 in the European Food Additives List as dye and CI 45430 in the Colour Index International.

Dental Uses

 Erythrosine is sometimes used in dental plaque disclosing agents to highlight the areas of plaque accumulation on teeth.

Medicine

 It has been used as a diagnostic aid in certain medical imaging procedures.

Safety

Has an effect on the thyroid gland and is proposed in scientific literature as secondary tumorigenic agent (1).

• Moleular Formula:   C₂₀H₆I₄Na₂O₅   C₂₀H₆I₄Na₂O₅H₂O
• Molecular Weight:  879.86 g/mol
• CAS:   16423-68-0
• 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. 

Abstract. Erythrosine (FD & C Red No. 3) is an iodine-containing food colour which was used as an example in the application of the proposed approach of data-derived safety factors. The effect of erythrosine on the thyroid and the mechanism by which the effect is induced has been central to the discussion of the establishment of an Acceptable Daily Intake (ADI), or not, and a short account is given of the effect of erythrosine on the thyroid. The evaluation of erythrosine as a secondary tumorigenic agent was based on the evaluations of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Scientific Committee for Food of the Commission of the European Communities (SCF). In the proposed decision tree scheme, three different possibilities were examined. One was based on the long-term data and the second on the hormone data in the rat; the third was based on the NOEL for hormonal changes in humans. The three approaches with different NOEL and default values resulted in the following ADIs: 0.25, 0.3 and 0.1 mg/kg bw. The cases are discussed and it is concluded that the ADI based on the NOEL in human studies seems most appropriate. As there is most uncertainty about the default value for human pharmacokinetic variability, it is suggested that further human studies might elucidate this point.