CI 26100 is a chemical compound, a disazo synthetic red dye also known by the name Solvent Red 23, Sudan III

Chemical name: 1-[(4-phenyldiazenylphenyl)diazenyl]naphthalen-2-ol

Description of the raw materials that form it:

• Chemical reagents. Solvent Red 23 can be synthesized using a combination of specific chemical reagents, such as organic or inorganic dyes, chemical precursors, and appropriate solvents.

Summary of the industrial chemical synthesis process step-by-step:

• Selection of reagents. Suitable reagents are selected that correspond to the desired specifications for the synthesis of Solvent Red 23.
• Accurate measurement:. The selected reagents are precisely dosed according to specific proportions required to achieve the desired color and characteristics.
• Chemical reactions. The reagents are mixed together in an appropriate reactive system, such as a chemical reactor, and subjected to specific chemical reactions. These reactions may involve condensation processes, oxidation or reduction processes, among others, to form Solvent Red 23.
• Monitoring of reaction conditions. The reaction conditions, such as temperature, pressure, and pH, are monitored and controlled to ensure that the reactions occur efficiently and in a controlled manner.
• Purification of the product. The reaction product undergoes purification processes to remove any impurities or unwanted residual reagents.
• Characterization of the product. Solvent Red 23 is characterized through chemical and physical analyses to confirm its identity and evaluate its properties, such as color, solubility, and stability.
• Packaging of Solvent Red 23 into appropriate containers for distribution and use.

It comes in the form of brown powder.

What it is used for and where

It is a restricted ingredient as IV/51 (CI 26100) II/1353 (Solvent Red 23; CI 26100: when used as a substance in hair dye products)  a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported: 1-(4-(Phenylazo)phenylazo)-2-naphthol

Cosmetics

It is an ingredient that makes the final product more attractive from an aesthetic point of view, but can pose a potential health risk with undesirable side effects especially when used continuously as it can be absorbed through the skin or mucous membranes.

Safety

It is an ingredient that has some important health-related contraindications: it should not come into contact with mucous membranes.

Use in hair colouring products is prohibited.

The problem associated with azo dyes (monoazo or diazo) is photocatalytic degradation leading to eventual oxidation and subsequent formation of impurities such as aromatic amines some of which have carcinogenic activity (1).

• Molecular Formula   C₂₂H₁₆N₄O
• Molecular Weight    352.4 g/mol
• CAS   85-86-9
• UNII ND733RX3JN
• EC number 201-638-4
• DTXSID3041742

Synonyms:

• D&C Red No. 17
• Sudan III

References__________________________________________________________________________

(1) SCIENTIFIC COMMITTEE ON CONSUMER PRODUCTS SCCP. Opinion on the use of CI 26100 (CI Solvent Red 23) as a colorant in cosmetic products. Adopted by the SCCP during the 4th plenary of 21 June 2005 

Abstract.....On the basis of provided data the SCCP cannot assess the risk to consumers when CI 26100 is used as a colorant in cosmetic products. - For a sound risk assessment further studies are needed a) on percutaneous absorption of CI 26100 and 4-aminoazobenzene as well as b) on the rate of azo cleavage under experimental conditions mimicking the use conditions. The results should allow an estimation of exposure of the consumers to both substances. Depending on these data the need of further studies on subchronic toxicity and teratogenicity would be a matter of discussion. - Studies are required to assess the local mutagenic/carcinogenic potential of CI 26100 after topical application....

Andoh SS, Nyave K, Asamoah B, Kanyathare B, Nuutinen T, Mingle C, Peiponen KE, Roussey M. Optical screening for presence of banned Sudan III and Sudan IV dyes in edible palm oils. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2020 Jul;37(7):1049-1060. doi: 10.1080/19440049.2020.1726500. Epub 2020 Feb 20. PMID: 32077804.

Abstract. Due to the proven carcinogenicity of Sudan III and IV dyes, they are considered global public health issues. They are banned in all forms as food colourants. We propose the monitoring of simple and easy-to-measure optical properties of palm oils, such as the refractive indices and spectrophotometric properties, as efficient indicators to detect adulteration. Coupling these results with principal component analysis, excess refractive index, and integration of transmittance introduces a novel detection tool for the authentication of edible palm oil. This opens a new opportunity for accurate handheld devices to detect adulteration and provide control in the field. This work assessed in total of 49 samples, some collected from different parts of Ghana and others, in-house adulterated samples. The Ghana Food and Drugs Authority, who performed a complex and expensive chemical analysis of the samples, confirmed our results with good agreement.

Fonovich TM. Sudan dyes: are they dangerous for human health? Drug Chem Toxicol. 2013 Jul;36(3):343-52. doi: 10.3109/01480545.2012.710626. Epub 2012 Sep 5. PMID: 22947042.

Abstract. Azo and diazo compounds include Sudan dyes, which were widely used in industry. Although they are not permitted in food, they had been found contaminating different food products and their presence is investigated regularly (since 2003) in these products. Sudan III, as well as Sudan Black B, was included in different laboratory techniques for tissue ceroid and lipofucsin analysis and blood-cell staining. Also, Sudan Black B has been recently included in in vivo evaluations in human beings (through oral intake), and Sudan III is still allowed in cosmetics. These azo dyes were metabolized to possible carcinogenic colorless amines, both in the liver of mammalians and by the micro flora present in human skin and the gastrointestinal tract. Both human and laboratory animal cytochrome P450s (CYPs) were able to oxidize Sudan I, whereas Sudan III modified CYP activities. In vitro genotoxic effects were reported for Sudan I, and some DNA adducts formed through exposure to its metabolites were identified. Sudan I was also found to be carcinogenic in the rat, but not in the mouse. The aim of the present review is to put together the most relevant information concerning Sudan dye uses and toxicity to provide some tools for the identification of the risk they represent for human health.

Okada J, Kanbe R, Kuzukawa M, Ikeda Y, Yoshimura K, Hayakawa R, Matsunaga K. Identification of contact allergens in C.I. Solvent Red 23 (commercial Sudan III) by chemical analysis and animal testing. Contact Dermatitis. 1991 Nov;25(5):313-8. doi: 10.1111/j.1600-0536.1991.tb01880.x. PMID: 1725669.

Abstract. C.I. Solvent Red 23, commercial Sudan III, is widely used in cosmetic products. Chemical analyses and guinea pig sensitization tests were carried out to identify its contact allergens. In the Magnusson & Kligman guinea pig maximization test, C.I. Solvent Red 23 showed 20% positive reactions. By conducting chemical analyses with HPLC and GLC, 2-naphthol (82 ppm), azobenzene (48 ppm), Sudan I (570 ppm) and many unknown impurities, as well as the main constituent pigment Sudan III (87%), were found. The chemical structure of one unknown impurity was identified as an isomer of Sudan III. We found that purified Sudan III showed no positive reaction, while the isomer elicited 30% positive reactions, in the same guinea pig test. Furthermore, cross-sensitization with p-phenylenediamine was investigated using the guinea pig test. Animals sensitized with p-phenylenediamine also showed positive elicitation reactions with purified Sudan III. From these results, the contact allergenicity of C.I. Solvent Red 23 is considered to be due to impurities, including the isomer of Sudan III, 1-(o-phenylazophenylazo)-2-naphthol. Positive reactions to Sudan III previously demonstrated in hairdressers are due to cross-sensitivity with p-phenylenediamine.

Ohno M, Ikenaka Y, Ishizuka M. Sudan III dye strongly induces CYP1A1 mRNA expression in HepG2 cells. J Biochem Mol Toxicol. 2012 Jan;26(1):16-22. doi: 10.1002/jbt.20408.