Sudan I (also known as CI Solvent Yellow 14 or Solvent Orange R) is an organic compound typically classified as an azo dye. It is an orange-red solid, used to color waxes, oils, petrol, solvents, and polishes. Historically, Sudan I used to serve as a food coloring agent, notably for curry powder and chili powder. However, along with its derivatives Sudan III and Sudan IV, the compound has been banned for use in food in many countries (including the United States and the European Union) due to its classification as a category 3 carcinogen by the International Agency for Research on Cancer (not classifiable as to its carcinogenicity in humans). Nevertheless, Sudan I remains valuable as a coloring reagent for non-food-related uses, such as in the formulation of orange-colored smoke.
Application The Sudan dyes are a group of azo compounds which have been used to color hydrocarbon solvents, oils, fats, waxes, shoes, and floor polishes. As recently as 1974, about 270,000 kg (600,000 lb) of Sudan I, 236,000 kg (520,000 lb) of Sudan II, 70,000 kg (150,000 lb) of Sudan III, and 1,075,000 kg (2,370,000 lb) of Sudan IV was produced in the United States. Sudan I and Sudan III (1-(4-(phenyldiazenyl)phenyl) azo naphthalen-2-ol) are primarily used for the same application. Sudan III melts at a 68°C (154.4°F), a much lower temperature than Sudan I, which melts at 131°C (268°F).
Synthesis There are two steps in synthesizing this compound: The first step is the preparation of a benzene diazonium chloride solution, a diazonium salt created from the reaction of aniline with nitrous acid generated by the reaction of sodium nitrite and hydrochloric acid. The second step involves adding the solution of the diazonium salt to 2-naphthol, to produce the diazo dye. Sudan I is prone to photodegradation when exposed to light. This process involves the breakdown of the dye due to the interaction with singlet oxygen and free radicals. As a result, the colorfastness of Sudan I on materials is poor.
Degradation and metabolism The metabolism of Sudan I, as characterized in rabbits, involves both oxidative and reductive reactions. The biological breakdown of the nitrogen-nitrogen bond by hydrogenation of the Sudan I molecule (azo-reduction) produces aniline and 1-amino-2-naphthol. This reaction appears to contribute to the detoxification observed in animal studies. After oxidation of Sudan I, C-hydroxylated metabolites are formed as major oxidation products and are excreted in urine. These metabolites are also found after oxidation with rat hepatic microsomes in vitro. The C-hydroxylated metabolites may be considered as the detoxification products, while the benzene diazonium ion (BDI), formed by the microsome-catalyzed enzymatic splitting of the azo group of Sudan I, reacts with DNA in vitro. The major DNA adduct formed from this reaction is the 8-(phenylazo)guanine adduct, which was also found in the liver DNA of rats who were exposed to Sudan I. The formation of C-hydroxylated metabolites and DNA-adducts from Sultan I oxidation was also demonstrated with human cytochrome P450 (CYP) enzymes, with CYP1A1 being the major enzyme involved in the oxidation of Sudan I in human tissues rich in this enzyme, while CYP3A4 is also active in human liver. CYP1A1 constitutes less than 0.7% of the total hepatic CYP expression in human livers but can be responsible for up to 30% of the oxidation of Sudan I in a set of human liver microsomes. Moreover, Sudan I strongly induces CYP1A1 in rats and human cells in culture due to the activation of the cytosolic aryl hydrocarbon receptor. In addition to oxidation by CYP enzymes, Sudan I and its C-hydroxylated metabolites are oxidized by peroxidases, such as a model plant peroxidase and the mammalian enzyme cyclooxygenase. In bladder tissue, CYP enzymes are not detectable, but relatively high levels of peroxidases are expressed. As a consequence, DNA, RNA, and protein adducts are formed. Therefore, peroxidase-catalyzed activation of Sudan I has been suggested as mechanism. This is similar to other carcinogens, such as the carcinogenic aromatic amines. It has been suggested that a CYP- or peroxidase-mediated activation of Sudan I or a combination of both mechanisms may be responsible for the organ specificity of this carcinogen for the liver and urinary bladder in animals. The Sudan I metabolites formed by peroxidase are much less likely to be formed at physiological conditions because in vivo there are many nucleophilic molecules present which scavenge the Sudan I reactive species. Hence, the formation of adducts in the Sudan I reactive species with nucleophilic species (such as DNA, tRNA, proteins, polynucleotides, and polydeoxynucleotides) seems to be the preferred reaction under physiological conditions, with deoxyguanosine as the major target for Sudan-I DNA binding, followed by deoxyadenosine.
Effect on humans Sudan I is determined to be a health hazard by EU chemical regulators as well as the IARC. It may cause allergic skin reactions and skin irritation. Exposure to the skin can happen by textile workers being subjected to direct exposure, or by wearing tight-fitting textiles dyed with Sudan I. Allergic reactions are induced when the azo dye binds to the human serum albumin (HSA), forming a dye-HSA conjugate which immunoglobulin E binds to, leading to an eventual release of histamine. Sudan I is also suspected of causing genetic defects. The mutagenicity and genetic hazard have been evaluated with the Ames test and animal experiments. Furthermore, it is suspected of causing cancer. The carcinogenicity was estimated merely through animal testing. It has not been verified in human subjects yet.
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