Sudan I (also commonly known as CI Solvent Yellow 14 and Solvent Orange R), is an organic compound, typically classified as an azo dye. It is an intensely orange-red solid that is added to colourise waxes, oils, petrol, solvents, and polishes. Sudan I has also been adopted for colouring various foodstuffs, especially curry powder and chili powder, although the use of Sudan I in foods is now banned in many countries, because Sudan I, Sudan III, and Sudan IV have been classified as category 3 carcinogens (not classifiable as to its carcinogenicity to humans) by the International Agency for Research on Cancer. Sudan I is still used in some orange-coloured smoke formulations and as a colouring for cotton refuse used in chemistry experiments. 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 of Sudan I, of Sudan II, of Sudan III, and of Sudan IV were produced in the United States. Sudan I and Sudan III (1-(4-(phenyldiazenyl)phenyl) azonaphthalen-2-ol) are used for mostly the same application. Sudan III melts at a 68 °C higher temperature than Sudan I. Synthesis The synthesis of Sudan I involves the reaction of phenyldiazonium salts with 2-naphthol. Sudan I suffers from oxidative photo-degradation by two mechanisms, singlet oxygen degradation and free radical degradation, decreasing its fastness on materials. Degradation and metabolism The metabolism of Sudan I, as characterized in rabbits, involves both oxidative or reductive reactions. Azo-reduction of Sudan I produces aniline and 1-amino-2-naphthol, and this reaction seems to be responsible for the detoxification. In vivo, 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 detoxication products, while the benzenediazonium ion (BDI) formed by microsome-catalyzed enzymatic splitting of the azo group of Sudan I, reacts with DNA in vitro. The major DNA adduct formed in this reaction is identified as the 8-(phenylazo)guanine adduct, which was also found in liver DNA of rats who were exposed to Sudan I. The formation of C-hydroxylated metabolites and DNA-adducts from Sultan I oxidation were also demonstrated with human CYP enzymes, with CYP1A1 being the major enzyme involved in the oxidation of Sudan I in human tissues rich in this