Nitrous acid is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.
Orange GGN, also known as alpha-naphthol orange, is an azo dye formerly used as a food dye. It is the disodium salt of 1-(m-sulfophenylazo)-2-naphthol-6-sulfonic acid. In Europe, it was denoted by the E Number E111, but has been forbidden for use in foods since 1 January 1978. It has never been included in the food additives list of the Codex Alimentarius. As such, it is forbidden for food use in general, because toxicological data has shown it is harmful.
Azo compounds are organic compounds bearing the functional group diazenyl.
Sudan I 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 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.
An acid dye is a dye that is typically applied to a textile at low pH. They are mainly used to dye wool, not cotton fabrics. Some acid dyes are used as food colorants, and some can also be used to stain organelles in the medical field.
Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N=N-C linkage. Azo dyes are synthetic dyes and do not occur naturally. Most azo dyes contain only one azo group, but some dyes contain two or three azo groups, called "diazo dyes" and "triazo dyes" respectively. Azo dyes comprise 60-70% of all dyes used in food and textile industries. Azo dyes are widely used to treat textiles, leather articles, and some foods. Chemically related derivatives of azo dyes include azo pigments, which are insoluble in water and other solvents.
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N+≡N]X− where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.
In organic chemistry, an azo coupling is an organic reaction between a diazonium compound and another aromatic compound that produces an azo compound. In this electrophilic aromatic substitution reaction, the aryldiazonium cation is the electrophile and the activated arene is a nucleophile. In most cases, including the examples below, the diazonium compound is also aromatic.
2-Naphthylamine is one of two isomeric aminonaphthalenes, compounds with the formula C10H7NH2. It is a colorless solid, but samples take on a reddish color in air because of oxidation. It was formerly used to make azo dyes, but it is a known carcinogen and has largely been replaced by less toxic compounds.
Sulfanilic acid (4-aminobenzenesulfonic acid) is an organic compound with the formula H3NC6H4SO3. It is an off-white solid. It is a zwitterion, which explains its high melting point. It is a common building block in organic chemistry.
Azobenzene reductase also known as azoreductase (EC 1.7.1.6) is an enzyme that catalyzes the chemical reaction:
2-Naphthol, or β-naphthol, is a fluorescent colorless (or occasionally yellow) crystalline solid with the formula C10H7OH. It is an isomer of 1-naphthol, differing by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol, but more reactive. Both isomers are soluble in simple alcohols, ethers, and chloroform. 2-Naphthol is a widely used intermediate for the production of dyes and other compounds.
Acid orange 5 is a compound with formula Na(C6H5NHC6H4N=NC6H4SO3). It is an azo dye. It is also used as a pH indicator; it is red in pH under 1.4, orange-yellow in pH over 3.2.
1-Naphthol, or α-naphthol, is a fluorescent organic compound with the formula C10H7OH. It is a white solid. It is an isomer of 2-naphthol differing by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol, with the hydroxyl group being more reactive than in the phenols. Both isomers are soluble in simple alcohols, ethers, and chloroform. They are precursors to a variety of useful compounds. Naphthols are used as biomarkers for livestock and humans exposed to polycyclic aromatic hydrocarbons.
Acid red 88 is an azo dye. Due to its intense colour, solid samples appear almost black. It is used to dye cotton textiles red. A closely related acid dye is Acid Red 13.
Naphthionic acid is an organic compound with the formula C10H6(SO3H)(NH2). It is one of several aminonaphthalenesulfonic acids, derivatives of naphthalene containing both amine and sulfonic acid functional groups. It is a white solid, although commercial samples can appear gray. It is used in the synthesis of azo dyes such as Rocceline (a. k. a. Solid Red A), during which the amino group of the acid (in the form of a salt) is diazotated and then coupled with, in the case mentioned, β-naphthol. It is prepared by treating 1-aminonaphthalene with sulfuric acid.
Disodium 4,4′-dinitrostilbene-2,2′-disulfonate is an organic compound with the formula (O2NC6H3(SO3Na)CH)2. This salt is a common precursor to a variety of textile dyes and optical brighteners
Naphthol AS is an organic compound with the formula C10H6(OH)C(O)NHC6H5. It is the anilide of 3-hydroxy-2-carboxynaphthalene. Many analogous compounds are known, designated with a differing suffix. For example, in Naphthol AS-OL, the aryl substituent on nitrogen is C6H4-2-OCH3. These compounds are used as coupling partners in the preparation of some azo dyes.
3-Hydroxy-2-naphthoic acid is an organic compound with the formula C10H6(OH)(CO2H). It is one of the several carboxylic acids derived from 2-naphthol. It is a common precursor to azo dyes and pigments. It is prepared by carboxylation of 2-naphthol via the Kolbe–Schmitt reaction.
o-Dianisidine is an organic compound with the formula [(CH3O)(H2N)C6H3]2. A colorless or white solid, it is a bifunctional compound derived via the benzidine rearrangement from o-anisidine.
