Coal tar dye

Description

An early general name for any of the thousands of synthetic organic colorants obtained from coal-tar based products (i.e. hydrocarbons), such as benzene, toluene, xylene, naphthalene, anthracene, and aniline. The first observation of a colored compound of this class was made by Runge in 1834. This was followed by specific goal of creating a synthetic dye, which was achieved in 1856 when William Perkin made mauveine, an aniline dye. He took out a patent and began manufacturing it in England. Many other colorants quickly followed. Important steps were made when Graebe and Liebermann (1868) synthetically made alizarin, the colorant found in madder root, then in 1880 synthetic indigo was derived. Even though the artificial indigo and alizarin are chemically identical to the natural dyestuffs, the synthetics surpassed them in purity as well as simplifying the printing and dyeing process.

The first synthetic dyes were usually named by their discoverer. This system, quickly became confusing. For example, azocarmine contains no azo group, alizarine yellow is not chemically related to alizarine and anthracene brown was not derived from anthracene. As the number of synthetic colorants grew and numbering system was developed based on color (R for red, B for blue, etc.) and mode of application (Acid dye, Pigment, etc.) for more information, see Colour Index.

The table below shows some chemical groups of dyestuffs, sub-groups and example colorants derived from coal-tars.

Chemical Dye Family	Description	Examples
Nitroso	A minor group that contains only mordants dyes. They are nitroso-phenols made by the action of nitrous acid on phenols. These dyes are usually applied on an iron mordant and are various shades of green	Fast Green O (dinitoso-resorcinol); Naphthol Green B
Nitro-Dyes	These dyes have a nitro-group that is the chromophore. They are all acid dyes and are usually sold a sodium or ammonium salts. Nitro-dyes were primarily used for coloring silk and wool. They were fugitive and are no longer used.	Picric acid (trinito-phenol); Martius Yellow; Naphthol Yellow S (most important nitro-dye)
Azo Dyes	Largest group, primarily composed of acid dyes. May contain one or more azo groups. Often a subsequent reaction was used to position additional components in the ortho position. Thus the group of azo dyes can vary widely and be quite complex. They are often brilliant in color, ranging from yellow to red and purple. Early types were not very permanent.	Aniline Yellow (first discovered in azo group: aminoazobenzene); Methyl Orange; Congo Red; Sun Yellow (Curcumin S); Para Red; Pyrazolone; Tartrazine (Yellow 5), Sunset Yellow FCF; Ponceau 4R; Carmoisine;
Triphenylmethane Dyes	A large group of dyes that are amino- or oxy- derivatives of triphenylmethane. They are generally divided into four groups: 1) Malachite Green group; 2) Fuschsine or Rosaniline group; 3) Aurines or Rosolic acid group, and 4) the Phthalein or Rhodamine group. All known for their bright blue, green, and violet shades. In particular, the Phthaleins achieved the first examples of fluorescent dyes.	Azo Green; Fuschine; Rosaniline; Methyl Violet; Aniline Blue; Victoria Blue; Chrome violet R; Phenolphthalein; Fluorescein; Phloxine; Rhodamine; Eosin
Azines	The most important dyes in this group are amino-azine and azonium compounds (including Safranines and induline). The azines act as the chromophore in both types.	Chrysoidine; Neutral Violet; Azo carmine G; Induline; Mauveine; Safranine; Basic Blue; Aniline Black
Oxazines and Thiazines	These are similar in structure, but oxazines have an oxygen instead of a sulfur. These compounds produce interesting colors but tend to have low yields. Methylene Blue, a thiazine, received the first patent for a synthetic dye fron the German Patent Office.	Nile Blue A (oxazine); Methylene Blue (thiazine)
Indigoid Dyes	The indigoid class of dyes are all vat dyes. They are generally sub-divided into indigo and thioindigo groups. Indigo, itself, is the most important member. Based on the structure of indigo, commonly used for blue shades.	Indigo; Indigo Carmine (fugitive); Ciba yellow; Thioindigo Red B;
Anthraquinone	Derived from anthracene, these dyes are generally separated into three classes: 1 Mordant dyes, 2) Acid dyes and 3) Vat dyes. Mordant dyes combine with metal oxides to form highly colored salts with the color depending on the metal. For example, alizarine is red on aluminum and violet on chrome. The acid dyes are used to dyes wool in an acid bath. The vat dyes form very intense and permanent on cotton.	Alizarin; Purpurin
Quinoline dyes	Heterocyclic compounds derived from quinoline. Quinoline Red dyes silk and wool readily but the colors are not lightfast. Quinoline yellow is sulfonated and used as an acid wool dye.	Cyanine; Quinoline Red; Quinoline Yellow
Acridine dyes	Pale yellow colors that are noted for the fluorescence they exhibit. The first acridine dye was obtained in 1863 as a by-product of magenta. Acridine dyes are generally used for dyeing leather	Acridine Yellow; Benzoflavine; Acridine Orange
Sulfur colors	Sulfur dyes are only applicable to cottons by using a bath containing sodium sulfide. The dyes produce dark, dull, lightfast shades of yellow, brown, blue, violet and black. Once on the fabric dries, the dye is oxidized, and thereby, set, as a water-insoluble color.	Indophenol; Sulfur Black; Hydrone Blue

Synonyms and Related Terms

aniline dyes; colorante al catrame (It.); aniline colors; coal tar colors; coal-tar colors

Risks

• Some coal tar dyes are carcinogenic.

Resources and Citations

• Barry Barbett, Coal Tar Dyes and Intermediates, Industrial Chemistry, London, 1919.
• Ralph Mayer, A Dictionary of Art Terms and Techniques, Harper and Row Publishers, New York, 1969 (also 1945 printing)
• Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986