The indamines are produced by oxidizing an equimolecular mixture of a p-diamine and a monamine in cold dilute solution. Phenylene blue, Bindschedler's green and toluylene blue are examples. The indamines are not used in dyeing because they hydrolyse in the presence of acids. They are used as raw material for making the oxazine, thiazine and azine dyes.
The indophenols are also sensitive to acids, and are used as raw material for making sul phur dyestuffs.
The thiazines contain a characteristic ring composed of nitrogen, carbon and sulphur. Lauth's violet is an example of the subdivision thiazimes, and methylene blue of the subdivision thiazones.
The oxazines differ from the thiazines only by the substitution of an oxygen atom for the characteristic sulphur atom of the latter. If the auxochromes introduced are amido- or alkyl amido- groups, the resulting dyestuffs are oxazimes: if hydroxy-groups, they are oxya zones. Capri blue and Meldola's blue are ex amples of the first division, and resorufine and resazurine of the second.
The azine dyestuffs are all phenazonium de rivatives. They are subdivided into eurhodines, eurhodoles, safranines, mauveines and indu lines. The eurhodines are weak bases, of which & the monoacid salts are red, and the acid salts, green. The most important dye of this group is toluylene red. The eurhodoles are obtained by heating eurhodines with concentrated hydro chloric acid at 180°. The safranines are basic dyestuffs, which form three series of salts. The monoacid salts dye wool, silk and tanned cotton shades of red. The mauveines are phenyl-derivatives of the safranines. The group is now only of historic interest, mauveine having been the first coal-tar color discovered. The indulines are considered phenylamido-de rivatives of the mauveines. They are used in the printing of cotton fabrics. The gray dye stuffs known as nigrosines belong to this group.
Indigo and Indigoid Dyestuffs.— The produc tion synthetically of indigotine (the coloring matter of the indigo plant) was accomplished in 1875 by the oxidation of indol by ozone. But it was not until 1890 that Heumann's syn thesis with phenylglycine and its carboxylic acid afforded a profitable method of commercial manufacture. The sodamide modification of this process is the one now chiefly employed. Indirubine, a red dyestuff, is the isomer of indigotine, with which it occurs in the natural sources of indigo. It is synthesized by con densing isatin chloride with oxindol. Not used itself as a dye, its bromo-derivatives are vain-, able.
The indigoid dyestuffs are characterized by the presence of the indigo group, and are of two classes: symmetrical, obtained by oxidizing products similar to indoxyl; and asymmetrical, prepared by condensing a compound similar to indoxyl with a cyclic ketone, such as isatin. The principal commercial dyestuffs in this di vision are the thioindigo series of fast starlets, reds and violet-reds used on cotton; and the substituted indigoid dyestuffs. The latter group includes the ciba dyes, polyhalogenated derivatives of the indigoid division and the Helindone series. The first are vat dyestuffs
for wool, cotton and silk, in shades of yellow; the second, wool dyes of orange, scarlet, pink and red.
Thiazol Dyestuffs.— The thiazol ring is het erocyclic, containing three carbon atoms, one nitrogen atom and one sulphur atom. The first known derivative of this class was phenylbenzthiazol, obtained by fusing benzani tide with sulphur. The most important deriva tive is primuline, containing a free NH, group, which may be diazotised on the fibre and then combined with amines or phenols to give vari ous shades. This class includes the so-called "Ingrain dyes," which are fast to washing, but not fast to light. The colors are yellow, red, garnet and brown. Chlorophenine, thioflavine T and thiazol yellow belong to this class.
Sulphur The sulphur or sulphide colors result from -heating various organic sub stances with sulphur. They are direct dyes for vegetable fibres. Commercially, the sulphur dyes are lcnown by many different names. They are nearly all colored powders, insoluble in water, acids and the other usual solvents, but soluble in cold alkalis in the presence of re ducing agents. Two methods of preparing.them are employed: the first is to treat substituted aromatic amines with chlordinitrobenzene; the second, to reduce indophenols or indamines. Several fine blacic dyes— vidal black, fast blacic, immedial black, etc.—blues, yellows and olives, maroon, browns and bronzes are found in this valuable class.
The sulphurized vat dyestuffs form a dis tinct division under the sulphur class. They are produced by the action of polysulphides on certain organic compounds, but they are in soluble in sodium sulphide. They are divided into (1) sulphurized anthracene derivatives, and (2) sulphurized vat dyestuffs of indo phenols and allied compounds. The first are prepared by melting anthracene.and some of its more complicated derivatives with sulphur at high temperatures. Indanthrene olive is a type of this class : it is obtained by melting anthra cene with sulphur at 480° F. Other colors in this group are the cibarones— blue, black, green, yellow, orange and brown. The second division includes indocarbon and most of the hydron series—blue, blue-black and violet.
Aniline An insoluble dye obtained bv treating aniline with acid oxidizing agents. In its solid form it is not used in printing cot ton fabrics, but is always developed on the fibre by special processes. Aniline black is perhaps the most important of all dyes for cot ton fabrics. Depending for its color upon oxidation, it is thoroughly fast, and ungreen able. See COAL TAR ; COAL-TAR PRODUCTS.
Beacall, Dyestuff s and Coal-Tar Products) (1915) ; Cain and Thorpe, (The Synthetic Drstuffs) (1913) ; Fay, (Coal Tar Dyes' (1911) ; Green, 'Analysis of Dye stuffs) (1915); Lewes, (The Carbonization of Coal) (1912); Wahl, (Organic Dyestuffs' (1914); Warnes, (Coal Tar Distillation) (1913).