Violet, Acid INDEX

The Colour Index (up to June 1991) Hsts 21 direct violets with disclosed chemical constitutions. Commercially important are Cl Direct Violet 9 [6227-14-1] (79) (Cl 27885) (sulfanihc acid coupled to cresidiue followed by alkaline coupling to V-phenyl J-acid) and Cl Direct Violet 66 [6798-03-4] (80) (Cl 29120) (a copper complex of 2-arniao-l-phenol-4-sulfonarnide (2 mol) coupled to 6,6 -imiQobis-l-naphthol-3-sulfonic acid). 

Although treated as separate classes in the Colour Index, these structural types are closely related and the few diphenylmethane dyes such as auramine (1.28 Cl Basic Yellow 2) are now of little practical interest. Commercial usage of the triarylmethane dyes and pigments has also declined considerably in favour of the major chemical classes. They were formerly noteworthy contributors to the acid, basic, mordant and solvent ranges, primarily in the violet, blue and green sectors. Numerous structural examples are recorded in the Colour Index. The terminal groupings can be amine/quinonimine, as in auramine and crystal violet (1.29 Cl Basic Violet 3), hydroxy/quinone, or both. The aryl nuclei are not always benzenoid (section 6.5). 

The application range designated by this generic name in the Colour Index incorporates those acid, direct and mordant dyes with substantivity for leather and satisfactory fastness on that substrate [55]. It is a commercially important sector, the number of products listed being exceeded only by the complete acid or direct dye ranges. As expected from the sources of this selection, about 85% of leather dyes are azo compounds (35% disazo, 30% monoazo, 20% metal-complex monoazo) and the remainder are mainly yellow to orange stilbene dyes and anthraquinone or triarylmethane types in the violet to green sectors. 

Colorless tetragonal crystals faint violet luminescence refractive index 1.378 density 3.148 g/cm Moh s hardness 6 melts at 1261°C vaporizes at 2,260°C practically insoluble in water (76 mg/L at 18°C) soluble in nitric acid slightly soluble in dilute acids and acetone insoluble in ethanol. 

The new aniline dye companies in Europe displayed their wares at the 1862 London International Exhibition, where Hofmann, as juror, acquired a number of samples. They included a blue (7) discovered, almost by chance, by two French chemists working near London in 1861. It had first appeared when excess aniline was erroneously added to the aniline red reaction mixture. E. C. Nicholson in 1862 treated the aniline blue with sulfuric acid to yield a more valuable product, the soluble alkali blue, later better known as Cl [Colour Index] Pigment Blue 61. In May 1863, Hofmann found that the aniline blue was a substitution product of aniline red in which three phenyl groups had replaced three hydrogens (Scheme 2). This immediately suggested that other substituted derivatives might be made and perhaps even provide new aniline dyes. Alkylation with ethyl iodide showed that this was indeed correct. Hofmann achieved stepwise replacement of three hydrogens to afford colorants that were, successively, reddish violet, violet blue and then violet, what were soon known as the Hofmann s violets (8). Hofmann next turned to the aniline red process, and found that the colorant was formed not from aniline alone... 

Properties Yellow crystals or light-yellow liquid mild odor. Mp 15C, bp 51C, d 1.14 (20/20C), bulkd 10.0 lb/gal (20C), vapor has a green color and burns with a violet flame, refr index 1.3826 (20C). Polymerizes on standing or in presence of a trace of water. An aqueous solution contains monomolecu-lar glyoxal and reacts weakly to acid. Undergoes many addition and condensation reactions with amines, amides, aldehydes and hydroxyl-containing materials. Glyoxal VP resists discoloration. 

According to the Colour Index (1971 Cl 77305), chromium sulfate (Ct2(S04)3) is said to occur in three forms (a) a violet or red anhydrous form (b) Cr2(S04)3.15H20, which is dark green (c) Cr2(S04)3.18H20. It is prepared by treating chromium hydroxide with sulfuric acid and then crystallising, and has been used in green paints, varnishes and inks. 

According to the Co/o r/ ultramarine violet (. v.) with gaseous hydrochloric acid at 200 C for four hours or at a higher temperature with gaseous nitric acid. The Colour Index further comments that ultra-marine red is the acid of which ultramarine violet is the salt... 

Several derivatives can be made of ultramarine (q.v.) by substituting various constituent elements. In the case of ultramarine violet, ultramarine blue is mixed with about 2.5 5% ammonium chloride, heated to 200-250 C for four days and exposed to air until the purple colour develops alternatively ultramarine can be heated with chlorine and hydrochloric acid (Heaton, 1928 Colour Index, 1971 Buxbaum, 1998). Ultramarine red (q.v.) is produced as a derivative of this pigment. 

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