Vat Violet

Purple Pigments. Methyl violet is the most commonly used purple pigment. It is also widely used for toning black inks. In packaging, although very expensive, Carbazole and Vat violets are used where permanence and resistance properties are needed. 

Dichloroanthraquinone [82-46-2] (46) is an important iatermediate for vat dyes and disperse blue dyes. Examples are Cl Vat Violet 13 [4424-87-7] (170), Cl Vat Orange 15 [2379-78-4] (154), and Cl Disperse Blue 56 [31810-89-6] (11). 1,5-DichloroantliraquiQone is prepared by the reaction of anthraquiQone-l,5-disulfonic acid with NaClO iu hot hydrochloric acid solution. Alternative methods from 1,5-dinitroanthraquiaone (49) by reaction of chlorine at high temperature ia the presence of phthaUc anhydride have been proposed (66). 

Anthrimides. Despite the facts that anthrimides have excellent leveling properties and cover a wide range of colors from yellow to black, they have htde commercial importance because of their duller shades and lower tinctorial strength. However, the anthrimides are important intermediates for manufacturing anthrimidocarbazoles. Some examples of anthrimide dyes are Cl Vat Orange 20 [6370-69-0] (149), (Cl 6302S), Cl Vat Violet 16 [4003-36-5] (150) (Cl 65020] Cl Vat Black 28 [128-79-0] (151) (Cl 65010] and Cl Vat Red 48 [4478-06-2] (152) (Cl 65205) (Fig. 6). 

Derivatives of 1,4- and 1,5-diaminoanthraquinone provide some important examples in this class. Relatively simple dyes include Cl Vat Yellow 3 (6.61 X = H) and Cl Vat Violet 15 (6.61 X = OH). 

In 1904 Bally obtained a bluish violet solid by alkali fusion of benzanthrone at approximately 220 °C. Two isomeric compounds were isolated by vatting the reaction mixture and filtering off a sparingly soluble sodium salt. Oxidation of the filtrate gave a blue vat dye, violanthrone (6.75 Cl Vat Blue 20), as the main component. The less soluble residue similarly afforded a violet product, isoviolanthrone (6.76 Cl Vat Violet 10). The formation of isoviolanthrone can be suppressed by carrying out the fusion in a solvent such as naphthalene or a polyethylene glycol in the presence of sodium acetate and sodium nitrite. Dyes of this type are often referred to as dibenzanthrones. 

Various complex carbazole-acridone dyes have been exploited to obtain brown, khaki, grey and olive hues. The fused carbazole-acridone Cl Vat Brown 55 (6.92), which possesses excellent all-round fastness properties, is currently available. This compound can be obtained from the 6,10,12-trichloro derivative (Cl Vat Violet 14) by condensation with two equivalents of l-amino-5-benzoylaminoanthraquinone, followed by carbazolisation. 

Cellulose has a strong affinity for many of the sodium salts of the leuco compounds of vat dyes, and precautions such as temperature and salt control and gradual addition of the dye may be necessary to avoid unlevel dyeing. With those colours which develop their maximum affinity at 50° to 60°C (122° to 140°F), dyeing may be commenced at 30°C (86°F) and the temperature raised slowly. When penetration is extremely difficult the temperature may be raised above that of maximum adsorption to assist migration and the liquor allowed to cool back to complete exhaustion before the goods are taken out. There are, however, some vat dyes, such as Caledon Blue. XRC (C.I. VAT BLUE 6) and Caledon Brilliant Purple 4RP (C.I. VAT VIOLET 1), which are unstable at higher temperatures. 

Vat Violet 1 (Pigment Violet 31) This is so bright that it is used as a fluorescent dye in polystyrene, SAN, and ABS. It is not suggested for olefinic formulations due to migration problems. 

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