Aryl dyes, preparation

Aryl dyes may be prepared by forming a methine chain between a quaternary salt of a heterocyclic compound having a methyl group in the 2- or 4-position and an aryl compound, e.g. PAHs [6]. The best known compounds in this group are the styryl dyes. Following a synthetic route similar to that used in the preparation of styryl dyes, other dyes containing aryl groups may be prepared. For example, styryl dyes are prepared by the condensation of benzaldehydes with the quaternary salt of heterocyclic compounds [6]. 

The (A/-alkylated) lactam of 8-aminonaphthalenecarboxylic acid (47) also is a valuable dye iatemiediate, eg, for cyclometbine-type dyes used for dyeiag polyacrylonitrile fibers and other synthetics. 1,8-Naphtholactams are prepared in high yield and purity by the reaction of naphtholactones with RNH2 (R = H, Cl—4 alkyl, cycloalkyl, or optionally substituted aryl) in aqueous medium, usually in the presence of bisulfite at 150°C over a period of 15 h (143). 

Cyanine dyes have been prepared from the salts obtained by the quatemization of 4,6-dimethyl-2-phenylpyrimidine and 2-alkyl- or 2-aryl-4,6-dimethylthiopyrimidines, but there can be no ambiguity in the structure of these quaternary salts. 

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

Unlike triarylmethane dyes, comparatively little work has been done with diaryl heteryl-, and aryl diheteryl methane compounds. Analogous to triarylmethanes, triheterylmethane dyes are also prepared using POCl3 and a ketone. The intermediate leuco compounds (similar to 65, see Scheme 8) are not isolated40 in the case of triheterylmethane leuco dyes. 

Weiss and co-workersprepared a series of oxazohnylidene steroids 343 as luminescence dyes for application as potential intracellular diagnostic agents (Scheme 6.72). The key intermediate 2-aryl-5,5-dimethyl-4(57/)-thiooxazolones 341 were readily available from the corresponding 4(57/)-oxazolones 339. Reaction of 341 with 342, generated in situ from the hydrazone 340, gave 343 as expected. It was not possible to prepare 343 from 3-thio-androsta-l,4-dien-17-one since the requisite corresponding heterocyclic diazo compounds could not be prepared. 

Not surprisingly, azo derivatives of indolizines are readily prepared since the aryl diazonium ion is a good electrophile. Many compounds of this type (e.g., 129188) have been synthesized,183 188,189 some of which are used as dyes.190... 

In dyeing, surfactants are used as wetting agents. They are also used in the formulation of disperse dyes. A stable suspension of the dye is prepared with the help of an anionic surfactant, such as alkyl or aryl alkyl sulfonate. It has been shown that dyeing takes place through the aqueous phase by the slow dissolution of the solid dye particles (61, 62). The presence of the surfactant helps the dissolution of the dye. 

A preparative application of the Chapman rearrangement was used by many authors for the synthesis of diarylamines170,171 and A-aryl-substituted heterocycles172 as well as dyes and brighteners173. The related Chapman-type isourea rearrangement (98 —99) can also be referred to the anionic rearrangements174 (equation 40). 

Chlorobenzene is employed in the synthesis of certain amino-containing vat dye intermediates. When reacted with phthalic anhydride, the product is 2-chloroanthraquinone, which, with ammonia, is converted readily into 2-aminoanthraquinone (61). Other routes include replacement of halogen by amino groups, with ammonia or ammonium salts of urea, and alkyl- and aryl amines to afford secondary amines. Modification of the amino group by alkylation, with dimethyl sulfate, alkyl halides or esters of toluenesul-fonic acids, is of synthetic value. Arylation of the amino groups is of importance only in the reaction between aminoanthraquinones and nitro- or chloroanthraquinones to yield dianthraquinonylamines, or anthrimides48. For example, the reaction between 62 and 63 yields 64, which can then be converted into carbazole 65, Cl Vat Brown R (Scheme 14). Amination of haloanthraquinones such as l-amino-4-bromoanthraquinone-2-sulfonic acid (bromamine acid) (66), prepared from 1-aminoanthraquinone, is of industrial use. 

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