Triphenylmethane dyes, preparation

Crystal violet is an example of a triphenylmethane dye. Its preparation in the laboratory may be illustrated by the condensation of 4 4 -tetramethyl-diaminobenzophenone (Michler s ketone) and dimethylaiiiliue in the presence of phosphorus oxychloride ... 

The technical preparation of crystal violet and of its methyl-free parent substance, parafuchsine, almost the oldest of the triphenylmethane dyes, is not so easily explained. As is well known, in this process aniline and p-toluidine are united by oxidation in an acid melt. (In the preparation of fuchsine itself, which contains a methyl group attached to one of the benzene rings, o-toluidine is an additional ingredient.) Although all the phases of this important synthesis have not yet been experimentally established, we may nevertheless explain it on the basis of a dehydrogenation similar to that involved in the formation of malachite green. Moreover, the union of several molecules of base proceeds exactly according to the principle on which indamines are formed (p. 321) (Bucherer). 

Benzotrichloride Method. The central carbon atom of the dye is supplied by the trichloromcthyl group from p-chlorobenzotrichJoridc. Both symmetrical and unsymmetrical triphenylmethane dyes suitable for acrylic fibers are prepared by this method. 

Benzotrichloride Method. The central carbon atom of the dye is supplied by the trichloromethyl group fromy>-chlorobenzotrichloride. Both symmetrical and unsymmetrical triphenylmethane dyes suitable for acrylic fibers are prepared by this method. 4-Chlorobenzotrichloride is condensed with excess chlorobenzene in the presence of a Lewis acid such as aluminium chloride to produce the intermediate aluminium chloride complex of 4,4, 4"-trichlorotriphenylmethyl chloride (18). Stepwise nucleophilic substitution of the chlorine atoms of this intermediate is achieved by successive reactions with different a.rylamines to give both symmetrical (51) and unsymmetrical dyes (52), eg, N-(2-chlorophenyl)-4-[(4-chlorophenyl) [4-[(3-methylphenyl)imino]-2,5-cyclohexadien-l-yhdene]methyl]benzenaminemonohydrochloride [85356-86-1] (19) from / -toluidine and a-chloroaniline. 

Triamidotriphenylmethane.—The Farbwerken vorm. Meister, Lucius, Briining,2 by electrolytically oxidizing those substances which are formed in the treatment of the hydrochloric-acid salts of homologues of triamidotriphenylmethane with fuming sulphuric acid in the presence or absence of sulphur, succeeded in preparing blue, basic triphenylmethane dyes. 

Triphenylmethane dyes are usually prepared in two steps 1) condensation of an N,N-dialkylaniline with a benzaldehyde compound and 2) oxidation of the resultant leuco base (27). The synthesis of C.I. Basic Green 4 (Malachite Green) is given as an example in Fig. 13.106. Alternatively, C.I. Acid Green 50 is prepared in three steps 1) condensation of... 

Technical Observations. Michler s ketone and its homologs are important starting materials for the preparation of valuable triphenylmethane dyes such as Victoria blue B and Victoria pure blue BO. 

Chloro-2-aminophenol is used chiefly for the preparation of blue azo dyes which can be after-chromed. Its combinations with chromotropic acid and with acetyl-H acid were the purest chrome blues known before the discovery of the chroming triphenylmethane dyes (eriochrome azurol). The latter dyes are superior in depth and brilliance of color, but are not as fast to light as the azo dyes from 4-chloro.2-aminophenol and chromotropic acid or acetyl-H acid. 

The hydrol can also be prepared, although less satisfactorily, by alkaline reduction of Michler s ketone. The hydroxyl group in the hydrol is extremely reactive it is alkylated, for example, merely by boiling with alcohol. The technical importance of the hydrol arises from the ease with which it condenses with various aromatic compounds to form leuco compounds of triphenylmethane dyes (see wool green S, page 307). 

Benzaldehyde is used not only as an intermediate for the preparation of various triphenylmethane dyes, but to a still greater extent for perfuming almond oil soaps. 

The preparation of fuchsine illustrates the formation of a typical triphenylmethane dye but does not show the relations of the colored substance to the compounds which are formed in the intermediate steps. These may be represented by equations. When p-toluidine is oxidized it forms p-aminobenzaldehyde, which condenses with aniline to form triaminotriphenyhnethane. 

Triphenylmethane, (C6H5)3CH, is an important hydrocarbon on account of its relation to the triphenylmethane dyes. It is prepared from chloroform and benzene by the Friedel and Crafts synthesis —... 

In 1985, polymeric triphenylmethane dyes based on condensation polymers such as polyesters and polyurethanes were prepared [252] ... 

Ellis, G. D. Dimarcello, B. J. Bradshaw, D. J. Preparation of a dye for coloring protein-based fibers and cellulose-based materials from the oxidation byproducts of the manufacture of a triphenylmethane dye. Eur. Pat. Appl. EP 909794, 1999 Chem. Abstr. 1999, 130, 313189. 

Basic Red 9 (Pararosaniline) is the simplest triphenylmethane dye. It is prepared by the condensation of one mole of p-toluidine and two moles of aniline, usually by heating in nitrobenzene, which serves as solvent and oxidant. The first product is a colorless carbinol, which is converted to the dye with hydrochloric acid. 

For uniformity with the stmctures given in the Colourindex the ammonium radical (9) is used for the amino-substituted xanthenes and the keto form for the hydroxy derivatives. The xanthene dyes may be classified into two main groups diphenylmethane derivatives, called pyronines, and triphenylmethane derivatives (eg, (4)), which are mainly phthaleins made from phthaUc anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted ben2aldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

The first triaryknethane dyes were synthesized on a strictiy empirical basis in the late 1850s an example is fuchsine, which was prepared from the reaction of vinyl chloride with aniline. Thek stmctural relationship to triphenylmethane was estabHshed by Otto and Fmil Fischer (5) with the identification of pararosaniline [569-61-9] as 4,4, 4 -triaminotriphenyknethane and the stmctural elucidation of fuchsine. Several different stmctures have been assigned to the triaryknethane dyes (6—8), but none accounts precisely for the observed spectral characteristics. The triaryknethane dyes are therefore generally considered to be resonance hybrids. However, for convenience, usually only one hybrid is indicated, as shown for crystal violet [548-62-9] Cl Basic Violet 3 (1), for which = 589 nm. 

Membrane eleetrodes with obtained PVP-dye adduets in polymerie matrixes are developed to measure free eoneentrations of polymer in solution. Membrane film eleetrodes ar e prepar ed using polyvinyl ehloride as a matrix. We investigated properties of eleetrodes eontaining triphenylmethane - PVP and azodye - PVP adduets in water solution of polymer in presenee of different eleetrolytes. 

Quaternary ammonium salts of triphenylmethane acetonitriles Process of preparing cyanides of triarylrnethane dyes... 

The dyes of this group are not prepared from triphenylmethane, but the synthesis of pararosaniline from the hydrocarbon is of importance, as it established the structure of this dye which is the simplest member of the class. The steps involved in the transformation of triphenylmethane into pararosaniline are indicated by the following formulas —... 

Towards the end of the 19th century, many of the newly established firms developed aniline- and triphenylmethane dyestuffs. In 1859, Ciba began the production of fuchsine, which enabled the dyeing of silk. In 1877, BASF was granted the first German patent for a coal tar dye entitled Preparation of Blue Dyestuffs from Dimethylaniline (viz. Methylene Blue) (Fig. 2.2). 

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