Acid dyes triphenylmethane

The photochemistry of four triphenylmethane acid dyes was studied in poly(vinyl alcohol), methylcellulose and gelatin films. These model systems were chosen with a view to elucidating the complex free-radical reactions taking place in the heterogeneous dyed wool/ water/air system on exposure to UV radiation. The dye fading mechanism seems to involve an excited triplet state of the dye molecule [ 164] The rate of fading is governed by ... 

A study of some triphenylmethane acid dyes on model polymer systems has revealed the operation of a complex fading mechanism which probably involves excited triplet-state dye molecules [70]. 

Nonchelating dyes include basic triphenylmethane dyes (e.g., Brilliant Green, Malachite Green, Crystal Violet), xanthene dyes (e.g., Rhodamine B, Rhodamine 6G), azine dyes (e.g., Methylene Blue), and acid dyes (e.g., Eosin, Erythrosin). These are intensely colored and when paired with an oppositely charged analyte ion lead to high sensitivities. 

Most of the chromophore systems common in dye chemistry (nitro, azo, anthraquinone, triphenylmethane, and azomethine) are currently used [37,39, pp. 526-533], Disperse, cationic (basic), and anionic (acidic) dyes are employed. 

Scheme 13 Chemical structure of poly(L-glutamic acid) containing triphenylmethane dyes in the side chains (XXII, Y =-OH and...

According to their chemical structures and the Cl system, dyes can be classified into 17 groups nitro dyes, triphenylmethane derivatives, xanthenes, acridine derivatives, quinoline derivatives, azines, ant-hraquinones, indigoid dyes, phthalocyanines dyes, oxydation bases, insoluble azo dye precursors, and azo dyes (classes XII-XVII). In practice, dyes are classified into different application classes disperse, acid, basic, direct, vat, fiber-reactive, sulfur, preme-tallic, solvent dyes, and naphthols. 

This consists of the phthalocyanine dyes, an example of this group being Coomassie Turquoise Blue 3G. This is a trisulphonated derivative of copper phthalocyanine. It dyes wool a very bright greenish blue shade. Its fastness to light is better than the triphenylmethane acid dyes which alone will give comparable shades. 

Use has been made of ion-pairs formed by the cationic complex of zinc with 1,10-phenanthroline or 2,2 -dipyridyl and acid dyes, such as eosin, Erythrosin, Rose Bengal, dibromofluorescein (xanthene dyes) [72-74], Bromophenol Blue, Bromophenol Red (triphenylmethane dyes) [75,76]. In some of these methods, molar absorptivities are -10. Chloroform is the usual extraction solvent. 

It has been reported that y3-CD could improve the selectivity of the color reactions of various metal ions with triphenylmethane, xanthene acid dyes and some other coloring reagents. The effect of fi-CD on the association compound system of metal (Mo, Zn, Co)-thiocyanate basic dyes such as malachite green, crystal violet, rhodamine B, rhodamine 6G and butyhhodamine B, has been investigated and the result shows that /3-CD could contribute to a more sensitive and stable system which improve the solubility of the basic dyes and produce a favorable microenviromnent for the color reactions [63]. /3-CD could be employed to solubilize the 1,2-amino anthraquinone in water due to the formation of inclusion complex which acts as a ligand for metal ions could be used for the determination of palladium at trace levels by spectrophotometry. In the spectrophotometric determination of microamounts of Zn based on the Zn-dithizone color reaction, -CD could increase the apparent molar absorptivity at 538 nm by 8.37 times. In the presence of cr-CD, the determination sensitivity of copper in leaves based on the color reaction of Cu(II) and mesotetrakis (4-methoxy-3-sulfophenyl) porphyrin was enhanced by 50% in the spectrophotometric analysis [64,65]. 

Commercial acid dyes of monoazo, biazo-anthraquinonc, and triphenylmethane types... 

Oxalic acid. Reduction of this acid with magnesium and chromotropic acid gives rise to glycolic acid, from which cone. H2SO4 liberates formaldehyde, which can be detected, for example, with chromotropic acid. When melted with diphenylamine or carbazole, oxalic acid gives triphenylmethane dyes. 

Triphenylmethane acid dye. Commercially available. Used as 0.1% soln. in 20% EtOH or 0.04% aq. soln. in extraction-photometric detn. of Fe (//), Zn, Cu, Cd, Ag acid-base indicator (pH range 3-4.6 colour change yellow- purple) adsorption indicator. Blue cryst. (AcOH/Me2CO). Sol. EtOH, alkalis si. sol. H2O, Et20. Mp 279° dec. 3.89 (H2O). Available as acid or monosodium salt. 

Naphthalenesulfonic acids are important chemical precursors for dye intermediates, wetting agents and dispersants, naphthols, and air-entrainment agents for concrete. The production of many intermediates used for making a2o, a2oic, and triphenylmethane dyes (qv) involves naphthalene sulfonation and one or more unit operations, eg, caustic fusion, nitration, reduction, or amination. 

Hydroxy-2-Naphthalenecarboxylic Acid. l-Hydroxy-2-naphthoic acid is made similarly to the isomer (2-hydroxy-1-naphthoic acid) by reaction of dry sodium 1-naphthalenolate with CO2 in an autoclave at ca 125°C. It has been used in making triphenylmethane dyes and metalli able a2o dyes. Alkylamides and arylamides of l-hydroxy-2-naphthalenecarboxyhc acid are cyan couplers, ie, components used in indoaniline dye formation in color films (see Color PHOTOGRAPHY). 

The triaryknethane dyes are broadly classified into the triphenyknethanes (Cl 42000—43875), diphenylnaphthyknethanes (Cl 44000—44100), and miscellaneous triphenylmethane derivatives (Cl 44500—44535). The triphenyknethanes are classified further on the basis of substitution in the aromatic nuclei, as follows (/) diamino derivatives of triphenylmethane, ie, dyes of the malachite green series (Cl 42000—42175) (2) triamino derivatives of triphenylmethane, ie, dyes of the fuchsine, rosaniline, or magenta series (Cl 42500—42800) (J) aminohydroxy derivatives of triphenylmethane (Cl 43500—43570) and (4) hydroxy derivatives of triphenylmethane, ie, dyes of the rosoHc acid series (Cl 43800—43875). Monoaminotriphenyknethanes are known but they are not included in the classification because they have Httie value as dyes. 

Primary alcohols can be selectively detected using reagent sequences involving an initial oxidation to yield aldehydes that are then reacted in acid medium with electron-rich aromatics or heteroaromatics, according to the above scheme, to yield intensely colored triphenylmethane dyes. 

Classical examples of this type of reaction are the various dimethylaminobenz-aldehyde reagents (q.v.) and vanillin-acid reagents, of which one, the vanillin-phosphoric acid reagent, is already included in Volume 1 a. The aldol condensation of estrogens is an example for the reaction mechanism (cf. Chapter 2, Table 6). According to Maiowan indole derivatives react in a similar manner [1]. Longo has postulated that catechins yield intensely colored triphenylmethane dyes [2]. 

In the presence of strong acids catechins react with aromatic aldehydes to yield triphenylmethane dyes [14] according to Malowan [15] indole derivatives form the following condensation product ... 

The general aspects of the aldehyde-acid reaction were discussed in Chapter 2. Thus it is readily understood that catechins, for example, can react with aromatic aldehydes in the presence of strong acids to yield colored triphenylmethane dyes [26]. 

Anodic oxidation has been employed for water-soluble triphenyl-methane dyes. It has been shown that the formation of dye is an irreversible two-electron oxidation process.21-23 This method has been used for the oxidation of diamino triphenylmethane leuco compounds containing two to four sulfonic acid groups to obtain food-grade colored materials.24... 

Pressure-sensitive recording materials are obtained by dissolving a triphenylmethane leuco dye in a solvent composed of paraffin oils. The microcapsules are formed from a water-soluble106 or water-dispersible material.107,108 Leuco dyes dissolved in sunflower oil are microencapsulated in a solution containing a melamine-HCHO precondensate and coated on the back side of a paper sheet. Contact of the microcapsule-coated sheet with an acid-coated receptor sheet allows the color formation to occur. 

Triphenylmethane leuco dyes are used for photographic materials. The photographic system requires a polymer binder such as acrylic acid-methyl methacrylate copolymer115 or a copolymer of isophthalic and terephthalic acids116 a sensitizer such as 4-(4-n-amyloxyphenyl)-2,6-bis(3-ethylphenyl)-thiapyrilium perchlorate,117 a photo initiator such as hexaarylbisimi-dazole,118 and phenyl tribromomethyl sulfone, cycloalkane such as 1,2,3, 4,5-pentabromo-6-chlorocyclohexane,119 or 3-benzylidene-9-methyl-2,3-dihydro- 1 TZ-cyclopenta [b] quinoline.120... 

DC11 Malachite Green, Basic Blue efficiency (95-98%) achieved within 6 h for 100 mM Acid Blue 25 (anthraquinone dye), 4 h for 55 mM Malachite Green (triphenylmethane dye), and 2 h for 750 mM Basic Blue X-GRRL under anaerobic conditions ... 

The decolorization potential of immobilized P. chrysosporium MTCC 787 for azo dyes Acid Orange, Acid Red 114, triphenylmethane dye Methyl Violet, diazoic dye Congo Red, vat dye Vat Magenta, thiazine dye Methylene Blue, and anthraqui-none Acid Green was demonstrated by Radha et al. [53]. Decolorization experiments were carried out with immobilized calcium alginate (Ca-ALG) beads of different sizes (2-6 mm). 

Table 6.5 Spectral data for some triphenylmethane dyes in 98% acetic acid...

A. The Basic Series.—In general, aromatic aldehydes condense with aromatic amines in the presence of zinc chloride to form triphenylmethane derivatives (0. Fischer) phenols and phenyl ethers behave similarly in the presence of concentrated sulphuric acid (Baeyer). The products formed are the leuco-compounds of well-known dyes. 

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). 

Wien a little concentrated hydrochloric acid is added the green solution becomes yellow, because now the trichloride is formed and the influence of the second benzene ring is also suppressed, so that the (yellow) fuchsonimine type is formed. All triphenylmethane dyes dissolve in concentrated sulphuric acid with an orange-yellow colour exactly like triphenylcarbinol itself (carbonium salts, Kehrmann). By diluting the solution with water a colourless solution of the tri-acid benzenoid carbinol salt can be obtained. 

In some countries (Great Britain) ammonium nitrate is used with an admixture of triphenylmethane dye, Acid Magenta which inhibits the transformation of one crystalline form into the other at 32°C (Vol. II, p. 454). 

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