Pararosanilin

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. 

The synthesis of pararosaniline from triphenylmethane is one which has gone far to solve the problem of the constitution of the important class of triphenylmethane colouring matters. 

Rosaniline or magenta was originally obtained by oxidising with arsenic acid a mixture of aniline with 0- and />-toluidine. The product was then lixiviated and treated with common salt, which converted the ai senate into the hydrochloride of rosaniline. Pararosaniline was prepared in a similar way fiom a niixtuie of aniline and /-toluidine. The series... 

Hexa(hydroxyethyl)pararosaniline nitrile has been used in a chemical radiochromic dosimeter.130 Ferricyanide oxidation of leuco Crystal Violet to Crystal Violet dye finds use in detection of various heavy metals131 at trace quantities. Oxidation of leuco triphenylmethanes by chloramine-T is catalyzed by iodide and therefore is used for detection of iodide.132 On the other hand, the inhibition of the catalytic effect of iodide by some ions can be used for determining traces of Ag(I), Hg(II), Pd(II). In addition, the triphenylmethane leuco dyes, phenolphthalein or phenol red are used extensively as indicators in calorimetric and titrimetric determinations. 

Kumar BSM, Balasubramanian N. 1993. Pararosaniline as a new chromogen for the extractive spectrophotometric determination of trace amounts of hydrogen sulfide in air. J AOAC Int 76 730-734. 

Measurements show some variation depending upon the staining solution used and the method of application. In dried and fixed smears, the cell wall and slime layer do not stain with weakly staining dyes such as methylene blue but do stain with the intensely staining pararosaniline, new fuchsin, crystal violet, and methyl violet. The great majority of bacteria have been measured in fixed and stained preparations. In some instances dried, negatively stained smears have been used. Therefore, the method employed should be specified when measurements of bacteria are reported otherwise the results will be of doubtful v alue. 

The more important triphenylmethane dyes probably date from 1834, when Runge obtained red compounds of unknown constitution from crude phenol and from crude aniline. Shortly after Perkin s discovery of mauveine (section 6.6.1) in 1856 Natanson obtained the triphenylmethane dye magenta from crude aniline by oxidation. Although many related dyes were made empirically over the following two decades, it was not until 1880 that Fischer was able to establish structural relationships within this group of dyes. The essential triphenylmethane ring system was identified by its conversion (Scheme 6.28) into 4,4,4,-triaminotriphenylmethane (6.160), the source of pararosaniline (6.161 Cl Basic Red 9). 

Several examples of typical triarylmethane dyes have already been mentioned, in particular, pararosaniline (6.161), malachite green (6.162) its o-chloro derivative (6.169), crystal violet (6.164), rosaniline (6.165) and diphenylamine blue (6.173). Cl Basic Green 1 (6.168 R = C2H5), the ethyl analogue of malachite green, is prepared by the aldehyde route and is isolated as the sulphate. The ethyl analogue of crystal violet is Cl Basic Violet 4 (6.167 R = C2H5) and is obtained by the ketone route. 

These compounds are triphenylmethane pigments. Strictly speaking, they should be referred to as triaminophenylmethane derivatives. The parent structure is known as reddish violet parafuchsin (118) or its anhydro base pararosaniline (119). The parent compound may bear between one and three methyl substituents (fuchsin, new fuchsin). 

The most important starting materials for process A are 4,4, 4"-triamino-triphenylmethane, pararosaniline (119), and parafuchsin (118). Aniline and formaldehyde are treated at 170°C to form, apart from some formaldehyde-aniline intermediates, 1,3,5-triphenylhexahydrotriazine as the main component. Subsequent treatment with an acidic catalyst, for instance with hydrochloric acid, in excess aniline as a solvent initially affords 4,4 -diaminodiphenylmethane, which is finally oxidized to yield parafuchsin (118). Iron(III)chloride and nitrobenzene, which in the past were used as oxidants, are no longer used. The reaction is now performed by air oxidation in the presence of vanadium pentoxide as a catalyst. 

Pararosaniline, after being formed from parafuchsin with sodium hydroxide, is fused at 175°C with aniline and/or m-toluidine, for instance in the presence of catalytic amounts of benzoic acid, and thus arylated. 

It is prepared by air oxidation of dimethylaniline in the presence of phenol and copper salts as well as sodium chloride. The reaction product consists of tetra- to hexamethylated pararosanilines (see 119, p. 541) ... 

Pararosaniline 4-((4-Aminophenyl)(4-imino-2,5-cyclohexadien-l-ylidene) mehtyl) benzenamine monohydrochloride... 

Other commercially radiochromic films are poly(methyl methacrylate) (PMMA), cellulose triacetate (CTA),i polyamide (nylon) films, poly(vinyl butyrate) with pararosaniline and p-nitrobenzoic acid, and alanine films. The CTA films are undyed PMMA films are available undyed and dyed (red and amber). ... 

Problem 18.64 In the presence of C,H,NOj, 2 mol of C HjNH reacts with 1 mol of p-toluidine to give a triarylmethane that is converted to the dye pararosaniline (Basic Red 9) by reaction with PbO followed by acid Show the steps, indicating the function of (a) nitrobenzene, (b) PbO, (c) HCI. ... 

Acid Magenta. A mixt of di sulfonic and tri-sulfonic acids of pararosaniline, used as a dye or stain. Was proposed for coating crystsof AN to render them non-hygroscopic and thus make them more suitable for use in expls, propellants and fertilizers. Quantities as low as 0,01-0.03% proved to be sufficient for effective waterproofing... 

Crystal violet (20) can be produced directly from formaldehyde and dimethyl-aniline. The methane base (18), WAfW,W-tetramethyl-4,4 -mcthylcncdianilinc, is formed initially. This is then oxidized to Michler s hydrol (12), which condenses with another molecule of dimethylaniline to give leuco crystal violet (19). The latter is converted to the dye in a second oxidation step. Pararosaniline, methyl violet, and Victoria blue can also be obtained by this reaction sequence. 

Nucleophilic substitution of chlorine, sulfonic acid, or amino groups by aromatic amines is a common process for producing triaminotriarylmethane dyes. Spirit blue (23) can be formed from the trichlorotriphenylmethyl cation (21) [6,7] and from pararosaniline (22) [8,9] by reaction with aniline. 

The earliest detectors of S02 in the atmosphere were automated calorimetric wet chemical devices. The reference technique for determining the SOz content of atmospheric air is based on the absorption of S02 from an air sample by a solution of sodium tetrachloromercurate, which, upon the addition of formaldehyde and a pararosaniline dye, forms a strong purple dye complex. Several manufacturers have automated this procedure. Properly maintained, these units provide an excellent record of S02 concentration in the air, because they operate on the basis of a chemical reaction that is specific for S02. 

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