Leuco crystal Violet

When a benzene solution of benzaldehyde and leuco Crystal Violet is irradiated in air, it undergoes an exceptionally fast photochemical reaction and the dye is formed in an excellent yield.38... 

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. 

As already mentioned, tertiary amines can not form similar addition products. With stabilized amines such as leuco crystal violet, leucomalachite green and similar dyes neutral and stable charge-transfer complexes were formed [94]. 

All forms of iodine including the elemental iodine, hypoiodous acid (HOI), hypoiodite anion (OI ), free iodide anion (I-), and triiodide anion (I3 ) in water also may be measured by the Leuco crystal violet method. The sample is treated with potassium peroxymonosulfate to oxidize all iodide species in the sample. It then is treated with leukocrystal violet reagent for color development. Interference from free chlorine may be eliminated by addition of an ammonium salt. 

Elemental composition K 23.55%, I 76.45%. Potassium may be measured by various instrumental methods (see Potassium). Iodide ion in an aqueous solution can be measured by ion chromatography or leuco crystal violet colorimetric method (see Iodine). 

The kinetics of oxidation of Leuco Crystal Violet, depicted in equation 26 (Section III.B.2.a), can be applied for the determination of organic hydroperoxides after elimination of H2O2 with catalase . 

The concentration of H2O2 in seawater may be measured following the HRP-catalyzed conversion from Leuco Crystal Violet (78, kmax = 260 nm) to the colored form (79, kmax = 592 nm, s = 1 x 105 M-1 cm-1), at pH 4, according to equation 26. LOD is ca 0.02 p,M, with RSD ca 1% at 0.03 p,M261-262. Equation 26 can be used as the basis for a kinetic method for the simultaneous determination of H2O2 and relatively unreactive species, such as t-butyl and cumyl hydroperoxides, however, not in the presence of MHP or ethyl hydroperoxide (see also Section V.B.2.a)252. 

Instead of MV2+ (in the photo-oxidation of leuco crystal violet (LCV)), a neutral species is sensitized by pyrene containing polymers and the Coulombic effect is not as drastic as in the case of MV2+. As shown in Figure 8, the cationic polymer is more effective than the neutral or anionic polymer. This is attributed to the Coulombic repulsion between LCV- and Py assisted by the cationic environment of the polycation. However, the Coulombic effect occurs only after forward electron transfer. 

Condensation of Michler s hydrol (12) with 3-dimethylaminobenzoic acid (13) gives leuco crystal violet carboxylic acid (14), which is then oxidized to crystal violet lactone. 

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. 

In the early 1990s, Fuji Photofilm Ltd. Introduced Copiart 3 proofing materials, which also depended on HABI chemistry. The chemistry used the lower cost o-Cl-HABI and Leuco Crystal Violet along with tribromomethyl phenyl sulfone, which were microencapsulated in selected vehicles. The image stabilization was achieved by a thermal aftertreatment, which ruptured the microcapsules, which then interacted with phenidone, or other reducing agents to prevent subsequent color formation. 

A sample (0.5-1 ml) of the test solution is added to an equal volume of 4,4 -bis(dimethylamino)benzophenone (Michler s ketone) in dry toluene. A few drops of water are added, and the mixture is shaken." A few drops of a 0.2% solution of iodine in glacial acetic acid are added, resulting in the formation of a blue or green colour. A recent variation employs tris(4-dimethylaminophenyl)methane (leuco crystal violet, LCV), followed by aerial oxidation [1]. 

The Dylux system operates somewhat like the above photoxidation of leuco crystal violet, but the initiation step is different. Triarylimidazolyl radicals are generated by ultraviolet (365 nm) irradiation of their stable dimers (HABI s hexaarylbiimidazoles, 11) [44]. The persistent free radicals (called lophyl radicals because they were historically derived from the parent lophine, triphenylimidazolyl... 

The oxidation of hydroarenes to arenes by quinones such as 2,3-dichloro-5,6-dicyano-l,4-quinone (DDQ) is frequently used for the synthesis of aromatic compounds. Brower et al. have already shown that the dehydrogentaion 1,4-cyclo-hexadiene to benzene [128] or tetraline to naphthalene [129] by thymoquinone is accelerated by pressure giving a negative volume of activation ((AV = —33 (75 °C) and —28 (175 °C) cm mol respectively). A similar effect of pressure has been observed for the oxidation of leuco crystal violet with p-chloranil ((AV = -25 cm mol (21 °C) [130]. The pressure-dependent kinetic isotope effect of this reaction (29 °C kn/ D = H-5 (1 bar) and 8.2 (1.5 kbar)) indicates that hydrogen transfer occurs in the rate-determining step. The large kn/ko value at 1 bar and it pressure dependence was attributed to a quantum mechanical tunneling. 

Kesari et al. (Kesari et al., 1998) developed a simple and sensitive spectrophotometric method for the determination of iodine in tap water, sea water, soil, iodized salt and pharmaceuticals samples. The said method was based on oxidation of F to lOs" with bromine water and liberation of free I2 from IQ3" by addition of K1 in acidic medium. I2 is then reacted with leuco crystal violet and the crystal violet dye liberated shows maximum absorbance at 591 nm. Beer s law is obeyed over the concentration range from 0.04 to 0.36 mg/1 of iodine in a final solution volume of 25 ml. The method is free of interference of other major toxicants. 

Other spectrophotometric methods Other methods for the determination of dissolved chlorine include the use of leuco crystal violet and syringaldazine as color-developing reagents. In the leuco crystal violet method, a colorless precursor (leuco crystal violet) is oxidized to crystal violet (reaction [XIX]), which has an absorption maximum at 588 nm. Interference from combined available chlorine can be avoided if the test is carried out within 5 min of indicator addition. Total chlorine determination can be accomplished by the addition of iodide ion to produce hypoiodous acid (FIIO), which reacts instantly with the indicator. Combined available chlorine is determined by difference. 

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