Triarylmethanes oxidants

A useful classification of sensitizing dyes is the one adopted to describe patents in image technology. In Table 1, the Image Technology Patent Information System (ITPAIS), dye classes and representative patent citations from the ITPAIS file are Hsted as a function of significant dye class. From these citations it is clear that preferred sensitizers for silver haUdes are polymethine dyes (cyanine, merocyanine, etc), whereas other semiconductors have more evenly distributed citations. Zinc oxide, for example, is frequendy sensitized by xanthene dyes (qv) or triarylmethane dyes (see Triphenylmethane and related dyes) as well as cyanines and merocyanines (see Cyanine dyes). 

The hexoses that are the initial products of acid hydrolysis of sucrose (1) react at el vated temperature under the influence of acids to yield furfural derivatives (2). Thed condense, for example, with the phenols to yield triarylmethanes (3), these react furthei by oxidizing to yield colored quinoid derivatives (2, 4). Polyhydric phenols, e. g. resorj cinol, on the other hand, yield condensation products of Types 5 and 6 [2],... 

Arylmethane leuco dyes are converted into di- or triarylmethane dyes on oxidation. This class of dye precursors sometimes is referred to as leuco di- or triphenylmethane dyes, or di- or triphenylmethane leuco dyes. The use of the term di- or triarylmethane dyes can be misleading as the central carbon atom is a carbonium ion. Instead, the term di- and triarylmethine dye is recommended for this class as it correlates with the well-known polymethine dyes. Nevertheless, it has not been commonly used. 

Triarylmethanes also inhibit oxidation by hydrogen transfer to a peroxy radical. In this case it is the triarylmethyl radical which traps the second peroxy radical. 

Compared to simple alkyl cations, triarylmethyl cations are well characterized in terms of structure and stability, and react with a number of readily oxidized species including aliphatic amines (El tsov et al., 1978) and ethers (Kabir-ud-Din and Plesch, 1978). Their reduction by alcohols in acidic medium have an historic importance in the area (Bartlett and McCollum, 1956), and the use of triarylmethanes as hydride carriers is an area of continuing interest (Ivanov et al., 1982). 

Dyes in general and triarylmethane dyes in particular are rarely subjected to chemical processing once they have been formed. The introduction of substituents is usually carried out during the manufacture of the intermediates where the position and number of the groups introduced may be more precisely controlled. Dyes are sometimes exposed to oxidizing and reducing conditions during application and afterward. 

The preparation of triarylmethane dyes proceeds through several stages formation of the colorless leuco base in acid media, conversion to the colorless carbinol base by using an oxidizing agent, eg, lead dioxide, manganese dioxide, or alkali dichromates, and formation of the dye by treatment with acid (Fig. 1). The oxidation of the leuco base can also be accomplished with atmospheric oxygen in the presence of catalysts. 

The current organic photoreceptors are triarylamines, triarylmethanes, hy-drazones, oxadiazoles, pyrazolines, oxazoles, and more recently, stilbene derivatives. The polymer matrix, on the other hand, is constituted by polyesters and polycarbonates (Fig. 5). The common presence of aromatic amines as substituents in all these materials contributes to efficient hole transport [44]. The nonbonding electron pair on the nitrogen atom, in fact, confers on these molecules a low oxidation potential, and consequently, the production of a chemically stable radical cation with the possibility of an effective overlap of nonbonding molecular orbitals between neighboring molecules. 

The earlier review drew attention to photo-oxidation reactions which ensue on irradiation of complexes formed between hydrocarbons and oxygen, sulphides and oxygen, and amines and oxygen. Triarylmethanes are photo-oxidised (38) to give triarylmethyl cations (Kuder et ai, 1979). The ease... 

The oxidation of the methyl group in toluene derivatives to the aldehyde is an important stage in triarylmethane dye manufacture, p- toluene sul-fonyl chloride is first hydrolyzed in concentrated sulfuric acid and then subjected to the oxidizing action of a manganese compound to produce benzaldehyde-4-sulfonic acid [11]. 

Azo compounds by coupling with intermediate oxidation of triarylmethanes to triarylcarbinols s. 14, 170... 

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