Di- and triarylmethanes

The diphenylmethyl and triphenylmethyl cations can be considered the basic chromophores of di- and triarylmethane dyes 11 —41. However, the electronic state of the donor-substituted di- and triarylmethine dyes can be described better by breaking down the chromophore of these dyes into a straight- or branched-chain polymethine subchromophore, respectively, and two ethylene units (from the formal cleavage of the benzene rings) [2], This model allows the similarities between the di- and triarylmethine dyes and the polymethine s to be recognized. 

A number of papers concerning the formation of carbocations by photolysis of mono-, di-, and triarylmethane derivatives have been... 

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. 

In general, the triarylmethane leuco skeleton can be represented by structures 1-4. Traditional leuco di- and triphenylmethane dyes frequently include compounds of type 1 and 3. The closely related compounds 2 and 4 are derived from 1 and 3. Another closely related type is the lactone or phthalide 5 (see Chapter 4). In all of these leuco dyes, one or more of the phenyl rings can be replaced by a hetaryl ring or by a fused aromatic ring such as a naphthalene. 

Cationic dyes form positively charged dye ions by dissociation, and the positive electric charge is delocalized over the entire molecule. They are usually di- and triarylmethine dyes such as C.I. Basic Green 4, 42000 [569-64-2] (31), which are also known as triarylmethane dyes or triaryl carbenium ions [15], oxazine dyes such as C.I. Basic Blue 3, 51005 [2787-91-9] (32), orthiazine dyes. 

The synthetic food colorants, according to their chemical structure, belong to mono-, di-, and trisazo, triarylmethane, xanthene, quinoline, and indigoid. They can also be divided into water-soluble, oil-soluble, insoluble (pigment), and surface marking colors. 

Shi et al. [161-164] studied a different reaction of an array of triphenylmethane and triarylmethane derivatives such as alkanes, alkenes, alkynes, phosphonates, phosphonic acids and esters, dialkylamines, triaryl acetic acid, triaryl acetonitriles, triaryl acetates, and tetraarylmethanes and published a review of their work [65]. Mainly from product studies they proposed the special case of di-Jt-methane and oxa-di-7u-methane reactions [165], viz. a,a-elimination gives a biaryl and the corresponding carbenes and operates in polar and nonpolar sol-... 

In this reaction, usually carried out in an acid medium (H2SO4, HCl), di- or triarylmethane derivatives are formed which are intensely colored (seep. 47). Pomeroy and Pollard (7) investigated 11 phenolic compotmds and their... 

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