Triphenylmethane radical from

For uniformity with the stmctures given in the Colourindex the ammonium radical (9) is used for the amino-substituted xanthenes and the keto form for the hydroxy derivatives. The xanthene dyes may be classified into two main groups diphenylmethane derivatives, called pyronines, and triphenylmethane derivatives (eg, (4)), which are mainly phthaleins made from phthaUc anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted ben2aldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

Mechanisms depending on carbanionic propagating centers for these polymerizations are indicated by various pieces of evidence (1) the nature of the catalysts which are effective, (2) the intense colors that often develop during polymerization, (3) the prompt cessation of sodium-catalyzed polymerization upon the introduction of carbon dioxide and the failure of -butylcatechol to cause inhibition, (4) the conversion of triphenylmethane to triphenylmethylsodium in the zone of polymerization of isoprene under the influence of metallic sodium, (5) the structures of the diene polymers obtained (see Chap. VI), which differ. both from the radical and the cationic polymers, and (6)... 

For example, in the photolysis of (30) in toluene solution, the product of insertion of DPC into the benzylic C—H bonds, 1,1,2-triphenylmethane (31), was accompanied by substantial amounts of 1,1,2,2-tetraphenylethane (32) and bibenzyl (33).When solvents such as cyclohexane are used, tetraphenylethane (32) is formed as the major product, indicating that direct C—H insertion in the singlet state is not the main process in most diarylcarbenes (Scheme 9.7). ° In contrast, 9-cyclohexylfluorene (37) is produced by photolysis of diazofluorene (36) in cyclohexane as a main product (65%) along with a small amount of escaped products (38 and 39). One can estimate in this case that at most 14% of 37 arises from free radical processes. Similarly, direct or sensitized photolysis of diazomalonate in 2,3-dimethylbutane gives C—H insertion products, but in the triplet-sensitized... 

Troth (32) has studied the polymerization of vinyl acetate in the presence of triphenylmethane and observed the effects discussed above. In practice, there are complications resulting from reactions involving the initiator radicals and the transfer agent. These complications were found also when carbon tetrabromide was used as a transfer agent in the polymerization of styrene in this case, the bromine contents of the polymers were determined by neutron activation analysis (17). 

Hydride Abstraction from Organic Ligands The removal of a hydride ion from an organic radical is an important method of generating carbonium ions stabilized by metal carbonyl systems. Dauben and Honnen (61) in 1958 were the first to exploit this method by use of the powerful hydride abstractor, triphenyl methyl (or trityl) carbonium ion, which is converted thereby into triphenylmethane. 

Homolytic photodissociation of a benzyl-anilino C—N bond has also been observed in a series of iV-(arylmethyl)anilines. The main products identified for 27 are aniline, triphenylmethane and 9-phenylfluorene (28) (equation 4)126. The quantum yields for the formation of Pt C are high (0.6-0.8, 248-nm excitation) and independent of solvent. On the basis of the results of laser flash photolysis and ESR studies, the formation of 28 occurs via the intermediate 29 as a result of electrocyclization of Pt C (Scheme 5). In contrast, the dimerization of the benzyl and diphenylmethyl radicals, leading to the formation of 1,2-diphenylethane and 1,1,2,2-tetraphenylethane, respectively, are efficient in the cases of 30 and 31 (equations 5 and 6)127. In addition, products resulting from the coupling of the photodissociated benzyl and aniline radicals are also observed for 31, presumably due to the less sterically hindered PhCH2 radical when compared with Ph2CH and Ph3C radicals. 

An important class of hydrocarbons includes substances which contain two or more benzene rings. Such hydrocarbons may be considered as derived from methane and its homologues by replacing hydrogen atoms by phenyl radicals. Diphenylmeth-ane, triphenylmethane, and tetraphenylmethane, the formulas of which are given below, belong to this class. 

The radical cation of a reactant formed via electron-hole oxidation may also be subject to nucleophilic attack. For example, the radical cation of p-dimeth-oxybenzene is attacked by cyanide and leading the formation of cyanoanisole [Eq. (13)] [118]. Similarly, selective fluorination of triphenylmethane on irradiated TiOj in the presence of AgF has been reported [Eq (14)] [119]. A stable carbocation, which is formed after a sequential electron transfer and proton elimination from the reactant, is key for successful fluorination (Fig. 4). Phogocatalytic fluorination employs safe and easy-to-handle reagents and eliminates the need for toxic fluorine gas or other problematic fluorination reagents. 

Several observations indicate that this is reasonable. When a mixture of benzaldehyde and wo-butyryl chloride is treated with the organotin hydride, benzyl iro-butyrate is formed, but iro-butyl benzoate is not. Similarly when a mixture of benzoyl chloride and wo-butyraldehyde is reduced wo-butyl benzoate is formed, but benzyl iso-butyrate is not. Ethyl chloro-formate is reduced very slowly at 80° C by tri-n-butyltin hydride, but the addition of 2 mole-% of azobisisobutyronitrile leads to facile reduction. When triphenylacetyl chloride is reduced at 100° C with the same hydride the products include triphenylacetaldehyde, triphenylmethane, and carbon monoxide, but little, if any, j8,j8,j3-triphenylethyl triphenylacetate. The formation of carbon monoxide and triphenylmethane can be attributed to decarbonylation of the intermediate acyl radical to the more stable trityl radical, Eq. (61), which subsequently abstracts a hydrogen atom from the... 

Photoinitiation is not the only access to this chemistry, e.g., cathodic induced reduction or the use of alkali metals or other inorganic reducing reagents are also possible, but irradiation often is advantageous for preparative purposes. Since this is a chain process, the use of low-power lamps or a low quantum yield initiation step are not necessarily a limitation. Due to the requirement of a fast cleavage at the radical anion stage, aryl halides are by far the most used reagents, in particular iodides and, to a lower extent, bromides. Nucleophiles are carbanions from sufficiently acidic hydrocarbons, e.g., 1, 3-diphenylindane, fluorene or triphenylmethane [35-37] or, more commonly enolates from ketones [38], esters [39], MA -dialkylamides [40], nitriles [41]. C-C bond formation is obtained also with phenoxide or naphthoxide anions [42,43]. A few representative examples of synthetic applications of the S l... 

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