Tetraphenylethane

Tetraphenylethane (2). A solution of diphenylacetic acid 1 (2f fS g, O.f mol) In OMF was electrolyzed for 17 h and the voltage was increased from f 20 to 220 V dunng electrotysts. The reaction mixture was poured into water and extracted with EtjO. The extract was filtered, washed and the solvent evaporated. Recrystallization from CHCI3 gave 4 g of 2 (24%), mp 207-208 C. 

The reaction of active uranium (U ) and benzophenone gives tetraphenylethylene (TPE) and 1,1,2,2-tetraphenylethane (TPA). 

Palladium-catalyzed reaction of 2-hydroxy-2-methylpropiophenone with aryl bromides shows a unique multiple arylation via successive C-C and C-H bond cleavages, giving tetraarylethanes.96 For example, the reaction of 2-hydroxy-2-methylpropiophenone with bromobenzene in the presence of Pd(OAc)2, P(/-Bu)3, and CS2CO3 gives 1,1,2,2-tetraphenylethane quantitatively, together with l,4,4-triphenyl-7-methylisochroman-3-one (13% yield) (Equation (74)). 

Evident cases of abstraction/recombination mechanism are observed with phenylsubstituted carbenes. Diphenyl-diazomethane, which is photolyzed to give the triplet diphenyl-carbene, very readily abstracts a hydrogen atom from the benzyl group of toluene. The primarily formed radicals can now recombine to give a formal "insertion product — 1,1,2-triphenylethane — or they can recombine to form 1,1,2,2-tetraphenylethane and 1,2-diphenylethane... 

In this connection, it is interesting to compare the cation-radicals of 1,2-diphenyl- and 1,1,2,2-tetraphenylethanes in their ability to expel a proton or to cleave the exocyclic C-C bond. The former cation-radical preferentially reacts by deprotonation (Camaioni and Franz 1984, Baciocchi et al. 1986). The C-C bond strength of 121.5 kJ moC in 1,2-diphenylethane cation-radical is too high. At the same time, the C-C scission induced by electron transfer is only feasible if the strength of this bond is lesser than 42 kJ mol In the case of 1,1,2,2-tetraphenylethane cation-radical, this magnitude is equal to 38 kJ mol only, and the C-C scission indeed takes place (Arnold and Lamont 1989). 

Whereas 1,1,1-triphenylethane 551 gave only 2% of triphenylacetic acid 552 after treatment with lithium and a substoichiometric amount (50%) of biphenyl, followed by carbonation and acidic hydrolysis, the same process carried out starting from 1,1,1,2-tetraphenyl ethane 553 or 1,1,2,2-tetraphenylethane 554 gave tri- 552 or diphenylacetic acid 555, respectively, with excellent yields (Scheme 148). ... 

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... 

In a cold bath or in an explosion-proof refrigerator, a solution of 1.3 gm (approximately 0.0035 mole) of crude Y,Y -benzhydrylhydrazine (m.p. 114°-130°C) in a mixture of 40 ml of acetone and 50 ml of ethanol and 1.25 gm (0.0096 mole) of 30% hydrogen peroxide is maintained at 10°-15°C for 8 hr. The solvent is rapidly removed by evaporation under reduced pressure with only moderate warming. The residue is rapidly recrystallized from ethanol. Yield 1 gm (76%), m.p. 115°C dec. (NOTE On melting, azobis(diphenyl-methane) decomposes with loss of nitrogen to form a solid with m.p. 205°-210°C, which has been identified as the expected 1,1,2,2-tetraphenylethane.)... 

Diphenylmethylenetriphenylphosphine (44), synthesized by heating benzophenone triphenylphosphazine under a reduced nitrogen atmosphere89,90, produces, after irradiation in cyclohexene solution, diphenylmethane (45), 1,1,2,2-tetraphenylethane (46), l,T-bicyclohex-2-ene (47) and triphenylphosphine (48) (equation 18)84. 

Perhaps the earliest recorded illustration of the use of hydrogen iodide ia the reaction of tetraphenylethylene oxide (Eq. 404), which yields 1,1,2,2-tetraphenylethane in the presence of phosphorus.171 ... 

Products which can be ascribed to the intermediate formation of radicals have long been observed in carbene reactions. In the gas phase these products could arise by homolytic decomposition of excited primary products before collisional deactivation rather than from radicals generated in the course of insertion. This is not so in solution. It is found that, in the thermal decomposition of diphenyldiazomethane (Bethell et al., 1965) or photolysis of diphenylketene (Nozaki et al., 1966) in toluene solution, the product of insertion of diphenylmethylene into the benzylic carbon-hydrogen bonds, 1,1,2-triphenylethane, is accompanied by substantial amounts of 1,1,2,2-tetraphenylethane and bibenzyl. This is a strong indication that discrete diphenylmethyl and benzyl radicals are formed, and, taken in conjunction with EPR (Section IIB) and other evidence (Etter et al., 1959) that diphenylmethylene is a ground-state triplet, would support the view that equation (20) is an adequate representation of triplet insertion. 

Tetraphenylethane [21]. Diphenylmethane (4g) and p-benzoquinone (1.2g) in thiophene-free, sodium-dried benzene (20g) were exposed to sunlight for one month in Cairo. The reaction was carried out in a sealed glass tube filled with carbon dioxide. Quinhydrone began to separate out after only an hour after a month the complete precipitate was filtered off. The benzene was evaporated under vacuum and the oily residue steam-distilled, in order to remove diphenylmethane and p-benzoquinone, and then ether extracted. The extract was dried (sodium sulfate) and the ether removed under vacuum. The residue was extracted with petroleum ether. A semisolid mass was obtained which was recrystallized from petroleum (100-110°) to give colorless crystals of the title compound (m.p. 210°, yield 0.7 g). 

One-electron oxidation of an olefin, arene, or a bibenzyl group can lead to C—H or C—C bond cleavage to produce an allyl or benzyl radical [40, 41]. This area has been pioneered by Arnold [41], The PET reaction of 1,1,2,2-tetraphenylethane and methyl-3,3-diphenylethyl ether have been reported by Arnold and coworkers [41] to provide heterolytic C—C bond cleavage through an intermediate tetra-phenylethane cation-radical. The cation-radical intermediate fragments to di-phenylmethyl radical and diphenylmethyl carbocation. 

The photodecomposition of benzylamine has recently been investigated. Terenin et reported that the major decomposition products, as analyzed by kinetic mass spectroscopy, are H + PhCH2NH, with only a trace of the species NHj and PhCH2. However, irradiation of A -methylbenzylamine or A, A -dimethylbenzyl-amine in ether, yields toluene (f> = 0.085) and dibenzyl, presumably via C-N cleavage the effective radiation was about 2700 The photodecomposition of A-methyl-l,l-diphenylmethylamine and other derivatives also proceeds via C-N cleavage since the major product is diphenylmethane varying amounts of 1,1,2,2-tetraphenylethane were also detected, depending on the solvent viscosity, viz. 

Bond, D. R., Bourne, S. A., Nassimbeni, L. R., and Toda, F. Complexation with diol host compounds. Part 2. Structures of 1,1,2,2,-tetraphenylethane-... 

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. 

A Pyrex tube containing diphenyldiazomethane (1.94 g, 10 mmol) and freshly distilled cyclopenta-1,3-diene (25 mL) was immersed in an ice bath alongside a 450-W Hanovia well and irradiated for 4h at 0-5 °C. After concentration and collection of 1,1,2,2-tetraphenylethane (529 mg) and tetraphenylketazine (72 mg), the residue was chromatographed on a Florisil column packed with hexane to give cyclopentadiene dimer (2.25 g), a semisolid containing the product (625 mg), 1,1,2,2-tetraphenylethane 96 mg) and benzo-phenone (457 mg). Crystallization of the second fraction afforded 456 mg (20%) of the product mp... 

The reaction of thiobenzophenone with tri-n-butylphosphine at 100 °C gives 1,1,2,2-tetraphenylethane, tetraphenylethylene, and the phosphine sulphide. A similar reaction occurs with dibenzocyclopentadienethione. ... 

Japanese chemists2 have also reported cases in which the addition of the copper chelate modifies the reactions of carbenes. Thus diphenylcarbene (thermal decomposition of diphenyldiazomethane, 1) is converted mainly into benzophenone azine (2) when generated in an aprotic medium and into 1,1,2,2-tetraphenylethane (3) when generated in a protic medium. The second reaction is considered to proceed by abstraction of hydrogen from the solvent to form benzhydryl radicals which then... 

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