Bibenzyl ketone

Benzyl halides have been reported to react with nickel carbonyl to give both coupling and carbonylation (59). Carbonylation is the principal reaction in polar nonaromatic solvents, giving ethyl phenylacetate in ethanol, and bibenzyl ketone in DMF. The reaction course is probably similar to that of allylic halides. Pentafluorophenyl iodide gives a mixture of coupled product and decafluorobenzophenone. A radical mechanism has been proposed (60). Aromatic iodides are readily carbonylated by nickel carbonyl to give esters in alcoholic solvents or diketones in ethereal solvent (57). Mixtures of carbon monoxide and acetylene react less readily with iodobenzene, and it is only at 320° C and 30 atm pressure that a high yield of benzoyl propionate can be obtained (61). Under the reaction conditions used, the... 

Bibenzyl ketone PhCH2-C(0)CH2Ph 65.4 273.6 Review 1982MCM/GOL... 

The first application of the time-resolved CIDNP method by Closs and co-workers involved tire Norrish 1 cleavage of benzyl phenyl ketone [24, 25]. Geminate RPs may recombine to regenerate the starting material while escaped RPs may fonn the starting ketone (12), bibenzyl (3), or benzil (4), as shown below. 

Mechanistic aspects of the reduction of benzyl halides at mercury have been extensively investigated [35, 38]. From the reduction of benzyl iodide at platinum, Koch and coworkers [39] obtained toluene, bibenzyl, and hydrocinnamonitrile. Electrolysis of benzyl chloride in the presence of acyl chlorides can be used to synthesize alkyl benzyl ketones [40], whereas alcohols are formed by electrolysis of... 

CoNO(CO)3] (93) catalyzes the carbonylation of benzyl bromides and chlorides to give carboxylic acids.403 The reactions, carried out in a two-phase system, occurred at normal temperature and pressure and their behaviour was quite different to that observed when [Co2(CO)8] is used as catalyst. The anion [CoH(NO)(CO)2] is believed to be a key intermediate, formed by attack of hydroxide on (93) followed by loss of C02. Ketones, bibenzyls and other by-products were detected in low yields. The mechanism of the carbonylation is given in Scheme 24. 

By incorporation of transparent process cell, performing photochemical reactions is possible. The example shows the conversion of dibenzyl ketone to bibenzyl by irradiation of the reaction mixture with a 450 W xenon lamp. The CO produced by the reaction is vented and the bibenzyl product is purified, if desired, through a micro structured chromatographic separator unit and withdrawn off-line [84] ... 

As mentioned in Sec. 15.2.2, hydrogen abstraction of benzylic hydrogens by the /77i triplet state of ketones is generally efficient and offers an access to benzylic radicals. However, the method is rarely of preparative interest since benzylic and ketyl radicals couple statistically giving a mixture of bibenzyls, alcohols, and pinacols, although the initial hydrogen abstraction may show some interesting intramolecular selectivity with polymethylbenzenes and substituted alkylbenzenes [220,221]. However, in... 

Nitroaromatics also sensitize the oxidation of methylarenes and it has been found that silica-grafted 2,4,6-trinitrobenzene is a convenient heterogeneous sensitizer, giving the aldehydes in 79-90% yields with 100% selectivity [229]. Bibenzyls, pinacols and pinacol ethers are likewise oxidized to ketones or respectively esters through carbon-carbon bond fragmentation upon dicyanonaphthalene sensitization [230]. A good method for benzylic oxidation is based on titanium dioxide photocatalysis [231-233]. 

A particular case of oxidative functionalization is the formation of bibenzyls. This occurs with medium to good yield when the benzyl radical is highly stabilized (e.g., benzhydryl, xanthyl) using aromatic ketones as the sensitizers [19-21]. Better results are obtained with titanium dioxide, particularly when starting form benzylsilanes, in view of the easy fragmentation of the radical cation [239]. 

Finally, there is one aspect of the photoreduction of phenyl ketones which has been resolved only recently. It is now well established that benzyl radicals couple to form l-alkylidene-2,5-cyclohexadienes as well as bibenzyls, the ratio depending primarily on steric factors 121>. Schenck first showed that the semi-pinacol radicals involved in the photoreduction of benzophenone also form such products 122>. These compounds absorb very strongly in the near UV and often... 

Methylenation. The reagent reacts with ketones at - 10° to give essentially quantitative yields of the corresponding methylene derivatives. The reagent effects coupling of benzyl halides to bibenzyl (85% yield). 

The 4,5-corane (84) is obtained in SOX yield on photo-decarbonylation of the pentacyclic ketone (85). Photochemical decomposition of the carbonate (86), by the loss of carbon dioxide, affords a mixture of products containing oxirane. styrene oxide, bibenzyl and phenylacetaldehyde. Triplet sensitized irradiation yields products solely from benzyl radicals. - An earlier study of the irradiation (at 254 nm) of the carbonate (87) reported that benzaldehyde, phenyl carbene, and carbon dioxide were produced. A reinvestigation of the irradiation of this compound (at 254 nm in acetonitrile) has provided evidence that the cis- and trans-stilbene oxides (88) and (89) are formed as well as deoxybenzoin and smaller amounts of diphenylacetaldehyde and bibenzyl. When methanol is used as the solvent the same products are produced accompanied by benzylmethyl ether, 1,2-diphenylethanol, and 2,2-diphenylethanol. These authors suggest that the oxiranes (88) and (89) are formed by way of... 

Irradiation (254 nm) of phenylacetic anhydride (169) in acetonitrile results in elimination of COa and CO and formation of bibenzyl (170) and 1,3-diphenyl-propanone (171).97 The ketone is known to eliminate CO rather efficiently via a short-lived triplet, and at least part of the bibenzyl may therefore originate in this way. 

A novel example of the cleavage of an imine to a nitrile has been reported.142 Irradiation of i T-(l-phenyl-2-propylidene)benzylamine (223) affords acetonitrile, toluene, and bibenzyl, by a process which is at least formally analogous to the Norrish type I cleavage of ketones. On irradiation, the amine (224) is converted into the quinoline (225) by an unprecedented photoelimination of water.143... 

The photochemistry of dibenzyl sulfoxide 10 was briefly reported in the mid 1960s [21,22]. It was said to decompose mainly to benzyl mercaptan (isolated as the disulfide 17) and benzaidehyde 16. Though no mechanism was suggested at the time, it is now clear that these products arise from a standard a-cleavage mechanism, followed by secondary photolysis of the sulfenic ester 13. The careful reader will note that the yield of bibenzyl (19) is very low in comparison to photolysis of dibenzyl ketone. Sulfinyl radicals rarely lose SO, though some net extrusions are discussed later. 

A degassed soln. of benzyl methyl ketone in acetonitrile irradiated (300 nm) in a Pyrex vessel for 2 days using a Rayonet RPR-208 photoreactor (equipped with eight RUL-3000 lamps) -> bibenzyl. Y > 98%. F.e.s. M.J.C.M. Koppes et al., Rec. Trav. Chim. Pays-Bas 107, 676-83 (1988). 

Benzoic acid Benzoic anhydride Benzonitnle Benzophenone 3,4 Benzopvrene Benzopyrene Benzoyl acetone Benzovi chloride Benzyl acetate Benzyl alcohol Benzylamine Benzvl chloride Benzyl formate Benzyhdeneaniline Benzylidene chloride Benzylidenemethylamme Benzyl methyl ketone Bibenzyl... 

The aqueous phase was extracted with chloroform, and the combined extracts were washed with water, dried over anhydrous sodium sulfate, and concentrated. Crude oil was chromatographed on silica gel and eluted with chloroform to give benzyl phenyl ketone (1.04 g, 73%) mp 55-56°C (lit. [95] mp 56°C). Bibenzyl formed by the homocoupling reaction of benzyl chloride [45] was also isolated in 14% yield. 

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