Nitrogen diphenylketene

Taylor et alJ prefer a modification of Staudinger s second method. Diphenyl-acetyl chloride is obtained in 82-94% yield by reaction of the acid with thionyl chloride in ether and a solution in ether of triethylamine, added by drop with ice cooling under nitrogen. Diphenylketene is obtained by distillation at 118-119 / mm. in yield of 78-84%. The method utilizes inexpensive, nontoxic starting materials, involves two simple steps, and has the advantage that the diphenylketene, until the final distillation, is never exposed to temperatures greater than 30-35 and hence that polymerization is minimized. 

When this substance is heated in benzene with the exclusion of air and moisture, nitrogen is eliminated and the rest of the molecule undergoes rearrangement to diphenylketene ... 

The benzene solution of the diazo compound is poured into a separatory funnel protected with a drying tube and connected to a 125-cc. Claisen distilling flask provided with a condenser set for downward distillation and arranged so that it can be heated in a bath of Wood s metal. The temperature of the metal bath being maintained at 100-110°, the benzene solution is dropped slowly into the hot flask. Under these conditions, the benzene is removed by distillation, and the diazo compound transformed into diphenylketene. The residue is distilled in vacuo in an atmosphere of nitrogen, and the fraction boiling at 115-125° at 3-4 mm. (Note 5) is collected. The yield is 31 g. (64 per cent of the theoretical amount) of a product which, on redistillation, yields 28 g. of diphenylketene boiling at 119-121° at 3.5 mm. (58 per cent of the theoretical amount). 

Diphenylketene is best stored in an atmosphere of nitrogen the addition of a small crystal of hydroquinone serves to inhibit polymerization (Note 6). 

Ultraviolet irradiation of CCXLV, which is obtained by the condensation of diphenylketene and diphenyldiazomethane, in hydroxylic solvents, effects its cleavage into the starting materials in the presence of carboxylic acids or alcohols, photoaddition takes place with the formation of benzilic acid derivatives.167 On the other hand, irradiation of CCXLV in benzene containing acetic acid and/or methanol produces CCXLVI and CCXLVII, respectively. Irradiation in the presence of diphenylmethane under nitrogen atmosphere yields phenylacetic acid. 

Azido-l-methylbenzimidazole with diphenylketene gave the imidazobenzimidazole (232 R = Ph), but decomposition of the azide to give a nitrene, followed by cycloaddition to the ketene, was ruled out as a mechanism. Instead, the authors propose that 232 is formed by attack of the endocyclic ring nitrogen on the C=C bond of the ketene followed by nucleophilic displacement of N2 from the azide.168 Preparation of an analog (232, R = H) would constitute a possible route to an aromatic azapentalene 233. 

Oxadiazoline (59), on irradiation in benzene, forms an equilibrium mixture with its synthetic precursors diphenylketene and diphenyldiazomethane. Ring opening occurs on irradiation in the presence of alcohols (66AHC(7)183). Photolysis of oxadiazolinones (60a) proceeds similarly to thermolysis and a ketone R COR2 is produced concurrently with loss of nitrogen and carbon dioxide. In the presence of cyclohexene the major product is the hydrazone (63) which is believed to arise from a bimolecular photoreaction of the alkene with the oxadiazolinone. Similar photoreactions occur with 2-phenylpropene and diethyl ether (78S535). 

As the (Eqs. 99,100) demonstrate, the secondary amides and amidines can be alkylated at the nitrogen 95148>. Push-pull amidines 58 can in certain cases be N-acylated with diphenylketene whereas methylene sulfone introduces a methylsulphonyl group u8). 

Ddydrohmlogaialiom (1,1201 1202 2,428). Diphenylketene is prepared by adding Iriethylamine dropwise to a stirred solution of diphenylaoctyl chloride in ether under nitrogen, with ice cooling distillation at I mm. gives diphenylketene as an orange oil in yield of 53-57%. ... 

The only example of the ring system of Type I was prepared by Woemer et al. when 3-phenyl-2H-azirine (1) was treated with diphenylketene-/ -tolyli-mine (2) in benzene at 65 °C for 65 h besides benzophenone, a 1 1 isomeric mixture of the azirino[ 1,2-c]quinazoline 3 and the 1,3-benzodiazepine 4 was formed. During heating in trichlorobenzene under a nitrogen atmosphere. 

Diphenylketene when heated with the reagent at 215° under nitrogen is converted into diphenylacetylene. This reaction involves deoxygenation and migration of a phenyl group. 

Benzil monohydrazone is converted by yellow mercuric oxide into a-azobenzyl phenyl ketone, which affords diphenylketene and nitrogen when heated at 100-110° 175... 

Schroter172 in 1909 found that azideoxybenzoin loses nitrogen when warmed, yielding diphenylketene ... 

According to Smith and Hoehn,173 diphenylketene is obtained in 64% yield when a benzene solution of azideoxybenzoin is dropped slowly into a Claisen flask placed in an oil-bath at 110° at this temperature the benzene distils off and the residual azideoxybenzoin loses nitrogen and rearranges. 

Azideoxybenzoin (4.4 g) was dissolved in anhydrous ether (170 ml) and illuminated for 3 h while a slow stream of nitrogen was passed in. At the end of the reaction the ether was removed under nitrogen, and the diphenylketene was distilled in a vacuum (yield 3.5 g). 

Six-membered Rings Containing More than One Nitrogen. - The tetrahydropyrimidones (229) are formed in excellent yields via a [4+2] cycloaddition of the 1,3-diazabutadienes (227) with diphenylketene (228),131 134 and mild base-catalysed isomerization of the 1,2-dialkylindazolones (230) gives the dihydroquinazolinones... 

The stable nitrogen-free heterocyclic carbene (5) has been generated by addition of a diphenylketene to a phosphagermaallene at low temperature and isolated by precipitation from diethyl ether its reactivity towards ttansition metals has been investigated. 

Vinyl azides undergo slow cycloaddition with diphenylketen involving loss of nitrogen to give five-membered-ring enamino-ketones (84). The non-concerted mechanism suggested involves nucleophilic attack of the )5-carbon... 

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