Benzil hydrogenation

A similar mechanism can be written for the formation of phenyl acetone in an irradiated aqueous solution of biacetyl and phenylacetic acid.55 Abstraction of a benzilic hydrogen from phenylacetic acid by a photoexcited biacetyl would produce 3 and a benzylic radical which can add to a second biacetyl molecule. Cleavage of this intermediate would yield a jS-keto acid which, on... 

Early preparations of the product from benzil, hydrogen cyanide, and hydrogen chloride (315) and by the action of hydrogen chloride on mandelonitrile (benz-aldehyde cyanohydrin) (316) were formulated by Japp and Knox (317) as 3-hydroxy-2,5-diphenylpyrazine, and a mechanism for the reaction was proposed by Ingham (318). The structure of the product, however, has been refuted by Gallagher et al. (282). 

The catalytic effect of aromatic nitro groups in the substrate and product or in an added inert nitro compoimd (e.g., w-dinitrobenzene in 18) has been observed in the reaction of 2,4-dinitrochlorobenzene with an amine in chloroform. Hydrogen bonding to benzil or to dimethyl sulfone and sulfoxide also provided catalysis. It is clear that the type of catalysis of proton transfer shown in structure 18 will be more effective when hydrogen bonding is to an azine-nitrogen. 

Diketones 1 can be converted into the salt of an a-hydroxy carboxylic acid upon treatment with alkali hydroxide after acidic workup the free a-hydroxy carboxylic acid 2 is obtained. A well-known example is the rearrangement of benzil (R, R = phenyl) into benzilic acid (2-hydroxy-2,2-diphenyl acetic acid). The substituents should not bear hydrogens a to the carbonyl group, in order to avoid competitive reactions, e.g. the aldol reaction. 

Mechanistically closely related is the benzilic acid rearrangement, where an alkyl or aryl group migrates instead of the hydrogen. 

N-methyl-4-piperidvl benzi/ata and the methiodide An intimate mixture of 0.1 mol of N-methyM-piperidinol hydrochloride and 0.1 mol diphenylchloroacetyl chloride is heated at 160°C to 180°C until the evolution of hydrogen chloride ceases (usually about 4 to 5 hours). The melt is then dissolved in 500 ml of water and the resultant mixture heated on a steam bath for about Vi hour, after which time complete solution is effected. The acid solution is cooled and rendered alkaline with ammonium hydroxide solution whereupon the ester is precipitated.The ester is purified either by removal by filtration and recrystallization from benzene petroleum ether or by extracting the mixture with benzene and precipitating the ester by the addition of petroleum ether. After recrystallization there is obtained about 0.06 mol of N-methyl-4-piperidyl benzilate, melting point 1 62°C to 163°C. 

Photoredox systems involving carbonyl compounds and amines are used in many applications. Carbonyl compounds employed include benzophenone and derivatives, a-diketones [e.g. benzil, cainphoroquinone (85),2W 291 9,10-phenanthrene quinone], and xanthone and coumarin derivatives. The amines are tertiary and must have a-hydrogens [e.g. N,A7-dimethylani 1 ine, Michler s ketone (86)]. The radicals formed are an a-aminoalkyl radical and a ketyl radical. 

Other complex sulphones, e.g., 69 with several labile hydrogens, were studied54. Thus disulphonyl pinacols can be reduced (by four-electron cleavage) into pinacols in protic solution or decomposed by means of EGBs into benzil and methyl phenyl sulphone (R = Ph). With R = alkyl, other modes of cleavage by EGBs were found5 5- 57, especially the scission of the central C—C bond when 50% of the /i-ketosulphone could be isolated. 

Only a few other cobalt complexes of the type covered in this review (and therefore excluding, for example, the cobalt carbonyls) have been reported to act as catalysts for homogeneous hydrogenation. The complex Co(DMG)2 will catalyze the hydrogenation of benzil (PhCOCOPh) to benzoin (PhCHOHCOPh). When this reaction is carried out in the presence of quinine, the product shows optical activity. The degree of optical purity varies with the nature of the solvent and reaches a maximum of 61.5% in benzene. It was concluded that asymmetric synthesis occurred via the formation of an organocobalt complex in which quinine was coordinated in the trans position (133). Both Co(DMG)2 and cobalamin-cobalt(II) in methanol will catalyze the following reductive methylations ... 

The diketo acids were transformed to their methyl esters under the action of diazomethane (5), SOCl2/CH3OH (102), or methanolic hydrogen chloride (117). Like other benzils, JV-methyloxohydrasteine (109) when... 

A mixture of 45.6 g. (0.2 mole) of benzilic acid (Note 1) in 700 ml. of anhydrous thiophene-free benzene, contained in a 2-1. three-necked flask fitted with a reflux condenser (attached to a calcium chloride drying tube) and a motor-driven sealed stirrer, is cooled in an ice bath until a crystalline mass results. To the stirred mixture is added, in one portion, 80 g. (0.6 mole) of anhydrous aluminum chloride. The stirred mixture is heated until refluxing begins and is maintained at this temperature for 3 hours. During this period much hydrogen chloride is evolved, and the initially yellow solution soon becomes deep red. The solution is cooled and decomposed by the cautious addition of small pieces of ice, and then 400 ml. of water is added cautiously, followed by 200 ml. of concentrated hydrochloric acid. The benzene is removed by steam distillation, and the product is separated by filtration from the hot mixture. The lumps of product are crushed and extracted with 400 ml. of boiling 10% sodium carbonate solution. The mixture is filtered, and the extraction is repeated on the undissolved residue with an additional 200 ml. of hot 10% sodium carbonate solution. The basic filtrates are... 

This ring system could be prepared by thionation of benzil monohydrazone 172 with Lawesson s reagent (LR) followed by cyclization. The reaction gives 2,3-diphenyl-7,8,9,9a-tetrahydro-27/,677-pyrido[2,TA][l,3,4]thiadiazine 173 in a diastereoselective way, with the hydrogens at 2- and 9a-position in trans orientation. Benzil monohydrazone 172 was obtained by condensation of benzil 170 with 1 equiv of iV-aminopiperidine 171 (Scheme 23) <1998TA1531>. 

The treatment of aliphatic monoamines, benzil monooxime, benzil monohydrazone, and alkyl, monohaloalkyl arylketoximes bearing two or three a-hydrogens with tetrasulfur tetranitride to afford 1,2,5-thiadiazoles was presented in CHEC(1984) and CHEC-II(1996). 

In the presence of benzylamine, which coordinates trans to an active site, and quinine, the noncoordinated chiral component, optical purities up to 80% ee were again attained for hydrogenation of benzil. Convincing evidence was presented for the mechanism outlined in Eqs. (56)-(58), where L is the macrocyclic ligand, Q is quinine, and R = Ph (benzylamine, and charges of the complexes are omitted) ... 

The phenylhydrazone of acetone gave on hydrogenation over colloidal platinum a 90% yield of A(-isopropyl-A(-phenylhydrazine [950], and the semi-carbazone of benzil on electroreduction a 70% yield of A(-aminocarbonyl-N - 1,2-diphenyl-2-ketoethyl)hydrazine [95/]. 

Hydrogen sulfide is introduced into an ice-cooled solution of 0.2 mol of a 1,2-diketone and 0.02 mol of piperidine in 30 ml of dimethylformamide for 1 -4 hours. Elemental sulfur is precipitated during the introduction of hydrogen sulfide. The mixture is acidified with dilute hydrochloric acid the sediment is filtered with suction and dissolved in warm methanol the undissolved sulfur is separated, and the product is isolated by evaporation of the methanol and purified by crystallization. If the product after the acidification is liquid it is isolated by ether extraction and distillation after drying of the ether extract with sodium sulfate. Yield of benzoin from benzil after 1 hour of treatment with hydrogen sulfide is quantitative. 

A Raney nickel surface is also suitable for electrocatalytic hydrogenation [205]. This surface is prepared by electrodepositing nickel from a solution containing suspended Raney nickel alloy (Ni 50% A1 50%). Some alloy particles stick to the surface, which is then activated by leaching the aluminium using hot aqueous sodium hydroxide. Cyclohexanone, acetophenone and benzil have been converted to the corresponding alcohol and there is no stereoselectivity for the formation of hydrobenzoin from benzil. 

Reports have appeared claiming that triperoxo vanadates behave as nucleophilic oxidants. In particular, triperoxo vanadium complexes, A[V(02)3]3H20 (A=Na or K), are proposed as efficient oxidants of a,-unsaturated ketones to the corresponding epoxide, benzonitrile to benzamide and benzil to benzoic acid, reactions which are usually carried out with alkaline hydrogen peroxide. Subsequent studies concerning the oxidation of cyclobutanone to 4-hydroxybutanoic acid, carried out with the above-cited triperoxo vanadium compound, in alcohol/water mixtures, clearly indicated that such a complex does not act as nucleophilic oxidant, but only as a source of HOO anion. 

Benzil forms an adduct with acenaphthene when a mixture of the two is irradiated in benzene solution, presumably by cross coupling of the radicals produced by abstraction of a hydrogen atom from acenaphthene by ben-zii 12,13,66 xhe other products of this reaction were not reported. 

Not all of these reactions can be fitted to a single simple reaction scheme. It is apparent that in cyclohexene and in isopropyl alcohol at room temperature the first step is hydrogen abstraction from the solvent followed by radical coupling. Most of the major products from the reaction in cyclohexane can be accounted for by a reaction scheme similar to that invoked to account for the products observed from the irradiation of biacetyl and benzil in cyclo-... 

Phenanthrenequinone has been prepared by treatment of phe-nanthrene with chromic acid in acetic acid 5 potassium dichromate in sulfuric acid 3-6 hydrogen peroxide in acetic acid 6 7 and selenium dioxide above 250°.8 It can also be prepared from benzil with aluminum chloride at 120° 9 and from biphenyl-2,2 -dialdehyde with potassium cyanide.10... 

The crude benzil is dissolved in 500 ml. of chloroform. To remove the impurity that remains (Note 5), the solution is shaken with three 400-ml. portions of 6% aqueous hydrogen peroxide solution containing 1.0 g. of sodium hydroxide in each portion, and finally with 500 ml. of water. The aqueous layers are combined, warmed to drive off dissolved chloroform, and filtered to separate about 1.5 g. of a yellow-green solid, which is dissolved in the chloroform solution. 

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