Benzil preparation procedure

The benzilic acid rearrangement of steroid a-diketones is often the preferred method for ring contraction. Yields are generally excellent, and in several instances the reaction has been shown to be stereospecific. Preparation of the starting a-diketones is discussed below and illustrated with several excellent experimental procedures. 

The procedure described is essentially that of Ballard and Dehn.1 Stilbene has also been prepared by reduction of desoxy-benzoin,20 benzaldehyde,23 and benzil 2o-2c by dehydrogenation of ethyl benzene,30 toluene,30- 33- 3, and bibenzyl 33-3alkaline reduction of phenylnitromethane,40 phenylnitroacetonitrile,40 and desoxybenzoin 43 by distillation of benzyl sulfone,50 benzyl sulfide,60-63 calcium cinnamate,5 cinnamic acid,5d phenyl cinna-mate,6e-6/ and diphenyl fumarate ie by dehydrohalogenation of a,a -dichlorobibenzyl60 and benzyl chloride 63 by dehalogenation of a,a,c/,a -tetrachlorobibenzyl70 and benzal chloride 73 by the coupling of cinnamic acid and phenyldiazonium chloride 8 by de-... 

Eastman Kodak Company white label grade benzil or material prepared by the procedure described in Organic Syntheses 2 is satisfactory. 

The present procedure is reported by the submitters to be a general way of making 4,4 -bis(dialkylamino)benzils and, with a somewhat modified purification scheme (Note 4), has been used by them to prepare 4,4 -bis(diethylamino)benzil from N,N-di-ethylaniline and 4,4 -bis(dipropylamino)benzil from N,N-di-propylaniline. 

The submitters recommend that the following purification procedure be used from this point for the preparation of 4,4 -bis(diethylamino)benzil (72% yield) and 4,4 -bis(di- -propyl-amino)benzil (58% yield). The procedure has also been used as an alternative to the one given for 4,4 -bis(dimethylamino)benzil. 

The preparation of certain substituted benzils by treatment of aryl benzyl ketones with selenium dioxide is discussed later (method 183). If a methyl ketone is treated under these conditions, the methyl group is oxidized to an aldehyde group/ The reaction is carried out by refluxing a mixture of selenium dioxide and ketone in dioxane or alcohol for several hours. Preparative details are found in the procedures for phenylglyoxal (72%) and glyoxal (74%) the latter is isolated as its bisulfite derivative. 

Corey and Schaefer studied the kinetics of the oxidation of desoxybenzoin to benzil and suggested a mechanism for the reaction. They also developed an efficient synthesis of a-keto esters involving oxidation of an a-bromoketone in an anhydrous solvent, as illustrated by a procedure for the preparation of ethyl benzoyl formate. o OO OO... 

Preparation. The reagent is readily prepared by the condensation of benzil with dibenzyl ketone in the presence of a basic catalyst. Dilthey s original procedure, adopted by Organic Syntheses specifies ethanol as solvent and a solution of potassium hydroxide in ethanol as the base. This procedure suffers from the low boiling point of the alcohol and the limited solubility of both potassium hydroxide and the reaction product in ethanol. In an improved procedure - use of the better solvent triethylene glycol permits operation at a higher temperature, and use of the readily soluble benzyltrimethylammonium hydroxide as base eliminates the step of dissolving potassium hydroxide in ethanol, A mixture of 0.2 mole each of benzil and... 

Oxidation of Benzoin to Benzil by MnOz as a Typical Procedure for the Oxidation of Biaryl Acyloins. A mixture of benzoin 3 a (0.212 g, 1 mmol) and Mn02 (0.174 g, 2 mmol) was prepared and magnetically agitated in an oil bath at 90 °C for 4 h. The progress of the reaction was monitored by TLC. The reaction mixture was applied on a silica gel pad (3 g) and washed with Et20 (20 mL) to afford pure benzil 4 a quantitatively (mp 94 °C). The same reaction with BaMn04 proceeded to completion after 2 h using 1.5 mmol of the oxidant. 

Diarylquinoxalines are similarly prepared by reaction of o-phenylenediamine with benzils. The required benzils have been prepared traditionally by oxidation of the corresponding benzoins, which in turn have been prepared by treatment of the appropriate aldehydes with potassium cyanide. In a more recent procedure, benzils have been obtained in good yield by oxidation of para-substituted diphenyloxazoles with bromine in acetic acid. The oxazoles themselves are readily prepared by cyclization of the benzoin acetate with urea (Scheme 3). ... 

Eq. 3.1) and intramolecular mode. Selective oxidation of ethers to esters by irradiation in the presence of benzil and oxygen was reported by Seto [29]. By this procedure, a tricyclic y-lactone is prepared from the corresponding fused tetrahy-drofuran as shown in Scheme 3, Eq. (3.2). The mechanism presumably involves a hydrogen abstraction by an acylperoxyl radical. 

By earlier procedures benzoins were converted into diketones by nitric acid, but this dehydrogenation is better effected by means of copper compounds. For instance, benzoin itself gives 86% of benzil on treatment with copper sulfate in pyridine.440 Cholestenone has been prepared as follows by Diels and Abderhalden 441... 

Curtius et ah206 showed that acetylenes can also be prepared by oxidizing vicinal dihydrazones with yellow mercuric oxide. Diphenylacetylene, for example, is thus obtained in 75% yield from benzil dihydrazone.207 In a variant of the Curtius procedure diacetylenes can be prepared in 80-85% yield by oxi-... 

NOTE. The benzil used in this reaction must be free of benzoin impurity. If benzil is prepared according to Experiment [A2J, it should be purified by the chromatographic procedure cited therein if benzoin is detected by thin-layer chromatography. 

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