Benzophenone, sodium reduction

An efficient way for microwave-assisted reduction of liquid and solid ketones using sodium borohydride without solvent has also been reported. An excess amount of NaBH without alumina or any support was used for die reduction of acetophenone and the yield of the product was 81% under microwave irradiation. It was concluded that the powder of excess NaBH disperses the aggregation of ketone and made a useful contact successfully to provide an efficient reaction, but in case of benzophenone, the reduction needs more time and NaBH to complete die reaction. This lower conversion may be due to some steric reasons (Chen et al., 1999). 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

Diphenylmethane has been prepared with aluminum chloride as a catalyst from methylene chloride and benzene, from chloroform and benzene as a by-product in the preparation of triphenylmethane, and from benzyl chloride and benzene. It has been prepared by the reduction of benzophenone with hydriodic acid and phosphorus, or with sodium and alcohol. It has also been made by heating a solution of benzyl chloride in benzene with zinc dust, or with zinc chloride. The above method is only a slight modification of the original method of Hirst and Cohen. ... 

Two classes of charged radicals derived from ketones have been well studied. Ketyls are radical anions formed by one-electron reduction of carbonyl compounds. The formation of the benzophenone radical anion by reduction with sodium metal is an example. This radical anion is deep blue in color and is veiy reactive toward both oxygen and protons. Many detailed studies on the structure and spectral properties of this and related radical anions have been carried out. A common chemical reaction of the ketyl radicals is coupling to form a diamagnetic dianion. This occurs reversibly for simple aromatic ketyls. The dimerization is promoted by protonation of one or both of the ketyls because the electrostatic repulsion is then removed. The coupling process leads to reductive dimerization of carbonyl compounds, a reaction that will be discussed in detail in Section 5.5.3 of Part B. 

Ketones - in sharp contrast to enols - are electron acceptors in a wide variety of organic transformations that occur at the carbonyl carbon. For example, the familiar dark-blue benzophenone anion radical is produced via one-electron reduction of benzophenone with sodium in anhydrous THF (equation 21). 

As mentioned, electronically excited states are both easily reduced (since an electron can be accepted in the half vacant HOMO) and easily oxidized (since an electron can be donated from the half-hlled LUMO) under much milder conditions than the corresponding ground states. As an example, reducing the ground state of benzophenone requires the use of a highly reactive reductant, such as sodium metal... 

Figure 3.5 Reduction of benzophenone by sodium and of the excited state by Et3N.

Reduction of Solid Benzophenones with Sodium Borohydride (Epple and Ebbinghaus, 1998)... 

It is prepared by treating p-chloromethylaniline with benzoyl chloride and hydroxylamine to produce the benzophenone oxime. Reaction of the oxime with chloroacetyl chloride in the presence of sodium hydroxide, and subsequent reduction, yields diazepam. 

An unusual type of reaction is anodic reduction which can be performed at certain metal anodes. Thus, when magnesium is used as an anode in the electrolysis of benzophenone in pyridine/sodium iodide solution, the anode is consumed and benzopinacol can be isolated from the anolyte 15S). Here reduction by univalent magnesium ion is postulated ... 

The sodium salt, Na2N202, is made by Na reduction of NO in 1,2-dimethoxyethane containing benzophenone or quantitatively by absorption of N20 into Na2051 ... 

Benzohydrol (Coll. Vol. i, 84) In almost quantitative yield by the photochemical reduction of benzophenone in the presence of fio-propyl alcohol and sodium fre-propoxide. Bachmann, J. Am. Chem. Soc. SS, 393 (1933)-... 

A convenient procedure for the reduction of small amounts of ketones involves the periodic addition of small pieces of sodium to a slowly stirred mixture of an ethereal or benzene solution of the ketone and water or a concentrated solution of sodium carbonate. Sodium and alcohol are used for the conversion of methyl n-amyl ketone to 2-heptanol (65%). These reagents are used to prepare secondary alcohols from olefinic ketones obtained by the aldol condensation. Benzophenone and related compounds are reduced by zinc dust and sodium hydroxide, magnesium and methanol, and sodium amalgam. With the last reagent the reaction has been shown to take place through the intermediate sodium ketyl, (C,H,)jCONa. 

Reduction. Benzophenone and fluorenone are reduced to bcnzhydrol and fluorcnol, respectively, by sodium hydride. The best results (92-97% yields) arc obtained with HMFr, DMF, or pyridine as solvent. Nonenolizable ketones, or ketones which enolize with difficulty, are reduced to the corresponding alcohols in very good yields. Side... 

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