Metal Bouveault reaction

The Bouveault reaction is the preparation of an aldehyde by a one pot reaction between an organic halide and lithium metal in dimethylformamide. Ultrasound has been found to markedly enhance this reaction when it is performed in tetrahydrofuran [93]. Use of an ultrasonic bath at 10-20 °C affords short reaction times of between 5 and 15 min and generates yields in the range 70-88%. Using this methodology the conversion of 1-bromobutane to pentanal (88%) can be achieved in only 5 minutes. This must be contrasted with the yield of less than 10 % which is obtained under the normal stirred conditions in the same time period. This result confirms that the effect of irradiation goes beyond mere agitation (Eq. 3.11). 

Methods to transform ketones into alcohols are based on using of alkali metals as electron donors. One of these methods is the Bouveault-Blanc reaction A ketone is dissolved in an alcohol and boiled with an excess of sodium. Sometimes, a ketone-alcohol mixture is rapidly added to molten sodium. Sodium reacts with both ketone and alcohol. 

The reaction of esters with sodium in ethanol is referred to as the Bouveault-Blanc reaction. Prior to the discovery of complex metal hydrides, this reaction was the only method for the reduction of esters to alcohols. The diesters shown in Figure 17.59 produce a diol in this way. 

Alcohols will form metal salts. Thus treatment with sodium, potassium or magnesium leads to the evolution of hydrogen and the formation of the alkoxides (Scheme 2.11b). The liberation of hydrogen in this reaction is used in the Bouveault-Blanc reduction of ketones, esters and nitro compounds. 

Saturated ketones are reduced to the thermodynamically more stable alcohols in the Bouveault Blanc reduction by an almost identical mechanism. This old reaction has been largely superseded by the advent of complex metal hydrides like NaBH4 and LiAlH4, but it is still useful when the metal hydride gives the undesired, nonthermodynamic product. 

Sodium metal in conjunction with a protic solvent such as an alcohol is sometimes used as a less expensive substitute for lithium aluminum hydride for reducing esters to alcohols in an industrial setting. This is the Bouveault-Blanc reaction. A modem version of this old reaction employs sodium-in-silica-gel (Na-SG), a safe fi ee-flowing powder, instead of the bulk metal (B. S. Bodnar, P. F. Vogt, J. Org. Chem. 2009, 74, 2598-2600) ... 

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