Bouveault–Blanc reduction

The Bouveault–Blanc reduction is a

This reaction is used commercially although for laboratory scale reactions it was made obsolete by the introduction of lithium aluminium hydride.^[1]

Reaction mechanism

Sodium metal is a one-electron reducing agent. Four equivalents of sodium are required to fully reduce each ester.

RCOOR'   +   6 Na   +   4 CH
₃CH
₂OH   →   RCH
₂ONa   +   R'ONa   +   4 CH
₃CH
₂ONa

In practice, considerable sodium is consumed by the formation of hydrogen. For this reason, an excess of sodium is often required. Because the hydrolysis of sodium is rapid, not to mention dangerous, the Bouveault-Blanc reaction requires anhydrous ethanol.^[9][8] The mechanism of the reaction follows:^[1]

Consistent with this mechanism, sodium-ethanol mixtures will also reduce ketones to alcohols.^[10]

This approach to reducing esters was widely used prior to the availability of hydride reducing agents such as lithium aluminium hydride and related reagents. It requires vigorous reaction conditions and has a significant risk of fires, explaining its relative unpopularity. One modification involves encapsulating the alkali metal into a silica gel, which has a safety and yield profile similar to that of hydride reagents.^[11] Another modification uses a sodium dispersion.^[12][13]

See also

• Acyloin condensation – The reductive coupling of esters, using sodium, to yield an α-hydroxyketone
• Akabori amino-acid reaction – The reduction of amino acid esters, by sodium, to yield aldehydes
• Birch reduction – For the reduction of alkenes using sodium
• Bouveault aldehyde synthesis – Another organometallic reaction by Bouveault where a Grignard reagent is converted to an aldehyde

References