將羧酸酯用金屬鈉和無水醇直接還原生成相應(yīng)地伯醇的反應(yīng)。主要用于高級脂肪羧酯的還原。
由于Birch還原和氫化鋁鋰的廣泛應(yīng)用，此法在實(shí)驗(yàn)室中已經(jīng)很少采用，但是因?yàn)槠浜啽阋仔?，在工業(yè)上仍然廣泛應(yīng)用。
反應(yīng)機(jī)理
Bouveault-Blanc反應(yīng)的歷程可能如下：首先，酯從鈉獲得一個(gè)電子還原為自由基負(fù)離子，然后從醇中奪取一個(gè)質(zhì)子轉(zhuǎn)變?yōu)樽杂苫?，自從鈉得到一個(gè)電子變成碳負(fù)離子，消除烷氧基成為醛，醛再經(jīng)過相同的步驟還原成醇鈉，醇鈉再得到一個(gè)質(zhì)子變成相應(yīng)的醇。
反應(yīng)實(shí)例
The central neck of a 5-l. three-necked round-bottomed flask is fitted with astopper carrying a mercury-sealed mechanical stirrer. One of the side necks isconnected by means of a short piece of heavy rubber tubing to a large refluxcondenser about 2 m. long, with an inner tube 2.5 cm. in diameter. The thirdneck is fitted with a separatory funnel.
In the flask are placed 70 g. (3 moles) of sodium and200 cc. of dry toluene. The flask is heated in an oil bath until the sodium ismelted. The stirrer is then started; when the sodium is finely divided, the oilbath is removed and the mixture allowed to cool. Stirring must be continuedduring the cooling in order to keep the sodium finely divided.
Whenthe mixture has cooled to about 60°, there are added from the separatoryfunnel, first, a solution of 114 g. (0.5 mole) of ethyl laurate in 150 cc. ofabsolute alcohol, then 500 cc. more of alcohol, as rapidly as is possiblewithout loss of material through the condenser. The time required for theaddition of the ester solution and the alcohol is less than five minutes,usually two or three minutes. When the reaction has subsided, the flask isheated on a steam bath until the sodium is completely dissolved. The mixture isthen steam-distilled to remove the toluene and ethyl alcohol. The contents ofthe flask are transferred to a separatory funnel while still hot and washedthree times with 200-cc. portions of hot water to remove the sodium laurate.The lauryl alcohol is extracted with ether from the cooled mixture and thewashings. The combined ether extracts are washed with water, sodium carbonatesolution, and again with water, and dried over anhydrous magnesium sulfate. Theether is evaporated and the lauryl alcohol distilled under diminished pressure.The yield is 60–70 g. (65–75 per cent of the theoretical amount) of a productboiling at 143–146°/18 mm. or 198–200°/135 mm.
【Organic Syntheses, Coll. Vol. 2,p.372; Vol. 10, p.62.】
