Reduction of a,-Unsaturated Ketones in Hexamethylphosphoric Triamide

Hexamethylphosphoric triamide (HMPT) is a high-boiling solvent particularly satisfactory for dissolving metals or organometallic compounds. It has been found to be an ideal solvent in which to conduct the reduction of a,jS-unsaturated ketones by alkali metals. 

In a three-necked flask fitted with a thermometer, a stirrer, a condenser (drying tube), and a pressure-equalizing addition funnel, HMPT (25 ml, 0.14 mole) and anhydrous ether (30 ml) are introduced. Finely divided lithium (1.75 g, 0.25 g-atom) is then added 

A solution of 0.1 mole of the a,/S-unsaturated ketone dissolved in 15 ml of anhydrous ether is added dropwise, whereupon the solution is rapidly decolorized. The stirring is continued for 4 hours during which time it slowly becomes blue or green. 

Excess lithium is destroyed by the c irc/w/addition of 1-2 ml of ethanol, and hydrolysis of the reaction mixture is then effected by the addition of a mixture of ice (50 g) and water (100 ml). The solution is then acidified to pH 2 by the addition of 5 A hydrochloric acid, followed by rapid stirring for 1 or 2 minutes to hydrolize the HMPT. The aqueous solution is extracted with ether, the ether solution is dried with magnesium sulfate, then filtered, and the ether is evaporated. The product is isolated by distillation of the residue. 

2-Methyl-2-penten-4-one (mesityl oxide) Treatment of 9.8 g (0.1 mole) of the ketone by the above procedure gives on distillation 6.6 g of methyl isobutyl ketone, bp 117-1187I atm and a residue of 3 g. 

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