SYNTHESIS OF BENZOYLACETONE

Sodium ethoxide:

• Prepare a suspension of 1 1.5 g (0.5 mol) of granulated sodium (Section 4.2.68, p. 462) in 75 ml of dry xylene, transfer it to a 1-litre three-necked flask, and decant the xylene. 

• Wash the sodium by decantation with two 20 ml portions of dry ether and cover with 200 ml of dry ether. 

• Set the flask on a water bath and fit it with a sealed stirrer unit, and with a reflux condenser and a dropping funnel, each protected by a calcium chloride guard-tube. 

• Start the stirrer and run in 23 g (29 ml, 0.5 mol) of absolute ethanol from the dropping funnel during 1-2 hours with gentle refluxing, and continue to reflux the mixture with stirring until nearly all of the sodium has reacted (up to 6 hours; a little residual sodium does no harm). 

• Stop the stirrer, set the condenser for downward distillation and distil off the ether as completely as possible. 

• The residual sodium ethoxide should be white and finely divided. 

• All moisture must be excluded during the preparation.

Benzoylacetone:

• Return the condenser (protected by the calcium chloride guard-tube) to the reflux position, surround the flask with ice and introduce 200 ml (2 mol) of pure, dry ethyl acetate. 

• Start the stirrer and add 60 g (58 ml, 0.5 mol) of acetophenone from the dropping funnel; the reaction commences with the separation of the sodium salt of benzoylacetone. 

• Continue stirring for 2 hours and then allow to stand in an ice box overnight. 

• Filter the solid at the pump with the aid of the addition of a little dry ether. 

• Dissolve the air-dried solid in cold water, and acidify the solution with acetic acid. 

• Filter off the crude benzoylacetone, and dry in the air.

•  Purify by distillation under reduced pressure; collect the benzoylacetone at 128-130 °C/10mmHg. It solidifies on cooling to a colourless crystalline solid, m.p. 61 °C. The yield is 50 g (62%). 

• Record the p.m.r. spectrum (CDC1 3 ) assign the absorptions and estimate the keto:enol ratio.