SYNTHESIS OF HEXANE-2,5-DIONE (Acetonylacetone)

• Place 11.5g (0.5 mol) of granular sodium (Section 4.2.65, p. 462) covered with 250 ml of dry ether in a 1 -litre three-necked flask fitted with a sealed stirrer unit, a reflux condenser and a dropping funnel. 

• Start the stirrer and add gradually a solution of 65 g (63.5 ml, 0.5 mol) of redistilled ethyl acetoacetate in 250ml of dry ether, cooling the flask if the reaction becomes too vigorous. 

• Continue stirring until all of the sodium has reacted, and then add steadily a solution of 63.5 g (0.25 mol) of powdered iodine in 350 ml of dry ether until the iodine colour persists. 

• Filter off the sodium iodide, wash it with ether and evaporate the combined filtrate and washings (rotary evaporator).

• A somewhat sticky residue of diethyl 2,3-diacetosuccinate remains; crystallise a small portion from 50 per cent aqueous acetic acid to obtain a specimen, m.p. 88 °C. 

• Boil the bulk of the crude product under reflux for 1 hour with 250 ml of 20 per cent aqueous potassium carbonate solution and treat the cooled clear yellow solution with 50 g of anhydrous potassium carbonate. 

• Separate the organic phase, and extract the aqueous layer with four 25 ml portions of ether. 

• Combine the ether extracts with the original organic layer and dry over anhydrous sodium sulphate. 

• Remove the ether by flash distillation and distil the residue, collecting the hexanedione as a fraction of b.p. 185-192°C. The yield is 7.5g (26%).