SYNTHESIS OF DIETHYL (2-CYANOETHYL)MALONATE

 

CAUTION: Acrylonitrile vapour is highly toxic; it should therefore be handled with great caution and all operations with it should be conducted in a fume cupboard provided with an efficient extraction system.

• Assemble in a fume cupboard a 1 -litre three-necked flask containing 480g (455 ml, 3 mol) of diethyl malonate and fitted with a stirrer, a dropping funnel and a thermometer. 

• Start the stirrer, add to the flask a solution of sodium ethoxide prepared from 3.5g of sodium in 100 ml of absolute ethanol and then run in slowly 80g ( 100 ml, 1.5 mol) of acrylonitrile ( 1 ) (CAUTION: toxic and lachrymatory vapour) at a rate such that the temperature does not exceed 35 °C. 

• When the addition is complete, continue to stir for 1 hour more and then remove the stirrer. 

• Equip the flask for distillation under reduced pressure through a short fractionating column and remove the ethanol by distillation using a water pump. 

• Continue the distillation of the residue using an oil pump at a recorded pressure of about 0.2mmHg, and collect (i) recovered diethyl malonate at 52 °C (240g), and (ii) somewhat crude diethyl (2-cyanoethyl) malonate at 130-1 40 °C (200 g). 

• Redistil the latter to obtain 175g (55%) of the purified product of b.p. 102-106 °C/0.2mmHg (127-130°C/3mmHg); i.r. spectrum (thin film), 2250 (CN) and 1725 cm⁻¹ (C=O); p.m.r. spectrum (CCl₄ ,TMS), 𝛅1.29 (t,6H), 1.90-2.70 (m,4H), 3.41 (t,1H) and 4.19 (q,4H).

Notes to keep in mind:

1. Acrylonitrile forms an azeotropic mixture with water, b.p. 70.5 °C (12.5% water). The commercial product may contain the polymer; it should be redistilled before use and the fraction, b.p. 76.5-78 °C, collected separately as a colourless liquid.