Distillation under diminished pressure with rotary evaporator

Benzyl cyanide. Place 100 g (2 mol) of powdered sodium cyanide and 90 ml of water in a 1-litre round-bottomed flask provided with a reflux condenser. Warm on a water bath until the sodium cyanide dissolves. Add down the condenser a solution of 200 g (181.5 ml, 1.58 mol) of benzyl chloride (Expt 5.27) in 200 g of rectified spirit during 30-45 minutes. Heat the mixture in a water bath for 4 hours, cool and filter off the precipitated sodium chloride with suction wash with a little alcohol. Distil off as much as possible of the alcohol using a rotary evaporator. Cool the residual liquid, filter if necessary and separate the layer of crude benzyl cyanide. (Sometimes it is advantageous to extract the nitrile with ether.) Dry over a little magnesium sulphate, and distil under diminished pressure. Collect the benzyl cyanide at 102-103 °C/ 10 mmHg. The yield is 160 g (86%). 

Note. (1) The steam distillation may be omitted, if desired, by utilising the following method of purification. Allow the reaction mixture to cool, decant the aqueous layer and dissolve the residue in about 150 ml of toluene. Wash the toluene solution with water, 1 per cent sodium hydroxide solution and finally with water dry with magnesium sulphate, distil off the toluene on a water bath (rotary evaporator) and distil the residue under diminished pressure. 

Suspend 76 g (1 mol) of thiourea (CAUTION see Section 2.3.4, p. 50) in 200 ml of water in a 500-ml three-necked flask sited in a fume cupboard and equipped with a sealed stirrer unit, a reflux condenser and a dropping funnel. Stir and add 92.5 g (80 ml, 1 mol) of chloroacetone (1) over a period of 30 minutes. The thiourea dissolves as the reaction proceeds and the temperature rises. Reflux the yellow solution for 2 hours. To the cold solution immersed in an ice bath add, with stirring, 200 g of solid sodium hydroxide. Transfer to a separatory funnel, add a little ice-water, separate the upper oil layer and extract the aqueous layer with three 100 ml portions of ether. Dry the combined oil and ether extracts with anhydrous sodium sulphate, remove the ether using a rotary evaporator and distil the residual oil under diminished pressure. Collect the 2-amino-4-methylthiazole at 130-133 °C/18mmHg it solidifies on cooling in ice to a solid, m.p. 44-45 °C. The yield is 84 g (74%). 

Diethyl ethylphenylmalonate. In a dry 500-ml round-bottomed flask, fitted with a reflux condenser and guard-tube, prepare a solution of sodium ethoxide from 7.23 g (0.315 mol) of clean sodium and 150 ml of super-dry ethanol in the usual manner add 1.5 ml of pure ethyl acetate (dried over anhydrous calcium sulphate) to the solution at 60 °C and maintain this temperature for 30 minutes. Meanwhile equip a 1-litre three-necked flask with a dropping funnel, a sealed mechanical stirrer and a double surface reflux condenser the apparatus must be perfectly dry and guard-tubes should be inserted in the funnel and condenser respectively. Place a mixture of 74 g (0.315 mol) of diethyl phenylmalonate and 60 g (0.385 mol) of ethyl iodide in the flask. Heat the apparatus in a bath at 80 °C and add the sodium ethoxide solution, with stirring, at such a rate that a drop of the reaction mixture when mixed with a drop of phenolphthalein indicator is never more than faintly pink (1). The addition occupies 2-2.5 hours continue the stirring for a further 1 hour at 80 °C. Allow the flask to cool, and remove the ethanol under reduced pressure using a rotary evaporator. Add 100 ml of water to the residue in the flask and extract the ester with three 100 ml portions of toluene. Dry the combined extracts with anhydrous sodium sulphate, distil off the toluene at atmospheric pressure and the residue under diminished pressure. Collect the diethyl ethylphenylmalonate at 159-160 °C/8mmHg. The yield is 72 g (87%). 

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