SYNTHESIS OF ETHYL VALERATE (Ethyl pentanoate)

 

• Place 200 g (250 ml) of rectified spirit in a 1-litre round-bottomed flask fitted with a reflux condenser. 

• Cool in ice and run in, slowly and with frequent shaking, 200g (109ml) of concentrated sulphuric acid. 

• Add 83g (104ml, 1 mol) of butyl cyanide to the mixture and reflux the whole for 10 hours. 

• Allow to cool, pour the reaction mixture into ice water, separate the upper layer of ester and alcohol, and dry over anhydrous calcium sulphate. 

• Distil through a fractionating column and collect the ethyl valerate at 143-146 °C. 

• A further amount of the pure ester may be obtained by redrying the fraction of low boiling point and redistilling. The yield is 100 g (85%).

Cognate preparation: Ethyl phenylacetate

• Place 75g (74 ml, 0.64 mol) of benzyl cyanide, 125g (153 ml) of rectified spirit and 150 g (68 ml) of concentrated sulphuric acid in a round-bottomed flask, fitted with an efficient reflux condenser. 

• Reflux the mixture, which soon separates into two layers, gently for 8 hours, cool and pour into 350 ml of water. 

• Separate the upper layer. 

• Dissolve it in about 75 ml of ether (1) in order to facilitate the separation of the layers in the subsequent washing process. 

• Wash the ethereal solution carefully with concentrated sodium hydrogen carbonate solution until effervescence ceases and then with water. 

• Dry over 10g of anhydrous calcium sulphate for at least 30 minutes. 

• Remove the solvent by flash distillation and distil the residue from an air bath. 

• The ethyl phenylacetate passes over at 225-229 °C (mainly 228 °C) as a colourless liquid; the yield is 90g (86%). 

• Alternatively, the residue after removal of ether may be distilled under diminished pressure; collect the ester at 116-118°C/20mmHg.

Notes to keep in mind: 

1.  Alternatively use 20 ml of carbon tetrachloride. The carbon tetrachloride solution then forms the lower layer in all washing operations.