SYNTHESIS OF 2-PHENYLPROPANAL (Hydratropaldehyde)

Ethyl 3-phenyl-2,3-epoxybutanoate:

• In a 500-ml three-necked flask, fitted with a mechanical stirrer and a thermometer, place a mixture of 60 g (58.5 ml, 0.5 mol) of acetophenone, 61.5 g (53 mol, 0.5 ml) of ethyl chloroacetate (b.p. 142-143 °C) and 100ml of sodium-dried benzene. 

• Add, with stirring 23.6g (0.6 mol) of finely powdered sodamide over a period of 2 hours; maintain the temperature at 15-20°C with the aid of external cooling. 

• Ammonia is evolved. 

• Stir for 2 hours at room temperature and pour the reddish mixture on to 350 g of crushed ice with hand stirring. 

• Separate the organic layer and extract the aqueous layer with 100 ml of benzene. 

• Wash the combined benzene solutions with three 150 ml portions of water, the last one containing 5 ml of acetic acid, and then dry with magnesium sulphate. 

• After removal of the benzene on a rotary evaporator, distil the residue under reduced pressure through a short fractionating column. 

• Collect the fraction of b.p. 1 1 1-1 14 °C/3 mmHg as the glycidic ester; the yield is 67 g (65%).

2-Phenylpropanal (hydratropaldehyde):

• Prepare a solution of sodium ethoxide in a 500-ml round-bottomed flask from 7.6 g (0.33 mol) of clean sodium and 150 ml of absolute ethanol. 

• Add 66.5 g of the above glycidic ester slowly and with shaking. 

• Cool the flask externally to 15 °C and add 6 ml of water slowly; much heat is evolved and the sodium salt soon separates. 

• Keep the reaction mixture overnight. 

• Collect the salt by suction filtration, wash it with 25 ml of ethanol followed by 25 ml of ether. 

• Add the salt to dilute hydrochloric acid (prepared from 28 ml of the concentrated acid and 1 50 ml of water) contained in a 500-ml flask fitted with a reflux condenser. 

• Warm the mixture gently; carbon dioxide is evolved and an oil separates. 

• Heat on a steam bath for 90 minutes, cool and extract the oil with 75 ml of benzene. 

• Wash the extract with 100 ml of water, and distil the benzene solution under reduced pressure. Collect the 2-phenylpropanal at 90-93 °C/10 mmHg; the yield is 30g (70%).

Cognate preparation: Ethyl 2,1'-epoxycyclohexylacetate

• Add a mixture of 55 g (48 ml, 0.45 mol) of ethyl chloroacetate and 43 g (0.44 mol) of cyclohexanone dropwise to a suspension of finely divided sodium (1 1 g, 0.48 mol) in anhydrous xylene (165 ml) with stirring and cooling in an ice-salt bath. 

• Regulate the rate of addition so that the temperature of the reaction mixture does not exceed 8 °C. 

• Pour the resulting dark-red clear solution into water, wash the organic layer repeatedly with water, dry with magnesium sulphate and distil. 

• Collect the glycidic ester at 81-83 °C/0.04 mmHg or at 115-117 °C/10mmHg. The yield is 37g (46%).