SYNTHESIS OF 4-OXOPENTANOIC ACID

CAUTION: All procedures should be conducted behind a safety screen; particular care should be taken in the handling of acrolein, for the measures to be taken in the handling of 30 per cent hydrogen peroxide.

4-Nitropentanal:

• A 100-ml two-necked flask equipped with a mechanical stirrer is charged with nitroethane (3.75g, 0.05 mol) and cooled with an ice-water bath. Acrolein (2.8g, 0.05 mol) is added and the mixture stirred for 5 minutes. 

• Chromatographic alumina (activity I on the Brockmann scale; 10g) is added and stirring is continued for 6 hours. 

• The reaction is monitored by t.l.c. (ethyl acetate-hexane, 2:8 as eluent). At the end of the reaction, the alumina is washed with ether (4 x 50 ml) and the filtered extract evaporated under reduced pressure. 

• The product is purified by distillation to give 4-nitro-pentanal (50%), b.p. 71 °C/0.4mmHg; i.r. 1720 (C=0) and 1545cm⁻¹ (NO₂).

 

4-Oxopentanoic acid

• Aqueous hydrogen peroxide (30 ml, 30%) is added to a cooled (0°C) and stirred solution of the foregoing 4-nitroalkanal (1.96g, 0.015 mol) in methanol (70 ml). 

• To the resultant solution, potassium carbonate (12g) is added, and stirring is continued for 15 hours at room temperature. 

• The solution is then acidified with 2 m hydrochloric acid and extracted with dichloromethane (3 x 40 ml). 

• The organic layer is washed with water (40 ml), and dried with magnesium sulphate. 

• The solvent is removed under vacuum to leave the crude product which can be used without further purification. 

• The pure 4-oxopentanoic acid (60%) is obtained by distillation and has b.p. 120°C/10mmHg.