SYNTHESIS OF 2-METHYLPROPANOIC ACID (Isobutyric acid)

• Place a mixture of 52g (0.7 mol) of 2-methylpropan-l-ol and a solution of 15 g of sodium carbonate in 1 50 ml of water in a 5-litre round-bottomed flask. 

• Add a solution of 142 g (0.9 mol) of potassium permanganate in 2750 ml of water, with vigorous stirring, during 3-4 hours, cooling the mixture to 4-5 °C by immersion in a bath of ice-water. 

• Then allow the reaction mixture to attain room temperature gradually. 

• After 12 hours, filter off (or preferably, centrifuge) the precipitated manganese dioxide, concentrate the filtrate to about 150 ml under reduced pressure and then cool. 

• Cover the solution with a layer of ether and acidify with dilute sulphuric acid. 

• Separate the ether layer and extract the aqueous layer two or three times with 50 ml portions of ether. 

• Dry the combined ethereal extracts over anhydrous sodium sulphate, remove the ether on a water bath and fractionate the residual liquid. 

• Collect the 2-ethylpropanoic acid at 153-1 55 °C. The yield is 45 g (76%); i.r. spectrum (thin film), 2200-3800 (br. OH) and 1700 cm⁻¹ (br. C = O). Record the p.m.r. spectra and assign the signals; note the hydroxyl proton may not be observed.