SYNTHESIS OF ISOPROPYL LACTATE

• Place a mixture of 53 g (0.5 mol) of 'AnalaR' lactic acid (85-88% acid), 75 g (95.5 ml, 1 .25 mol) of commercial anhydrous propan-2-ol (isopropyl alcohol), 300 ml of benzene and 20g of Zerolit 225 (acid form) (1) in a 1-litre flask, equipped with an automatic water separator (e.g., a large modified Dean and Stark apparatus with a stopcock at the lower end) carrying an efficient reflux condenser at its upper end. 

• Reflux the mixture using a magnetic stirrer/hotplate unit for 5 hours or until water no longer collects in appreciable amount in the water separator; run off the water from time to time. 

• Filter off the resin at the pump and wash it with two 25 ml portions of benzene. 

• Shake the combined filtrate and washings with about 5 g of precipitated calcium carbonate, filter, and wash with a little benzene. 

• Distil the benzene solution under reduced pressure (water pump) through a short fractionating column; the isopropyl alcohol-benzene azeotrope (2) passes over first, followed by benzene. 

• Collect the isopropyl lactate at 76°C/24mmHg; it is a colourless liquid and weighs 40 g (61%). The ester boils, with slight decomposition, at 157°C/771 mmHg.

Notes to keep in mind:

1. This resin is available as the sodium form. It may be converted into the hydrogen form by treating it with about twice its volume of 1 m sulphuric acid and stirring frequently: the resin is thoroughly washed by decantation with distilled water until the washings have a pH of 6-7, filtered and dried in the air.

2. The b.p. of the propanol-benzene azeotrope at atmospheric pressure is 71-72 °C.

Cognate preparations: Butyl oleate

• Proceed as for isopropyl lactate using 28 g (0.1 mol) of redistilled oleic acid, 37.0 g (46 ml, 0.5 mol) of butan-1-ol (the excess of the latter acts as the water carrier) and 8.0 g of Zerolit 225/H® in a 250-ml flask. 

• Reflux the mixture with magnetic stirring for 4 hours, allow to cool, separate the resin by suction filtration and wash it with three 5 ml portions of butan-1-ol. 

• Remove the butanol from the combined filtrate and washings by distillation under reduced pressure (water pump); the residue consists of crude ester. 

• Distil the residue under diminished pressure (oil pump) and collect the butyl oleate at 232 °C/9 mmHg. The yield is 27 g (85%).

Furfuryl acetate:

• Reflux a mixture of 39.2 g (34.8 ml, 0.4 mol) of redistilled furfuryl alcohol, 48 g (0.67 mol) of glacial acetic acid, 150 ml of benzene and 20 g of Zerolit 225/H® in a 500-ml flask, using the apparatus described for isopropyl lactate. 

• After 3 hours, when the rate of collection of water in the water separator is extremely slow, allow to cool, separate the resin by suction filtration and wash it with three 15 ml portions of benzene. 

• Remove the benzene, etc., from the combined filtrate and washings under reduced pressure (water pump) and then collect the crude ester at 74-90 °C/ 10 mmHg; a small solid residue remains in the flask. 

• Redistil the crude ester through a short fractionating column; pure furfuryl acetate passes over at 79-80°C/17mmHg. The yield is 14.5 g (26%).