In a
3-l. round-bottomed flask (Note
1) fitted with a
1-meter fractionating column1 are placed
450 g. (7.5 moles) of anhydrous isopropyl alcohol (Note
2),
212 g. (2 moles) of u.s.p. 85 per cent lactic acid,
1 l. of benzene, and
5 cc. of concentrated sulfuric acid. The flask is placed in an
air bath on an electric hot plate (Note
3) and heated until the benzene-isopropyl alcohol-water ternary mixture distils at 66.5°. Distillation is continued slowly (six to seven hours) until the temperature at the head of the column rises to and persists at 71–72° (isopropyl alcohol-benzene binary mixture), and no further separation of water occurs.
Ten grams of precipitated calcium carbonate is then added to the mixture, and distillation is continued until the temperature rises to 80° in order to remove most of the
benzene and excess
isopropyl alcohol (Note
4) and (Note
5). The contents of the flask are then filtered into a
modified Claisen flask and distilled under reduced pressure. Cuts are taken to 60°, 60–75°, 75–80°, and 80–100° at 32 mm. The fraction boiling at
75–80°/32 mm. is
isopropyl lactate and weighs
130–160 g. By redistilling the high and low fractions an additional
30–60 g. is obtained, bringing the total yield to
160–180 g. (
60–68 per cent of the theoretical amount). The ester may be redistilled at atmospheric pressure (with some loss due to decomposition) at 166–168°.