A
2-l. three-necked round-bottomed flask is fitted with a
condenser arranged for distillation, a
200-ml. dropping funnel, and a
mercury-sealed mechanical stirrer. Connections are most conveniently made with ground-glass joints, and the flask is heated on a steam cone.
Cupric bromide (0.4 g.),
39.2 g. (0.60 g. atom) of freshly sand-papered zinc foil cut into narrow strips, and
1.2 l. of benzene previously dried over
sodium are added to the flask. To dry the apparatus and contents,
300 ml. of benzene is slowly distilled from the flask with stirring. Heating is interrupted, and the condenser is quickly arranged for reflux and fitted with a
calcium chloride drying tube. To the flask are added rapidly with stirring
38.9 g. (0.40 mole) of n-capronitrile (Note
1) and
125.4 g. (0.60 mole) of sec-butyl α-bromopropionate (Note
2). Refluxing is resumed, and after a 3–5 minute induction period blackening of the
zinc surface and clouding of the solution are noted as the first signs of reaction. Heating is maintained a total of 45 minutes, after which the solution is cooled for 15 minutes in an
ice bath (Note
3).
To the cooled solution is added with vigorous stirring
400 ml. of ice-cold 12N sulfuric acid. The ice bath is removed, and stirring is continued at room temperature for a total of 2 hours (Note
4). The reaction mixture is poured into a
2-l. separatory funnel; after separation, the aqueous lower layer is drained into a 2-l. separatory funnel containing 800 ml. of water which has been used to wash the reaction flask. The aqueous layer is extracted twice with
200-ml. portions of benzene which have also been employed to rinse the reaction flask. The original organic layer and the combined
benzene extracts are kept separate and are washed successively with 400-ml. portions of water, saturated
sodium bicarbonate solution, and again with water. The two organic portions are combined and allowed to stand over anhydrous
sodium sulfate until clear. The solvent is removed at atmospheric pressure by flash distillation through a fractionating column (Note
5). For this operation, a side-arm distilling flask equipped with a dropping funnel is heated by an
oil bath whose temperature is maintained at 140–150°. After all the solvent has been added, the dropping funnel is replaced by a capillary, and the last of the solvent is removed at reduced pressure furnished by a water pump. Finally, an
oil pump is attached and the product is fractionated at about 5 mm. pressure (Note
6). After a small fore-run,
sec-butyl α-n-caproylpropionate is obtained as a clear liquid; b.p.
112–114°/4.5 mm. (
134–136°/12 mm.),
n25D 1.4293 (Note
7) and (Note
8). The yield is
46.0–52.9 g. (
50–58% based on
n-capronitrile) (Note
9).