In a
5-l. flask, placed on a
steam bath and fitted with a
mechanical stirrer, a
separatory funnel, a
thermometer well (Note
1), and a
calcium chloride tube, is placed
182 g. (7.5 gram atoms) of magnesium turnings. To this are added a crystal of
iodine and
100 cc. of a solution of 1133 g. (7.5 moles) of 2-bromopentane (Note
2) in
750 g. of n-butyl ether (Note
3). The stirrer is started, and the flask is heated with steam until the reaction starts. This may take from fifteen minutes to one hour; the flask must be watched quite closely because the reaction, when once started, is very vigorous and evolves a large amount of heat. As soon as the reaction has started,
750 g. of n-butyl ether is added and then the balance of the solution of
2-bromopentane in
n-butyl ether is added at such a rate that the temperature is kept at 50–60°. External cooling is used in order to allow more rapid addition of the
2-bromopentane. After addition is complete (about three hours), the mixture is heated on a steam bath for one hour.
In the meantime, a
12-l. flask containing a solution of
450 cc. of concentrated sulfuric acid in 3 l. of water is placed on a steam bath and fitted with a stirrer, a separatory funnel, and an
efficient ice-cooled condenser set for distillation. The stirrer is started, and the solution of the Grignard reagent, prepared above, is added. The acid solution is allowed to become warm but is kept below the boiling point by external cooling. After all the Grignard reagent has been added, the mixture is heated on the steam bath until no more
pentane distils. The reaction flask is allowed to cool, and the
n-butyl ether layer is separated, transferred to a 5-l. flask connected with the condenser, and heated with a free flame until the boiling point of the
n-butyl ether is reached (Note
4). The combined distillate is separated from a small amount of water, washed twice with
125-cc. portions of cold, concentrated sulfuric acid, and allowed to stand overnight with anhydrous
potassium carbonate. After removing the
potassium carbonate, the
n-pentane is fractionated twice through an
efficient 100-cm. fractionating column. The yield is
270–290 g. (
50–53 per cent of the theoretical amount) of a product which boils at
35.5–36.5°.