In a
dry 2-l. three-necked flask, equipped with a
sealed wire stirrer, a
condenser protected by a drying tube, and a
dropping funnel, are placed
85.0 g. (3.5 gram atoms) of magnesium turnings and
150 ml. of dry ether (Note
1). A solution of
199 g. (1 mole) of carefully fractionated bromomesitylene and
218 g. (2 moles) of ethyl bromide (Note
2) in
1 l. of dry ether (Note
1) is placed in the funnel. Stirring is commenced, and about
25 ml. of the ether solution is added; the reaction begins almost at once. The rest of the solution of halides is added during the course of 1.25–1.5 hours to the vigorously refluxing mixture; moderate cooling is necessary to permit addition within the specified period. After completion of the addition, refluxing is maintained by external heating for 30 minutes. The reaction mixture is then cooled, and the solution of alkyl magnesium bromides is decanted slowly from the excess
magnesium onto 600 g. of Dry Ice which is stirred manually in a
4-l. beaker. The Dry Ice should be in the form of small lumps, and the addition must be slow enough to avoid spattering. The flask is rinsed with two
200-ml. portions of dry ether, which are added to the carbonation mixture. When most of the Dry Ice has evaporated, an additional 200-g. portion is added along with
250 ml. of dry ether. The viscous is stirred until it becomes largely granular.
When the bulk of the Dry Ice has evaporated,
800 ml. of 20% hydrochloric acid and enough ice to keep the mixture cold are added with stirring. After most of the solid has dissolved, the mixture is transferred to a
separatory funnel with the addition of ordinary
ether if the volume of the organic layer is much less than 1 l. After agitation until both layers are clear, the aqueous layer is rejected, and the ethereal layer is washed with three 1-l. portions of cold water to remove
hydrochloric acid and most of the
propionic acid formed in the carbonation. The product is extracted by shaking first gently and then vigorously with a
540-ml. (600-g.) portion of ice-cold 10% sodium hydroxide solution. After agitation for several minutes the aqueous solution should still be strongly basic as shown by testing with a suitable indicator paper. The aqueous layer is separated and acidified with stirring by the slow addition of
250 ml. of 20% hydrochloric acid. The suspension is cooled, and the nearly colorless product, consisting of small granules, is collected and washed well with water. The crude acid, amounting to
141–143 g. (
86–87%) (Note
3), melting at
152–154° (cor.), is satisfactory for most purposes. A purer product may be obtained as large, nearly colorless crystals, m.p.
153.4–154.4° (cor.), by crystallization from a solution, saturated at the boiling point, in
45% methanol. The yield of the recrystallized acid is
138–141.5 g. (
84–86%) (Note
4).