In a
5-l. round-bottomed flask, fitted with a
stopper holding a
separatory funnel and an
efficient reflux condenser (Note
1) closed at the top with a
calcium chloride tube (Note
2), are placed
80 g. (3.29 atoms) of magnesium turnings and
800 cc. of dry benzene (Note
3). Through the
dropping funnel is added gradually a solution of
90 g. of mercuric chloride in
400 g. (505 cc., 6.9 moles) of acetone (Note
4), carefully at first and then more rapidly after the reaction starts. The time of addition is about five to ten minutes (Note
5). Sometimes the reaction does not commence until a considerable proportion of the
acetone solution of
mercuric chloride has been added. In this case the reaction proceeds very vigorously when it does start, and the flask must be cooled in running water to avoid loss through the condenser. As soon as the first vigorous reaction is over, a mixture of
200 g. (258 cc., 3.45 moles) of acetone and
200 cc. of benzene is added (Note
6). When the reaction slows down, the flask is heated on a
water bath until no further reaction is evident (about two hours). During this time the
magnesium pinacolate swells until it fills the flask about three-fourths full. The flask is removed from the condenser and shaken until the reaction mass is well broken up (Note
7). The condenser is again attached and the heating continued for another hour.
Through the separatory funnel is then added 200 cc. of water, and the reaction mixture is heated for another hour. The flask should be shaken occasionally during this time. The reaction mixture is cooled to about 50° and filtered. The solid is returned to the flask and heated for ten minutes with a fresh
500-cc. portion of benzene to dissolve any remaining
pinacol. The original filtrate and the second portion of
benzene, after it is filtered from the
magnesium hydroxide, are mixed and distilled to one-half the original volume in order to remove the
acetone; the remaining
benzene solution is treated with 300 cc. of water and cooled to 10–15°. The
pinacol hydrate separates, and after about thirty minutes (Note
8) it is collected on a
suction filter and washed with
benzene, or better, the mixture is centrifuged in a
basket centrifuge. The
pinacol hydrate, air-dried at room temperature (Note
9), weighs
325–375 g. (
43–50 per cent of the theoretical amount based on the
magnesium used) (Note
2). The product melts at
46–47°. It is sufficiently pure for most purposes. Occasionally the product is slightly yellow. If such a product is dissolved in an equal weight of boiling water, treated with a little animal charcoal, filtered, and the filtrate cooled in ice, over
95 per cent of the material may be recovered in large white crystals (Note
10).