IN a 2-l. flask are placed 375 g. of commercial sodium dichromate,
225 cc. of water, and 300 g. of dichlorohydrin (b. p.
68-75'0/14 mm.). The flask is set in a water bath and equipped
with a thermometer and mechanical stirrer. The contents are
vigorously stirred, and 450 g. of sulfuric acid, diluted with 115 g.
of water, are introduced during the course of seven to eight hours.
It is convenient to add the acid at ten-minute intervals.
The temperature is kept between 20'0 and 25'0 during the entire reaction;
this is accomplished by adding a little ice to the water bath from
time to time. The stirring is continued for sixteen to seventeen
hours after all the acid has been added; as there is very little
heat evolved during this part of the reaction, the water bath may
be allowed to come to room temperature.
Sufficient water is now added to the mixture to dissolve the pasty
chromium salts (300-800 cc.). The mass of crystals is then rapidly
filtered on a Buchner funnel and sucked as dry as possible.
The crystals are then transferred to a small laboratory centrifuge
and centrifuged for several minutes. The crystals are washed in
the centrifuge with about 15-25 cc. of ice water, then with 10-15 cc.
of cold petroleum ether, and finally centrifuged till as dry as possible.
The crude dichloroacetone is dried in a vacuum desiccator over
sulfuric acid overnight It weighs about 220 g.
The crude product is best purified by distillation from
a 250-cc. distilling flask fitted with an air condenser.
A very small fraction (10-15 g.) of low-boiling material is obtained,
and the dichloroacetone (170-175'0) is then collected. It solidifies
in the receiver to a white crystalline mass which weighs 200-220 g.
(65-70 per cent of the theoretical amount). A few grams more may
be obtained by chilling the low-boiling fraction and filtering
off the water.