Organic Syntheses | Page 8

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.
2. Notes
Great caution should be exercised in working with dichloroacetone, as
it is extremely lachrymatory and blisters the skin.
In transferring the crystals from the reaction flask to the Buchner funnel
it is necessary to use a certain amount of water to dissolve the pasty
chromium salts which are otherwise quite impossible to filter. The
amount necessary varies greatly in different runs, according to the
manner in which the chromium salts separate. The amount of this water
is kept low in order to dissolve as little of the product as possible.
Nevertheless, 10-15 g. of dichloroacetone are thus dissolved; this
material, together with a little unchanged dichlorohydrin, may be
recovered by a long procedure involving extraction with ether and
sodium bisulfite. This is not profitable, however.
It is not necessary to wash the crystals in the centrifuge until they are
white. A small amount of chromic salt will not interfere with the
subsequent purification.
Commercial sodium dichromate is hygroscopic and contains varying
amounts of water. The 375 g. required in these directions are equivalent
to 319 g. of anhydrous material.

The total time required for the oxidation is twenty-four hours. It is
convenient to start the reaction in the morning. In this way the last part
of the reaction, which requires no attention, will be accomplished
during the night. The regulation of the temperature is necessary, as the
reaction proceeds very slowly below 20'0; on the other hand, the
dichloroacetone itself is oxidized at a somewhat higher temperature
than 25'0. 3. Other Methods of Preparation
The preparation of dichloroacetone by the following methods is
described in the literature: the direct chlorination of acetone;[1] the
oxidation of dichlorohydrin;[2] the action of silver chloride on
diiodoacetone;[3] the action of dichloropropene (CH2Cl-CCl=CH2)
and hypochlorous acid;[4] the action of hydrochloric acid on
ethoxymonochloroacetoacetic ester;[5] and the hydrolytic cleavage of
dichloroacetoacetic ester.[6]
[1] Jahresb. 1859, 345; 1871, 531; J. prakt. Chem. (2)4, 52 (1871); Ber.
7, 467 (1874); 8, 1330, 1438 (1875); 26, 598 (1893); 42, 3233 (1909);
Ann. 279, 315 (1894)
[2] Ber. 6, 1210 (1873); 13, 1706 (1880); 42, 3233 (1909); Ann. 208,
355 (1881); 269, 46 (1892); Ann. chim. phys. (6) 9, 145 (1886); Bull.
soc. chim. (2) 36, 19 (1881).
[3] Ann. 192, 93 (1878).
[4] Compt. rend. 94, 1428 (1882).
[5] Ann. 269, 18 (1892).
[6] Ber. 43, 3533 (1910).

V
_p_-DIMETHYLAMINOBENZALDEHYDE
(CH3)2NC6H5 + HNO2--> (CH3)2NC6H4NO + H2O
(CH3)2NC6H4NO + 2HCHO + 2C6H5N(CH3)2 --> (CH3)2NC6H4N
= CHC6H4N(CH3)2 + 2H2) + (CH3)2NC6H4CHO (CH3)2NC6H4N =
CHC6H4N(CH3)2 + HCHO-->( CH3)2NC6H4N = CH2 +
(CH3)2NC6H4CHO
Prepared by ROGER ADAMS and G. H. COLEMAN. Checked by H.
T. CLARKE and W. W. HARTMAN.
1. Procedure
IN a 3-l. round-bottom flask fitted with a mechanical stirrer 150 g. of
technical dimethylaniline are dissolved in 750 cc. of diluted

hydrochloric acid (1 part concentrated acid to 1 part water). This
solution is now cooled to 0'0 and a solution (previously cooled to 0'0)
of 90 g. of technical sodium nitrite in 150 cc. of water is added through
a separatory funnel. During the addition of the nitrite solution,
mechanical stirring should be employed and the flask cooled well with
ice and salt. The addition is made at such a rate (thirty to forty