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.