Part 2 (2/2)

(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_-DIMETHYLAMIn.o.bENZALDEHYDE

(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.

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