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Preparation of Chloroacetone and Bromoacetone


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Chloroacetone [1]

Good method of preperation 150 ml acetone 50 ml water 12 g Cupric chloride 6 g lithium chloride. Reflux till reaction completes. Literature states 24 hours but the reaction has a half-life of about 24 minutes at 20C (same article half of marker in 24 minutes, the marker being oxygen consumption in a slightly different reaction), therefore 5 hours is probably sufficient at reflux.

After reacting, distill everything below 123C. The still bottoms can be reprocessed to recover cuprous chloride and lithium chloride. Both can be recovered by disolving with minimum water. The mix is easily converted to cupric chloride-lithium chloride by boiling with 20-35% hydrochloric acid.

Redistill slowly through a packed column to remove acetone. This leaves two fractions one distilling at 89C which is water and chloroacetone and the second distilling at 121C which is ?pure? chloroacetone. The second fraction may contain unsymetrical dichloroacetone I haven't had a sample analysed. Calcium Chloride will crash the water-chloroacetone mix which tends to form a colloidal solution.

Chloroacetone must be stabalized with 1% calcium carbonate or 0.1% water if it is stored or it forms an explosive sludge. Distillation of a water-chloroacetone mix at 89C is the most efficient way of separating unsym-dichloroacetone from commercial products.

Chloroacetone [2]

This produces a product absolutely free from polychlorinated acetone, which usually is formed in the chlorination of acetone, and is almost impossible to completely remove by distillation.

A dried ether solution (approximately 500ml) containing 0.5 mole of diazomethane was placed in a 1000ml three-necked flask and practical grade acetyl chloride (0.25 mole) was added slowly from a dropping funnel with constant stirring of the solution which was maintained at a temperature not greater than 5C. The reaction mixture was allowed to stand for two hours after the addition of the acetyl chloride and was then saturated with anhydrous HCl over a period of two hours. The bulk of the ether was removed by distillation, and the residual solution fractionated through a small column. The product boiling at 118-119C at weighed 15.8g (68%), d 1.126.

Bromoacetone [3]

A 5-L, three-necked, round-bottomed flask is provided with an efficient mechanical stirrer, a 48-cm. Allihn reflux condenser, a thermometer, and a 500ml separatory funnel, the stem of which reaches nearly to the bottom of the flask.

Through the separatory funnel are introduced 1.6 1. of water, 500ml of pure acetone, and 372 ml of glacial acetic acid. The stirrer is started and the temperature of the water bath is raised to 70-80C, so that the mixture in the flask is at about 65C. Then 354 ml (7.3 moles) of bromine is carefully added through the separatory funnel. The addition, which requires one to two hours, is so regulated as to prevent the accumulation of unreacted bromine As a rule the solution is decolorized in about twenty minutes after the bromine has been added. When the solution is decolorized, it is diluted with 800 ml of cold water, cooled to 10C, made neutral to Congo red with about 1 kg. of solid anhydrous sodium carbonate, and the oil which separates is collected in a separatory funnel and dried with 80g of anhydrous calcium chloride. After drying, the oil is fractionated and the fraction boiling at 38-48C/13 mmHg is collected. The yield is 470-480 g. (50-51% yield). If a purer product is desired, the above product is refractionated and the fraction boiling at 40-42C/13 mmHg is collected. The yield is 400-410 g. (43-44% yield).

The higher-boiling fraction contains a mixture of isomeric dibromoacetones.

References

[1] JACS 77, 5274-5278 (1955)
[2] JACS 76, 1186 (1954)
[3] Organic Synthesis Collective Volume II, p 88-89