Submitted by K. C. Gulati, S. R. Seth, and K. Venkataraman.
Checked by John R. Johnson and M. T. Bush.
1. Procedure
In a
250-cc. filtering flask, fitted with a
calcium chloride tube and a
rubber stopper carrying an inverted thistle tube (Note
1) for the introduction of
hydrogen chloride, are placed
20 g. (0.16 mole) of well-dried phloroglucinol (Note
2),
13 g. (0.32 mole) of anhydrous acetonitrile,
80 cc. of anhydrous ether, and
4 g. of finely powdered, fused zinc chloride. The flask is cooled in an ice-salt mixture and shaken occasionally while a rapid stream of dry
hydrogen chloride is passed through the solution for two hours. The flask is allowed to stand in an
ice chest for twenty-four hours, and
hydrogen chloride is again passed into the mixture, now pale orange in color, for two hours. The flask is stoppered and allowed to stand in an ice chest for three days.
The bulky orange-yellow precipitate of the
ketimine hydrochloride is separated by decanting the
ether and washed twice with
20-cc. portions of dry ether. The solid is transferred to a
2-l. round-bottomed flask with 1 l. of hot water. The flask is provided with a
reflux condenser, and the yellow solution is boiled vigorously over a
wire gauze for two hours. About
3 to 4 g. of Norite is added; the solution is boiled for five minutes longer and filtered with suction while hot. The
decolorizing carbon is extracted with two 100-cc. portions of boiling water and this filtrate added to the main portion.
After standing overnight the colorless or pale yellow needles of
phloroacetophenone are filtered with suction and dried in an oven at 120° (Note
3). The yield is
20–23.5 g. (
74–87 per cent of the theoretical amount) of a product which melts at
217–219° (corr.). This product is quite pure and may be used directly for many purposes. It may be recrystallized from thirty-five times its weight of hot water, with a loss of about 5 per cent. The recrystallized material melts at
218–219° (corr.).
2. Notes
3.
Phloroacetophenone crystallizes from aqueous solutions with one molecule of water of hydration.
1 The oven-dried crystals take up water readily on exposure to the air.
Phloroacetophenone gives a wine-red color with
ferric chloride in contrast to the violet color given by
phloroglucinol.
2
3. Discussion
The Hoesch reaction is the most satisfactory method for preparing
phloroacetophenone.
3 The procedure described above is that of Robinson and Venkataraman.
4 Phloroacetophenone has been obtained also by the action of
acetyl chloride on
phloroglucinol in the presence of
aluminum chloride.
2
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