Org. Synth. 1948, 28, 42
DOI: 10.15227/orgsyn.028.0042
2,5-DIHYDROXYACETOPHENONE
[Acetophenone, 2,5-dihydroxy-; quinacetophenone]
Submitted by G. C. Amin and N. M. Shah.
Checked by R. S. Schreiber and W. W. Prichard.
1. Procedure
A mixture of
50 g. (0.257 mole) of dry hydroquinone diacetate (p. 452) and
116 g. (0.87 mole) (Note 1) of anhydrous aluminum chloride is finely powdered in a
mortar and introduced into a dry
500-ml. round-bottomed flask fitted with an air condenser protected by a
calcium chloride tube and connected to a gas-absorption
trap. The flask is placed in an
oil bath (Note 2) which is heated slowly from room temperature so that at the end of about 30 minutes the temperature of the oil reaches 110–120°, at which point the evolution of
hydrogen chloride begins. The temperature is then raised slowly to 160–165° and maintained at that point for about 3 hours
(Note 3); at the end of about 2 hours the evolution of
hydrogen chloride becomes very slow and the mass assumes a green color and becomes pasty in consistency
(Note 4).
The flask is removed from the oil bath and allowed to cool to room temperature. The excess aluminum chloride is decomposed by treating the reaction mixture with 350 g. of crushed ice followed by 25 ml. of concentrated hydrochloric acid. The solid obtained is collected on a Büchner funnel and washed with two 100-ml. portions of cold water. The crude product weighs about 35 g. (89–90%). Recrystallization from 4 l. of water yields 25–30 g. (64–77%) of green, silky needles melting at 202–203° (Note 5).
2. Notes
1.
Ordinary commercial
aluminum chloride can be used. If the amount of this reagent is less than 3 moles per mole of the ester the yield diminishes. To compensate for any inert ingredients in the commercial
aluminum chloride, the reagent is employed in an excess of about 10% over 3 moles.
2.
The flask should not touch the bottom of the oil bath; if it does, the lower portion of the mixture may char.
3.
If the evolution of the
hydrogen chloride becomes vigorous, the
calcium chloride tube may be removed temporarily and the top of the condenser connected directly to the gas-absorption trap. When the gas evolution slackens and there is no longer any danger that the
calcium chloride tube will be blown off, the guard tube is reinserted.
4.
The reaction requires about 2 hours, but the heating is continued another hour to ensure its completion.
5.
The product may be recrystallized from
250 ml. of 95% ethanol rather than from the much larger quantity of water.
3. Discussion
2,5-Dihydroxyacetophenone has been prepared in
54% yield
1 by heating
hydroquinone diacetate,
hydroquinone, and anhydrous
aluminum chloride. It has also been prepared
2 by the reaction of
hydroquinone with
acetic acid in the presence of
zinc chloride.
The procedure given has also been applied in the Fries rearrangement of
hydroquinone dipropionate, with the production of
2,5-dihydroxypropiophenone in good yields.
3This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
2,5-Dihydroxyacetophenone
2,5-dihydroxypropiophenone
ethanol (64-17-5)
calcium chloride (10043-52-4)
hydrogen chloride,
hydrochloric acid (7647-01-0)
acetic acid (64-19-7)
hydroquinone (123-31-9)
Acetophenone (98-86-2)
aluminum chloride (3495-54-3)
zinc chloride (7646-85-7)
Hydroquinone diacetate (1205-91-0)
hydroquinone dipropionate (7402-28-0)
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