Org. Synth. 1942, 22, 37
DOI: 10.15227/orgsyn.022.0037
2,3-DIMETHYLANTHRAQUINONE
[Anthraquinone, 2,3-dimethyl-]
Submitted by C. F. H. Allen and Alan Bell.
Checked by R. L. Shriner and John C. Robinson, Jr..
1. Procedure
A solution of
80 g. (0.5 mole) of 1,4-naphthoquinone [
Org. Syntheses Coll. Vol. 1, 375 (1932),
383 (1941)] and
80 g. (1 mole) of 2,3-dimethylbutadiene-1,3 (p. 312) in
300 ml. of alcohol is refluxed for 5 hours, using a
1-l. round-bottomed flask and an
efficient reflux condenser. The solution is cooled and placed in a
refrigerator for 10–12 hours. The crystalline mass is then broken up with a
spatula, and the
addition product is filtered and washed with
50 ml. of cold ethanol. The product forms white, feathery crystals melting at
147–149° (Note 1). The yield is
116 g. (
96% based on the
1,4-naphthoquinone).
For the dehydrogenation, 40 g. of the addition product is dissolved in 600 ml. of 5% ethanolic potassium hydroxide solution (Note 2) in a 1-l. three-necked flask equipped with a reflux condenser and inlet tube. A current of air is bubbled through the solution for 24 hours; considerable heat is generated, and the initial green color soon changes to yellow. The yellow quinone that has separated is then filtered with suction and is washed, first with 200 ml. of water, then with 100 ml. of ethanol, and finally with 50 ml. of ether. The yield of air-dried product (m.p. 209–210°) is 36.5–37.5 g. (94–96%) (Note 3). The over-all yield for both steps is 90% (Note 4).
2. Notes
1.
The addition product is usually pure enough for the next step. It may be purified by recrystallization from
acetone,
ethanol, or
methanol, and then it melts sharply at 150°. If the crude product is deeply colored, it should be recrystallized, using a
decolorizing carbon.
2.
This is prepared by dissolving
30 g. of potassium hydroxide in
570 g. of 95% ethanol.
3.
The melting points given in the literature vary from 183°
1 to 208°.
24.
Essentially the same percentage yield has been obtained using three times the amounts given.
3. Discussion
2,3-Dimethylanthraquinone has been obtained by ring closure of the corresponding
o-benzoylbenzoic acid;
1,2,3 by oxidation of the corresponding
anthrone;
4 by decarboxylation of
2,3-dimethylanthraquinone-5-carboxylic acid;
5 from
2-chloro- and 2,3-dichloro-1,4-naphthoquinone and
2,3-dimethylbutadiene-1,3 by the action of
sodium hydroxide;
6 and from
2-methyl-1,4-naphthoquinone and
2,3-dimethylbutadiene-1,3 with subsequent dehydrogenation by
sulfur.
7 The addition product employed in the present procedure has been described.
8
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
2-chloro- and 2,3-dichloro-1,4-naphthoquinone
ethanol (64-17-5)
methanol (67-56-1)
ether (60-29-7)
sodium hydroxide (1310-73-2)
sulfur (7704-34-9)
Anthrone (90-44-8)
acetone (67-64-1)
decolorizing carbon (7782-42-5)
potassium hydroxide (1310-58-3)
Quinone (106-51-4)
1,4-Naphthoquinone (130-15-4)
2,3-Dimethylanthraquinone,
Anthraquinone, 2,3-dimethyl- (6531-35-7)
2,3-dimethylbutadiene-1,3 (513-81-5)
2,3-dimethylanthraquinone-5-carboxylic acid
2-methyl-1,4-naphthoquinone
o-benzoylbenzoic acid (85-52-9)
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