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Org. Synth. 1949, 29, 70
DOI: 10.15227/orgsyn.029.0070
2-METHYL-4-HYDROXYQUINOLINE
[4-Quinolinol, 2-methyl-]
Submitted by George A. Reynolds and Charles R. Hauser.
Checked by Arthur C. Cope and William R. Armstrong.
1. Procedure
In a 500-ml. three-necked round-bottomed flask equipped with a dropping funnel, a sealed mechanical stirrer, and an air condenser is placed 150 ml. of Dowtherm (Note 1). The Dowtherm is stirred and heated at the reflux temperature while 65 g. (0.32 mole) of ethyl β-anilinocrotonate (p. 374) is added rapidly through the dropping funnel. Stirring and refluxing are continued for 10–15 minutes after the addition is completed. The ethanol formed in the condensation reaction may be allowed to escape from the condenser through a tube leading to a drain, or it may be collected by attaching a water-cooled condenser set for distillation to the top of the air condenser. The mixture is allowed to cool to room temperature, at which stage a yellow solid separates. Approximately 200 ml. of petroleum ether (b.p. 60–70°) is added; the solid is collected on a Büchner funnel and washed with 100 ml. of petroleum ether (b.p. 60–70°). After air drying, the crude product is treated with 10 g. of Darco or Norit in 1 l. of boiling water (Note 2). The hot solution is filtered and allowed to cool. The white, hairlike needles of 2-methyl-4-hydroxyquinoline are separated by filtration. The yield of product, melting at 235–236° (cor.), is 43–46 g. (85–90%).
2. Notes
1. Dowtherm is a mixture of diphenyl and diphenyl ether, obtainable from the Dow Chemical Company.
2. If the treatment with decolorizing carbon is omitted, the product has a low melting point after several crystallizations.
3. Discussion
The present procedure is a modification of preparations described previously.1,2,3 The cyclization has been effected by allowing a solution of ethyl β-anilinocrotonate in concentrated sulfuric acid to stand at room temperature for several hours; by rapidly heating the ester to 240–250° without a solvent;2 or by adding the ester to paraffin oil at 250°3 or to refluxing diphenyl ether.4 The procedure described has been applied to the preparation of other 2-substituted 4-hydroxyquinolines.5

References and Notes
  1. Knorr, Ber., 16, 2593 (1883).
  2. Conrad and Limpach, Ber., 20, 944 (1887).
  3. Cavalito and Haskell, J. Am. Chem. Soc., 66, 1166 (1944).
  4. Kaslow and Marsh, J. Org. Chem., 12, 456 (1947).
  5. Hauser and Reynolds, J. Am. Chem. Soc., 70, 2402 (1948).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

petroleum ether

Dowtherm

diphenyl

ethanol (64-17-5)

sulfuric acid (7664-93-9)

decolorizing carbon,
Norit (7782-42-5)

diphenyl ether (101-84-8)

ETHYL β-ANILINOCROTONATE (6287-35-0)

2-Methyl-4-hydroxyquinoline,
4-Quinolinol, 2-methyl- (607-67-0)