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Org. Synth. 1977, 57, 78
DOI: 10.15227/orgsyn.057.0078
OXIDATION WITH BIS(SALICYLIDENE)ETHYLENEDIIMINOCOBALT(II) (SALCOMINE): 2,6-DI-tert-BUTYL-p-BENZOQUINONE
[2,5-Cyclohexadiene-1,4-dione, 2,6-bis(1,1-dimethylethyl)-]
Submitted by C. R. H. I. De Jonge1, H. J. Hageman, G. Hoentjen, and W. J. Mijs.
Checked by K. Balasubramanian, Robert K. Boeckman, and Carl R. Johnson.
1. Procedure
A 200-ml., three-necked flask equipped with a mechanical stirrer, a thermometer, and a gas-inlet tube is charged with 41.2 g. (0.200 mole) of 2,6-di-tert-butylphenol (Note 1) in 75 ml. of N,N-dimethylformamide (Note 2) and 2.5 g. (0.0075 mole) of salcomine (Note 3). With stirring, oxygen is introduced at such a rate that the temperature does not exceed 50°. This is continued for 4 hours, and at the end of the reaction the temperature drops to about 25°. The reaction mixture is then poured onto 500 g. of crushed ice and 15 ml. of 4 N hydrochloric acid. A yellow-brown precipitate is formed, collected by suction filtration, and washed on the filter with three 50-ml. portions of 1 N hydrochloric acid, with three 100-ml. portions of water, and twice with 25-ml. portions of cold ethanol. Drying under reduced pressure at 50° for 3 hours gives 43 g. of crude 2,6-di-tert-butyl p-benzoquinone as a dark-yellow crystalline solid. Recrystallization from ethanol gives 36.5 g. (83%) of pure 2,6-di-tert-butyl-p-benzoquinone, m.p. 65–66° (Note 4), (Note 5).
2. Notes
1. 2,6-Di-tert-butylphenol purchased from Aldrich Chemical Company, Inc., was used.
2. When chloroform or methanol is used as the solvent for the oxidation of phenols, other products, originating from coupling of aryloxy radicals, e.g., polyphenylene ethers and/or diphenoquinones, are also formed.2
3. Bis(salicylidene)ethylenediiminocobalt(II) can be prepared according to the procedure described in Inorg. Synth.3
4. 2,6-Di-tert-butyl-p-benzoquinone should be stored in a brown bottle.
5. The product has the following spectral properties; IR (CHCl3) cm.−1: 1652, 1597; 1H NMR (CDCl3), δ 1.33, 6.56.
3. Discussion
Various 2,6-disubstituted p-benzoquinones have been prepared by oxidation of the corresponding 2,6-disubstituted phenols with potassium nitrosodisulfonate4,5 or lead dioxide in formic acid.6 Oxidative coupling of 2,6-disubstituted phenols to poly-2,6-disubstituted phenylene ethers followed by treatment of the polymers in acetic acid with lead dioxide is reported7 to give low yields of the corresponding 2,6-disubstituted p-benzoquinones.
Salcomine is a useful catalyst for the selective oxygenation of 2,6-disubstituted phenols to the corresponding p-benzoquinones when N,N-dimethylformamide is used as the solvent; laborious procedures are avoided and high yields of pure p-benzoquinones are obtained. Following the procedure described above, the authors have prepared 2,6-diphenyl-p-benzoquinone (m.p. 134–135°, yield 86%) and 2,6-dimethoxy-p-benzoquinone (m.p. 252°, yield 91%) from the appropriate phenols.

References and Notes
  1. Organic and Polymer Chemistry Department, Akzo Corporate Research Laboratories, Arnhem, The Netherlands.
  2. H. M. van Dort and H. J. Geursen, Recl. Travl. Chim. Pays-Bas, 86, 520 (1967).
  3. H. Diehl and C. C. Hack, Inorg. Synth., 3, 196 (1950).
  4. H. J. Teuber and W. Rau, Chem. Ber., 86, 1036 (1953).
  5. H. J. Teuber and O. Glosauer, Chem. Ber., 98, 2643 (1965).
  6. C. R. H. I. de Jonge, H. M. van Dort, and L. Vollbracht, Tetrahedron Lett., 1881, (1970).
  7. H. Finkbeiner and A. T. Toothaker, J. Org. Chem., 33, 4347 (1968).

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

BIS(SALICYLIDENE)ETHYLENEDIIMINOCOBALT(II) (SALCOMINE)

salcomine

ethanol (64-17-5)

hydrochloric acid (7647-01-0)

acetic acid (64-19-7)

methanol (67-56-1)

chloroform (67-66-3)

oxygen (7782-44-7)

formic acid (64-18-6)

N,N-dimethylformamide (68-12-2)

Bis(salicylidene)ethylenediiminocobalt(II)

2,5-Cyclohexadiene-1,4-dione, 2,6-bis(1,1-dimethylethyl)-,
2,6-Di-tert-butyl-p-benzoquinone,
2,6-di-tert-butyl p-benzoquinone (719-22-2)

potassium nitrosodisulfonate

2,6-di-tert-butylphenol (128-39-2)

lead dioxide

2,6-diphenyl-p-benzoquinone

2,6-dimethoxy-p-benzoquinone