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Org. Synth. 1971, 51, 82
DOI: 10.15227/orgsyn.051.0082
DEHYDROXYLATION OF PHENOLS; HYDROGENOLYSIS OF PHENOLIC ETHERS: BIPHENYL
Submitted by Walter J. Musliner and John W. Gates Jr1.
Checked by D. Robert Coulson and Richard E. Benson.
1. Procedure
Caution! Benzene has been identified as a carcinogen; OSHA has issued emergency standards on its use. All procedures involving benzene should be carried out in a well-ventilated hood, and glove protection is required.
A. 4-(1-Phenyl-5-tetrazolyloxy)biphenyl. A 1-l., round-bottomed flask fitted with an efficient condenser and a magnetic stirring bar is charged with 17 g. (0.10 mole) of 4-phenylphenol, 18.1 g. (0.100 mole) of 1-phenyl-5-chlorotetrazole (Note 1), 27.6 g. (0.200 mole) of anhydrous potassium carbonate, and 250 ml. of acetone. The mixture is stirred and heated under reflux for 18 hours (Note 2). Water (250 ml.) is added to the hot mixture producing a clear solution that is chilled in ice. After 1 hour, the solid is collected by filtration and dried in air, giving 32–33 g. of the crude product, m.p. 151–153°, which is then dissolved in 250 ml. of hot ethyl acetate. The solution is filtered while hot to remove a small amount of insoluble material and cooled on ice, yielding 25 g. of 4-(1-phenyl-5-tetrazolyloxy)biphenyl, as white crystals, m.p. 150–153°. An additional 2–3 g. of product is recovered from the filtrate by concentration to 125 ml. bringing the total yield to 27–28 g. (86–89%).
B. Biphenyl. Added to a solution of 10 g. (0.032 mole) of the product from Part A in 200 ml. of benzene is 2 g. of 5% palladium-on-charcoal, and the mixture is shaken with hydrogen in a Parr apparatus at 40 p.s.i. and 35–40° for 8 hours (Note 3). The mixture is filtered, and the insoluble residue is washed with three 100-ml. portions of hot ethanol (Note 4). The filtrates are combined, and the solvent is removed with a rotary evaporator at 60° (12 mm.), leaving a solid residue, which is dissolved in 100 ml. of benzene. After adding 100 ml. of 10% aqueous sodium hydroxide the mixture is shaken, and the layers separated. The aqueous layer is extracted with 100 ml. of benzene, and the original benzene layer is washed with 100 ml. of water (Note 5). The benzene solutions are combined and dried over magnesium sulfate. Removal of the benzene by distillation yields 4.0–4.7 g. (82–96%) of biphenyl as a white powder, m.p. 68–70° (Note 6). The IR spectrum is identical with that of an authentic sample, and a purity of at least 99.5% was indicated by GC analysis.
2. Notes
1. 4-Phenylphenol and 1-phenyl-5-chlorotetrazole were obtained from Eastman Organic Chemicals.
2. A reflux period of 18 hours was chosen because it represents an overnight reaction time; the reaction is essentially completed in 8 to 10 hours.
3. The hydrogenolysis can also be carried out in ethanol or tetrahydrofuran. An amount of catalyst equivalent to 10–20% by weight of tetrazolyl ethers is most satisfactory for this reaction. Platinum oxide also catalyzes this hydrogenolysis.
4. A large portion of 1-phenyl-5-tetrazolone (and a small amount of biphenyl) remains mixed with and adsorbed to the catalyst and is removed by the ethanol treatment.
5. 1-Phenyl-5-tetrazolone can be recovered from the combined aqueous solutions by acidification with dilute hydrochloric acid. The yield is 4.2–4.7 g. (82–92%), m.p. 190–191°.
6. Benzoxazolyl ethers can also be used in this reaction sequence but an amount of catalyst equivalent to 20–40% by weight of ether is necessary in the hydrogenolysis step. 2-Chlorobenzoxazole is available from Eastman Organic Chemicals.
3. Discussion
The preparation is essentially that described by the submitters2 and is cited as an example of this general procedure for replacement of phenolic hydroxyl groups by hydrogen.
The reaction sequence, which involves the conversion of the phenolic hydroxyl groups to a phenyltetrazolyl ether (see (Note 6)) followed by reduction to effect removal of the phenolic hydroxyl group, illustrates a mild, efficient, general, and convenient procedure. It has been applied successfully by the submitters2 to a variety of substituted phenols, as shown in Table I.
TABLE I
HYDROGENOLYSIS OF PHENOLIC ETHERS

Substituted Phenol

Yield of Tetrazolyl Ether, %

Hydrogenolysis Time, hours

Hydrogenolysis

Product

Yield, %


Guaiacol

94

15

Anisole

86a

3-Methoxyphenol

95

16

Anisole

85a

4-Methoxyphenol

97

6

Anisole

83a

2-Phenylphenol

98

8

Biphenyl

82

4-Aminophenol

86

9

Aniline

46b

4-Carbethoxyphenol

91

16

Ethyl benzoate

89a

Thymol

93

15

p-Cymene

72a

1-Naphthol

88

7

Naphthalene

50

2-Naphthol

94

17

Naphthalene

65

4-Chlorophenol

92

18

Benzenec

70a


aFiltered solution analyzed directly by gas chromatography with toluene as internal standard.

bIsolated as the hydrochloride salt.

cFrom hydrogenolysis of carbon-chlorine bond.

Phenols having a variety of substituents including alkyl, alkoxyl, aryl, amino, and carbalkoxyl have been successfully converted to the desired product in good yield. The only limitation yet found is in the hydrogenolysis of the halogen–carbon bond. Thus 4-chlorophenol was converted to benzene using this procedure.
Other procedures include zinc-dust distillation, not generally useful except for exhaustive degradation of phenols to hydrocarbons, and various sodium and liquid ammonia cleavages of phenol ethers.3,4,5,6,7 These latter reactions lack generality and are often unpredictable. They require conditions too harsh for certain aromatic substituents, and the yields are frequently low.

References and Notes
  1. Research Laboratories, Eastman Kodak Company, Rochester, New York 14650.
  2. W. J. Musliner and J. W. Gates, Jr., J. Am. Chem. Soc., 88, 4271 (1966).
  3. W. H. Pirkle and J. L. Zabriskie, J. Org. Chem., 29, 3124 (1964) and references cited therein.
  4. Y. K. Sawa, N. Tsuji, and S. Maeda, Tetrahedron, 15, 144, 154 (1961); Y. K. Sawa, N. Tsuji, K. Okabe, and T. Miyamoto, Tetrahedron, 21, 1121 (1965); Y. K. Sawa and J. Irisawa, Tetrahedron, 21, 1129 (1965); Y. K. Sawa, M. Horiuchi, and K. Tanaka, Tetrahedron, 21, 1133 (1965).
  5. P. A. Sartoretto and F. J. Sowa, J. Am. Chem. Soc., 59, 603 (1937); A. L. Kranzfelder, J. J. Verbanc, and F. J. Sowa, J. Am. Chem. Soc., 59, 1488 (1937); F. C. Weber and F. J. Sowa, J. Am. Chem. Soc., 60, 94 (1938).
  6. M. Tomita, H. Furukawa, S.-T. Lu, and S. M. Kupchan, Tetrahedron Lett., 4309 (1965).
  7. E. J. Strojny, J. Org. Chem., 31, 1662 (1966).

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

palladium-on-charcoal

efficient condenser

ethanol (64-17-5)

potassium carbonate (584-08-7)

hydrochloric acid (7647-01-0)

ammonia (7664-41-7)

Benzene (71-43-2)

ethyl acetate (141-78-6)

ether (60-29-7)

aniline (62-53-3)

hydrogen (1333-74-0)

sodium hydroxide (1310-73-2)

phenol (108-95-2)

1-Naphthol (90-15-3)

2-naphthol (135-19-3)

platinum oxide

Anisole (100-66-3)

acetone (67-64-1)

toluene (108-88-3)

sodium (13966-32-0)

Biphenyl (92-52-4)

Naphthalene (91-20-3)

Guaiacol (90-05-1)

ethyl benzoate (93-89-0)

thymol (89-83-8)

p-cymene (99-87-6)

magnesium sulfate (7487-88-9)

Tetrahydrofuran (109-99-9)

4-Carbethoxyphenol (120-47-8)

4-Methoxyphenol (150-76-5)

4-phenylphenol (92-69-3)

1-phenyl-5-chlorotetrazole (14210-25-4)

4-(1-Phenyl-5-tetrazolyloxy)biphenyl (17743-27-0)

1-phenyl-5-tetrazolone

2-Chlorobenzoxazole (615-18-9)

phenyltetrazolyl ether

Tetrazolyl Ether

3-Methoxyphenol (150-19-6)

2-Phenylphenol (90-43-7)

4-Aminophenol (123-30-8)

4-Chlorophenol (106-48-9)