p-Quinols and p-Quinol Ethers from 2,4,6-Trialkylphenols

Abstract

The oxidation of 2,4,6-trialkylphenols with lead(IV) oxide and 70% perchloric acid in water-acetone or in alcohols gives p-quinols or p-quinol ethers, respectively. Some nonmetallic oxidants serve the same purpose.

Key words

oxidations - 2,4,6-trialkylphenols - p-quinols - p-quinol ethers - lead(IV) oxide - perchloric acid - nonmetallic oxidants

References

• 2a Yamamura S. In The Chemistry of Phenols   Part 1:  Rappoport Z. Wiley; Chichester: 2003.  p.1153 
• 2b Stavber S. Jereb M. Zupan M. ARKIVOC  2001,  (v):  98 
• 2c Stavber S. Zupan M. Acta Chim. Slov.  2005,  52:  13 
• 2d Sels BF. De Vos DE. Jacobs PA. Angew. Chem. Int. Ed.  2005,  44:  310 
• 2e Quideau S. Pouységu L. Deffieux D. Synlett  2008,  467 
• 3 Oxidation of phenols to p-benzoquinones with PbO₂/70% HClO₄ has been reported. See: Omura K. Synthesis  1998,  1145 
• 4 Oxidation of 1a with PbO₂/70% HClO₄ in MeOH under conditions different from those employed in this study has recently been reported. The mechanism of the formation of 2al was shown. Thus, the phenoxyl radical as a poor base, generated by dehydrogenation of 1a with PbO₂, is protonated by the strong acid giving the phenol cation radical, which can efficiently abstract an electron from more of the phenoxyl radical, thus yielding the phenoxyl cation that adds MeOH. See: Omura K. J. Org. Chem.  2008,  73:  858 
• 5 Becker H.-D. Gustafsson K. J. Org. Chem.  1979,  44:  428 
• 6 Pelter A. Elgendy SMA. J. Chem. Soc., Perkin Trans. 1  1993,  1891 
• 7 McKillop A. Perry DH. Edwards M. J. Org. Chem.  1976,  41:  282 
• 9 Rieker A. Drehher E.-L. Geisel H. Khalifa MH. Synthesis  1978,  851 
• Oxidation of phenols with I₂ and aq H₂O₂ in hydroxylic solvents giving products including p-benzoquinones has been studied. See:
• 12a Cressman HWJ. Thirtle JR. J. Org. Chem.  1966,  31:  1279 
• 12b Minisci F. Citterio A. Vismara E. Fontana F. De Bernardinis S. J. Org. Chem.  1989,  54:  728 
• 12c Omura K. J. Org. Chem.  1996,  61:  2006 
• 14 Ronlán A. Parker VD. J. Chem. Soc. C  1971,  3214 
• 15 Coppinger GM. Campbell TW. J. Am. Chem. Soc.  1953,  75:  734 

1

Current address: 4-5-2, Matsuodai, Inagawa, Hyogo 666-0261, Japan.

8

More recently, an N-F reagent has been shown to slowly oxidize 1 (except 1b) in MeCN-protic solvent (H₂O, MeOH, and primary alcohols) mixtures affording the p-quinols and p-quinol ethers. An attempt to prepare 2an, 2ao, or 2cn by the use of the reagent was not made in this laboratory. See ref. 2b.

10

The mechanism of the NaIO₃/70% HClO₄ oxidation awaits further investigation.

11

The reaction involves a bromination-debromination mechanism. Details will be discussed in a subsequent paper.

13

The reaction would involve an iodination-deiodination mechanism. See ref. 12c.

16

^¹H NMR (90 MHz, CDCl₃): δ = 0.92 (s, 9 H), 1.09 (d, J = 6.2 Hz, 6 H), 1.24 (s, 18 H), 3.40 (sept, J = 6.2 Hz, 1 H), 6.59 (s, 2 H). The ^¹H NMR spectrum of 2cn in CCl₄ has been reported. See ref. 9.

17

For purification and identification of the product, see ref. 4.