Phenols from Benzaldehydes using Hydrogen Peroxide

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When a solution of 2-methoxybenzaldehyde (a) (5.0 g, 36.7 mmol) and 31% aqueous H₂O₂ (5.3 g, 48 mmol) in methanol (50 mL) was stirred with sulfuric acid (0.5 mL) at room temperature for 24 h, 2-methoxyphenol was produced in a 94% yield. Similarly, a wide variety of other benzaldehydes 1 were oxidized to the corresponding phenols and/or methyl benzoates as cited in Table I.

Table I.
Acid-Catalyzed Oxidation of Benzaldehydes by H₂O₂^a
Run	Benzaldehyde	Time, h	Yield, %^c
Run	Benzaldehyde	Time, h	Phenol	Ester
a	2-methoxy	24	93
b	3-methoxy	68		68
c	4-methoxy	24	90
d	2,3-dimethoxy	63	30	14
e	2,4-dimethoxy	14	90
f	3,4-dimethoxy	5	60
g	2,3,4-trimethoxy	1	97
h	2,4,5-trimethoxy	4	89
i	2,4,6-trimethoxy	2	89
j	3,4-methylenedioxy	24	67	8
k	4-methyl	24^b	28	51
l	4-chloro	24^b		87
m	4-nitro	24^b		80

a Unless otherwise stated, benzaldehyde 1 (5 mmol) and 31% H₂O₂ (6.4 mmol) were stirred in the presence of H₂SO₄ (0.1 mL) in methanol (10 mL) under an argon atmosphere at room temperature.
b The reaction mixture was heated at refluxing temperature.
c All the products were isolated by chromatography (SiO₂).

References

[1] J. Org. Chem. 1984,49, 4740-4741