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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 H2O2a
Run Benzaldehyde Time, h Yield, %c
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 24b 28 51
l 4-chloro 24b   87
m 4-nitro 24b   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