ASCII by GC_MS
HTML by Rhodium
Sodium percarbonate, a readily available, inexpensive and easy to handle reagent efficiently oxidizes hydroxylated benzaldehydes and hydroxylated acetophenones to hydroxyphenols.
Phenols and their derivatives are fundamentally important substrates used extensively in organic synthesis. In the Dakin reaction, hydroxylated benzaldehydes are converted to hydroxy-phenols through the replacement of formyl groups by a hydroxyl moiety using alkaline hydrogen peroxide1. Other reagents have been employed to oxidize aromatic aldehydes to arylformates; these include peroxyacetic acid2, peroxybenzoic acid3, m-chloroperoxybenzoic acid4 and organoperoxyselenic acid5.
Entry |
Substrate | Time |
Product | Yield |
01 |
Salicylaldehyde | 5 h |
Catechol | 91% |
02 |
4-OH-BA | 8 h |
Hydroquinone | 86% |
03 |
3-OH-BA | 20 h |
||
04 |
o-Vanillin | 1 h |
3-MeO-Catechol | 95% |
05 |
2-OH-4-MeO-BA | 2 h |
4-MeO-Catechol | 83% |
06 |
Vanillin | 4 h |
2-MeO-Hydroquinone | 93% |
07 |
5-Cl-2-OH-BA | 5 h |
4-Cl-Catechol | 92% |
08 |
2-Cl-4-OH-BA | 7 h |
2-Cl-hydroquinone | 62% |
09 |
2-OH-5-Nitro-BA | 7 h |
4-Nitrocatechol | 60% |
10 |
4-OH-3-Nitro-BA | 20 h |
||
11 |
2-OH-Acetophenonea | 8 h |
Catechol | 90% |
12 |
4-OH-Acetophenonea | 20 h |
||
13 |
2-OH-4-MeO- Acetophenonea |
7 h |
4-MeO-Catechol | 78%b |
14 |
Acetosyringonea | 20 h |
||
Notes
a. THF-DMF-H2O (3:1:1) used as solvent for the acetophenons.
b. Based on 80% conversion of the starting material.
c. No reaction.
Sodium percarbonate (Na2CO3·1.5H2O2) is a very inexpensive large scale industrial chemical which is extensively used in the detergent industry as a bleaching agent6. It has been used for the oxidation of sulfides7, amines7,8, organoboranes9 as well as for the epoxidation of olefins7 and hydrolysis of nitriles to amides10. We now wish to report that sodium percarbonate oxidizes hydroxylated benzaldehydes and acetophenones to hydroxy phenols in good yields (Table).
p-Hydroxybenzaldehydes react more slowly than the corresponding o-hydroxy- benzaldehydes. m-Hydroxy- benzaldehyde fails to undergo oxidation. 4-hydroxy- 3-nitrobenzaldehyde also failed to react with Na2CO3·1.5H2O2 which may be due to intramolecular hydrogen bonding. In addition to aromatic aldehydes, we examined the conversion of hydroxylated acetophenones to hydroxyphenols. 2-hydroxy- acetophenones (entries 11 and 13) were oxidized to catechols while 4-hydroxy- acetophenones (entries 12 and 14) failed to undergo oxidation.
A mixture of aromatic aldehyde (3.0 mmol) and sodium percarbonate (3.0 mmol) is dissolved in tetrahydrofuran (10.0 mL) and water (4.0 mL) and sonicated in an ultrasound bath under an argon atmosphere. The reaction is quenched with acetic acid (1.0 mL) and the solvent removed under vacuum. Methanol is added to the residue and the mixture filtered. The filtrate is concentrated under reduced pressure and chromatographed (silica gel; 30% ethyl acetate in hexanes).