Sodium percarbonate and the Dakin reaction

GC_MS
(format & minor edits by metanoid)
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This bee found a rather interesting reference today when reading a new chem book on reaction mechanisms. It involves the so-called Dakin reaction. http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR91.htm

Tetrahedron Letters 33(7) (1992) 865-866
Title: Sodium Percarbonate: A Convenient Reagent for the Dakin Reaction
Authors: G W Kabalka (*), N K Reddy, C Narayana Departments of Chemistry and Radiology, The University of Tennesse,
Knoxville, TN 37996-1600.

Abstract: 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 peroxide (1). Other reagents have been employed to oxidize aromatic aldehydes to arylformates; these include peroxyacetic acid (2), peroxybenzoic acid (3), m-chloroperoxybenzoic acid (4) and organoperoxyselenic acid (5).

Sodium percarbonate (Na2CO3.1,5H2O2) is a very inexpensive large scale industrial chemical which is extensively used in the detergent industry as a bleaching agent (6). It has been used for the oxidation of sulfides (7), amines (7,8), organoboranes (9) as well as for the epoxidation of olefins (7) and hydrolysis of nitriles to amides (10). We now wish to report that sodium percarbonate oxidizes hydroxylated benzaldehydes and acetophenones to hydroxy phenols in good yields (Table).

In a typical procedure, 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). Para-hydroxybenzaldehydes react more slowly than the corresponding ortho-hydroxybenzaldehydes. Meta-hydroxybenzaldehyde 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-hydroxyacetophenones (entries 11 and 13) were oxidized to catechols while 4-hydroxyacetophenones (entries 12 and 14) failed to undergo oxidation.

Table. Oxidation of hydroxylated benzaldehydes and acetophenones to hydroxyphenols
Entry Substrate Time (h) Product Yield (%)
01 salicylaldehyde 5 catechol 91
02 4-hydroxybenzaldehyde 8 hydroquinone 86
03 3-hydroxybenzaldehyde 20 ----------------- --
04 o-vanillin 1 3-methoxycatechol 95
05 2-hydroxy-4-methoxybenzaldehyde 2 4-methoxycatechol 83
06 vanillin 4 2-methoxyhydroquinone 93
07 5-chloro-2-hydroxybenzaldehyde 5 4-chlorocatechol 92
08 2-chloro-4-hydroxybenzaldehyde 7 2-chlorohydroquinone 62
09 2-hydroxy-5-nitrobenzaldehyde 7 4-nitrocatechol 60
10 4-hydroxy-3-nitrobenzaldehyde 20 ----------------- --
11 2-hydroxyacetophenone (#) 8 catechol 90
12 4-hydroxyacetophenone 20 ----------------- --
13 2-hydroxy-4-methoxyacetophenone 7 4-methoxycatechol 78 (*)
14 3,5-dimethoxy-4-hydroxyacetophenone 20 ----------------- --
# A mixture of THF-DMF-H2O (3:1:1) was used as a solvent for acetophenone reactions.
* Based on 80% conversion of the starting material.
Acknowledgement: We thank the Department of Energy for support of this research.
Dedication: Dedicated to Professor Herbert C. Brown on the occasion of his 80th library.
References:
  1. Hassal CH. "Org Reaction"; Wiley, New York, 1957, vol 9, pp 73-106.
  2. Boeseken J, Cohen WD, Kip CJ; Rec Trav Chim Pays-Bas 55 (1936) 815.
  3. Ogata Y, Sawaki Y; J Org Chem 34 (1969) 3985.
  4. Camps F, Coll J, Messeguer A, Pericas MA; Tetrahedron Lett 22 (1981) 3895.
  5. Syper L; Synthesis (1989) 167.
  6. Das TK; Mandavawalla AK, Dalta SK; Colourage 301 (1983) 25.
  7. Ando T, Conk DG, Kimura T; Chem Lett (1986) 665.
  8. Zajac WW, Walters TR, Woods JM; Synthesis (1988) 808.
  9. Kabalka GW, Wadgaonkar PP, Shoup TM; Organometallics 9 (1990) 1316.
  10. Kabalka GW, Deshpande SM, Wadganonkar PP, Chatla N; Syn Commun 20 (1990) 1445.

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Didn't find it in TFSE. Since the applied substances (sodium percarbonate) are not only extremely OTC but also relatively cheap, and since yields don't look that bad, SWiM thought by himself... "hell, let's share that one" ;). Hint: think further, think methylating... This procudure might be an alternative to *some* Baeyer-Villiger oxidations.

Ave Hive, synthetisandi te salutant!