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Synlett 2007(3): 0411-0414  
DOI: 10.1055/s-2007-967951
LETTER
© Georg Thieme Verlag Stuttgart · New York

Biomimetic Oxidation of Veratryl Alcohol with H2O2 Catalyzed by Iron(III) Porphyrins and Horseradish Peroxidase in Ionic Liquid [1]

Anil Kumar*a,b, Nidhi Jainb, S. M. S. Chauhan*b
a Chemistry Group, Birla Institute of Technology and Science, Pilani 333031, India
b Bioorganic Laboratory, Department of Chemistry, University of Delhi, Delhi 110007, India
Fax: +91(1596)244183; e-Mail: anilkumar@bits-pilani.ac.in; e-Mail: smschauhan@chemistry.du.ac.in;
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Publication History

Received 10 September 2006
Publication Date:
07 February 2007 (online)

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Abstract

3,4-Dimethoxybenzyl alcohol (veratryl alcohol) is a model compound for lignin substructures and its oxidation with H2O2 catalyzed by iron(III) porphyrins and horseradish peroxidase (HRP) in ionic liquids has been described. Veratraldehyde and 2-hydroxymethyl-5-methoxy-2,5-cyclohexadiene-1,4-dione were the two major products of the oxidation of veratryl alcohol at room ­temperature. The iron(III) porphyrin or HRP immobilized in ionic liquids showed increased catalytic activity and can be recycled and this is believed due to the stabilization of highvalent oxo­iron(IV) π-cation radical intermediate generated in the reaction.

Key words

ionic liquid - veratryl alcohol - oxidation - iron(III) porphyrins - horseradish peroxidase (HRP)

1

Part of the work was presented at: Modern Trends in Inorganic Chemistry-X (MTIC-X), Bombay, India, December, 2003.

1

Part of the work was presented at: Modern Trends in Inorganic Chemistry-X (MTIC-X), Bombay, India, December, 2003.

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Representative Procedure for Oxidation of Veratryl Alcohol ( 1) with H 2 O 2 Catalyzed by Iron(III) Porphyrins in Ionic Liquid: H2O2 (30%; 113 µL, 100 mmol) was added with stirring at r.t to a solution of water-soluble iron(III) porphyrin (1 mmol, 10%) and veratryl alcohol (100 mmol) in the ionic liquid [bmim][PF6] (2.0 mL). The 20-µL aliquots were taken at 30 min interval and analyzed by HPLC analysis at 280 nm. After completion of the reaction the reaction mixture was extracted with Et2O and the ionic liquid containing iron(III) porphyrin was recovered. The Et2O layer was dried over anhyd Na2SO4 and evaporated under reduced pressure. The residue was column chromatographed over silica gel and the products were identified by 1H NMR, IR and MS spectral data.
Representative Procedure for Oxidation of Veratryl Alcohol ( 1) with H 2 O 2 Catalyzed by HRP in Ionic Liquid: Veratryl alcohol (100 mmol) was dissolved in the ionic liquid [bmim][PF6] (2.0 mL) in a 5-mL round-bottomed flask fitted with a magnetic stirrer. HRP [100 µL, 1.0 mg dissolved in 1 mL buffer (pH 4.5)] was added to the reaction mixture and H2O2 (30%; 113 µL, 100 mmol) was added to the reaction mixture with stirring. The stirring was continued at r.t. and 20-µL aliquots were taken at 30 min interval and analyzed by HPLC at 280 nm. After completion of the reaction the reaction mixture was extracted with Et2O and the ionic liquid containing HRP was recovered. The Et2O layer was dried over anhyd Na2SO4 and evaporated under reduced pressure. The residue was column chromatographed over silica gel and the products were identified by 1H NMR, IR and MS spectra.

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Spectroscopic Data3,4-Dimethoxybenzaldehyde (Veratraldehyde; 2): IR (KBr): 2987, 2934, 1729, 1623, 1511, 1256, 1167, 1046, 986, 913, 789, 725 cm-1. 1H NMR (CDCl3): δ = 3.89 (s, 6 H), 6.86 (s, 1 H), 6.98 (d, J = 7.35 Hz, 1 H), 7.03 (d, J = 7.35 Hz, 1 H), 10.67 (s, 1 H). MS (ESI): m/z = 166 [M+], 151, 138, 136, 123, 94, 73.
2-Hydroxymethyl-5-methoxy-2,5-cyclohexadiene-1,4-dione ( 3): IR (KBr): 3310, 2948, 1665, 1644, 1619, 1607, 1226, 1144 cm-1. 1H NMR (CDCl3): δ = 3.85 (s, 3 H), 3.92 (s, 1 H), 4.52 (d, J = 2.3 Hz, 2 H), 6.10 (s, 1 H), 6.78 (t, J = 2.3 Hz, 1 H). MS (ESI): m/z = 168 [M+], 153, 150, 44.