Abstract:The oxidation of alcohols and ethers by O2 with the enzyme laccase, mediated by the stable N‐oxyl radical TEMPO, affords carbonylic products. An ionic mechanism is proposed, where a nucleophilic attack of the oxygen lone‐pair of the alcohol (or ether) onto the oxoammonium form of TEMPO (generated by laccase on oxidation) takes place leading to a transient adduct. Subsequent deprotonation of this adduct α to the C−O bond leads to the carbonylic product. Additional mechanistic considerations for the laccase‐medi… Show more
“…Deprotonation of the adduct gives rise to the aldehyde and to the reduced form of TEMPO. Laccase oxidizes the reduced TEMPO to regenerate TEMPO, and further oxidation leads to the oxoammonium ion 18. This is a corresponding mechanism to those suggested for TEMPO‐mediated oxidation of alcohols with oxidation sources other than laccase 19, 20…”
Section: Introductionmentioning
confidence: 62%
“…We first describe the analysis of pure TEMPO and its redox forms in the laccase–TEMPO system. The measurements were made to determine if our system provides results comparable to those obtained earlier by theoretical and indirect methods 17, 18. We also wished to clarify the reaction mechanism, i.e.…”
Substituted benzyl alcohol was oxidized enzymatically with a laccase-mediator system and the products were investigated as a function of time by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (nanoESI-FTICRMS). With Trametes versicolor laccase (TVL), the mediator, 2,2',6,6'-tetramethylpiperidine-N-oxyl radical (TEMPO), undergoes oxidation and forms oxoammonium ion. Oxidized TEMPO oxidizes the alcohol and is simultaneously reduced to the N-OH form. The laccase then restores TEMPO back to the normal radical form and the oxidation cycle starts again. The role of TEMPO and the structures of its oxidized and reduced forms in the enzymatic oxidation process were clarified in collision-induced dissociation experiments and gas-phase hydrogen/deuterium (H/D) exchange reactions. The amounts of enzyme and mediator were significant for product formation: with greater amounts overoxidation products, the corresponding benzoic acid and benzonitrile were formed. Smaller amounts of laccase and mediator generated benzaldehyde in high yield. The reaction pathway for benzonitrile formation is discussed and it is suggested to start from benzaldehyde and the ammonia in the ammonium acetate buffer.
“…Deprotonation of the adduct gives rise to the aldehyde and to the reduced form of TEMPO. Laccase oxidizes the reduced TEMPO to regenerate TEMPO, and further oxidation leads to the oxoammonium ion 18. This is a corresponding mechanism to those suggested for TEMPO‐mediated oxidation of alcohols with oxidation sources other than laccase 19, 20…”
Section: Introductionmentioning
confidence: 62%
“…We first describe the analysis of pure TEMPO and its redox forms in the laccase–TEMPO system. The measurements were made to determine if our system provides results comparable to those obtained earlier by theoretical and indirect methods 17, 18. We also wished to clarify the reaction mechanism, i.e.…”
Substituted benzyl alcohol was oxidized enzymatically with a laccase-mediator system and the products were investigated as a function of time by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (nanoESI-FTICRMS). With Trametes versicolor laccase (TVL), the mediator, 2,2',6,6'-tetramethylpiperidine-N-oxyl radical (TEMPO), undergoes oxidation and forms oxoammonium ion. Oxidized TEMPO oxidizes the alcohol and is simultaneously reduced to the N-OH form. The laccase then restores TEMPO back to the normal radical form and the oxidation cycle starts again. The role of TEMPO and the structures of its oxidized and reduced forms in the enzymatic oxidation process were clarified in collision-induced dissociation experiments and gas-phase hydrogen/deuterium (H/D) exchange reactions. The amounts of enzyme and mediator were significant for product formation: with greater amounts overoxidation products, the corresponding benzoic acid and benzonitrile were formed. Smaller amounts of laccase and mediator generated benzaldehyde in high yield. The reaction pathway for benzonitrile formation is discussed and it is suggested to start from benzaldehyde and the ammonia in the ammonium acetate buffer.
“…69 Under certain conditions, benzylic alcohols can be oxidized with high selectivity (albeit in low yield) in the presence of primary alcohols, as the example shown in Scheme 12.5 demonstrates. 70 …”
Section: Chemoselectivity: Oxidation Of Primary Vs Benzylic Alcoholsmentioning
confidence: 99%
“…192 Ether carbons are also generally stable, but again, exceptions were reported for select benzyl ethers. 70,193,194 …”
“…In terms of removing color from dyes pulps, redox potentials are important and the choice of mediator influences the extent of color removal [27]. TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) was selected as laccase mediator for this study of recycled blue dyed pulp, based on a previous report of laccase-TEMPO treatment increasing carbonyl products [28]. This mediator has been shown to be an oxidative agent for selective oxidation of 6-hydroxy groups of cellulose [29].…”
Recycled blue colored paper was treated with laccase under various combinations of physical and chemical parameters including enzyme concentration, temperature, oxygen, and reaction time. Laccase treatment of recycled dyed pulp increased acid group content, tear index, tensile index, and color removal in a dose-dependent manner. Lengthening the treatment time from 2 to 4 h was beneficial to acid group content (12% increase), dye removal, and tensile index but had a detrimental 8% decrease on the tear index. A higher reaction temperature (65 vs. 45 degrees C) had a beneficial effect on acid group content (+31%), and tensile index (+26%) and a slightly negative effect on tear index (-5%), but significantly reduced the ability of laccase to remove color. Comparison of reactions subjected to different levels of oxygen supplementation showed the greatest beneficial effect for laccase treatment with slow oxygen bubbling. The experimental results indicate that laccase treatment increases fiber carboxylic acid content and tensile strength, in addition to reducing the color of the enzyme treated paper.
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