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Akira Isogai - One of the best experts on this subject based on the ideXlab platform.
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TEMPO-Mediated Oxidation of Celluloses
2020Co-Authors: Akira Isogai, Yumiko Kato, Tsuguyuki Saito, Izumi Shibata, Masahiro Yanagisawa, Kengo Magara, Naoto HabuAbstract:TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical)-Mediated Oxidations of cellulose, chitin and other polysaccharides, which were carried out in our laboratory in terms of reaction conditions, structural analyses and biodegradability of the obtained products, their chemical and physical properties etc., were reviewed in this paper. When regenerated cellulose, alpha- and beta-chitins and starch were used as the starting materials in the TEMPO-Mediated Oxidation, the corresponding water-soluble polyuronic acid sodium salts having mostly homogeneous chemical structures were obtained quantitatively. All the new water-soluble polyuronic acids prepared had biodegradability, although they were artificially prepared by the TEMPO-Mediated Oxidation of the polysaccharides and have not been isolated so far as natural compounds. This result indicates that there are two biodegradation pathways of the polysaccharides in nature; one is the well-known hydrolysis route by enzymes, and the other is Oxidation at the C6 primary hydroxyl groups in the initial stage followed by hydrolysis or beta-elimination of the formed uronic acid residues by enzymes. On the other hand, when native celluloses were used as the starting materials in the TEMPO-Mediated Oxidation, significant amounts of both carboxylate and aldehyde groups were introduced into crystal surfaces and disordered regions of the celluloses, maintaining their crystal sizes and crystallinities. Thus, TEMPO-Mediated Oxidation of polysaccharides under aqueous conditions provides interesting fundamental and applied research subjects.
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changes in the degree of polymerization of wood celluloses during dilute acid hydrolysis and tempo Mediated Oxidation formation mechanism of disordered regions along each cellulose microfibril
International Journal of Biological Macromolecules, 2017Co-Authors: Ryunosuke Funahashi, Tsuguyuki Saito, Reina Tanaka, Morihiko Yokoi, Kunihiko Daido, Toru Inamochi, Yoshiki Horikawa, Akira IsogaiAbstract:Abstract Most commercially available plant celluloses, such as kraft pulps and cotton celluloses, have so-called leveling-off degrees of polymerization (LODPs) when subjected to dilute acid hydrolysis. The formation of LODPs is hypothesized to be caused by disordered regions that are present periodically along each cellulose microfibril in plant celluloses. Here, we prepared never-dried wood cellulose, and wood celluloses at different drying stages, and subjected them to dilute acid hydrolysis. The viscosity average degrees of polymerization (DPv) of the wood celluloses decreased in DPv with increasing dilute acid-hydrolysis times. However, the DPv values after 4 h of acid hydrolysis differed from those of softwood bleached kraft pulp (SBKP), which showed typical patterns of LODPs. Thus, the disordered regions corresponding to LODPs that were observed for SBKP are probably not synthesized in the native wood. Instead, such disordered regions are formed secondarily or artificially during the isolation/purification and/or drying processes of plant cellulose fibers. The results of the dilute acid hydrolysis and the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-Mediated Oxidation of SBKP and softwood unbleached soda-anthraquinone pulp showed that the structures of disordered regions can be controlled via the preparation and drying conditions of wood cellulose used as starting materials.
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TEMPO-Mediated Oxidation of Hemp Bast Holocellulose to Prepare Cellulose Nanofibrils Dispersed in Water
Journal of Polymers and the Environment, 2013Co-Authors: Buapan Puangsin, Ryota Kuramae, Tsuguyuki Saito, Shuji Fujisawa, Akira IsogaiAbstract:Hemp bast holocellulose fiber (Cannabis sativa L. Subsp. Sativa) was oxidized by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-Mediated Oxidation at various NaClO addition levels in water at pH 10. When carboxylate contents of the oxidized products were 1. 5-1. 7 mmol/g, TEMPO-oxidized cellulose nanofibrils almost completely dispersed at the individual nanofibril were obtained by mechanical disintegration of the TEMPO-oxidized hemp bast holocelluloses in water, where the nanofibrillation yields were 98-100 %. The sugar composition analysis revealed that most of hemicelluloses originally present in the hemp bast holocellulose were degraded and removed from the solid oxidized products, providing almost pure TEMPO-oxidized celluloses. X-ray diffraction patterns of all TEMPO-oxidized hemp bast holocelluloses had the same cellulose I crystal structure and similar crystallinity indices and crystal widths, indicating that carboxylate groups formed by the Oxidation were selectively present on the crystalline cellulose microfibril surfaces in the holocellulose. However, the weight recovery ratios and viscosity-average degrees of polymerization of the TEMPO-oxidized hemp bast holocelluloses decreased to 69-59 % and 470-380, respectively, when their carboxylate contents increased to 1. 5-1. 7 mmol/g by the TEMPO-Mediated Oxidation. Atomic force microscopy height images showed that the nanofibril widths were 2. 7-2. 9 nm, and the average nanofibril lengths decreased from 590 to 400 nm as the NaClO addition level was increased from 7. 5 to 12. 5 mmol/g in the TEMPO-Mediated Oxidation. © 2012 Springer Science+Business Media New York.
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TEMPO-Mediated Oxidation of Hemp Bast Holocellulose to Prepare Cellulose Nanofibrils Dispersed in Water
Journal of Polymers and The Environment, 2012Co-Authors: Buapan Puangsin, Ryota Kuramae, Tsuguyuki Saito, Shuji Fujisawa, Akira IsogaiAbstract:Hemp bast holocellulose fiber (Cannabis sativa L. Subsp. Sativa) was oxidized by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-Mediated Oxidation at various NaClO addition levels in water at pH 10. When carboxylate contents of the oxidized products were 1.5–1.7 mmol/g, TEMPO-oxidized cellulose nanofibrils almost completely dispersed at the individual nanofibril were obtained by mechanical disintegration of the TEMPO-oxidized hemp bast holocelluloses in water, where the nanofibrillation yields were 98–100 %. The sugar composition analysis revealed that most of hemicelluloses originally present in the hemp bast holocellulose were degraded and removed from the solid oxidized products, providing almost pure TEMPO-oxidized celluloses. X-ray diffraction patterns of all TEMPO-oxidized hemp bast holocelluloses had the same cellulose I crystal structure and similar crystallinity indices and crystal widths, indicating that carboxylate groups formed by the Oxidation were selectively present on the crystalline cellulose microfibril surfaces in the holocellulose. However, the weight recovery ratios and viscosity-average degrees of polymerization of the TEMPO-oxidized hemp bast holocelluloses decreased to 69–59 % and 470–380, respectively, when their carboxylate contents increased to 1.5–1.7 mmol/g by the TEMPO-Mediated Oxidation. Atomic force microscopy height images showed that the nanofibril widths were 2.7–2.9 nm, and the average nanofibril lengths decreased from 590 to 400 nm as the NaClO addition level was increased from 7.5 to 12.5 mmol/g in the TEMPO-Mediated Oxidation.
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TEMPO-oxidized cellulose nanofibers
Nanoscale, 2011Co-Authors: Akira Isogai, Tsuguyuki Saito, Hayaka FukuzumiAbstract:Native wood celluloses can be converted to individual nanofibers 3-4 nm wide that are at least several microns in length, i.e. with aspect ratios>100, by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-Mediated Oxidation and successive mild disintegration in water. Preparation methods and fundamental characteristics of TEMPO-oxidized cellulose nanofibers (TOCN) are reviewed in this paper. Significant amounts of C6 carboxylate groups are selectively formed on each cellulose microfibril surface by TEMPO-Mediated Oxidation without any changes to the original crystallinity (∼74%) or crystal width of wood celluloses. Electrostatic repulsion and/or osmotic effects working between anionically-charged cellulose microfibrils, the ζ-potentials of which are approximately -75 mV in water, cause the formation of completely individualized TOCN dispersed in water by gentle mechanical disintegration treatment of TEMPO-oxidized wood cellulose fibers. Self-standing TOCN films are transparent and flexible, with high tensile strengths of 200-300 MPa and elastic moduli of 6-7 GPa. Moreover, TOCN-coated poly(lactic acid) films have extremely low oxygen permeability. The new cellulose-based nanofibers formed by size reduction process of native cellulose fibers by TEMPO-Mediated Oxidation have potential application as environmentally friendly and new bio-based nanomaterials in high-tech fields.
Tsuguyuki Saito - One of the best experts on this subject based on the ideXlab platform.
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TEMPO-Mediated Oxidation of Celluloses
2020Co-Authors: Akira Isogai, Yumiko Kato, Tsuguyuki Saito, Izumi Shibata, Masahiro Yanagisawa, Kengo Magara, Naoto HabuAbstract:TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical)-Mediated Oxidations of cellulose, chitin and other polysaccharides, which were carried out in our laboratory in terms of reaction conditions, structural analyses and biodegradability of the obtained products, their chemical and physical properties etc., were reviewed in this paper. When regenerated cellulose, alpha- and beta-chitins and starch were used as the starting materials in the TEMPO-Mediated Oxidation, the corresponding water-soluble polyuronic acid sodium salts having mostly homogeneous chemical structures were obtained quantitatively. All the new water-soluble polyuronic acids prepared had biodegradability, although they were artificially prepared by the TEMPO-Mediated Oxidation of the polysaccharides and have not been isolated so far as natural compounds. This result indicates that there are two biodegradation pathways of the polysaccharides in nature; one is the well-known hydrolysis route by enzymes, and the other is Oxidation at the C6 primary hydroxyl groups in the initial stage followed by hydrolysis or beta-elimination of the formed uronic acid residues by enzymes. On the other hand, when native celluloses were used as the starting materials in the TEMPO-Mediated Oxidation, significant amounts of both carboxylate and aldehyde groups were introduced into crystal surfaces and disordered regions of the celluloses, maintaining their crystal sizes and crystallinities. Thus, TEMPO-Mediated Oxidation of polysaccharides under aqueous conditions provides interesting fundamental and applied research subjects.
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changes in the degree of polymerization of wood celluloses during dilute acid hydrolysis and tempo Mediated Oxidation formation mechanism of disordered regions along each cellulose microfibril
International Journal of Biological Macromolecules, 2017Co-Authors: Ryunosuke Funahashi, Tsuguyuki Saito, Reina Tanaka, Morihiko Yokoi, Kunihiko Daido, Toru Inamochi, Yoshiki Horikawa, Akira IsogaiAbstract:Abstract Most commercially available plant celluloses, such as kraft pulps and cotton celluloses, have so-called leveling-off degrees of polymerization (LODPs) when subjected to dilute acid hydrolysis. The formation of LODPs is hypothesized to be caused by disordered regions that are present periodically along each cellulose microfibril in plant celluloses. Here, we prepared never-dried wood cellulose, and wood celluloses at different drying stages, and subjected them to dilute acid hydrolysis. The viscosity average degrees of polymerization (DPv) of the wood celluloses decreased in DPv with increasing dilute acid-hydrolysis times. However, the DPv values after 4 h of acid hydrolysis differed from those of softwood bleached kraft pulp (SBKP), which showed typical patterns of LODPs. Thus, the disordered regions corresponding to LODPs that were observed for SBKP are probably not synthesized in the native wood. Instead, such disordered regions are formed secondarily or artificially during the isolation/purification and/or drying processes of plant cellulose fibers. The results of the dilute acid hydrolysis and the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-Mediated Oxidation of SBKP and softwood unbleached soda-anthraquinone pulp showed that the structures of disordered regions can be controlled via the preparation and drying conditions of wood cellulose used as starting materials.
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TEMPO-Mediated Oxidation of Hemp Bast Holocellulose to Prepare Cellulose Nanofibrils Dispersed in Water
Journal of Polymers and the Environment, 2013Co-Authors: Buapan Puangsin, Ryota Kuramae, Tsuguyuki Saito, Shuji Fujisawa, Akira IsogaiAbstract:Hemp bast holocellulose fiber (Cannabis sativa L. Subsp. Sativa) was oxidized by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-Mediated Oxidation at various NaClO addition levels in water at pH 10. When carboxylate contents of the oxidized products were 1. 5-1. 7 mmol/g, TEMPO-oxidized cellulose nanofibrils almost completely dispersed at the individual nanofibril were obtained by mechanical disintegration of the TEMPO-oxidized hemp bast holocelluloses in water, where the nanofibrillation yields were 98-100 %. The sugar composition analysis revealed that most of hemicelluloses originally present in the hemp bast holocellulose were degraded and removed from the solid oxidized products, providing almost pure TEMPO-oxidized celluloses. X-ray diffraction patterns of all TEMPO-oxidized hemp bast holocelluloses had the same cellulose I crystal structure and similar crystallinity indices and crystal widths, indicating that carboxylate groups formed by the Oxidation were selectively present on the crystalline cellulose microfibril surfaces in the holocellulose. However, the weight recovery ratios and viscosity-average degrees of polymerization of the TEMPO-oxidized hemp bast holocelluloses decreased to 69-59 % and 470-380, respectively, when their carboxylate contents increased to 1. 5-1. 7 mmol/g by the TEMPO-Mediated Oxidation. Atomic force microscopy height images showed that the nanofibril widths were 2. 7-2. 9 nm, and the average nanofibril lengths decreased from 590 to 400 nm as the NaClO addition level was increased from 7. 5 to 12. 5 mmol/g in the TEMPO-Mediated Oxidation. © 2012 Springer Science+Business Media New York.
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TEMPO-Mediated Oxidation of Hemp Bast Holocellulose to Prepare Cellulose Nanofibrils Dispersed in Water
Journal of Polymers and The Environment, 2012Co-Authors: Buapan Puangsin, Ryota Kuramae, Tsuguyuki Saito, Shuji Fujisawa, Akira IsogaiAbstract:Hemp bast holocellulose fiber (Cannabis sativa L. Subsp. Sativa) was oxidized by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-Mediated Oxidation at various NaClO addition levels in water at pH 10. When carboxylate contents of the oxidized products were 1.5–1.7 mmol/g, TEMPO-oxidized cellulose nanofibrils almost completely dispersed at the individual nanofibril were obtained by mechanical disintegration of the TEMPO-oxidized hemp bast holocelluloses in water, where the nanofibrillation yields were 98–100 %. The sugar composition analysis revealed that most of hemicelluloses originally present in the hemp bast holocellulose were degraded and removed from the solid oxidized products, providing almost pure TEMPO-oxidized celluloses. X-ray diffraction patterns of all TEMPO-oxidized hemp bast holocelluloses had the same cellulose I crystal structure and similar crystallinity indices and crystal widths, indicating that carboxylate groups formed by the Oxidation were selectively present on the crystalline cellulose microfibril surfaces in the holocellulose. However, the weight recovery ratios and viscosity-average degrees of polymerization of the TEMPO-oxidized hemp bast holocelluloses decreased to 69–59 % and 470–380, respectively, when their carboxylate contents increased to 1.5–1.7 mmol/g by the TEMPO-Mediated Oxidation. Atomic force microscopy height images showed that the nanofibril widths were 2.7–2.9 nm, and the average nanofibril lengths decreased from 590 to 400 nm as the NaClO addition level was increased from 7.5 to 12.5 mmol/g in the TEMPO-Mediated Oxidation.
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TEMPO-oxidized cellulose nanofibers
Nanoscale, 2011Co-Authors: Akira Isogai, Tsuguyuki Saito, Hayaka FukuzumiAbstract:Native wood celluloses can be converted to individual nanofibers 3-4 nm wide that are at least several microns in length, i.e. with aspect ratios>100, by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-Mediated Oxidation and successive mild disintegration in water. Preparation methods and fundamental characteristics of TEMPO-oxidized cellulose nanofibers (TOCN) are reviewed in this paper. Significant amounts of C6 carboxylate groups are selectively formed on each cellulose microfibril surface by TEMPO-Mediated Oxidation without any changes to the original crystallinity (∼74%) or crystal width of wood celluloses. Electrostatic repulsion and/or osmotic effects working between anionically-charged cellulose microfibrils, the ζ-potentials of which are approximately -75 mV in water, cause the formation of completely individualized TOCN dispersed in water by gentle mechanical disintegration treatment of TEMPO-oxidized wood cellulose fibers. Self-standing TOCN films are transparent and flexible, with high tensile strengths of 200-300 MPa and elastic moduli of 6-7 GPa. Moreover, TOCN-coated poly(lactic acid) films have extremely low oxygen permeability. The new cellulose-based nanofibers formed by size reduction process of native cellulose fibers by TEMPO-Mediated Oxidation have potential application as environmentally friendly and new bio-based nanomaterials in high-tech fields.
Michel R Vignon - One of the best experts on this subject based on the ideXlab platform.
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topochemistry of carboxylated cellulose nanocrystals resulting from tempo Mediated Oxidation
Macromolecules, 2005Co-Authors: Suzelei Montanari, Mohamad Roumani, Laurent Heux, Michel R VignonAbstract:Surface carboxylated cellulose nanocrystals with different sizes and degrees of Oxidation were prepared by TEMPO-Mediated Oxidation of cotton linters and microfibrils of parenchyma cell cellulose (PCC). The size of the oxidized crystals depended on (i) the starting material, (ii) an eventual acid prehydrolysis, and (iii) the Oxidation conditions. The oxidized cellulose nanocrystals were characterized by transmission electron microscopy, conductometric titration, and solid-state NMR spectroscopy. During TEMPO Oxidation, the main reaction corresponded to a selective Oxidation of surface primary hydroxyl groups into carboxylic groups. At the same time, a decrease of the crystal size occurred, resulting from some degradation in the amorphous areas of the starting material. The introduction of negative charges at the interface of the crystalline domains induced a better individualization of the crystallites. The degrees of Oxidation (DO) determined by conductometric titration were in agreement with those deduc...
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tempo Mediated Oxidation of cellulose iii
Biomacromolecules, 2003Co-Authors: Denilson Da Silva Perez, Suzelei Montanari, Michel R VignonAbstract:Various cellulose samples converted into cellulose III by two different ammonia treatments, either liquid or gaseous, were reacted with catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite, and sodium bromide in water. A substantial increase in the reactivity of cellulose III samples was observed in comparison to those in cellulose I, and a relationship between Oxidation conditions and cellulose primary hydroxyl groups accessibility was directly established. For the characterization, we have used several methods, mainly 13 C NMR, methylene blue adsorption, FTIR, and conductometric titration. In all samples, the primary alcohol groups were selectively oxidized into carboxyl groups, provided the sodium hypochlorite is added dropwise and the reaction is performed at constant pH 10.
Jozsef Balla - One of the best experts on this subject based on the ideXlab platform.
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Supression of hemin-Mediated Oxidation of low-density lipoprotein and subsequent endothelial reactions by hydrogen sulfide (H2S)
Free Radical Biology and Medicine, 2009Co-Authors: Viktoria Jeney, Edina Komódi, Emoke Nagy, Abolfazl Zarjou, Gyorgy Balla, Gregory M Vercellotti, John W. Eaton, Jozsef BallaAbstract:Heme-Mediated oxidative modification of low-density lipoprotein (LDL) plays a crucial role in early atherogenesis. It has been shown that hydrogen sulfide (H2S) produced by vascular smooth muscle cells is present in plasma at a concentration of about 50 μmol/L. H2S is a strong reductant which can react with reactive oxygen species like superoxide anion and hydrogen peroxide. The current study investigated the effect of H2S on hemin-Mediated Oxidation of LDL and oxidized LDL (oxLDL)-induced endothelial reactions. H2S dose dependently delayed the accumulation of lipid perOxidation products-conjugated dienes, lipid hydroperoxides (LOOH), and thiobarbituric acid reactive substances-during hemin-Mediated Oxidation. Moreover, H2S decreased the LOOH content of both oxidized LDL and lipid extracts derived from soft atherosclerotic plaque, which was accompanied by reduced cytotoxicity. OxLDL-Mediated induction of the oxidative stress responsive gene, heme oxygenase-1, was also abolished by H2S. Finally we have shown that H2S can directly protect endothelium against hydrogen peroxide and oxLDL-Mediated endothelial cytotoxicity. These results demonstrate novel functions of H2S in preventing hemin-Mediated oxidative modification of LDL, and consequent deleterious effects, suggesting a possible antiatherogenic action of H2S. © 2008 Elsevier Inc.
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Supression of hemin-Mediated Oxidation of low-density lipoprotein and subsequent endothelial reactions by hydrogen sulfide (H2S)
Free Radical Biology and Medicine, 2008Co-Authors: Viktoria Jeney, Edina Komódi, Emoke Nagy, Abolfazl Zarjou, Gyorgy Balla, Gregory M Vercellotti, John W. Eaton, Jozsef BallaAbstract:Heme-Mediated oxidative modification of low-density lipoprotein (LDL) plays a crucial role in early atherogenesis. It has been shown that hydrogen sulfide (H2S) produced by vascular smooth muscle cells is present in plasma at a concentration of about 50 mu mol/L. H2S is a strong reductant which can react with reactive oxygen species like superoxide anion and hydrogen peroxide. The current study investigated the effect of H2S on hemin-Mediated Oxidation of LDL and oxidized LDL (oxLDL)-induced endothelial reactions. H2S dose dependently delayed the accumulation of lipid perOxidation products-conjugated dienes, lipid hydroperoxides (LOOH), and thiobarbituric acid reactive substances-during hemin-Mediated Oxidation. Moreover, H2S decreased the LOOH content of both oxidized LDL and lipid extracts derived from soft atherosclerotic plaque, which was accompanied by reduced cytotoxicity. OxLDL-Mediated induction of the oxidative stress responsive gene, heme oxygenase-1, was also abolished by H2S. Finally we have shown that H2S can directly protect endothelium against hydrogen peroxide and oxLDL-Mediated endothelial cytotoxicity. These results demonstrate novel functions of H2S in preventing hemin-Mediated oxidative modification of LDL, and consequent deleterious effects, suggesting a possible antiatherogenic action of H2S. (C) 2008 Elsevier Inc. All rights reserved.
Shunjun Ji - One of the best experts on this subject based on the ideXlab platform.
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synthesis of isatins by i2 tbhp Mediated Oxidation of indoles
ChemInform, 2014Co-Authors: You Zi, Shunyi Wang, Shunjun JiAbstract:A convenient, simple, and metal-free protocol for the synthesis of isatins by direct Oxidation of commercially available indoles under mild conditions is developed.
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synthesis of isatins by i2 tbhp Mediated Oxidation of indoles
Organic Letters, 2014Co-Authors: You Zi, Shunyi Wang, Shunjun JiAbstract:An I2/TBHP Mediated Oxidation of commercially available indoles has been developed, which affords isatins in moderate to good yields.
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Synthesis of Isatins by I2/TBHP Mediated Oxidation of Indoles
Organic Letters, 2014Co-Authors: You Zi, Shunyi Wang, Shunjun JiAbstract:An I2/TBHP Mediated Oxidation of commercially available indoles has been developed, which affords isatins in moderate to good yields.