- Mechanism of reaction of an arenediazonium ion in aqueous solutions of acetamide, N-methylacetamide, and N,N-dimethylacetamide. A potential method for chemically tagging peptide bonds at aggregate interfaces
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The mechanism of dediazoniation of 2,4,6-trimethylbenzenediazonium ion, 1-ArN2+, in concentrated aqueous solutions of acetamide, N-methylacetamide, and N,N-dimethylacetamide (peptide bond models) was probed by a combination of techniques including HPLC, GC/MS, and H218O isotopic labeling. The kinetics and product distributions are completely consistent with the heterolytic dediazoniation mechanism, i.e., rate-determining loss of N2 followed by trapping of the aryl cation intermediate, 1-Ar+, by H2O and the oxygens and nitrogens of the amides. Aryl imidates formed from trapping by amide O hydrolyze rapidly into aryl ester/amine and amide/phenol product pairs. The results were used to estimate the selectivity of 1-Ar+ toward the amide oxygens and nitrogens versus H2O. 1-Ar+ is only 10-40% more selective toward H2O than amide O, but it is more than 10 times more selective toward H2O than the amide N. 1-Ar+ is slightly more selective toward the N of acetamide than N-methylacetamide. However, within the HPLC detection limit, 1-At+ does not give a product from reaction with the N,N-dimethylacetamide nitrogen. The selectivities are interpreted by using a preassociation model, i.e., selective solvation by the different nucleophiles of the reactive diazonio group in the ground state. These results indicate that chemical tagging (trapping by N) and cleaving (trapping by O) of the peptide bonds and the weakly basic side chains of polypeptides and proteins bound to association colloids, vesicles and biomembranes, and emulsions may provide new information on their topologies and orientations at the aggregates' interfaces.
- Romsted, Laurence S.,Zhang, Jianbing,Zhuang, Lanzhen
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- OXIDATION OF MESITYLENE BY HYDROGEN PEROXIDE IN AcOH-Ac2O-H2SO4
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By the oxidation of mesitylene by hydrogen peroxide in AcOH-Ac2O-H2SO4 one can obtain mesitol (2,4,6-trimethylphenol) with a selectivity of 57-69percent at a mesitylene conversion of 22-16percent and the acetate of mesitol with a selectivity of 72-85percent at 25-22percent conversion.The peroxide responsible for the oxidation of mesitylene in this system is in the form of peracetic acid, formed in situ.Over the concentration range studied, the reaction is first order in AcOOH, mesitylene, and H2SO4.Hydroxylation of mesitylene by AcOOH proceeds by an electrophilic substitution mechanism, the limiting step being the formation of the ?-complex.
- Kholdeeva, O. A.,Kozhevnikov, I. V.
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- Structure–activity comparison in palladium–N–heterocyclic carbene (NHC) catalyzed arene C[sbnd]H activation- functionalization
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A simple and efficient C[sbnd]H activation catalyst was identified through a model structure-activity screening applied to a noncooperative, nonsymmetric bimetallic palladium(II)-N-heterocyclic carbene complex. Mechanistic studies based on kinetics and DOSY NMR spectroscopy provided the origin of the higher efficiency of the identified catalyst.
- Mondal, Moumita,Choudhury, Joyanta
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p. 451 - 457
(2016/12/16)
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- Gold-catalyzed C-H oxidative polyacyloxylation reaction of hindered arenes
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The synthesis of polyacyloxylated aromatic derivatives was achieved in moderate yields using a gold-catalyzed C-H activation strategy and di(acetoxy)iodobenzene as an oxidant. Georg Thieme Verlag Stuttgart · New York.
- Pradal, Alexandre,Faudot Dit Bel, Pierre,Toullec, Patrick Y.,Michelet, Veronique
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experimental part
p. 2463 - 2468
(2012/09/08)
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- Gold-catalyzed oxidative acyloxylation of arenes
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A variety of nonactivated hindered aromatic rings are acyloxylated (22 examples, up to 83% yield) in the presence of PPh3AuCl as the catalyst and di(acetoxy)iodobenzene as the oxidant. The reaction proceeds at 110 °C in an acid media and allows the formation of both hindered acetoxy and acyloxy derivatives. This methodology nicely complements the Pd-catalyzed arene acyloxylation reaction, which is not operating on hindered substrates and allows the Au-catalyzed unprecedented acyloxylation reaction of arenes, implying various carboxylic acids.
- Pradal, Alexandre,Toullec, Patrick Y.,Michelet, Veronique
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supporting information; experimental part
p. 6086 - 6089
(2011/12/22)
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- Gold(III)-catalyzed direct acetoxylation of arenes with iodobenzene diacetate
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AuCl3-catalyzed direct acetoxylation of electron-rich aromatic compounds has been achieved with iodobenzene diacetate as the acetoxylation reagent.
- Qiu, Di,Zheng, Zhitong,Mo, Fanyang,Xiao, Qing,Tian, Yu,Zhang, Yan,Wang, Jianbo
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p. 4988 - 4991
(2011/11/13)
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- Iodonium salts are key intermediates in Pd-catalyzed acetoxylation of pyrroles
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A mild, room-temperature Pd-catalyzed acetoxylation of pyrroles with phenyliodonium acetate is described. The acetoxylation was found to proceed via the initial formation of pyrrolyl(phenyl)iodonium acetates, which were converted to acetoxypyrroles in the presence of Pd(OAc)2. The acetoxylation could also be carried out as a one-pot sequential procedure without the isolation of the intermediate iodonium salts.
- Lubriks, Dmitrijs,Sokolovs, Igors,Suna, Edgars
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body text
p. 4324 - 4327
(2011/10/05)
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- Counterattack mode differential acetylative deprotection of phenylmethyl ethers: Applications to solid phase organic reactions
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A counterattack protocol for differential acetylative cleavage of phenylmethyl ether has been developed. The phenylmethyl moiety is liberated as benzyl bromide that is isolated and reused providing advantages in terms of waste minimization/utilization and atom economy. The applicability of this methodology has been extended for solid phase organic reactions with the feasibility of reuse of the solid support.
- Chakraborti, Asit K.,Chankeshwara, Sunay V.
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experimental part
p. 1367 - 1370
(2009/07/04)
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- Samarium trifluoromethanesulfonate: An efficient moisture tolerant acylation catalyst under solvent-free condition
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Samarium trifluoromethanesulfonate catalyzed the acylation of phenols, alcohols, thiols, free reducing sugars, and glycosides in excellent yields at ambient temperature under solvent-free condition using stoichiometric amounts of various anhydrides. (Chemical Equation Presented). Copyright Taylor & Francis Group, LLC.
- Roy, Bimalendu,Dasgupta, Somnath,Kumar Rajput, Vishal,Mukhopadhyay, Balaram
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- Widely useful DMAP-catalyzed esterification under auxiliary base- and solvent-free conditions
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With regard to atom economy and E-factor, catalytic condensation of carboxylic acids with equimolar amounts of alcohols is the most desirable. Although several highly active dehydration catalysts have been reported, more efficient alternatives are still strongly needed because the dehydrative esterification of tertiary alcohols, phenols, acid-sensitive alcohols, amino acids, and hardly soluble alcohols has never proceeded satisfactorily. Here we report new insights into the classical DMAP-catalyzed acylation of alcohols: surprisingly, only a 0.05-2 mol % of DMAP can efficiently promote acylation of alcohols with acid anhydrides under auxiliary base- and solvent-free conditions to give the corresponding esters in high yields. Furthermore, we achieved the recovery and reuse of commercially available polystyrene-supported DMAP without using any solvents. These serendipitous findings provide widely useful and environmentally benign esterification methods, which might be more practical and reliable than catalytic dehydrative condensation methods, in particular, for the less reactive alcohols which hardly condense with carboxylic acid directly.
- Sakakura, Akira,Kawajiri, Kimio,Ohkubo, Takuro,Kosugi, Yuji,Ishihara, Kazuaki
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p. 14775 - 14779
(2008/09/17)
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- Zirconiuni(IV) chloride as a new, highly efficient, and reusable catalyst for acetylation of phenols, thiols, amines, and alcohols under solvent-free conditions
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Zirconium(IV) chloride has been found to be a new, highly efficient, and reusable catalyst for acetylation of structurally diverse phenols, thiols, amines, and alcohols under solvent-free condtions. Acetylation of sterically hindered and electron deficient phenols is achieved in excellent yields with stoichiometric amounts of Ac2O at room temperature. Acid-sensitive alcohols undergo acetylation with excellent chemoselectivity without competitive side reactions such as dehydration or rearrangement. The mild Lewis acid property of the catalyst enables the acetylation to be carried out with optically active substrates without any detrimental effect on the optical purity.
- Chakraborti, Asit K.,Gulhane, Rajesh
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p. 627 - 630
(2007/10/03)
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- Copper(II) Tetrafluoroborate-Catalyzed Acetylation of Phenols, Thiols, Alcohols, and Amines
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Copper(II) tetrafluoroborate efficiently catalyzes acetylation of structurally diverse phenols, alcohols, thiols, and amines with stoichiometric amounts of Ac2O under solvent-free conditions at room temperature. Acid-sensitive alcohols are smoothly acetylated without competitive side reactions. The reaction is influenced by the steric and electronic factors associated with the substrate as well as the anhydride. Acetylation of a sterically hindered substrate requires excess of anhydride and longer time. Acylation with less electrophilic anhydrides affords poor to moderate yields.
- Chakraborti, Asit K.,Gulhane, Rajesh,Shivani
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p. 111 - 115
(2007/10/03)
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- Perchloric acid adsorbed on silica gel as a new, highly efficient, and versatile catalyst for acetylation of phenols, thiols, alcohols, and amines
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Perchloric acid adsorbed on silica gel efficiently catalyses acetylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions.
- Chakraborti, Asit K.,Gulhane, Rajesh
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p. 1896 - 1897
(2007/10/03)
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- Bismuth Oxide Perchlorate as a Highly Efficient Catalyst for Heteroatom Acylation under Solvent-Free Conditions
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Bismuth oxide perchlorate efficiently catalyzes the acetylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Sterically hindered and electron deficient phenols are acetylated in excellent yields with stoichiometric amounts of Ac2O at room temperature. Acylation of acid-sensitive alcohols is carried out efficiently without competitive side reactions. Optically active substrates are acetylated without any detrimental effect on the optical purity.
- Chakraborti, Asit K.,Gulhane, Rajesh,Shivani
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p. 1805 - 1808
(2007/10/03)
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- Fluoroboric acid adsorbed on silica gel as a new and efficient catalyst for acylation of phenols, thiols, alcohols, and amines
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Fluoroboric acid supported on silica gel efficiently catalyzes acylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Acid-sensitive alcohols are smoothly acylated without competitive side reactions.
- Chakraborti, Asit K.,Gulhane, Rajesh
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p. 3521 - 3525
(2007/10/03)
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- Electrostatic catalysis by ionic aggregates: Scope and limitations of Mg(ClO4)2 as acylation catalyst
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Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO4) 2>Ba(ClO4)2>LiClO4. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO4) 2. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.
- Chakraborti, Asit K.,Sharma, Lalima,Gulhane, Rajesh,Shivani
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p. 7661 - 7668
(2007/10/03)
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- Indium(III) chloride as a new, highly efficient, and versatile catalyst for acylation of phenols, thiols, alcohols, and amines
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Indium(III) chloride efficiently catalyses the acylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Acid sensitive alcohols are smoothly acylated without competitive side reactions. Acylation of 2-hydroxynaphthalene is carried out with carboxylic acids adopting the mixed anhydride protocol using trifluoroacetic anhydride.
- Chakraborti, Asit K.,Gulhane, Rajesh
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p. 6749 - 6753
(2007/10/03)
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- Single-pass reaction column system with super br?nsted acid-loaded resin
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Various acid-promoted reactions gave the desired products in high yields by passing a solution of reactants through a reaction column packed with polystyrene-bound super Br?nsted acid (1) just once. Polar and nonpolar organic solvent-swellable 1 is much superior to Nafion SAC-13 (2) as a Br?nsted acid-loaded resin packed in the column.
- Ishihara, Kazuaki,Hasegawa, Aiko,Yamamoto, Hisashi
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p. 1296 - 1298
(2007/10/03)
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- Lithium perchlorate catalyzed acetylation of alcohols under mild reaction conditions
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Lithium perchlorate is found to efficiently catalyze the acetylation of alcohols and phenols with acetic anhydride in good to excellent yields.
- Nakae,Kusaki,Sato
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p. 1584 - 1586
(2007/10/03)
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- Highly powerful and practical acylation of alcohols with acid anhydride catalyzed by Bi(OTf)3
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Bi(OTf)3-catalyzed acylation of alcohols with acid anhydride was evaluated in comparison with other acylation methods. The Bi(OTf)3/acid anhydride protocol was so powerful that sterically demanding or tertiary alcohols could be acylated smoothly. Less reactive acylation reagents such as benzoic and pivalic anhydride are also activated by this catalysis. In these cases, a new technology was developed in order to overcome difficulty in separation of the acylated product from the remaining acylating reagent: methanolysis of the unreacted anhydride into easily separable methyl ester realized quite easy separation of the desired acylation product. The Bi(OTf)3/acid anhydride protocol was applicable to a wide spectrum of alcohols bearing various functionalities. Acid-labile THP- or TBS-protected alcohol, furfuryl alcohol, and geraniol could be acylated as well as base-labile alcohols. Even acylation of functionalized tertiary alcohols was effected at room temperature.
- Orita,Tanahashi,Kakuda,Otera
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p. 8926 - 8934
(2007/10/03)
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- Highly efficient and versatile acylation of alcohols with Bi(OTf)3 as catalyst
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A very convenient route for the acylation of alcohols is provide by using a Bi(OTf)3 catalyst [Eq. (1)]. In this protocol hindered and functionalized alcohols are acylated at 25°C, and solvents can be employed without purification. R= primary, secondary, tertiary alkyl, aryl; R'=Me, Ph, tBu.
- Orita, Akihiro,Tanahashi, Chiaki,Kakuda, Atsushi,Otera, Junzo
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p. 2877 - 2879
(2007/10/03)
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- Endothelin antagonists: Substituted mesitylcarboxamides with high potency and selectivity for ET(A) receptors
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We have previously disclosed the discovery of 2,4-disubstituted anilinothiophenesulfonamides with potent ET(A)-selective endothelin receptor antagonism and the subsequent identification of sitaxsentan (TBC11251, 1) as a clinical development compound (Wu et al. J. Med. Chem. 1997, 40, 1682 and 1690). The orally active 1 has demonstrated efficacy in a phase II clinical trial of congestive heart failure (Givertz et al. Circulation 1998, 98, Abstr. 3044) and was active in rat models of myocardial infarction (Podesser et al. Circulation 1998, 98, Abstr. 2896) and acute hypoxia-induced pulmonary hypertension (Chen et al. FASEB J. 1996, 10 (3), A104). We now report that an additional substituent at the 6-position of the anilino ring further increases the potency of this series of compounds. It was also found that a wide range of functionalities at the 3-position of the 2,4,6-trisubstituted ring increased ETA selectivity by ~10-fold while maintaining in vitro potency, therefore rendering the compounds amenable to fine-tuning of pharmacological and toxicological profiles with enhanced selectivity. The optimal compound in this series was found to be TBC2576 (7u), which has ~10- fold higher ETA binding affinity than 1, high ET(A)/ET(B) selectivity, and a serum half-life of 7.3 h in rats, as well as in vivo activity.
- Wu, Chengde,Decker, E. Radford,Blok, Natalie,Bui, Huong,Chen, Qi,Raju,Bourgoyne, Andree R.,Knowles, Vippra,Biediger, Ronald J.,Market, Robert V.,Lin, Shuqun,Dupré, Brian,Kogan, Timothy P.,Holland, George W.,Brock, Tommy A.,Dixon, Richard A. F.
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p. 4485 - 4499
(2007/10/03)
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- OXYGENATION OF AROMATIC AND ALIPHATIC HYDROCARBONS BY A NEW REAGENT SYSTEM, Fe(CH3CN)6(2+)-H2O2-Ac2O: AN EFFECTIVE MODEL REAGENT FOR MONO-OXYGENASE
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Reactions of aromatic and aliphatic hydrocarbons with a new system, Fe(CH3CN)6(2+) - H2O2 - Ac2O in CH3CN, gave oxygenation products with fairly high reaction efficiency ( Tables I and II )compared to known to reagent systems used as enzyme models for mono-oxygenases.Investigations of the mechanism of these reactions indicated the involvement of either complex C.FeIV(OH)(OAc)(2+), or complex D, FeIV(OAc)(2+), dependig on the organic substrate.Keywords-oxygenation; aromatic hydrocarbon; aliphatic hydrocarbon; hexakisacetonitrile iron(II) perchlorate; hydrogen peroxide; enzyme model; mono-oxygenase
- Kotani, Eiichi,Kobayashi. Shigeki,Ishii, Yoko,Tobinaga, Seisho
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p. 4671 - 4679
(2007/10/02)
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- Metal Ion Oxidation. VIII. Oxidation of Organic Compounds by Copper(III)
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The copper(III) complex of biuret has been shown to oxidize aromatic and alicyclic compounds in acetic and trifluoroacetic acid, yielding acetates and dehydro dimers.The product pattern of these reactions supports an electron transfer mechanism.Aryl halides, e.g. fluorobenzene, are hydrolyzed to phenols and the mechanism is postulated to be an electron transfer chain mechanism, the SON2 mechanism.Substituted arylacetic acids are decarboxylated when treated with 1 in acetic acid at reflux temperature.This decarboxylation is proposed to be a one-electron process, the rate-determining step being the decomposition of an arylacetic acid-copper(III) complex to a benzylic radical.
- Joensson, Lennart
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p. 683 - 690
(2007/10/02)
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- Electron-transfer Chain Catalysis of Substitution Reactions. Experimental Evidence for the SON2 Mechanism
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Two possible cases of an oxidative electron-transfer chain catalysis mechanism, the SON2 mechanism, are presented: the anionic 'oxidation' of 4-fluoroanisole in the presence of acetate ion to give 4-acetoxyanisole, and the CuIII 'oxidation' of chloro- and fluoro-benzene in the presence of water to give phenol.
- Eberson, Lennart,Joensson, Lennart
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p. 1187 - 1188
(2007/10/02)
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- Metal Ion Oxidation. VII. Oxidation of Aromatic Hydrocarbons by Potassium 12-Wolframocobalt(III)ate, a "Soluble Anode"
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The oxidation of aromatic compounds with potassium 12-wolframocobalt(II)ate in acetic acid media has been investigated.A wide range of alkylaromatics can be acetoxylated in the α position, whereas nuclear substitution can be effected in the presence of acetate ion.In a few cases acetoxymethylation is observed, presumably via intermediate arylacetic acid. 4-Fluoroanisole is converted to 4-acetoxyanisole.In all preparative aspects, the reaction is closely similar to anodic and Ag(II) mediated acetoxylation.A study of substituted effects upon α acetoxylation showed a good linear relationship between log krel and Eo for oxidation of the alkylaromatic substrates (slope -3.2 V-1).A strong deuterium isotope effect (KH/kD ca. 6) is indicative of a rate-determining step involving hydrogen atom transfer ("concerted electron/proton transfer") from the α C-H bond to an oxygen of the heteropoly ion.
- Eberson, Lennart,Wistrand, Lars-Goeran
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p. 349 - 358
(2007/10/02)
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