- A convenient and efficient H2SO4-promoted regioselective monobromination of phenol derivatives using N-bromosuccinimide
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A convenient, rapid H2SO4-promoted regioselective monobromination reaction with N-bromosuccinimide was developed. The desired para-monobrominated or ortho-monobrominated products of phenol derivatives were obtained in good to excellent yields with high selectivity. Regioselective chlorination and iodination were also achieved in the presence of H2SO4 using N-chlorosuccinimide and N-iodosuccinimide, respectively.
- Wu, Yong-Qi,Lu, Hai-Jia,Zhao, Wen-Ting,Zhao, Hong-Yi,Lin, Zi-Yun,Zhang, Dong-Feng,Huang, Hai-Hong
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supporting information
p. 813 - 822
(2020/02/15)
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- Graphene Oxide Promoted Oxidative Bromination of Anilines and Phenols in Water
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The mildly acidic and oxidative nature of graphene oxide, with its large surface area available for catalytic activity, has been explored in aromatic nuclear bromination chemistry for the first time. The versatile catalytic activity of graphene oxide (GO) has been used to selectively and rapidly brominate anilines and phenols in water. The best results were obtained at ambient temperatures using molecular bromine in a protocol promoted by oxidative bromination catalyzed by GO; these transformations proceeded with 100% atom economy with respect to bromine and high selectivities for the tribromoanilines and -phenols. Reduced graphene oxide (r-GO) was observed to form after the second recycle (third use) of GO. This technique is also effective with N-bromosuccinimide (NBS) as the brominating reagent. In the case of NBS, reactions were instantaneous and the GO displayed excellent recyclability without any loss of activity over several cycles.
- Ghorpade, Prashant Vasantrao,Pethsangave, Dattatray Appasha,Some, Surajit,Shankarling, Ganapati Subray
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p. 7388 - 7397
(2018/07/29)
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- IMPROVED PROCESSES FOR THE PREPARATION OF SOFOSBUVIR AND INTERMEDIATES THEREOF
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The present disclosure provides new procedures and intermediates for the preparation of Sofosbuvir.
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- Biodegradation of bromoxynil using the cascade enzymatic system nitrile hydratase/amidase from Microbacterium imperiale CBS 498-74. Comparison between free enzymes and resting cells
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This work investigates the biodegradation of bromoxynil to the corresponding acid to reduce its acute toxicity. Sequential reactions catalysed by nitrile hydratase (NHase) and amidase (AMase), naturally present in Microbacterium imperiale CBS 498-74, have been used. The kinetic behaviour of the crude extract (CE) and of the resting cell (RC) confined enzymes (NHase and AMase) is compared. In both preparations the same NHase/AMase ratio has been measured. The study was performed using batch and continuous UF-membrane reactor configurations. This paper highlighted a different pH-optimum for each enzyme; a high acid to amide ratio at pH 5.5; and exponential temperature dependence for both enzymes. The halved activation energy indicated the presence of diffusional limitations for the RC-enzymes. However, the higher stability at pH 7.0 for RC-NHase (half-life = 1386 h) and the correct choice of operational conditions allowed the driving to completeness of the bromoxynil biotransformation into the corresponding acid in the batch reactor.
- Pasquarelli, Fabrizia,Spera, Agata,Cantarella, Laura,Cantarella, Maria
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p. 36913 - 36923
(2015/05/13)
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- Peroxidative bromination and oxygenation of organic compounds: Synthesis, X-ray crystal structure and catalytic implications of mononuclear and binuclear oxovanadium(V) complexes containing Schiffbase ligands
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Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H 2L1) in methanol with aqueous NH4VO3 solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL1(MeOH)]·ClO4 (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H2L1) with aqueous solution of VOSO 4 leads to the formation of di-(μ-oxo) bridged vanadium(V) complex [VO2L2]2 (2) as green solid where HL 2 = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL 2 is generated in situ by the hydrolysis of one of the imine bonds of HL1 ligand during the course of formation of complex [VO 2L2]2 (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H2O2 and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by 1H NMR spectroscopic studies.
- Si, Tapan Kumar,Drew, Michael G.B.,Mukherjea, Kalyan Kumar
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experimental part
p. 2286 - 2293
(2011/10/11)
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- An instant and facile bromination of industrially-important aromatic compounds in water using recyclable CaBr2-Br2 system
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Various industrially-important brominated intermediates have been instantly synthesized using aq. CaBr2-Br2 system as an efficient and recyclable brominating reagent under aqueous conditions at room temperature without the need for metal catalysts or acidic additives. Structurally-diverse phenol and aniline derivatives with strong electron-withdrawing groups such as carboxylic, nitro and formyl show remarkable reactivity to the brominating reagent and brominated in 92-98% yield with high purity (>99%) in a very short reaction time. Organic solvent-free conditions, a feature of the green chemistry, were successively used not only for the reactions but also for the isolation of products at the end of the reaction. The recycling of HBr by its neutralization, thereby generating additional amounts of industrially-important CaBr2 has been designed and developed. The brominating reagent has been recycled and regenerated, and the process was repeated up to 4 cycles after the fresh batch using the regenerated brominating reagent having almost identical selectivity and isolated yields, which seems to be the most promising methodology from the viewpoint of the green approach to organic synthesis.
- Kumar, Lalit,Mahajan, Tanu,Agarwal
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experimental part
p. 2187 - 2196
(2011/09/16)
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- An efficient regioselective NBS aromatic bromination in the presence of an ionic liquid
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A simple, efficient, and rapid method was developed for high-yielding regioselective monobromination of activated aromatic compounds using NBS in combination with ionic liquid 1-butyl-1-methylimidazolium bromide ([Bmim]Br) or dioxane. The ionic liquid is recyclable and can be reused with minimal loss in the catalytic efficiency if the ionic liquid is rapidly microwaved prior to reactions.
- Pingali, Subramanya R.K.,Madhav, Monika,Jursic, Branko S.
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experimental part
p. 1383 - 1385
(2010/04/25)
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- Liquid-crystal engineering with anchor-shaped molecules: Honeycombs with hexagonal and trigonal symmetries formed by polyphilic bent-core molecules
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Anchored in hexagons: The molecules shown display two new complex liquid-crystalline phases formed by arrays of hexagonal cylinders, each hexagon comprising either three or six molecules. The phase type can be selected by choosing the right size ratio between the π-conjugated aromatic core (the anchor) and the flexible chain. One of the phases is the first columnar liquid crystal with trigonal symmetry. (Chemical Equation Presented).
- Glettner, Benjamin,Liu, Feng,Zeng, Xiangbing,Prehm, Marko,Baumeister, Ute,Ungar, Goran,Tschierske, Carsten
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supporting information; experimental part
p. 6080 - 6083
(2009/03/11)
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- Oxidative bromination in a liquid-liquid two-phase system to synthesize organic intermediates: 2-Bromophenol, 2,6-dibromophenol, and 2-bromo-4-methylphenol
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An alternative manufacturing process-scheme was developed to synthesize 2-bromophenol and 2,6-dibromophenol involving oxidative bromination of a substrate protected in the para position in a two-phase system followed by deprotection involving decarboxylation. Thus, selective oxidative bromination of 4-hydroxybenzoic acid in ethylenedichloride with HBr-H2O2, and subsequent decarboxylation in quinoline gave 90-95% yield to the mono- or dibromophenol depending upon the mol ratio of HBr:H2O2 employed in the oxidative bromination. Similarly, 4-methylphenol under identical reaction conditions gave 99.6% selectivity to 2-bromo-4-methylphenol at 89% conversion ratio of 4-methylphenol.
- Mukhopadhyay, Sudip,Ananthakrishnan,Chandalia, Sampatraj B.
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p. 451 - 454
(2013/09/08)
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- The Bromination of p-Hydroxybenzoic Acid in Aqueous Solution. Reaction via the Minor p-Carboxyphenoxide Anion Tautomer
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The kinetics of bromination of p-hydroxybenzoic acid have been measured in aqueous solution in the pH range 0-6.From the pH-log rate profile the reactive species appear to be the free acid (pH 5).However, the reactivity attributable to the monoanion is about 9 times higher than that predicted by a Hammett plot for the bromination of p-substituted phenols.This deviation is described to reaction via the tautomeric p-carboxyphenoxide monoanion which is present to the extent of 1 in 3100.Support for this proposal comes from related studies on ethyl p-hydroxybenzate, 3-bromo-4-hydroxybenzoic acid, and p-methoxybenzoic acid.In particular, the 3-bromo-4-hydroxybenzoate anion appears to be 5200 times more reactive than predicted and twice as reactive as the p-hydroxybenzoate anion.These anomalies are removed if reaction occurs via the minor tautomeric anion.
- Tee, Oswald S.,Iyengar, N. Rani,Kraus, Brigitte
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p. 973 - 976
(2007/10/02)
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