- Process development of the synthesis of 3,4,5-trimethoxytoluene
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3,4,5-Trimethoxytoluene (TMT) was synthesized, starting from p-cresol, through bromination followed by methylation to give 3,5-dibromo-4-methoxytoluene (DBMT). The methoxylation of the latter with sodium methoxide in methanol was studied under pressure and by continuous distillation of the solvent, methanol. The O-methylation reaction preceding the methoxylation was advantageous from the point of view of separation, purification, and isolation of the desired product and also in reducing the tar formation. The residue obtained was minimized to 0.6-0.7 wt % of the DBMT. The methoxylation reaction with distillative removal of methanol gave a conversion of 98% of DBMT to the mixture of methoxylated products, and the conversion to TMT was 86.5% as compared to 93% and 70.81%, respectively, when the reaction was carried out under pressure in a sealed reactor. However, the overall conversion to TMT based on p-cresol is 64.27% for the methoxylation reaction under pressure and 78.46% for the reaction by continuous removal of methanol calculated as isolated yield. The advantages of the methoxylation of the DBMT over the published literature procedures involving direct methoxylation of 3,5-dibromo-p-cresol followed by methylation of the dimethoxy-p-cresol are the ease of separation, purification, and isolation by vacuum fractionation of the desired product TMT.
- Sankaranarayanan, Ananthakrishnan,Chandalia
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Read Online
- Photocatalytic Degradation of 4,4′-Isopropylidenebis(2,6-dibromophenol) on Magnetite Catalysts vs. Ozonolysis Method: Process Efficiency and Toxicity Assessment of Disinfection By-Products
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Flame retardants have attracted growing environmental concern. Recently, an increasing number of studies have been conducted worldwide to investigate flame-retardant sources, environmental distribution, living organisms’ exposure, and toxicity. The presented studies include the degradation of 4,4′-isopropylidenebis(2,6-dibromophenol) (TBBPA) by ozonolysis and photocatalysis. In the photocatalytic process, nano-and micro-magnetite (n-Fe3 O4 and μ-Fe3 O4) are used as a catalyst. Monitoring of TBBPA decay in the photocatalysis and ozonolysis showed photocatalysis to be more effective. Significant removal of TBBPA was achieved within 10 min in photocatalysis (ca. 90%), while for ozonation, a comparable effect was observed within 70 min. To determine the best method of TBBPA degradation concentration on COD and TOC, the removals were examined. The highest oxidation state was obtained for photocatalysis on μ-Fe3 O4, whereas for n-Fe3 O4 and ozonolysis, the COD/TOC ratio was lower. Acute toxicity results show noticeable differences in the toxicity of TBBPA and its degradation products to Artemia franciscana and Thamnocephalus platyurus. The EC50 values indicate that TBBPA degradation products were toxic to harmful, whereas the TBPPA and post-reaction mixtures were toxic to the invertebrate species tested. The best efficiency in the removal and degradation of TBBPA was in the photocatalysis process on μ-Fe3 O4 (reaction system 1). The examined crustaceans can be used as a sensitive test for acute toxicity evaluation.
- Balawejder, Maciej,Barylyak, Adriana,Bobitski, Yaroslav,Kisa?a, Joanna,Tomaszewska, Anna
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- Regioselective monobromination of phenols with KBr and ZnAl–BrO3?–layered double hydroxides
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The regioselective mono-bromination of phenols has been successfully developed with KBr and ZnAl–BrO3?–layered double hydroxides (abbreviated as ZnAl–BrO3?–LDHs) as brominating reagents. The para site is much favorable and the ortho site takes the priority if para site is occupied. This reaction featured with excellent regioselectivity, cheap brominating reagents, mild reaction condition, high atom economy, broad substrate scope, and provided an efficient method to synthesize bromophenols.
- Wang, Ligeng,Feng, Chun,Zhang, Yan,Hu, Jun
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supporting information
(2020/02/22)
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- A Dearomatization/Debromination Strategy for the [4+1] Spiroannulation of Bromophenols with α,β-Unsaturated Imines
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A novel [4+1] spiroannulation of o- & p-bromophenols with α,β-unsaturated imines has been developed for the direct synthesis of a new family of azaspirocyclic molecules. Notably, several other halophenols (X=Cl, I) were also applicable for this transformation. Moreover, a catalytic asymmetric version of the reaction was realized with 1-bromo-2-naphthols by using a chiral ScIII/Py-Box catalyst. Mechanistic studies revealed that this domino reaction proceeded through electrophile-triggered dearomatization of phenol derivatives at their halogenated positions and followed by halogen-displacement with N-nucleophiles via a radical-based SRN1 mechanism.
- Bai, Lu,Ge, Yicong,Hao, Jiamao,Liu, Jingjing,Luan, Xinjun,Qin, Cheng
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supporting information
p. 18985 - 18989
(2020/08/26)
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- Stepwise mechanism for the bromination of arenes by a hypervalent iodine reagent
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A mild, metal-free bromination method of arenes has been developed using the combination of bis(trifluoroacetoxy)iodobencene and trimethylsilyl bromide. In situ-formed dibromo(phenyl)-λ3-iodane (PhIBr2) is proposed as the reactive intermediate. This methodology using PIFA/TMSBr has been applied with success to a great number of substrates (25 examples). The treatment of mono-substituted activated arenes led to para-brominated products (2u-z) in excellent 83-96% yields. Density functional theory calculations indicate a stepwise mechanism involving a double bromine addition followed by a type II dyotropic reaction with concomitant re-aromatization of the six-membered ring.
- Arrieta, Ana,Cossío, Fernando P.,Granados, Albert,Shafir, Alexandr,Vallribera, Adelina
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p. 2142 - 2150
(2020/03/11)
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- Method for photocatalytic synthesis of polybrominated phenol compound in water phase
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The invention discloses a method for photocatalytic synthesis of a polybrominated phenol compound in a water phase, comprising the following steps: adding a catalytic amount of a radical initiator, aphenol derivative and low-toxic and cheap bromide salt and water into a reaction vessel, reacting at room temperature at 5 W power in a photocatalytic reactor for a certain period, extracting with ethyl acetate and then re-crystallizing to obtain a polybrominated phenol compound. The above radical initiator is eosin, azobisisobutanol, sodium persulfate, ammonium persulfate or potassium persulfate.The free radical initiator and the bromine salt are cheap and easily available, and the method is an ideal synthesis method of the polybrominated phenol compound. According to the method, low-toxicity bromine salt instead of liquid bromine is used to carry out a bromination reaction, unstable and explosive hydrogen peroxide is replaced with the cheap and easily-available free radical initiator, and an emerging photocatalytic method is used. The polybrominated phenol compound can be obtained in a high yield by only using a 5W power lamp for the reaction, the reaction selectivity is high, by-products are less, and the post-treatment is simple.
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Paragraph 0012; 0032
(2019/08/30)
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- Synthesis of new oxido-vanadium complexes: Catalytic properties and cytotoxicity
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Reaction of 2,3-dihydroxy benzaldehyde with 2-({2-amino phenyl}diazenyl)phenol afforded the ligand 3-(2-(2-hydroxyphenyl)diazenyl)- 4-alkylphenyliminomethyl)benzene-1,2-diol. Reaction of H2L with VOSO4. 5H2O gave the oxido-vanadium(IV) complexes [(L)VO], which exhibited a quasi-reversible oxidative cyclic voltammetric response in a V(IV)/V(V) oxidative process. The complexes act as catalysts in the oxidation of organic thioethers and bromination of phenol. Their cytotoxic properties were examined for three cancer cell lines.
- Das, Uttam,Pattanayak, Poulami,Santra, Manas Kumar,Chattopadhyay, Surajit
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- Regioselective monobromination of aromatics via a halogen bond acceptor-donor interaction of catalytic thioamide and N-bromosuccinimide
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Regioselective monobromination of various aromatics was achieved at room temperature using N-bromosuccinimide and 5 mol% of thioamides in acetonitrile. With thiourea as catalyst, activated aromatics, such as anisole, acetanilide, benzamide and phenol analogues containing electron donating or withdrawing groups, were brominated with high regioselectivity. Room temperature brominations of weakly activated aromatics and deactivated 9-fluorenone were accomplished by 5 mol% thioacetamide, higher substrates concentrations and longer reaction times. A backbonding of the bromine lone pairs with the π*of C[dbnd]S group and a halogen bond between the halogen bond donor bromine and the halogen bond acceptor sulfur of the thioamide are thought to be the principal interactions and cause of N-bromosuccinimide activation.
- Bovonsombat, Pakorn,Teecomegaet, Pattaradra,Kulvaranon, Panisanun,Pandey, Aditi,Chobtumskul, Kittithorn,Tungsirisurp, Sireethorn,Sophanpanichkul, Punyanuch,Losuwanakul, Satreerat,Soimaneewan, Dechathon,Kanjanwongpaisan, Patcharida,Siricharoensang, Pornpawit,Choosakoonkriang, Sirirat
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p. 6564 - 6572
(2017/10/17)
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- Selective and efficient generation of ortho-brominated para-substituted phenols in ACS-grade methanol
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The mono ortho-bromination of phenolic building blocks by NBS has been achieved in short reaction times (15-20 min) using ACS-grade methanol as a solvent. The reactions can be conducted on phenol, naphthol and biphenol substrates, giving yields of >86% on gram scale. Excellent selectivity for the desired mono ortho-brominated products is achieved in the presence of 10 mol % para-TsOH, and the reaction is shown to be tolerant of a range of substituents, including CH3/ F,and NHBoc.
- Georgiev, David,Saes, Bartholomews W.H.,Johnston, Heather J.,Boys, Sarah K.,Healy, Alan,Hulme, Alison N.
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- Vanadium bromoperoxidase (VBrPO) mimics: Synthesis, structure and a comparative account of the catalytic activity of newly synthesized oxidovanadium and oxido-peroxidovanadium complexes
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The bioinspired catalytic activities of two newly synthesised vanadium(iv)dioxido (complex 1) and vanadium(v) oxido-peroxido (complex 2) complexes with the neutral tridentate benzimidazole ligand, 2,6-di-(1H-benzo[d]imidazol-2-yl)pyridine (Byim) have been established. The bromoperoxidase activities of these complexes have been established through the activation of C-H bonds of substrates like phenol, o-cresol and p-cresol. The products, characterized by GC analysis shows that good conversions have been achieved. Considering the catalytic efficiency of the complexes, complex 2, with one in-built peroxido group is found to be more potent than complex 1. The catalytic cycles of both the complexes have been established from experimental results.
- Palmajumder, Eshita,Patra, Swarup,Drew, Michael G. B.,Mukherjea, Kalyan K.
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p. 8696 - 8703
(2016/10/13)
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- Molybdenum and Tungsten Alkylidene Complexes That Contain a 2-Pyridyl-Substituted Phenoxide Ligand
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In the interest of preparing molybdenum and tungsten alkylidene complexes for olefin metathesis that are longer-lived at high temperatures (~150 °C or above), we synthesized complexes that contain a phenoxide ligand with a 2-pyridyl in one ortho position and a mesityl (Mes) or 2,4,6-i-Pr3C6H2 (Trip) in the other ortho position ([MesON]- or [TripON]-, respectively). The alkylidene (neophylidene) complexes that were prepared include W(O)(CHCMe2Ph)(Me2Pyr)(RON) (R = Mes or Trip), Mo(NC6F5)(CHCMe2Ph)(RON)Cl, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(RON)Cl, Mo(N-t-Bu)(CHCMe2Ph)(RON)Cl, and M(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(TripON)(OTf) (M = Mo or W). The reaction between Mo(NAr)(CHCMe2Ph)(TripON)(OTf) and ethylene yielded an ethylene complex, Mo(NAr)(C2H4)(TripON)(OTf)(ether). All neophylidene complexes were essentially unreactive toward terminal olefins at 22 °C and showed modest homocoupling activity (at 80 or 100 °C) and alkane metathesis activity (at 150 and 200 °C). W(O)(CHCMe2Ph)(Me2Pyr)(MesON) also stereoselectively polymerized several substituted norbornadienes at 100 °C.
- Sues, Peter E.,John, Jeremy M.,Bukhryakov, Konstantin V.,Schrock, Richard R.,Müller, Peter
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supporting information
p. 3587 - 3593
(2016/11/06)
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- A quick, mild and efficient bromination using a CFBSA/KBr system
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Bromination is a fundamental transformation in organic chemistry and brominated compounds as building blocks are of paramount importance in organic synthesis. In our study, we have developed an efficient method of bromination by using a CFBSA/KBr system at room temperature in a short reaction time. Notably, this approach has been proven to be applicable to a range of substrates including 1,3-diketones and β-keto esters, phenols, aromatic amines and heteroarenes with good to excellent yields.
- Jiang, Pan-Pan,Yang, Xian-Jin
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p. 90031 - 90034
(2016/10/09)
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- A highly efficient approach to vanillin starting from 4-cresol
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A highly efficient approach to the famous flavor and fragrance compound vanillin has been developed starting from 4-cresol with the attention focused on improving the sustainability of all the reactions. The approach involves a three-step sequence of the quasi-quantitative selective clean oxybromination of 4-cresol, the high-yield selective aerobic oxidation of 2-bromo-4-cresol, and the quantitative methoxylation of 3-bromo-4-hydroxybenzaldehyde with the recovery of pure methanol. Herein, the pivotal oxidation and methoxylation reactions are logically investigated and developed into two concise methodologies. As a green alternative, the approach holds significant value for the sustainable manufacturing of vanillin. the Partner Organisations 2014.
- Jiang, Jian-An,Chen, Cheng,Guo, Ying,Liao, Dao-Hua,Pan, Xian-Dao,Ji, Ya-Fei
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supporting information
p. 2807 - 2814
(2014/05/06)
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- Aerobic oxidation and oxidative bromination in aqueous medium using polymer anchored oxovanadium complex
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Polymer anchored oxovanadium catalyst was synthesized and characterized. Its catalytic activity was evaluated for the oxidation of various primary and secondary alcohols with molecular oxygen under mild reaction conditions. This catalyst was also effective for the oxidative bromination reaction of organic substrates with 90-100% selectivity of mono substituted products with H 2O2/KBr at room temperature. The above reactions require low temperature, short time period and most importantly all the above reactions occur in aqueous medium. The developed catalyst can be facilely recovered and reused six times without significant decrease in activity and selectivity. 2014 Elsevier B.V. All rights reserved.
- Islam, Sk. Manirul,Molla, Rostam Ali,Roy, Anupam Singha,Ghosh, Kajari,Salam, Noor,Iqubal, Md. Asif,Tuhina
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p. 169 - 178
(2014/05/06)
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- Preparation of carbazole and dibenzofuran derivatives by selective bromination on aromatic rings or benzylic groups with N-bromosuccinimide
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N-Bromosuccinimide (NBS), a bromine source, has been used to study the bromination of toluidine and cresols systematically to clarify the underlying mechanism and the orientation effect. It has been found that bromination of toluidine and cresols which possess electron-donating NH2/OH with NBS gives electrophilic aromatic substitution products quickly instead of the desired benzylic bromination products. In contrast, when the electronic effect of the substituted groups is reversed, only the benzylic bromination products are gained. Based on this methodology, several potential AChE inhibitors, such as 2-methoxy-5-(benzylamino)methyl-dibenzofuran, 3-bromo-2-methoxy-5-methyl-9H- carbazole, 3,6-dibromo-2-methoxy-5-methyl-9H-carbazole, and 5-(bromomethyl)-2- methoxy-9H-(phenylsulfonyl)-carbazole have been synthesized.
- Fang, Lei,Zhang, Haun,Fang, Xubin,Gou, Shaohua,Cheng, Lin
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p. 635 - 641
(2014/06/23)
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- Nuclear versus side-chain bromination of 4-methoxy toluene by an electrochemical method
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GRAPHICAL ABSTRACT The electrochemical bromination of 4-methoxy toluene by two-phase electrolysis yields 3-bromo 4-methoxy toluene at first, which subsequently undergoes side-chain bromination to give 3-bromo 4-methoxy benzyl bromide as a final product in 86% yield. The two-phase electrolysis consists of 25-50% NaBr as aqueous electrolyte and CHCl3 containing aromatic compound as organic phase. The reaction temperature is maintained at 10-25 °C. The probable orientation of bromine atom in an alkyl aromatic compound (nuclear versus side chain) is explained from the experimental result.
- Kulangiappar,Anbukulandainathan,Raju
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p. 2494 - 2502
(2014/08/05)
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- Discrete spherical hexadecavanadates incorporating a bromide with oxidative bromination activity
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Two discrete hexadecavanadates, (n-Bu4N)4[V 16O38(X)] (X = Cl- (1) and X = Br- (2)), were synthesized by a reaction of [V10O26] 4- with a template anion resulting in the incorporation of chloride or bromide in the {V16} spherical cluster framework. The reaction of [V 10O26]4- with p-toluenesulfonic acid proceeded under an aerobic environment to give 2 in the presence of an excess amount of bromide anion, which acted as both a template anion and a reducing reagent for the formation of the mixed-valence framework. For the synthesis of cluster 1, additional reductive conditions were required due to the weak reducing ability of the chloride anion. The crystal structures of 1 and 2 were determined using single-crystal X-ray diffraction analysis. Both were found to consist of a discrete [VV9VIV7O 38(X)]4- framework by the linkage of VO5 pyramidal units. Cyclic voltammetric studies of 1 and 2 in acetonitrile showed a series of stepwise reversible redox processes, which were due to the redox of the spherical polyoxovanadate frameworks. The oxidative bromination reactions of aromatic substrates were also investigated using cluster 2 as a catalyst under aerobic conditions. The Royal Society of Chemistry.
- Kato, Naohiro,Hayashi, Yoshihito
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p. 11804 - 11811
(2013/09/02)
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- Synthesis, structural characterization, VHPO mimicking peroxidative bromination and DNA nuclease activity of oxovanadium(v) complexes
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The two novel oxovanadium(v) complexes [VO(PyDC)(BHA)] (1) [PyDC = pyridine-2,6-dicarboxylate, BHA = benzohydroxamate] and [VO(PyDC)(BPHA)] (2) [BPHA = benzophenyl hydroxamate] were synthesized by successive addition of a methanolic solution of H2PyDC and the corresponding hydroxamic acid ligand to the aqueous solution of ammonium metavanadate (NH4VO 3). The hydroxamic acid ligands were characterized by elemental analysis, IR, UV-vis and NMR studies whereas the complexes were characterized by IR, UV-vis, CHN, molar conductance, magnetic moment, mass and NMR spectroscopic methods. The structures of the complexes were determined by single crystal X-ray crystallography. The structures of both complexes reveal that vanadium(v) has distorted octahedral geometry. The bromoperoxidase activities of these complexes have been demonstrated through the activation of C-H bonds of phenol, o-cresol and p-cresol. The catalytic products have been characterized by GC-MS analysis which shows that good conversions have been achieved. So far as the catalytic efficiency of the complexes are concerned complex 2 is found to be superior to complex 1. Both the complexes were tested for DNA nuclease activity with pUC19 plasmid DNA. The results show that both of them exhibited nuclease activity against pUC19 circular plasmid DNA. The complexes produced both nicked coils and linear forms. In this case also it is observed that complex 2 shows better nuclease activity than complex 1.
- Patra, Swarup,Chatterjee, Suparna,Si, Tapan Kr.,Mukherjea, Kalyan K.
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p. 13425 - 13435
(2013/09/23)
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- Dye molecules for simple co-sensitization process: Fabrication of mixed-dye-sensitized solar cells
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Sensitive kind of dye: Co-sensitization of the TiO2 electrode using PcS15 and the dye D131 results in a dramatic enhancement of the photocurrent response for the entire visible-light region. This method provides a simple design for accessing dye-sensitized solar cells. Copyright
- Kimura, Mutsumi,Nomoto, Hirotaka,Masaki, Naruhiko,Mori, Shogo
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supporting information; experimental part
p. 4371 - 4374
(2012/06/29)
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- An expeditious synthesis of syringaldehyde from para-cresol
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Syringaldehyde is prepared from p-cresol via a three step reaction sequence in overall yield of 63-67%. The synthesis involves selective bromination followed by high pressure and temperature methoxilation and catalytical oxidation. The use of copper chloride in different oxidation state as a catalyst in two key steps i.e. methoxilation in aromatic ring (by cuprous chloride) and oxidation of aromatic methyl to aldehyde (by cupric chloride) underscore fidelity of the process.
- Tripathi,Sama,Taneja
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experimental part
p. 379 - 381
(2010/10/18)
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- HETEROCYCLIC COMPOUNDS AS AGONISTS FOR THE THYROID RECEPTOR
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The invention provides Compounds of formula (I) or pharmaceutically acceptable esters, amides, solvates or salts thereof, including salts of such esters or amides, and solvates of such esters, amides or salts, wherein R3, R4, G, Y, W and R5 are as defined in the specification. The invention also provides the use of such Compounds in the treatment or Prophylaxis of a condition associated with a disease or disorder associated with thyroid receptor activity.
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Page/Page column 51-52
(2010/11/25)
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- NOVEL PHARMACEUTICAL COMPOSITIONS
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The invention provides the use of compounds of formula (I) or pharmaceutically acceptable esters, amides, solvates or salts thereof, including salts of such esters or amides, and solvates of such esters, amides or salts, for the manufacture of a medicament for the treatment or prophylaxis of a condition that may be treated with a thyroid receptor agonist or partial agonist wherein R1, R2, R3, R4, Y, W and R5 are as defined in the specification. The invention also provides compounds of formula (Ia) or pharmaceutically acceptable esters, amides, solvates or salts thereof, including salts of such esters or amides, and solvates of such esters, amides or salts, formula (Ia) wherein R1, R2, R3, R4, Y, W and R5 are as defined in the specification.
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Page/Page column 45-46
(2008/06/13)
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- INDOLE DERIVATIVES AND THEIR USE AS THYROID RECEPTOR LIGANDS
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The invention provides compounds of formula (I) or pharmaceutically acceptable esters, amides, solvates or salts thereof, including salts of such esters or amides, and solvates of such esters, amides or salts, (I) wherein R1, R2, R3, R4, R5, R6, Y and W are as defined in the specification. The invention also provides the use of such compounds in the treatment or prophylaxis of a condition that may be treated with a thyroid receptor agonist or partial agonist.
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Page/Page column 36
(2008/06/13)
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- Fluorescence enhancements of benzene-cored luminophors by restricted intramolecular rotations: AIE and AIEE effects
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Photoluminescence of simple arylbenzenes with ready synthetic accessibility is enhanced by two orders of magnitude through aggregate formation; viscosity and temperature effects indicate that the emission enhancement is due to the restriction of their intramolecular rotations in the solid state. The Royal Society of Chemistry.
- Zeng, Qi,Li, Zhen,Dong, Yongqiang,Di, Chong'an,Qin, Anjun,Hong, Yuning,Ji, Li,Zhu, Zhichao,Jim, Cathy K. W.,Yu, Gui,Li, Qianqian,Li, Zhongan,Liu, Yunqi,Qin, Jingui,Tang, Ben Zhong
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- An efficient, rapid and regioselective nuclear bromination of aromatics and heteroaromatics with NBS using sulfonic-acid-functionalized silica as a heterogeneous recyclable catalyst
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A simple, efficient and rapid method has been developed for high-yielding regioselective nuclear monobromination of aromatic and heteroaromatic compounds using NBS in the presence of sulfonic-acid-functionalized silica at room temperature. The catalyst works under heterogeneous conditions and can be recycled.
- Das, Biswanath,Venkateswarlu, Katta,Krishnaiah, Maddeboina,Holla, Harish
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p. 8693 - 8697
(2007/10/03)
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- Pyridinium dichlorobromate: A new stable brominating agent for aromatic compounds
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Pyridinium dichlorobromate (PyHBrCl2, 1) is a new example of iminium-trihalide complexes. The compound is prepared from pyridine and chlorine in the presence of aqueous hydrogen bromide. The crystalline trihalide is quite stable and acts as a safe source of positive bromine. It shows a remarkable reactivity towards aromatic compounds compared with other bromine complexes. It is also considered as a potential source for bromine chloride BrCl.
- Muathen, Hussni A.
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p. 169 - 171
(2007/10/03)
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- NBS-Promoted Reactions of Symmetrically Hindered Methylphenols via p-Benzoquinone Methide
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Symmetrically hindered methylphenols 1 react smoothly with NBS to form transient intermediates, p-benzoquinone methides (BM), which can be further processed to give hydroxybenzaldehydes in the presence of DMSO. This reaction is initiated by the formation of the phenoxy radical, followed by disproportionation to afford BM. None of the side-chain-brominated product is observed. The existence of BM is supported by the following observations: the formation of BM in solution can be monitored by GC and GC-MS; the electrophilic methine part participates in electrophilic aromatic substitution with anisoles to give hydroxybenzylated products 15; and the double bond character of the exocyclic methine plays a role in [4 + 2] cycloaddition with diene to afford Diels-Alder adducts. In contrast, unsymmetrically hindered or simple methylphenol (p-cresol) with NBS gives the nuclear brominated products, as usual. The energies of symmetrically hindered BMs, unsymmetrically hindered BM, and simple BM were calculated using density functional theories. Relative stabilization energies calculated at the B3LYP/6-31G*//B3LYP/6-31G* level by an isodesmic equation are enhanced 3-6 kcal/mol for symmetrically hindered BMs.
- Baik, Woonphil,Lee, Hyun Joo,Jang, Jung Min,Koo, Sangho,Kim, Byeong Hyo
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p. 108 - 115
(2007/10/03)
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- 4,4-Dibromo-3-methylpyrazol-5-one: New applications for selective monobromination of phenols and oxidation of sulfides to sulfoxides
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Dibromopyrazolone 1, a stable, crystalline solid effects para selective monobromination of phenols and aniline substrates under mild conditions. Selective oxidation of sulfides to sulfoxides can also be accomplished by using 1 in high yields.
- Mashraqui, Sabir H.,Mudaliar, Chandrashekar D.,Hariharasubrahmanian, Harini
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p. 4865 - 4868
(2007/10/03)
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- Electrophilic Aromatic Bromination Using Bromodimethylsulfoniuin Bromide Generated in Situ
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It has been shown that bromodimethylsulfonium bromide, generated in situ by treating dimethyl sulfoxide with aqueous hydrobromic acid, is a milder and more selective reagent for electrophilic aromatic bromination than elemental bromine.
- Majetich, George,Hicks, Rodgers,Reister, Steven
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p. 4321 - 4326
(2007/10/03)
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- A new mild and selective reagent for nuclear bromination
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Hexamethylene tetramine tribromide HMTAHBr3 - a new, mild and regioselective brominant is reported for bromination of aromatic hydrocarbons, substituted ethers, phenols and anilides in high yields.
- Bisarya,Rao
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p. 779 - 788
(2007/10/02)
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- Influence de la complexation sur la reactivite de nitrates d'halogenes
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Iodine nitrate or bromine nitrate in acetonitrile or in chloroform react with a variety of phenolic substrates to form both halogenated and nitrated products.In the presence of strong complexing agents of halonium ions, no reacting occurs, while in the presence of pyridine or triethylamine, only halogenated phenols exhibiting a strong ortho-directing effect of the phenolic function are produced. Keywords: phenols, iodine nitrate, bromine nitrate, halogenation, nitration.
- Gaude, Didier,Gellon, Gisele,Goaller, Raymond Le,Pierre, Jean-Louis
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p. 104 - 108
(2007/10/02)
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- Bis- or poly-(bromo-4-methyl-phenoxy)-alkanes and -alkenes, process for preparing same and use thereof as uv-stable fireprotective agents for synthetic materials
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Disclosed are novel bis- or poly-(bromo-4-methylphen-oxy)-alkanes and -alkenes having the formula (1) wherein, n is an integer of from 1 to 6,m is 2 (n + z) - y,x is an integer of from 1 to 4,y is an integer of from 2 to 4 and, z is 0 or 1,and a process for preparing said compounds by reacting alkali salts of nucleus-brominated p-cresols with bis- or poly-haloalkanes or -alkenes, preferably in a glycol monoalkylether as reaction medium. The materials are employed as UV-stable low-migrating fire-protective agents for thermoplastic synthetic materials, and more specifically for polybutylene terephthalate or acrylo-nitrile-butadiene-copolymer molding compositions, in combination with antimony trioxide.
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- Bromination of Phenols by Use of Benzyltrimethylammonium Tribromide
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The reaction of phenols with benzyltrimethylammonium tribromide in dichloromethane-methanol for 1 h at room temperature gave polybromophenols in good yields.
- Kajigaeshi, Shoji,Kakinami, Takaaki,Tokiyama, Hajime,Hirakawa, Takahiro,Okamoto, Tsuyoshi
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p. 627 - 630
(2007/10/02)
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- Nitrocyclohexadienones : a new class of nitrating agents
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Various nitrocyclohexadienones are proposed as new nitrating agents. These compounds are easy to prepare from corresponding phenols, easy to handle and stable. Nitrocyclohexadienones act as nitronium carriers using rearomatization as the driving force and permit nitration of highly activated substrates under mild conditions and with good yields.
- Lemaire, Marc,Guy, Alain,Roussel, Jacques,Guette, Jean-paul
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p. 835 - 844
(2007/10/02)
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- A SIMPLE SINTHESIS OF TROPONES AND RELATED COMPOUNDS
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Cyclohexa-2,4- and 2,5-dienones bearing position 2 or 4 a dihalomethyl group (halogen = chlorine or bromine) are smoothly reduced by tri-butyltin hydride to furnish appropriately substituted tropones.Modification of the substituents permits access to a tropolone and to less substituted tropones.The mechanism of this ring expansion process has been discussed.
- Barbier, Michael,Barton, Derek H. R.,Devys, Michel,Topgi, Ravindra Satish
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p. 5031 - 5038
(2007/10/02)
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- Preparation of p-hydroxybenzaldehyde derivatives
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A 4-hydroxybenzaldehyde derivative of the formula: STR1 wherein each of R1, R2, R3 and R4 is selected from the group consisting of hydrogen atom, halogen atoms, lower alkyl groups or lower alkoxy groups, which is useful as intermediate for the production of medicines or agricultural chemicals, or as flavor, is produced by the reaction of a p-cresol derivative of the formula: STR2 wherein each of R1, R2, R3 and R4 is as defined above, with oxygen or oxygen-containing gas in the presence of a base and a catalytic amount of cobalt compound or metallic cobalt.
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- Solvolytic Elimination and Hydrolysis promoted by an Aromatic Hydroxy Group. Part 1. The Reaction of 2,6-Dibromo-4-dibromomethylphenol and of 2,6-Dibromo-4-bromomethylenecyclohexa-2,5-dienone with Water in 95percent 1,4-Dioxane
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The reaction of 2,6-dibromo-4-dibromomethylphenol with water to give the quinone methide, 2,6-dibromo-4-bromomethylenecyclohexa-2,5-dienone, together with 2,6-dibromo-4-hydroxybenzaldehyde has been studied in 95percent 1,4-dioxane.U.v. spectroscopy has been used to study the kinetic form of the reaction.At very low acidities, rapid conversion into the quinone methide occurs through the aryl oxide ion, and is followed by addition and replacement to give the aldehyde.At acidities greater than 1E-3M, reaction of the un-ionised phenol is dominant and follows a conventional SN1 pathway through a mesomeric carbocationic intermediate.Subsequent loss of a proton from this intermediate to give the quinone methide is competitive with its capture by the solvent (to give in several steps the related aldehyde) and by bromide ion (to give starting material).The mass-law constant for capture of the carbocation by bromide ion is very large (ca. 1E4 in this solvent), so that relatively small concentrations of hydrogen bromide convert the quinone methide back into the dibromomethylphenol by 1,6-addition.Solvent kinetic isotope effects on the individual reaction stages are reported.The rate of solvolysis of the phenol is much greater than would be predicted by the use of conventional linear free-energy parameters.
- Mare, Peter B. D. de la,Newman, Paul A.
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p. 231 - 238
(2007/10/02)
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- ipso Halogenation. II. Bromination of phenols, isomerisation and disproportionation of bromophenols, and dione-phenol rearrangement of bromodienones
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Bromination of p-cresol, bromo-p-cresol, 3,4-dimethylphenol, and mesitol in trifluoromethanesulfonic acid gices as the main product the bromo derivative with bromine meta to hydroxyl, a result attributed to the intermediate formation of a bromodienone and its rearrangement.Phenols does not give m-bromophenol in trifluoromethanesulfonic acid. 4-Bromo-2,4,6-trimethylcyclohexa-2,5-dienone rearranges to 3-bromomesitol in trifluoromethanesulfonic acid and, similarly, 2,4,6-tribromo-4-methylcyclohexa-2,5-dienone rearranges to 3-bromomesitol in trifluoromethanesulfonic acid and, similarly, 2,4,6-tribromo-4-methylcyclohexa-2,5-dienone rearranges to 2,3,6-tribromo-4-methylphenol.Under appropriate conditions debromination of bromodienones is competitive with rearrangement.Tetramethylammonium bromide in trifluoromethanesulfonic acid is an effective reagent for isomerization and disproportionation of bromophenols.Tetramethylammonium iodide in trifluoromethanesulfonic acid is an effective reagent for selective debromination of bromophenols at the ortho and para position.
- Fischer, Alfred,Henderson, George Narayanan
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p. 1045 - 1052
(2007/10/02)
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- Electrophilic Substitution with Rearrangement. Part 9. Dienones derived from Brominations of o-, m-, and p-Cresol
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Regiospecific protodebromination of ring-substituted bromophenols derived from 2-, 3-, or 4-methylphenol can be effected by heating them with aqueous hydrogen iodide; the synthetic scope of this reaction has been explored.These di- and poly-bromophenols can generally be converted by further bromination in aqueous acetic acid into dienones , which have now been shown to have the 4-bromo-2,5-dienone rather than the 2-bromo-3,5-dienone structure.The rearrangemens of these dienones to ring-substituted polybromophenols by treatment with sulfuric acid have been investigated; where more than one product is formed, the regioselectivity differs from that prevailing in the corresponding direct bromination of the phenol with liquid bromine.The alternative rearrangements of these dienones in aprotic solvents with and without illumination have been compared with results obtained by reaction of methylphenols with bromine under the same conditions.Characteristic differences between the behaviours of 2-, 3-, and 4-methyl-substituted compounds reflect the specific reactions available to the particular dienones.
- Brittain, Judith M.,Mare, Peter B. D. de la,Newman, Paul A.
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- Selective Bromination of Polyenes by 2,4,4,6-tetrabromocyclohexa-2,5-dienone
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2,4,4,6-Tetrabromocyclohexa-2,5-dienone (TBCO) liberates bromonium ion when treated with polyenes to form brominated products.The results of the reaction of TBCO with simple olefins are presented.The analogous bromo-ketones, 4-bromo-2,4,6-trichloro- and 2,4,6-tribromo-4-methyl-cyclohexa-2,5-dienone, (4) and (5) respectively, afford the same products (3a), (6), and (7) when treated with geranyl cyanide (1; R = CN).The evidence suggests that formation of the dibromide (3a) may be due to sequential reactions.TBCO in the presence of cetyltrimethylammonium bromide serves as an excellent reagent for selective bromination of polyenes under very mild conditions.
- Kato, Tadahiro,Ichinose, Isao
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p. 1051 - 1056
(2007/10/02)
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- Process for aromatic ethers
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A process for the preparation of aromatic ethers by the bromination of a compound of the formula STR1 wherein R1, independently, is hydrogen, hydroxy, lower alkoxy, lower alkyl; m is an integer from 1-4, and A is --CHO, --COOR3 or lower alkyl, and subsequently treating the reaction product of the bromination step with an alkali metal alkoxide in the presence of cuprous halide or oxide, is described.
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