- Triptycenyl Sulfide: A Practical and Active Catalyst for Electrophilic Aromatic Halogenation Using N-Halosuccinimides
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A Lewis base catalyst Trip-SMe (Trip = triptycenyl) for electrophilic aromatic halogenation using N-halosuccinimides (NXS) is introduced. In the presence of an appropriate activator (as a noncoordinating-anion source), a series of unactivated aromatic compounds were halogenated at ambient temperature using NXS. This catalytic system was applicable to transformations that are currently unachievable except for the use of Br2 or Cl2: e.g., multihalogenation of naphthalene, regioselective bromination of BINOL, etc. Controlled experiments revealed that the triptycenyl substituent exerts a crucial role for the catalytic activity, and kinetic experiments implied the occurrence of a sulfonium salt [Trip-S(Me)Br][SbF6] as an active species. Compared to simple dialkyl sulfides, Trip-SMe exhibited a significant charge-separated ion pair character within the halonium complex whose structural information was obtained by the single-crystal X-ray analysis. A preliminary computational study disclosed that the πsystem of the triptycenyl functionality is a key motif to consolidate the enhancement of electrophilicity.
- Nishii, Yuji,Ikeda, Mitsuhiro,Hayashi, Yoshihiro,Kawauchi, Susumu,Miura, Masahiro
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p. 1621 - 1629
(2020/02/04)
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- Molecular Vises for Precisely Positioning Ligands near Catalytic Metal Centers in Metal-Organic Frameworks
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We report the construction of a molecular vise by pairing a tritopic phenylphosphorus(III) linker and a monotopic linker in opposite positions within a metal-organic framework. The angle between these linkers at metal sites is fixed upon changing the functionality in the monotopic linker, while the distance between them is precisely tuned. This distance within the molecular vise is accurately measured by 1H-31P solid-state nuclear magnetic resonance spectroscopy. This unveils the impact of the distance on catalytic performance without interference from electrostatic effects or changes in the angle of the ligand, which is unprecedented in classic organometallic complexes.
- Yan, Wei,Li, Shenhui,Yang, Tao,Xia, Yucong,Zhang, Xinrui,Wang, Chao,Yan, Zier,Deng, Feng,Zhou, Qianghui,Deng, Hexiang
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supporting information
p. 16182 - 16187
(2020/10/26)
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- Molecular tweezers based on trivalent phosphine, preparation method of molecular tweezers, metal-molecular tweezers catalyst, and preparation method and application of metal-molecular tweezers catalyst
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The invention relates to the technical field of inorganic-metal organic crossing and relates to the technical field of molecular tweezers, in particular to molecular tweezers based on trivalent phosphine, a preparation method of the molecular tweezers, a metal-molecular tweezer catalyst, a preparation method of the metal-molecular tweezer catalyst and an application of the metal-molecular tweezercatalyst, the molecular tweezer based on trivalent phosphine is named as P-MV-PCN-521-R, and R is any one of benzoic acid, p-nitrobenzoic acid, formic acid, p-methylbenzoic acid and dichloroacetic acid. The molecular tweezers based on the trivalent phosphine have distance adjustability. The trivalent phosphine-based metal-molecular tweezer catalyst provided by the invention has a high crystallinesurface area and a high specific surface area. The trivalent phosphine-based metal-molecular tweezer catalyst has good chemical stability and thermal stability, and is a primary condition for applyingthe trivalent phosphine-based metal-molecular tweezer catalyst to the actual field. The trivalent phosphine-based metal-molecular tweezer catalyst with adjustable distance provided by the invention has good selectivity for bromination of aromatic compounds.
- -
-
Paragraph 0038; 0059-0060
(2020/12/14)
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- Regioselective Halogenation of Arenes and Heterocycles in Hexafluoroisopropanol
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Regioselective halogenation of arenes and heterocycles with N-halosuccinimides in fluorinated alcohols is disclosed. Under mild condition reactions, a wide diversity of halogenated arenes are obtained in good yields with high regioselectivity. Additionally, the versatility of the method is demonstrated by the development of one-pot sequential halogenation and halogenation-Suzuki cross-coupling reactions.
- Tang, Ren-Jin,Milcent, Thierry,Crousse, Benoit
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p. 930 - 938
(2018/01/28)
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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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- On the ionizing properties of supercritical carbon dioxide: Uncatalyzed electrophilic bromination of aromatics
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Supercritical carbon dioxide (scCO2), a solvent with a zero dipole moment, low dielectric constant, and no hydrogen bonding behavior, is a suitable medium to perform the uncatalyzed electrophilic bromination of weakly activated aromatics with no interference of radical pathways. The ability of scCO2 to promote these reactions matches those of strongly ionizing solvents such as aqueous acetic and trifluoroacetic acids. Conversely, carbon tetrachloride, with similar polarity parameters to scCO2, leads exclusively to side chain functionalization. The strong quadrupole moment, and the acidic, but non basic, Lewis character of carbon dioxide, are proposed as key factors for the singular performance of scCO2 in reactions involving highly polar and ionic intermediates.
- Delgado-Abad, Thais,Martnez-Ferrer, Jaime,Reig-Lpez, Javier,Mello, Rossella,Acerete, Rafael,Asensio, Gregorio,Gonzlez-Nez, Mara Elena
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p. 51016 - 51021
(2015/01/16)
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- A new recoverable Au(III) catalyst supported on magnetic polymer nanocomposite for aromatic bromination
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This Letter presents a facile alternative synthesis of a recoverable Au(III) catalyst supported on Fe3O4@SiO 2~MPS grafted by poly(N-vinyl-2-pyrrolidone) (PVP). The solid magnetic support was prepared by anchoring 3-methacryloxypropyltrimethoxysilane (MPS) onto the Fe3O4@SiO2 surfaces followed by free radical polymerization with N-vinyl-2-pyrrolidone. Au(III) was immobilized onto the magnetic support in aqueous media to afford Au(III)/Fe 3O4@SiO2~PVP (catalyst 1). Catalyst 1 was characterized by FT-IR, TEM, VSM, TGA, XRD, and ICP-AES. The amount of Au in catalyst 1 was measured to be 0.64 wt % by ICP-AES. This newly prepared catalyst can catalyze the aromatic bromination reaction with comparable activity as homogeneous AuCl3. Moreover, the supported catalyst is easy to recover and can be used in four cycles without apparent loss of activity.
- Li, Bai,Gao, Linfeng,Bian, Fengling,Yu, Wei
-
supporting information
p. 1063 - 1066
(2013/04/10)
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- Silver catalyzed bromination of aromatics with N-bromosuccinimide
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A heterogeneous silver catalyst was prepared and applied efficiently for the selective bromination of aromatics with NBS. The silver nanoparticles combined with the acidic support HMB can activate both the aromatic ring and NBS, and the synergistic effects between the silver nanoparticles and the HMB highly enhanced the efficiency of the bromination reaction.
- Zhang, Rui,Huang, Lei,Zhang, Yanfang,Chen, Xiaorong,Xing, Weihong,Huang, Jun
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experimental part
p. 378 - 383
(2012/06/18)
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- Aromatic substitution in ball mills: Formation of aryl chlorides and bromides using potassium peroxomonosulfate and NaX
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Aryl chlorides and bromides are formed from arenes in a ball mill using KHSO5 and NaX (X = Cl, Br) as oxidant and halogen source, respectively. Investigation of the reaction parameters identified operating frequency, milling time, and the number of milling balls as the main influencing variables, as these determine the amount of energy provided to the reaction system. Assessment of liquid-assisted grinding conditions revealed, that the addition of solvents has no advantageous effect in this special case. Preferably activated arenes are halogenated, whereby bromination afforded higher product yields than chlorination. Most often reactions are regio- and chemoselective, since p-substitution was preferred and concurring side-chain oxidation of alkylated arenes by KHSO5 was not observed. The Royal Society of Chemistry.
- Schmidt, Robert,Stolle, Achim,Ondruschka, Bernd
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p. 1673 - 1679
(2013/02/22)
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- Photochemical dehalogenation mediated by macrocyclic nickel(II) complexes
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A new photochemical dehalogenation system mediated by macrocyclic nickel(II) complexes was developed. Using this system, which consists of a macrocyclic nickel(II) complex catalyst, triethanolamine (TEOA) as a sacrificial reductant, and the ruthenium complex [Ru(bpy)3](ClO 4)2 as a photosensitizer, catalytic debromination of 1-bromo-4-t-butylbenzene in acetonitrile was effectively carried out. The catalytic capabilities of various macrocyclic nickel(II) complexes in debromination reactions were also elucidated.
- Mochizuki, Katsura,Suzuki, Mana
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experimental part
p. 902 - 905
(2011/06/23)
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- Regioselective bromination of organic substrates by LDH-CO3 2--Br- promoted by V2O5-H 2O2
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An efficient, fast, simple, mild, and selective monobromination of aromatic compounds, with high para-selectivity, is reported. The catalytic system is readily prepared from a Mg-Al-layered double hydroxide-CO3 2--Br- (LDH-CO32--Br-) as the source of bromide, V2O5 as a promoter and hydrogen peroxide as the oxidant. The use of hydrogen peroxide as a synthetically useful oxidizing agent is reported for generating electrophilic bromine in situ from easily available KBr as a bromine source, to brominate electron rich aromatic compounds, employing LDH-CO32--Br3- as the phase-transfer catalyst. The phase-transfer catalyst leads to nearly complete bromination in 3 h at room temperature with high selectivity. The reaction rate of p-bromoanisole and p-bromotoluene formation by LDH-CO 32--Br3- in a triphasic system was studied. The heterogeneity of the reaction system facilitates the recovery and recycling of the catalyst, and the reagent components are environmentally acceptable. The catalyst, LDH-CO32--Br3 -, and its precursors, LDH-CO32--Br- and LDH-CO32-, were characterized by powder XRD, FT-IR and UV-vis spectroscopy.
- Ghiaci,Sedaghat,Ranjbari,Gil
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experimental part
p. 18 - 26
(2011/01/05)
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- Gold-catalyzed halogenation of aromatics by N-halosuccinimides
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(Chemical Equation Presented) Golden bromination: A highly efficient and mild AuCl3-catalyzed bromination of aromatic rings with Nbromosuccinimide (NBS) has been developed. This method works with a low catalyst loading (down to 0.01 mol %) and can be combined with transition metal catalyzed transformations to deliver various aryl products.
- Mo, Fanyang,Yan, Jerry Mingtao,Qiu, Di,Li, Fei,Zhang, Yan,Wang, Jianbo
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scheme or table
p. 2028 - 2032
(2010/06/17)
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- Environmentally benign electrophilic and radical bromination 'on water': H2O2-HBr system versus N-bromosuccinimide
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A H2O2-HBr system and N-bromosuccinimide in an aqueous medium were used as a 'green' approach to electrophilic and radical bromination. Several activated and less activated aromatic molecules, phenylsubstituted ketones and styrene were efficiently brominated 'on water' using both systems at ambient temperature and without an added metal or acid catalyst, whereas various non-activated toluenes were functionalized at the benzyl position in the presence of visible light as a radical activator. A comparison of reactivity and selectivity of both brominating systems reveals the H2O2-HBr system to be more reactive than NBS for benzyl bromination and for the bromination of ketones, while for electrophilic aromatic substitution of methoxy-substituted tetralone it was higher for NBS. Also, higher yields of brominated aromatics were observed when using H2O2-HBr 'on water'. Bromination of styrene reveals that not just the structure of the brominating reagent but the reaction conditions: amount of water, organic solvent, stirring rate and interface structure, play a key role in defining the outcome of bromination (dibromination vs bromohydroxylation). In addition, mild reaction conditions, a straightforward isolation procedure, inexpensive reagents and a lower environment impact make aqueous brominating methods a possible alternative to other reported brominating protocols.
- Podgor?ek, Ajda,Stavber, Stojan,Zupan, Marko,Iskra, Jernej
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experimental part
p. 4429 - 4439
(2009/10/09)
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- Contrasting chemoselectivities in the ultrasound and microwave assisted bromination reactions of substituted alkylaromatics with N-bromosuccinimide
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Ultrasound and microwave assisted bromination reactions of various alkylaryls with N-bromosuccinimide, either neat or in water, shows diverse chemoselectivity. Thus, ring substitution occurs in water with ultrasound, whereas with microwaves both side-chain α-bromination and ring substitution occur. With neat reactants, side-chain α-bromination predominates for microwave assisted reactions. In the presence of water the chemoselectivity with microwave-promoted bromination is similar to that observed using classical methods.
- Heropoulos, Georgios A.,Cravotto, Giancarlo,Screttas, Constantinos G.,Steele, Barry R.
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p. 3247 - 3250
(2008/02/02)
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- Induced bromination of aromatic hydrocarbons with alkali metal bromides in the presence of oxidants
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The features of induced bromination of aromatic hydrocarbons in the NaBr(KBr)-HX-H2O2(NaOCl) system were studied. Pleiades Publishing, Inc., 2006.
- Sadygov,Alimardanov,Chalabiev
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p. 949 - 956
(2008/02/05)
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- A new ring bromination method for aromatic compounds under solvent-free conditions with NBS/Al2O3
-
Alumina supported N-bromosuccinimide was found to be an efficient reagent for ring bromination of a number of aromatic compounds under solvent-free conditions. In the absence of the alumina the reactions are slow and some of the substrates are recovered unchanged. Under the reaction conditions aromatic oximes are converted into the corresponding carbonyl compounds. The method is simple, safe and rapid.
- Imanzadeh, Gholamhassan K.,Zamanloo, Mohammad R.,Eskandari, Habibollah,Shayesteh, Keyvan
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p. 151 - 153
(2007/10/03)
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- Grindstone chemistry: (Diacetoxyiodo)benzene-mediated oxidative nuclear halogenation of arenes using NaCl, NaBr or I2
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A technique of "Grindstone chemistry" is applied to the solvent-free halogenation of arenes with NaCl, NaBr or I2 using (diacetoxyiodo)benzene as the oxidant. Improved yields and higher purities of the products are observed compared with those from established methods.
- Karade,Tiwari,Huple,Siddiqui
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p. 366 - 368
(2007/10/03)
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- Induced bromination of aromatic hydrocarbons by alkali metals bromides and sodium hypochlorite
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Induced bromination of aromatic compounds in a system MBr-acid-NaOCl was studied. Optimum conditions of the process were developed, kinetics of the reactions were investigated, and the process mechanism was suggested. The bromination occurs both with the bromine in statu nascendi and with the hypobromous acid by hydrogen substitution exclusively in the aromatic ring. 2005 Pleiades Publishing, Inc.
- Sadygov,Alimardanov,Chalabiev
-
p. 1631 - 1636
(2007/10/03)
-
- A new method for the oxybromination of aromatic compounds with copper(II)bromide and potassium dichromate
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A new and mild method for oxybromination of aromatic compounds with CuBr2 and K2Cr2O7 in HOAC is reported. Copyright Taylor & Francis Inc.
- Badri, Rashid,Shushizadeh, Mohammad Reza
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p. 533 - 536
(2007/10/03)
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- The conversion of phenols to the corresponding aryl halides under mild conditions
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Mild, novel procedures have been developed for the syntheses of aryl halides from the corresponding phenols in modest to good yields via boronate ester intermediates.
- Thompson, Alicia L. S.,Kabalka, George W.,Akula, Murthy R.,Huffman, John W.
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p. 547 - 550
(2007/10/03)
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- Ionic liquid promoted regioselective monobromination of aromatic substrates with N-bromosuccinimide
-
Aromatic substrates were monobrominated regioselectively with NBS in the ionic liquid 1,3-di-n-butylimidazolium tetrafluoroborate [bbim]BF4 in 5 min at 28°C in excellent isolated yields (80-98%) in the absence of a catalyst.
- Rajagopal,Jarikote,Lahoti,Daniel, Thomas,Srinivasan
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p. 1815 - 1817
(2007/10/03)
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- Efficient method for the preparation of aromatic bromides and iodides by ferrocenium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate-catalyzed halogenation with bromine and iodine monochloride
-
Direct iodination and bromination of various aromatic compounds with 1.1-2.0 molar amounts of iodine monochloride (ICl) and 1.1-3.0 molar amounts of bromine proceeded smoothly to afford the corresponding aromatic iodides and bromides, respectively, in good to excellent yields by using 0.05 molar amount of ferrocenium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, Cp2FeB[3,5-(CF3)2C6H 3]4 (1), in the presence of ZnO. Iodination of toluene in the co-existence of 0.5 molar amount of DDQ also proceeded to give iodotoluenes in high yield.
- Kitagawa, Hideo,Shibata, Tsuyoshi,Matsuo, Jun-Ichi,Mukaiyama, Teruaki
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p. 339 - 345
(2007/10/03)
-
- Novel process for generating useful electrophiles from common anions using Selectfluor fluorination agent
-
In the present work, the electrophile equivalents C1+, Br+, SCN+, and NO2+ are generated from their respective sodium, potassium, and in some cases ammonium salts (M+X-) by reaction with Selectfluor electrophilic fluorination agent in acetonitrile solution at room temperature. These generated electrophilic species subsequently react in situ with a variety of aromatic substrates containing one or more substituent groups including H, F, C1, CH3, COOH, C(O)CH3, NO2, and OR′ and NR′R″ where R′ and R″ are H or CH3. The resulting substitution products are, in most cases, isolable as pure compounds in high yield. Variations in the process include the use of other anions, electrophilic fluorination agents, and solvents.
- Syvret, Robert G.,Butt, Kathleen M.,Nguyen, Tung P.,Bulleck, Victoria L.,Rieth, Ryan D.
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p. 4487 - 4493
(2007/10/03)
-
- Increasing the selectivity of bromination of aromatic compounds using Br2/SiO2
-
Br2/SiO2 possessed considerable practical advantages over traditional reagents for the bromination of aromatic hydrocarbons, e.g., toluene, o-, m-, and p-xylene, anthracene and phenol. In the presence of SiO2, toluene reacted with bromine instantly. Compounds containing electron-donating substituents showed mainly bromination on the rings. The behavior of o-, m-, and p-xylene showed predominant substitution on the rings. The bromination of phenol to p-bromophenol showed good yield at 81%. Naphthalene was monobrominated to 1-bromonaphthalene with a yield of 84% in 2 has the potential to alter reaction selectivity. It may be able to switch a mechanism from radical to polar, or to influence the regioselectivity of the products formed. In the absence of SiO2, selectivity was lost and a mixture of products by substitution of bromine atom on the ring and on the side chain without any preferability was obtained. The nature of silica gel was important for the success of the reaction. Optimal results were obtained with silica gel dried at 250°C for 1 hr.
- Ghiaci,Asghari
-
p. 1151 - 1152
(2007/10/03)
-
- A new synthesis and application of N, N'-dibromo-N, N'-1,2-ethylene bis(2,5-dimethyl benzene sulfonamide); as a novel selective bromination agent for aromatic compounds
-
Reaction Between Novel Compound; N, N' dibromo-N, N'-1,2- ethylene bis(2,5- dimethyl benzene sulfonamide) and aromatic compounds in the carbontetrachloride produces bromo aromatic compounds. In the case of benzene rings that contain mono activated substituted, only para - bromo isomer was formed. At the presence of benzoyl peroxide in the reaction mixture α - Hydrogen from alkyl side chain was substituted with bromine.
- Ardeshir, Khazaei,Abbas, Shirdarreh
-
p. 4079 - 4085
(2007/10/03)
-
- Selectivity in bromination of alkylbenzenes in the presence of montmorillonite clay
-
Bromination of alkylbenzenes using bromine in carbon tetrachloride yields ring brominated products in the presence of K10-montmorillonite. In contrast, bromination without clay results only in side-chain bromination.
- Venkatachalapathy, Chockalingam,Pitchumani, Kasi
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p. 2581 - 2584
(2007/10/03)
-
- Aromatic Spiranes XX [1]: Syntheses of Dimethylsubstituted 2-Carboxymethyl-indan-1-ones and Benzylchlorides as Synthones for Syntheses of di- to tetramethylsubstituted Spirobiindandiones
-
The isomeric dimethyl methylbenzoates 5, obtained from the bromides via Grignard reactions with dimethylcarbonate, were reduced with LiAlH4 to the hydroxymethyl derivatives 6. The latter were then transformed both to the benzylchlorides 7 (with SOCl2) and to the aldehydes 8 (with pyridinium chlorochromate). Knoevenagel-Doebner reaction of 8 afforded the acrylic acids 9 which (after hydrogenation to 11) were cyclized to the desired indanones 12 with polyphosphoric acid. On the other hand, 12c and 12e were prepared from dimethyl 3-chloropropiophenone (14) by warming with sulfuric acid. After NaH-catalyzed reaction with dimethylcarbonate, the indanones 12 gave the ketoesters 15 which then could be hydrogenated to the indanes 16. All reactions proceeded with satisfactory to excellent yields (60-90%).
- Neudeck
-
p. 185 - 200
(2007/10/03)
-
- Ring Halogenations of Polyalkylbenzenes by Ionic Halides and Koser's Reagent
-
Ring chlorinations of polyalkylbenzenes such as mesitylene have been carried out at room temperature with LiCl or NaCl and stoichiometric amounts of Koser's reagent.Solvent range from water to methylene chloride.The procedures were extended to bromination and iodination.
- Bovonsombat, Pakorn,Djuardi, Elsa,Nelis, Edward Mc
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p. 2841 - 2844
(2007/10/02)
-
- Ring halogenations of polyalkylbenzenes with N-halosuccinimide and acidic catalysts
-
1-Bromo-2,5-pyrrolidinedione (NBS) and 1-chloro-2,5-pyrrolidinedione (NCS) with catalytic quantities of p-toluenesulfonic acid have been used for ring halogenations of polyalkylbenzenes. [Hydroxy(tosyloxy)iodo]benzene was effective as a catalyst with NBS but not NCS. Competition experiments with 1-iodo-2,5-pyrrolidinedione (NIS) were run to indicate selectivities in substrates, halogen sources and catalysts. With this information a mixed halogenated compound, 2-bromo-4-iodo-1,3,5-trimethylbenzene was prepared in high yield.
- Bovonsombat,McNelis
-
p. 237 - 241
(2007/10/02)
-
- A simple and improved procedure for selective ring bromination of alkyl-substituted aromatic hydrocarbons on the surface of alumina
-
Highly selective ring bromination of alkyl-substituted aromatic hydrocarbons has been achieved using molecular bromine adsorbed on the surface of alumina without any solvent.
- Ranu,Sarkar,Chakraborty
-
p. 1095 - 1099
(2007/10/02)
-
- Bromine/Bentonite Earth System, Promoter of Phenylmethanes from Toluene
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The condensation of toluene to produce o- and p-methylphenylmethanes by use of bromine with a bentonitic earth catalyst has been investigated and a mechanism is proposed based on the isolated intermediates and other related reactions.
- Salmon, Manuel,Angeles, Enrique,Miranda, Rene
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p. 1188 - 1190
(2007/10/02)
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- Halogenation Using Quaternary Ammonium Polyhalides. XIV. Aromatic Bromination and Iodination of Arenes by Use of Benzyltrimethylammonium Polyhalides-Zinc Chloride System
-
The reaction of arenes with benzyltrimethylammonium tribromide or benzyltrimethylammonium dichloroiodate in acetic acid in the presence of ZnCl2 at room temperature or at 70 deg C gave brome- or iodo-substituted arenes in good yield, respectively.
- Kajigaeshi, Shoji,Kakinami, Takaaki,Moriwaki, Masayuki,Tanaka, Toshio,Fujisaki, Shizuo,Okamoto, Tsuyoshi
-
p. 439 - 443
(2007/10/02)
-
- BROMINATION OF AROMATIC MOLECULES WITH POLYMER SUPPORTED REAGENTS
-
Crosslinked co poly/styrene-4-vinyl(N-hexylpyridinium bromide) was converted with bromine or chlorine to insoluble polymer supported complexes 1 or 2 respectively, and their reactivity studied in reactions with various aromatic molecules.Reagent 1 was found in all cases to be milder than reagent 2 and regiospecifically transformed alkoxy and amino substituted benzenes (3) into 4-bromo derivatives, while corresponding reactions with 2 resulted in dibromo derivatives.Several benzoheterocyclic molecules were converted with 1 to substitution or addition products, i.e. 2,3-dibromo-N-methylpyrrole, 3-bromobenzo/b/thiophene, and 2,3-dibromo-2,3-dihydrobenzofuran.In the series of ortho-alkyl disubstituted benzene derivatives, i.e. o-xylene, indane, and tetraline, where the Mills-Nixon effect was established with various electrophilic reagents, bromination reactions with 2 showed higher β-selectivity than the corresponding reactions with bromine.The rate of bromination in various alkyl substituted benzenes with reagent 2 depended on the magnitude of the alkyl group, as well as the para/ortho regioselectivity, amounting to 100percent in the case of tert-butylbenzene.
- Zajc, Barbara,Zupan, Marko
-
p. 7869 - 7878
(2007/10/02)
-
- CATALYTIC AND STOICHIOMETRIC BROMINATION OF AROMATIC COMPOUNDS IN AQUEOUS TRIFLUOROACETIC ACID IN THE PRESENCE OF NITROGEN-CONTAINING OXIDIZING AGENTS
-
The mono- and polybromination of benzene, halogenobenzenes, toluene, p-xylene, anisole, biphenyl, benzotrifluoride, benzoic acid, p-nitro- and p-carboxytoluene, p-methoxybenzonitrile, tetralin, and naphtalene were studied in trifluoroacetic acid and its aqueous solutions in systems containing stoichiometric amounts of bromine or alkali-metal bromide and stoichiometric or catalytic (in the presence of oxygen or air) amounts of nitrogen-containing oxidizing agent (nitrogen(IV) oxide, alkali-metal nitrate or nitrite).It is suggested that the brominating agent under the investigated conditions is nitryl bromide NO2Br.Under the conditions of catalytic bromination anthracene is oxidized to anthraquinone with a preparative yield.
- Cheprakov, A. V.,Makhon'kov, D. I.,Rodkin, M. A.,Beletskaya, I. P.
-
p. 217 - 223
(2007/10/02)
-
- Protonation-induced Isomerization of Gaseous Bromoxylenes : a Radiolytic and Mass Spectrometric Study
-
The isomerization of bromoxylenes following protonation by X3+ (X=H or D), CnH5+ (n=1 or 2), iso-C3H7+, and t-C4H9+ ions in the dilute gas state has been investigated.Further evidence has been derived from chemical ionization mass spectrometry and related radiolytic experiments concerning methylation of bromotoluenes by gaseous (CH3)2F+ ions.The results suggest that the observed intramolecular Br migration involves the intermediacy of a radical cation-bromine atom pair.The mechanistic relevance of the results to gas-phase aromatic substitution by free bromine cations is discussed.
- Cacace, Fulvio,Ciranni, Giovanna,Marzio, Annito Di
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p. 775 - 780
(2007/10/02)
-
- Phenyl Cations as Reactive Intermediates in the Solvolysis of Dien-in-yl Triflates
-
The synthesis, separation, and solvolysis of the stereoisomeric 1,4-dimethyl-1,3-hexadien-5-yn-1-yl triflates 15a - c in various solvents are described.In contrast to the (Z)-isomers 15a - c, the (E)-isomers 15a - c react preferably via an intermediate phenyl cation 16 to give the phenyl ethers 17.Further mechanistic investigations which support the formation of the intermediate phenyl cations 16 are described.The formation of the benzylic derivatives 18 is discussed.
- Holweger, Walter,Hanack, Michael
-
p. 3004 - 3020
(2007/10/02)
-
- Experimental Evidence for a Phenyl Cation Intermediate in the Solvolysis Reactions of Dienynyl Trifluoromethanesulphonates
-
The synthesis, separation, and solvolysis of the stereoisomeric dienynyl trifluoromethanesulphonates (1) are described, whereby the E-isomers, in contrast with the Z-isomers, rearrange to a remarkable extent to form the phenyl ethers (5) via the phenyl cations (2).
- Hanack, Michael,Holweger, Walter
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p. 713 - 714
(2007/10/02)
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- Regioselective Ring Opening in Substituted Benzocyclopropenes. An Alternative or Complementary Mechanism for Electrophilic Substitution Involving Attack at a ? Bond
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2-Methylbenzocyclopropene (5) reacts with bromine, iodine, and HCl to give the m-xylenes 12a,c,d as the major products, whereas it reacts with silver nitrate in the presence of ethanol and aniline to give the o-xylenes 11e,f as the major products.Similarly, 3-methylbenzocyclopropene (10) gives mainly m-xylenes 14a,c,d with halogens and HCl and gives p-xylenes 13e,f with silver nitrate and ethanol or aniline.Cyclopropabenzocyclobutene (15) also gives different products with halogens and silver nitrate, but in this case HCl gives the same type of product as the silver ion.The difference in electrophilic behavior of 5, 10, and 15 toward the two types of reagents is suggested to arise from attack of the silver ion (and the proton in the case of 15) on the ? electrons of the cyclopropyl ring.
- Bee, Lim Keow,Garratt, Peter J.,Mansuri, Muzamil M.
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p. 7076 - 7079
(2007/10/02)
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- ACCES AUX DINITRO-2,4 DIARYLAMINES PAR SUBSTITUTION NUCLEOPHILE SNAr-LIMITES DE LA REACTION ET APPLICATION A LA SYNTHESE DE CYANOCARBAZOLES
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3-Cyanocarbazoles, key-intermediates in the total synthesis of pyrido carbazoles, have been obtained starting from easily available materials and involving the cyclization of diarylamines.The first step of the preparation consists in a SNAr reaction between a para substituted aniline and a chloro- (or bromo)-dinitrobenzene.This nucleophilic substitution has been found to be hindered by the steric effect of a methyl group, explained in terms of inhibition of resonance and confirmed by X-ray determination.
- Henichart, J. P.,Bernier J. L.,Vaccher, C.,Houssin, R.,Warin, V.,Baert, F.
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p. 3535 - 3542
(2007/10/02)
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- Process for preparation of 2,5-dibromo-p-xylene
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Selective bromination process for 2,5-dibromo-p-xylene which comprises bromination of p-xylene using approximately stoichiometric amounts of bromine and a hydrated iron containing bromination catalyst to give selectively high yields of substantially pure 2,5-dibromo-p-xylene.
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