- Chemistry of ethanediyl S,S-acetals 6-an example of vicarious nucleophilic substitution of hydrogen in 1,4-benzodithians
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1,4-Benzodithians, when treated with bromine in anhydrous chloroform, undergo very fast monobromination at the aromatic ring. By the use of quantum mechanical semiempirical calculations, the reaction is shown to proceed most likely via a vicarious nucleophilic substitution of hydrogen.
- Caputo, Romualdo,De Nisco, Mauro,Palumbo, Giovanni,Adamo, Carlo,Barone, Vincenzo
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Read Online
- 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.
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Paragraph 0038; 0059-0060
(2020/12/14)
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- Carbocation Catalyzed Bromination of Alkyl Arenes, a Chemoselective sp3 vs. sp2 C?H functionalization.
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The versatility of the trityl cation (TrBF4) as a highly efficient Lewis acid organocatalyst is demonstrated in a light induced benzylic brominaion of alkyl-arenes under mild conditions. The reaction was conducted at ambient temperature under common hood light (55 W fluorescent light) with catalyst loadings down to 2.0 mol% using N-bromosuccinimide (NBS) as the brominating agent. The protocol is applicable to an extensive number of substrates to give benzyl bromides in good to excellent yields. In contrast to most previously reported strategies, this protocol does not require any radical initiator or extensive heating. For electron-rich alkyl-arenes, the trityl ion catalyzed bromination could be easily switched between benzylic sp3 C?H functionalization and arene sp2 C?H functionalization by simply alternating the solvent. This chemoselective switch allows for high substrate control and easy preparation of benzyl bromides and bromoarenes, respectively. The chemoselective switch was also applied in a one-pot reaction of 1-methylnaphthalene for direct introduction of both sp3 C?Br and sp2 C?Br functionality. (Figure presented.).
- Ni, Shengjun,El Remaily, Mahmoud Abd El Aleem Ali Ali,Franzén, Johan
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supporting information
p. 4197 - 4204
(2018/09/25)
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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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- Transition-metal-free decarboxylative bromination of aromatic carboxylic acids
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Methods for the conversion of aliphatic acids to alkyl halides have progressed significantly over the past century, however, the analogous decarboxylative bromination of aromatic acids has remained a longstanding challenge. The development of efficient methods for the synthesis of aryl bromides is of great importance as they are versatile reagents in synthesis and are present in many functional molecules. Herein we report a transition metal-free decarboxylative bromination of aromatic acids. The reaction is applicable to many electron-rich aromatic and heteroaromatic acids which have previously proved poor substrates for Hunsdiecker-type reactions. In addition, our preliminary mechanistic study suggests that radical intermediates are not involved in this reaction, which is in contrast to classical Hunsdiecker-type reactivity. Overall, the process demonstrates a useful method for producing valuable reagents from inexpensive and abundant starting materials.
- Quibell, Jacob M.,Perry, Gregory J. P.,Cannas, Diego M.,Larrosa, Igor
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p. 3860 - 3865
(2018/04/26)
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- A Metal-Free and Ionic Liquid-Catalyzed Aerobic Oxidative Bromination in Water
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A metal-free aerobic oxidative bromination of aromatic compounds in water has been developed. Hydrobromic acid is used as a bromine source and 2-methylpyridinium nitrate ionic liquid is used as a recyclable catalyst. Water is used as the reaction mediate. This is the first report of aerobic oxidative bromination using only catalytic amount of metal-free catalyst. This system shows not only high bromine atom economy, but also high bromination selectivity. The possible mechanism and the role of the catalyst in this system have also been discussed.
- Wang, Jian,Chen, Shu-Bin,Wang, Shu-Guang,Li, Jing-Hua
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p. 513 - 517
(2015/03/30)
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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
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supporting information
p. 1063 - 1066
(2013/04/10)
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- Fast and efficient bromination of aromatic compounds with ammonium bromide and Oxone
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A highly efficient, rapid and regioselective protocol was developed for the ring bromination of aromatic compounds under mild conditions with ammonium bromide as a source of bromine source and Oxone (potassium peroxysulfate) as an oxidant. No metal catalyst or acidic additive is required. A variety of aromatic compounds, including methoxy, hydroxy, amino, and alkyl arenes, reacted smoothly to give the corresponding monobrominated products in good to excellent yields in very short reaction times. Moreover, dibromination of deactivated anilines to give the corresponding dibromides proceeded in high yields. Interestingly, 1-(2-naphthyl)ethanone provided a ring-brominated product. Georg Thieme Verlag Stuttgart . New York.
- Naresh, Mameda,Arun Kumar, Macharla,Mahender Reddy, Marri,Swamy, Peraka,Nanubolu, Jagadeesh Babu,Narender, Nama
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p. 1497 - 1504
(2013/06/27)
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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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- 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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- Bromination of aromatic compounds using ammonium bromide and oxone
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A simple, efficient and mild method for the selective bromination of activated aromatic compounds using ammonium bromide as the source of bromine and Oxone as the oxidant in methanol or water as solvent is reported. The reaction proceeds at ambient temperature in yields ranging from moderate to excellent without a catalyst. Georg Thieme Verlag Stuttgart.
- Arunkumar, MacHarla,Rohitha, Chozhiyath Nappunni,Kulkarni, Shivanand Janardhan,Narender, Nama
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experimental part
p. 1629 - 1632
(2010/06/20)
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- Palladium-catalyzed conversion of aryl and vinyl triflates to bromides and chlorides
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The palladium-catalyzed conversion of aryl and vinyl triflates to aryl and vinyl halides (bromides and chlorides) has been developed using dialkylbiaryl phosphine ligands. A variety of aryl, heteroaryl, and vinyl halides can be prepared via this method in
- Shen, Xiaoqiang,Hyde, Alan M.,Buchwald, Stephen L.
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supporting information; experimental part
p. 14076 - 14078
(2011/01/10)
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- Synthesis of arylbromides from arenes and Nbromosuccinimide bromosuccinimide (NBS) in acetonitrile - A convenient method for aromatic bromination
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Regioselective and chemoselective electrophilic bromination of a wide series of activated arenes using N-bromosuccinimide (NBS) in acetonitrile occurs readily. Environmentally friendly conditions, large substrate scope, and ease of synthesis enhance the utility of this method over other electrophilic bromination conditions.
- Zysman-Colman, Eli,Arias, Karla,Siegel, Jay S.
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experimental part
p. 440 - 447
(2009/12/01)
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- Highly efficient halogenation of organic compounds with halides catalyzed by cerium(III) chloride heptahydrate using hydrogen peroxide as the terminal oxidant in water
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In this article a new environmentally friendly catalytic method is described for the efficient monoiodination and bromination of arenes and also iodoetherification and iodolactonization of olefins using hydrogen peroxide as the terminal oxidant. The method is based on using sodium iodide or sodium bromide, hydrogen peroxide (35%) and cerium(III) chloride as an effective catalyst in water at room temperature or under reflux conditions. By this protocol, iodination of anilines proceeded with high regioselectivity at the para position with the formation of small amounts of the ortho isomers. However, bromination of anilines proceeded with absolute regioselectivity to give the para isomers as the sole products in high yields. Iodinations and bromi-nations of m-xylene, toluene, chloro- and bromobenzenes were proceeded with excellent regioselectivity to produce the para isomers as the sole products. Benzene was also halogenated by this catalytic system to give the monohalogenated benzene in good yields. Iodoetherification and iodolactonization of olefins also proceeded easily in high yields at room temperature. However, the bromination of olefins by this protocol failed and the starting materials were detected intact.
- Firouzabadi, Habib,Iranpoor, Nasser,Kazemi, Somayeh,Ghaderi, Arash,Garzan, Atefeh
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experimental part
p. 1925 - 1932
(2011/03/18)
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- Direct halogenation of organic compounds with halides using oxone in water - A green protocol
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Direct bromination and iodination of various aromatic compounds with NaBr and NaI using oxone (2KHSO5·KHSO4·K 2S04) in water was accomplished successfully in high-to-excellent yields. The main benefit of this protocol is the performance of the reactions in water in the presence of a harmless oxidant without the use of any organic cosolvents. Using NaBr and NaI as the safe sources of halogens is another advantage of the protocol. This method is easily applicable to the large-scale operations. We have also applied this method successfully for the iodocyclization of an unsaturated alcohol and an unsaturated carboxylic acid.
- Firouzabadi,Iranpoor,Kazemi
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experimental part
p. 1675 - 1681
(2010/01/29)
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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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- 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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- A new ring bromination method for aromatic compounds under solvent-free conditions with NBS/Al2O3
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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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- 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
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p. 1631 - 1636
(2007/10/03)
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- 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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- (Diacetoxyiodo)benzene-Lithium Bromide as a Convenient Electrophilic Br+ Source
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A mild and versatile procedure for the bromination of olefins and activated arenes by in situ generation of 'Br+' using (diacetoxyiodo)benzene and lithium bromide is presented. The reactions were carried out in open vessels at room temperature and were typically complete in 30 minutes. The brominated products were isolated by column chromatography, which also allowed for the isolation of the iodobenzene by-product for recycle.
- Braddock, D. Christopher,Cansell, Gemma,Hermitage, Stephen A.
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p. 461 - 464
(2007/10/03)
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- Ionic liquid promoted regioselective monobromination of aromatic substrates with N-bromosuccinimide
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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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- Oxidative halogenation of aromatic compounds with metal halides and sodium bismuthate
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A new mild and efficient method for aromatic halogenation with a wide variety of halides in the presence of sodium bismuthate NaBO3 in AcOH is reported. Metal halides of groups Ia, IIa, IIIa, IVa, Va, and the first row of transition elements are suitable for this method.
- Muathen, Hussni A.
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p. 164 - 168
(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
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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)
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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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- Increasing the selectivity of bromination of aromatic compounds using Br2/SiO2
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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
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p. 1151 - 1152
(2007/10/03)
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- Regioselective bromination of organic substrates by tetrabutylammonium bromide promoted by V2O5-H2O2: An environmentally favorable synthetic protocol
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(matrix presented) Vanadium pentoxide very effectively promotes the bromination of organic substrates, including selective bromination of some aromatics, by tetrabutylammonium bromide in the presence of hydrogen peroxide; mild conditions, high selectivity, yield, and reaction rate, and redundancy of bromine and hydrobromic acid are some of the major advantages of the synthetic protocol.
- Bora, Upasana,Bose, Gopal,Chaudhuri, Mihir K.,Dhar, Siddhartha S.,Gopinath, Rangam,Khan, Abu T.,Patel, Bhisma K.
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p. 247 - 249
(2007/10/03)
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- Selectivity in bromination of alkylbenzenes in the presence of montmorillonite clay
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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)
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- 1,3-dibromo-5,5-dimethylhydantoin, a useful reagent for aromatic bromination
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1,3-dibromo-5,5-dimethylhydantoin (DBDMH) is a useful and easy to handle reagent for bromination of various aromatic derivatives substituted with electron donating groups. In the presence of trimethylsilyltrifluoromethanesulfonate, DBDMH showed increased reactivity, and in one case, the reaction followed another pathway, suggesting an alternative mechanism.
- Chassaing, Christophe,Haudrechy, Arnaud,Langlois, Yves
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p. 4415 - 4416
(2007/10/03)
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- Aromatic Spiranes XX [1]: Syntheses of Dimethylsubstituted 2-Carboxymethyl-indan-1-ones and Benzylchlorides as Synthones for Syntheses of di- to tetramethylsubstituted Spirobiindandiones
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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
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p. 185 - 200
(2007/10/03)
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- Biphasic Electrophilic Halogenation of Activated Aromatics and Heteroaromatics with N-Halosuccinimides Catalyzed by Perchloric Acid
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Catalytic amounts of 70percent perchloric acid (0.1 - 10, mostly 0.1 - 1, mol percent, based on substrate) initiate the regioselective halogenation of activated aromatics and heteroaromatics with N-halosuccinimide (NXS, X = Cl or Br) in two-phase solid-liquid systems (NXS/hexane or NXS/CCl4) at room temperature to give ring-halogenated products in high yields.For example, thiophene is transformed to 2-halo or 2,5-dihalo derivatives (yield 82-98percent) using 1 or 2 equiv of NXS, respectively.Unsymmetrical 2,5-dihalothiophenes are obtained in 70-82percent yield by reacting 2-halothiophenes with an appropriate NXS.The reaction of 3-bromothiophene with NBS affords 2,3-dibromothiophene in 93-99percent yield. 1,3-Dimethoxybenzene and 2,3-dimethylanisole are halogenated regiospecifically at the 4-position to give the corresponding products in 81-94percent yield.
- Goldberg, Yuri,Alper, Howard
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p. 3072 - 3075
(2007/10/02)
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- A simple and improved procedure for selective ring bromination of alkyl-substituted aromatic hydrocarbons on the surface of alumina
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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
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p. 1095 - 1099
(2007/10/02)
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- ON THE ABSOLUTE REACTIVITY OF ARYL CATIONS: SELECTIVITY TOWARD HALIDE IONS AS A FUNCTION OF VISCOSITY
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The selectivities toward bromide and chloride ions observed in the dediazoniation of three arenediazonium salts are found to be independent of viscosity.It is inferred that the capture of aryl cations by these halide ions is diffusion controlled.
- Lorand, John P.
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p. 7337 - 7340
(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
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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
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p. 439 - 443
(2007/10/02)
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- BROMINATION OF AROMATIC MOLECULES WITH POLYMER SUPPORTED REAGENTS
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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
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p. 7869 - 7878
(2007/10/02)
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- Protonation-induced Isomerization of Gaseous Bromoxylenes : a Radiolytic and Mass Spectrometric Study
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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)
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- Chemistry in Superacids. 6. Perfluoroalkanesulfonic Acid-Boron Perfluoroalkanesulfonates: New Superacid Systems for Generation of Carbocations and Catalysts for Electrophilic Transformations of Hydrocarbons
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Boron trihalides (BX3, X = Cl, Br) react with excess perfluoroalkanesulfonic acids to give conjugate superacids of the type RFSO2OH2+F)4>- (RF = CF3, C4F9, and C10F21).The systems were characterized by spectroscopy and their chemical (catalytic) properties were studied.The parent of the series CF3SO3H2+- (1) (first reported by Engelbrecht and Tschager) was found to O-protonate ketones and to generate stable tert-alkyl- and methyl-substituted benzylic cations at low temperature in SO2ClF.Stable ions are similarly generated in B(OSO2CF3)3/SO2ClF.The catalytic activity of the conjugate superacid 1 has been demonstrated in transbromination/transalkylation of aromatics as well as in isomerization of n-butane, n-hexane, and trimethylenenorbornane to adamantane under mild conditions.
- Olah, George A.,Laali, Khosrow,Farooq, Omar
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p. 4591 - 4594
(2007/10/02)
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- ETUDE CINETIQUE DE LA REACTION DE BROMINATION DANS LE SO2 LIQUIDE. REACTIVITES DU BENZENE, DES POLYMETHYLBENZENES ET D'ANISOLES SUBSTITUES. DETERMINATION DES REACTIVITES RELATIVES ET CALCUL DES FACTEURS DE VITESSE PARTIELLE
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Absolute rate constants for the bromination of a series of anisoles and polymethylbenzenes, have been measured in liquid sulfur dioxide at -23 +/- 2 deg C.Rate constants for benzene and toluene were determined by extrapolation as: 9.6E-7 and 4.2E-4 l mol-1 mn-1 respectively.Under these conditions, the bromination of anisole provides 0.56percent ortho- and 98.99percent para-bromoanisole, and the rate relative to benzene is 6.98E8/1.00.These date lead to the partial rate factors for the methoxy group: οOMef = 1.1E7 and pOMef = 4.12E9.The value mOMef = 1.4 is calculated from the rate constant for p-dimethoxy benzene, 10 l mol-1 mn-1.Similarly, in the case of bromination of toluene, a relative rate of 443/1.00, and an isomer distribution of 16percent ortho- and 84percent para, permit the calculation of partial rate for the methyl group:οMef = 212 mMef = 6.4 pMef = 2232 > correlations log k = f(Σ?+), established for the bromination of anisoles and polymethylbenzenes, exhibit large values for their slopes (ρAnisoles+ = -10.51; ρ+polymethylbenzenes = -9.5), and indicate satisfactory additivity of substituent effects.It appears that the + M effect of the methoxy group is less strong in this solvent than it is in water or acetic acid.Despite its low dielectric constant, (D = 17.5 at -20 deg C), liquid sulfur dioxide appearars to be quite a favourable medium for electrophilic aromatic substitution.Thus, for identical experimental conditions, the rate constants for bromination are 1E2 to 1E4 lower than those observed in water, but 1E3 to 1E5 larger than those in acetic acid.
- Castellonese, Paul,Villa, Pierre
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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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