- 1H NMR spectroscopic study of the tert-butyl chloride - Aluminum bromide cationic initiating system
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The interaction of tert-butyl chloride with aluminum bromide in methylene dibromide at -30 °C leads to the formation of two types of adducts, which give signals with δ 2.4 and 3.2 in the 1H NMR spectra in addition to that of free alkyl halide. These signals are attributed to a polarized complex (PC) and ion pair (IP), respectively. An excess of AlBr3 shifts the equilibria toward IP. The latter contains more AlBr3 than the polarized complex. Based on the spectral data, we calculated the limiting values of some equilibrium constants. The ability of AlBr3 to solvate counterions is consistent with the results of isobutylene polymerization under the action of the initiating Bu1Cl-AlBr3 system at different ratios of the starting concentrations [AlBr3]0/[Bu1Cl]0. An increase in this ratio results in both the acceleration of polymerization and an increase in the relative role of chain transfer reactions.
- Murachev,Byrikhin,Nesmelov,Ezhova,Orlinkov
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Read Online
- A Convenient Method for the Preparation of Highly Pure t-Alkyl Bromides and Iodides
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Highly pure (99-100 percent) t-butyl and t-pentyl bromides and iodides, and 3-bromo-3-ethylpentane were readily prepared in 83-95 percent yields by the reactions of the corresponding alcohols with hydrobromic or hydroiodic acid, using lithium or calcium halide.The metal halides remarkably increased the yield and the purity of the products.
- Masada, Hiromitsu,Murotani, Yoshiharu
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Read Online
- Thiourea-Mediated Halogenation of Alcohols
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The halogenation of alcohols under mild conditions expedited by the presence of substoichiometric amounts of thiourea additives is presented. The amount of thiourea added dictates the pathway of the reaction, which may diverge from the desired halogenation reaction toward oxidation of the alcohol, in the absence of thiourea, or toward starting material recovery when excess thiourea is used. Both bromination and chlorination were highly efficient for primary, secondary, tertiary, and benzyl alcohols and tolerate a broad range of functional groups. Detailed electron paramagnetic resonance (EPR) studies, isotopic labeling, and other control experiments suggest a radical-based mechanism. The fact that the reaction is carried out at ambient conditions, uses ubiquitous and inexpensive reagents, boasts a wide scope, and can be made highly atom economic, makes this new methodology a very appealing option for this archetypical organic reaction.
- Mohite, Amar R.,Phatake, Ravindra S.,Dubey, Pooja,Agbaria, Mohamed,Shames, Alexander I.,Lemcoff, N. Gabriel,Reany, Ofer
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p. 12901 - 12911
(2020/11/26)
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- Metal- and base-free synthesis of aryl bromides from arylhydrazines
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An efficient method was developed to synthesize brominated aromatic compounds from arylhydrazine hydrochlorides by using BBr3 in DMSO/CPME (cyclopentyl methyl ether) under air at 80 °C for 1 h without the use of bases or metal catalysts. In particular, this method could be carried out satisfactorily using electron-withdrawing groups to afford aryl bromides in a moderate to excellent yields.
- Phuc Tran, Dat,Nomoto, Akihiro,Mita, Soichiro,Dong, Chun-ping,Kodama, Shintaro,Mizuno, Takumi,Ogawa, Akiya
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supporting information
(2020/05/08)
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- Reliably Regioselective Dialkyl Ether Cleavage with Mixed Boron Trihalides
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A protocol for the regioselective cleavage of unsymmetrical alkyl ethers to generate alkyl alcohol and alkyl bromide products is described. A mixture of trihaloboranes triggers this conversion and exhibits improved reactivity profiles (regioselectivity and yield) compared with BBr3 alone. Additionally, this procedure allows the efficient synthesis of (B-Cl) dialkyl boronate esters. There are limited methods to generate acyclic dialkoxyboryl chlorides, and these intermediates constitute important synthons in main-group chemistry.
- Atienza, Bren Jordan P.,Truong, Nam,Williams, Florence J.
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supporting information
p. 6332 - 6335
(2018/10/09)
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- A mild method for the replacement of a hydroxyl group by halogen. 1. Scope and chemoselectivity
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α-Chloro-, bromo- and iodoenamines, which are readily prepared from the corresponding isobutyramides have been found to be excellent reagents for the transformation of a wide variety of alcohols or carboxylic acids into the corresponding halides. Yields are high and conditions are very mild thus allowing for the presence of sensitive functional groups. The reagents can be easily tuned allowing therefore the selective monohalogenation of polyhydroxylated molecules. The scope and chemoselectivity of the reactions have been studied and reaction mechanisms have been proposed.
- Munyemana, Fran?ois,George, Isabelle,Devos, Alain,Colens, Alain,Badarau, Eduard,Frisque-Hesbain, Anne-Marie,Loudet, Aurore,Differding, Edmond,Damien, Jean-Marie,Rémion, Jeanine,Van Uytbergen, Jacqueline,Ghosez, Léon
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p. 420 - 430
(2015/12/31)
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- Catalytic phosphorus(V)-mediated nucleophilic substitution reactions: Development of a catalytic appel reaction
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Catalytic phosphorus(V)-mediated chlorination and bromination reactions of alcohols have been developed. The new reactions constitute a catalytic version of the classical Appel halogenation reaction. In these new reactions oxalyl chloride is used as a consumable stoichiometric reagent to generate the halophosphonium salts responsible for halogenation from catalytic phosphine oxides. Thus, phosphine oxides have been transformed from stoichiometric waste products into catalysts and a new concept for catalytic phosphorus-based activation and nucleophilic substitution of alcohols has been validated. The present study has focused on a full exploration of the scope and limitations of phosphine oxide catalyzed chlorination reactions as well as the development of the analogous bromination reactions. Further mechanistic studies, including density functional theory calculations on proposed intermediates of the catalytic cycle, are consistent with a catalytic cycle involving halo- and alkoxyphosphonium salts as intermediates.
- Denton, Ross M.,An, Jie,Adeniran, Beatrice,Blake, Alexander J.,Lewis, William,Poulton, Andrew M.
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experimental part
p. 6749 - 6767
(2011/10/02)
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- Silver-catalyzed benzylation and allylation of tertiary alkyl bromides with organozinc reagents
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Silver salts catalyze the benzylation and allylation of tertiary alkyl bromides with organozinc reagents. The reactions create quaternary carbon centers efficiently. Treatment of gem-dibromoalkanes with benzylic or allylic zinc reagents under silver catalysis leads to dibenzylation or diallylation. The functional-group compatibility of the present reactions is wider than that of the previous reactions with Grignard reagents.
- Mitamura, Yukihiro,Asada, Yoshihiro,Murakami, Kei,Someya, Hidenori,Yorimitsu, Hideki,Oshima, Koichiro
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experimental part
p. 1487 - 1493
(2011/07/07)
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- Silicaphosphine (Silphos): A filterable reagent for the conversion of alcohols and thiols to alkyl bromides and iodides
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Silicaphosphine (Silphos), [P(Cl)3-n(SiO2) n], as a new heterogeneous reagent is introduced. This reagent converts alcohols and thiols to their corresponding bromides and iodides in the presence of X2 (X=Br, I) in refluxing CH3CN in high to quantitative yields. Use of Silphos provides a highly practical method for the easy separation of the Silphos oxide byproduct by a simple filtration.
- Iranpoor, Nasser,Firouzabadi, Habib,Jamalian, Arezu,Kazemi, Foad
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p. 5699 - 5704
(2007/10/03)
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- INTEGRATED PROCESS FOR SYNTHESIZING ALCOHOLS, ETHERS, AND OLEFINS FROM ALKANES
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Alcohols, ethers, and olefins are manufactured from alkanes by mixing an alkane and bromine in a reactor to form alkyl bromide and hydrogen bromide. The alkyl bromide only or the alkyl bromide and the hydrogen bromide are directed into contact with metal oxide to form an alcohol and/or an ether, or an olefin and metal bromide. The metal bromide is oxidized to form original metal oxide and bromine, both of which are recycled.
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- Integrated process for synthesizing alcohols, ethers, and olefins from alkanes
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Alcohols, ethers, and olefins are manufactured from alkanes by mixing an alkane and bromine in a reactor to form alkyl bromide and hydrogen bromide. The alkyl bromide only or the alkyl bromide and the hydrogen bromide are directed into contact with metal oxide to form an alcohol and/or an ether, or an olefin and metal bromide. The metal bromide is oxidized to form original metal oxide and bromine, both of which are recycled.
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- Integrated process for synthesizing alcohols, ethers, and olefins from alkanes
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Alcohols, ethers, and olefins are manufactured from alkanes by mixing an alkane and bromine in a reactor to form alkyl bromide and hydrogen bromide. The alkyl bromide only or the alkyl bromide and the hydrogen bromide are directed into contact with metal oxide to form an alcohol and/or an ether, or an olefin and metal bromide. The metal bromide is oxidized to form original metal oxide and bromine, both of which are recycled.
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- Integrated process for synthesizing alcohols, ethers, and olefins from alkanes
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Alcohols, ethers, and olefins are manufactured from alkanes by mixing an alkane and bromine in a reactor to form alkyl bromide and hydrogen bromide. The alkyl bromide is directed into contact with metal oxide to form an alcohol and/or an ether, or an olefin and metal bromide. The metal bromide from the alkyl bromide metal oxide reaction is oxidized to form original metal oxide and bromine, both of which are recycled. The hydrogen bromide is separately directed into contact with metal oxide to form water and metal bromide. The metal bromide from the hydrogen bromide metal oxide is oxidized to form the original metal oxide which is recycled.
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- New versatile halogenating reagents for hydroxy groups
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Two new halogenating reagents, viz. allyltriphenoxyphosphonium bromide (ATPB) and allyltriphenoxyphosphonium chloride (ATPC) have been prepared and characterised. These have been evaluated for their potential application in bromination/ chlorination of a variety of compounds including aliphatic straight chain alcohols, branched chain alcohols and also 3′- and 5′-hydroxy groups of deoxyribonucleosides.
- Kumar,Dubey,Singh,Misra
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p. 842 - 845
(2007/10/03)
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- Mild conversion of alcohols to alkyl halides using halide-based ionic liquids at room temperature
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Formula presented Alcohols were efficiently converted to alkyl halides using 1-n-butyl-3-methylylimidazolium halides (ionic liquids) in the presence of Bronsted acids at room temperature. The alkyl halide products were easily isolated from the reaction mixture via simple decantation or extraction, and the 1-n-butyl-3-methylimidazolium cation could be recycled for further uses.
- Ren, Rex X.,Wu, Jeff Xin
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p. 3727 - 3728
(2007/10/03)
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- A new supported reagent for the photochemical generation of radicals in solution
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matrix presented A new polymer-supported radical source was developed by loading an N-hydroxy thiazole 2(3)-thione on a Wang resin. This new supported reagent can be employed for a solid-phase version of the Hunsdiecker reaction or to liberate free alkoxy radicals, in a variant of the "catch and release" technique, under very mild conditions (irradiation with a discharge lamp) and simplifying the purification procedure.
- De Luca, Lidia,Giacomelli, Giampaolo,Porcu, Giancarlo,Taddei, Maurizio
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p. 855 - 857
(2007/10/03)
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- BiX3 as an efficient and selective reagent for the halogen exchange reaction
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Bismuth halides are efficient and selective reagents in the halogen exchange reactions carried out under mild conditions. This rapid, high yield reaction proceeds mainly with retention of configuration.
- Boyer, Bernard,Keramane, El Mehdi,Arpin, Severine,Montero, Jean-Louis,Roque, Jean-Pierre
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p. 1971 - 1976
(2007/10/03)
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- The versatile behavior of the PdCl2/Et3SiH system. Conversion of alcohols to the corresponding halides and alkanes
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The versatility of the palladium(II) chloride/triethylsilane system has been tested in the transformation of alcohols. The conversion to the corresponding halides and alkanes has been achieved in good yields and in the absence of solvent for a variety of substrates.
- Ferreri,Costantino,Chatgilialoglu,Boukherroub,Manuel
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p. 135 - 137
(2007/10/03)
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- Thermodynamic Stabilities of Phenonium Ions Based on Bromide-Transfer Equilibria in the Gas Phase
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The thermodynamic stabilities of the phenonium (ethylenebenzenium) ion and ring-substituted derivatives were determined based on the bromide-transfer equilibria in the gas phase. It has been shown that the phenonium ion is 2.4 kcal mol-1 more stable than the t-butyl cation, and that the substituent effect on its stability can be correlated with the Yukawa-Tsuno equation with a ρ value of -12.6 and an r+ of 0.62. An r+ value smaller than unity of the α-cumyl(1-methyl-1-phenylethyl) cation suggested that π-delocalization in the phenonium ion is essentially less effective than through a benzylic π-interaction. On the other hand, the ρ value of -12.6 is distinctly larger than that for the ordinary benzylic carbocation systems, but is comparable to that of the benzenium ion. In addition, it has been found that the r+ value of the phenonium ions in the gas phase is in complete agreement with that for the aryl-assisted process in the acetolysis of 2-arylethyl toluenesulfonates. This suggests that the degree of π-delocalization of the positive charge is the same in the transition state and the intermediate cation. It is concluded that an r+ value of 0.6, which is ranked at a unique position in the continuous spectrum of the resonance demand, is characteristic of the bridged structure of the phenonium ion intermediate and the transition state.
- Mustanir,Mishima, Masaaki,Fujio, Mizue,Tsuno, Yuho
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p. 1401 - 1407
(2007/10/03)
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- Alkyl radical generation using cyclohexa-1,4-diene-3-carboxylates and 2,5-dihydrofuran-2-carboxylates
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3-Methylcyclohexa-1,4-diene-3-carboxylic acid and 2-methyl-2,5-dihydrofuran-2-carboxylic acid were prepared by Birch reduction and alkylation of benzoic and furoic acid respectively and converted to alkyl esters. Cyclohexadienyl and 2,5-dihydrofuranyl radicals were generated by hydrogen abstraction and characterised by EPR spectroscopy. The esters decomposed thermally in the presence of a radical initiator to generate alkyl radicals which could be trapped with moderate efficiency by halogen donors or alkenes. Loss of methyl to afford an alkyl benzoate was an important side reaction at higher temperatures. From the thermal reaction of hex-5-enyl 3-methylcyclohexa-1,4-diene-3-carboxylate the rate constant for hydrogen abstraction from the ester by hexenyl radicals was determined to be 0.82 × 105 dm3 mol-1 s-1 at 140°C.
- Binmore, Gavin,Cardellini, Liberato,Walton, John C.
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p. 757 - 762
(2007/10/03)
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- Correlation of gas-phase stability of bridgehead carbocations with rates of solvolysis and ab initio calculations
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The stability of bridgehead carbocations has been determined by Fourier transform ion cyclotron resonance spectroscopy (FT ICR) based on dissociative proton attachment (DPA) of bromides and alcohols. The stability of the ions correlates with the solvolytic reactivity of bridgehead derivatives over a rate range of 23 log units, and with theoretical calculations for hydride transfer of bridgehead hydrocarbons at the MP2/6-311G** level.
- Abboud, José-Luis M.,Casta?o, Obis,Della, Ernest W.,Herreros, Marta,Müller, Paul,Notario, Rafael,Rossier, Jean-Claude
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p. 2262 - 2266
(2007/10/03)
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- Functionalization of saturated hydrocarbons by aprotic superacids 4. Ionic bromination of ethane and other alkanes and cycloalkanes with molecular bromine in the presence of systems based on polyhalomethanes and AlBr3 under mild conditions
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Aprotic organic superacids CBr4 · 2AlBr3, CBr4 · AlBr3, · CCl4 · 2AlBr3, CCl4 · 2AlBr3, and C6F5CF3 · 2AlBr3 efficiently catalyze the bromination of alkanes and cycloalkanes with Br2. Ethane is selectively brominated at 55-65 °C to give mostly 1,2-dibromoethane (stoichiometric reaction). Propane, butane, cyclopentane, cyclohexane, and methyl-cyclopentane react with Br2 at -40 to -20 °C with good selectivity affording monobromides in high yields (catalytic reactions).
- Akhrem,Orlinkov,Afanas'eva,Vol'pin
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p. 1148 - 1153
(2007/10/03)
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- Ionic Bromination of Ethane and Other Alkanes (Cycloalkanes) with Bromine Catalyzed by the Polyhalomethane*2AlBr3 Aprotic Organic Superacids under Mild Conditions
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The polyhalomethane*2AlBr3 aprotic organic superacids were shown to effectively catalyze low-temperature ionic bromination of (cyclo)alkanes.Ethane readily reacts with Br2 at 55-65 deg C, affording mainly 1,2-dibromoethane.Propane, butane, and C5-C6 cycloalkanes react at -40 - -20 deg C, resulting in monobromides with high yields and good selectivity.
- Akhrem, Irena S.,Orlinkov, Alexander V.,Afanas'eva, Lyudmila V.,Mysov, Evgenii I.,Vol'pin, Mark E.
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p. 9365 - 9368
(2007/10/02)
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- Radical-chain Decomposition of Cyclohexa-1,4-diene-3-carboxylates and 2,5-Dihydrofuran-2-carboxylates
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3-Methylcyclohexa-1,4-diene-3-carboxylates and 2-methyl-2,5-dihydrofuran-2-carboxylates decompose to generate free alkyl radicals which have been incorporated into chain reactions producing alkyl bromides, alkene adducts and ring-closure products.
- Binmore, Gavin,Walton, John C.,Cardellini, Liberato
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- Bromination of Alcohols by Boron Tribromide
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Boron tribromide was used as a brominating agent for the conversion of alcohols to bromides.Tertiary alcohols were more reactive than secondary alcohols which were more reactive than primary alcohols.
- Pelletier, Joelle D.,Poirier, Donald
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p. 1051 - 1054
(2007/10/02)
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- Reactivity of Alkaneselenyl Bromide: Conversion of Alcohols into the Corresponding Alkyl Bromides with Dialkylselenium Dibromide
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The reaction of alcohols with dialkylselenium dibromide gave the corresponding bromides in moderate to high yields.Alkaneselenyl bromide, produced by the thermal decomposition from dialkylselenium dibromide, acts as a brominating agent.The reaction of alcohol with dialkylselenium dichloride afforded the corresponding chlorides, although the yields were realtively low compared with those of the bromide.
- Akabori, Sadatoshi,Takanohashi, Yoshinori
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p. 3482 - 3484
(2007/10/02)
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- Thermodynamic Stabilities of Phenonium Ions in the Gas Phase
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Gas phase stabilities of substituted phenonium (ethylenearenium) ions have been determined based on bromide transfer equilibria.The phenonium ion has been found to be stable even more than t-butyl cation, and the substituent effect on its stability has been analyzed based on the LArSR Eq., giving a ρ value of -17.5 and a r of 0.60.
- Mishima, Masaaki,Tsuno, Yuho,Fujio, Mizue
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p. 2277 - 2280
(2007/10/02)
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- Kinetics of the Reactions of Alkyl Radicals (CH3, C2H5, i-C3H7, and t-C4H9) with Molecular Bromine
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The gase-phase kinetics of the reactions of four alkyl radicals (CH3, C2H5, i-C3H7, and t-C4H9) with molecular bromine have been studied over the temperature range 296-532 K.The reactions were isolated for quantitative study in a heatable tubular reactor coupled to a photoionization mass spectrometer.Radicals were homogeneously generated in the reactor by pulsed photolysis of suitable precursor molecules at 193 or 248 nm.The subsequent decays of the radical concentration in the presence of different Br2 concentrations were monitored in time-resolved experiments.Rate constants were obtained at five temperatures.The Arrhenius expressions (k = A exp(-E/RT)) that describe the temperature dependencies of the measured rate constants of the R + Br2 -> RBr + Br reactions are as follows 3 molecule-1 s-1), E/(kcal mol-1)>: R = CH3 ; R = C2H5 ; R = i-C3H7 ; R = t-C4H9 .The trend in the measured rate constants and the results of prior studies of the dynamics of the CH3 + Br2 reaction indicate that the reactivity of R + Br2 reactions is determined largely by long-range attractive forces and not by reaction thermochemistry.
- Timonen, R. S.,Seetula, J. A.,Gutman, D.
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p. 3005 - 3008
(2007/10/02)
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- A Simple Method for the Conversions of Adamantyl, Benzyl and Benzhydryl Alcohols to Their Corresponding Bromides and Chlorides and the Transhalogenation of Adamantyl, Benzyl, Benzhydryl and tertiary Alkyl Bromides and Chlorides
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Adamantyl, benzyl, and benzhydryl alcohols have been converted to their corresponding bromides and chlorides in the absence of a solvent, rapidly and in high yield using boron tribromide and tin(IV) chloride, respectively.Additionally the above bromides and chlorides can be interconverted by a transhalogenation process using the same reagents in the absence of solvent.
- Amrollah-Madjdabadi, A.,Pham, Tung N.,Ashby, E. C.
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p. 614 - 616
(2007/10/02)
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- The IR Photochemistry of Organic Compounds. II. The IR Photochemistry of Ethers: The Decomposition Patterns
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The infrared multiple-photon decomposition (IRMPD) of saturated open-chain ethers has been systematically investigated with the intention of establishing their decomposition patterns.The main products in the IRMPD of ethers (1a-f, 2) are H2CO, CO, H2, and lower hydrocarbons.Acetaldehyde is additionally formed in the IRMPD of 1b and 1d, while acetone is formed in the IRMPD of 1d.The observed results are explained on the basis of the decomposition of the highly vibrationally excited ethers produced in the IRMPD excitation.The initial process is the homolytic cleavage of a C-O bond to yield the corresponding alkyl and alkoxyl radicals.The alkyl radicals are trapped ny Br2.Sequential splitting and addition reactions of the radicals yield primary products with a high internal energy.The primary products also decompose sequentially into stable products, in part.The sequential processes compete with collisional deactivation.Therefore, the branching ratio depends on the internal energy of the radicals and the primary products.
- Majima, Tetsuro,Ishii, Tadahiro,Arai, Shigeyoshi
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p. 1701 - 1709
(2007/10/02)
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- REACTION OF 2-TERT-BUTOXY-4,5-BENZO-1,3,2-DIOXAPHOSPHOLANE WITH TRIBROMOACETALDEHYDE
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The reaction of 2-tert-butoxy-4,5-benzo-1,3,2-dioxaphospholane with tribromoacetaldehyde proceeds by initial halophilic attack on the bromine atom, leading to a product with retention of the P-Br bond (pyrocatechol bromophosphate) and an anion exchange product (pyrocatechol dibromovinylphosphate), and by initial attack at the carbon atom of the C=O group, which is accompanied by the elimination of isobutylene to form an α-hydroxyphosphonate.
- Sinyashina, T. N.,Mironov, V. F.,Ofitserov, E. N.,Konovalova, I. V.,Pudovik, A. N.
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p. 1755 - 1757
(2007/10/02)
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- Efficient Conversion of Alkyl Chlorides into Bromides
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The convenient and selective catalytic conversion of secondary and tertiary alkyl chlorides into bromides with hydrogen bromide in the presence of small amounts of anhydrous iron(III) bromide is described.
- Yoon, K. B.,Kochi, J. K.
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p. 1013 - 1014
(2007/10/02)
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- INVESTIGATION OF ORGANIC EQUILIBRIA. II. EFFECT OF SUBSTITUENTS ON THE HARDNESS SERIES OF ACIDS WITH AN ACCEPTING CARBON ATOM IN sp3 HYBRIDIZATION. SYMBIOSIS AND ANTISYMBIOSIS
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The ΔH0Me,H values, i.e., the changes in the standard enthalpy of the hypotetical gas-phase reactions RH + CH3X->/+ as acids.It was shown that the nature of R (primary, secondary, tertiary) has a predominant effect on the hardness, whereas the effect of functional substituents in R (at the β positions and positions more remote from the accepting atom), like the effect of the specific structural characteristics of R, is on the whole small.The effect of functional α substituents on the hardness of R+ does not obey simple relationships.The general nature of the symbiosis of the ligands, which is one of the main principles of the concept of hard and soft acids and bases, is not confirmed.Conversely, antisymbiosis was found in some of the ligands X, i.e., the system was destabilized with the accumulation of substituents of X of the same type at the given carbon atom.The constants of a series of liquid-phase equilibria of the R1X + R2Y->/1Y + R2X type were measured by direct experiments.It was shown that the state of the investigated equilibria corresponds to the predictions which can be reached on the basis of the hardness series of acids and bases derived for the gas phase.
- Bochkov, A. F.
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p. 1837 - 1848
(2007/10/02)
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- RHODIUM(I) CATALYZED CARBONYLATION REACTIONS OF HALIDES AND ETHERS
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Benzylic bromides and methyl ioide react with ethers, carbon monoxide, potassium iodide, and the dimer of chloro(1,5-hexadiene)rhodium(I) to give esters in good yields.
- Buchan, Caroline,Hamel, Nathalie,Woell, James B.,Alper, Howard
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p. 5743 - 5746
(2007/10/02)
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- Hydrocarbon Functionalization by the (Iodosylbenzene)manganese(IV) Porphyrin Complexes from the (Tetraphenylporphinato)manganese(III)-Iodosylbenzene Catalytic Hydrocarbon Oxidation System. Mechanism and Reaction Chemistry
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The two types of complexes isolated from the reaction of (tetraphenylporphinato)manganese(III) derivatives, XMnIIITPP, with iodosylbenzene - IVTPP(OIPh)>2O, 1, X = Cl- or Br-, and IVTPP>2O, 2, X = N3- - are capable of oxidizing alkane substrates in good yields at room temperature.Several lines of evidence establish the intermediacy of free alkyl radicals in the reactions of 1 and 2 with alkanes.Oxygen exchange with water in both the iodosyl (Mn-O-I) and μ-oxo (Mn-O-Mn) moieties of 1 suggests the formation of oxo manganese porphyrin complexes from these moieties.Hydrogen abstraction from the alkane substrate by an oxo manganese porphyrin intermediate is postulated to be mechanism for reaction of 1 and 2 with alkanes.Observation of a monomeric manganese(IV) porphyrin intermediate by EPR spectroscopy during the reactions of 1 with alkanes is consistent with the formation of a hydroxymanganese(IV) porphyrin complex resulting from substrate hydrogen abstraction by an oxo intermediate.The formation of RX product from oxidation of RH by 1 has been determined to result from ligand-transfer oxidation of free alkyl radicals by the porphyrin complexes in solution.Through competition reactions and time-dependent product formation studies, ligand-transfer oxidation by XMnIIITPP was found to be the major pathway for RX production.Observation of MnIITPP by EPR spectroscopy during the reactions of 1 with alkanes supports this conclusion.Formation of ROH product may result from ligand-transfer oxidation of free radicals or from the collapse of an intermediate caged radical pair.The mechanism of ROH product formation in the caged radical pair is postulated to be an outer-sphere electron-transfer process due to the expected slow rate of inner-sphere ligand transfer for the high-spin d3 hydroxymanganese(IV) porphyrin complex.Thus the ability of the substrate radical to undergo electron-transfer oxidation determines the ratio of radicals that undergo cage escape to give free radicals to radicals that undergo oxidation and subsequent formation of alcohol product in the caged species.Studies with tertiary substrates support these conclusions.
- Smegal, John A.,Hill, Craig L.
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p. 3515 - 3521
(2007/10/02)
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- Silylaminyl Radicals. Part 2. Free Radical Chain Halogenation of Hydrocarbons using N-Halogenobis(trialkylsilyl)amines
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The liquid-phase halogenation of a number of hydrocarbons and of 1-chlorobutane by N-halogenobis(trialkylsilyl)amines has been studied using product analysis techniques.The reactions take place by free radical chain mechanisms which involve the propagation steps generalised in equations (A) and (B) (X=Br or Cl).At 353 K, the molar reactivities of toluene (benzylic C-H) and cyclohexane towards (R3Si)2N+RH(R3Si)2NH+R (A) R+(R3Si)2NXRX+(R3Si)2N (B) (Me3Si)2N are approximately equal and toluene is 5.2 times more reactive than perdeuteriotoluene.The relative rates of hydrogen abstraction by (Me3Si)2N and (ButMe2Si)2N from the primary, secondary, and tertiary C-H groups in 2-methylbutane show that the silylaminyl radicals are not only highly reactive but also sterically demanding.Thus, at 333 K the average primary C-H reactivity is 0.6 times that of the tertiary C-H towards attack by (Me3Si)2N, but 4.2 times that of the tertiary C-H towards attack by the more bulky (ButMe2Si)2N.Silylaminyl radicals are much more reactive in hydrogen abstraction than are analogous dialkylaminyl radicals and this difference is interpreted in terms of thermodynamic and polar effects which arise because of the ?-donor-?-acceptor nature of the trialkylsilyl substituent.
- Cook, Malcolm D.,Roberts, Brian P.,Singh, Karamjit
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p. 635 - 644
(2007/10/02)
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- SELECTIVITIES OF pi - AND sigma -SUCCINIMIDYL RADICALS IN SUBSTITUTION AND ADDITION REACTIONS. APPENDIX: RESPONSE TO WALLING, EL-TALIAWI, AND ZHAO.
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A new method for studies of pi -succinimidyl (S// pi ) radicals is described, one that makes possible the study of reactions of this radical with a variety of substrates not accessible by the use of Br//2-NBS. NBS systems containing BrCCl//3 at mole fractions greater than 0. 3 show all the characteristics associated with S// pi behavior, and they function in the presence of olefins which serve as Br//2 scavengers. If CCl//4 is substituted for BrCCl//3, the system is clearly S// sigma . The S// pi behavior is contrasted with S// sigma and Br multiplied by (times) reactivities for H abstractions from a variety of substrates and for additions to tert-butylethylene, isobutylene, and 1,3-butadiene. In early-transition-state systems, for H transfer, the strength of the bond being broken and the strength of the bond being made are not the major factors in determining reactivities. The behavior in late-transition-state systems is influenced by both bond strengths. The S// pi radical shows intermediate behavior. These conclusions are supported by primary deuterium isotope effects for methylene chloride and chlororoform. The Appendix addresses a number of questions raised by the preliminary study of NBS reactions by Walling et al.
- Skell,Tlumak,Seshadri
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p. 5125 - 5131
(2007/10/02)
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- Interhalogen-Catalyzed Cleavages of Ethers and Esters with Trimethylsilyl Bromide or Chloride
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The cleavages of various dialkyl ethers, trimethylsilyl alkyl ethers, and alkyl esters by trimethylsilyl bromide are strongly catalyzed by iodine monobromide.This catalyzed cleavage procedure using iodine monobromide makes possible synthetic applications for trimethylsilyl bromide which were previously ruled out by problems with its low reactivity.Cleavages of benzylic and tertiary alkyl ethers and esters by trimethylsilyl chloride are feasible when catalyzed by iodine monochloride.However, other systems are essentially unreactive toward trimethylsilyl chloride even in the presence of iodine monochloride.
- Friedrich, Edwin C.,DeLucca, George
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p. 1678 - 1682
(2007/10/02)
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- Absolute Rates for Dimerization of Capto-dative Substituted Methyl Radicals in Solution: Absence of Kinetic Stabilization
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For three capto-dative substituted methyl radicals, t-butoxy(cyano)methyl radical (1), t-butylthio(cyano)methyl radical (2), and methoxy(methoxycarbonyl)methyl radical (3), absolute rates for dimerization have been measured by e.s.r. spectroscopy and substantiated by product analysis.Values for the rate constants of 1.0E8 - 1.5E9 l mol-1s-1 in the temperature range -60 to +60 deg C support the diffusion-controlled nature of the dimerization.The comparison of Arrhenius activation parameters for dimerization with those for the bulk viscosity of the solutions does not provide evidence for noticeable intrinsic barriers to recombination, indicating the absence of kinetic stabilization for capto-dative substituted methyl radicals.
- Korth, Hans-Gert,Sustmann, Reiner,Merenyi, Robert,Viehe, Heinz Guenther
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- Oxygen-Oxygen Cleavage in Bicyclic Trialkylperoxonium Intermediates
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Oxygen-oxygen cleavage in bicyclic trialkylperoxonium ions can account for the mixtures of bicyclic ethers and 2-methoxypropane derivatives obtained from the reaction of 5-t-butylperoxycyclo-octene with N-bromosuccinimide in methanol or with bromine in carbon tetrachloride.
- Bloodworth, A. J.,Courtneidge, J. L.,Eggelte, Henny J.
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p. 1267 - 1268
(2007/10/02)
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- Reactions of a Graded Set of Radicals with N-Bromosuccinimide; Two Transition States
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The reactions of N-bromosuccinimide with a series of radicals have been studied.These reactions fall into two categories, the more reactive radicals producing ?-succinimidyl and the less reactive radicals producing ?-succinimidyl.The threshold for the changeover from one reaction domain to the other occurs with radicals less reactive than secondary alkyls.These results are interpreted with two transition states, an in-line transition state for the more reactive radicals and an out-of-plane transition state for the less reactive radicals. An upper limit of 18 kcal/mol is established for the enthalpy difference, HS? - HS?.Two new methods for generating S? radicals are indicated.
- Tlumak, Robert L.,Skell Philip S.
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p. 7267 - 7274
(2007/10/02)
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- Thallium(I) Carboxylate Modification of the Hunsdiecker Reaction
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Treatment of a thallium(I) carboxylate with 1 molar equivalent of bromine gives the corresponding thallium(III) carboxylate dibromide.High yields of primary alkyl bromides are obtained if the thallium(III) carboxylate dibromide is treated with 0.5 mol equiv. of bromine in refluxing carbon tetrachloride.Pyrolysis of the thallium(III) derivative in the absence of added bromine gives a low yield of the corresponding alkyl bromide.The use of thallium(I) carboxylates for the preparation of alkyl bromides in high yields is limited to the salts of primary carboxylic acids.A simple procedure for the preparation of alkyl bromides from carboxylic acids using thallium(I) carbonate has been developed.
- Cambie, Richard C.,Hayward, Rodney C.,Jurlina, Jeffrey L.,Rutledge, Peter S.,Woodgate, Paul D.
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p. 2608 - 2614
(2007/10/02)
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- Carbon-Halogen Bonding Studies. Halogen Redistribution Reactions between Alkyl or Acetyl Halides and Tri-n-butyltin Halides
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The equilibrium positions have been determined for the halogen redistribution reactions of tri-n-butyltin halides with a variety of structurally different types of alkyl halides and with acetyl halides.These have been related through the reaction ΔGo values to carbon-halogen bond dissociation energy differences.It is suggested that the trends observed in the latter may provide evidence for the existence of a small steric bond weakening effect in the order C-I > C-Br > C-Cl bonds on going from methyl to primary, secondary, and tertiary alkyl halides.On the other hand, with the 2,3-? bond containing allyl, benzyl, and propargyl halides , α-haloacetones, and haloacetonitriles, there may be some type of electronic carbon-halogen bond strengthening effect which lies in order C-I > C-Br > C-Cl.Finally, for the acetyl halides, the data are in agreement with increases in bond strengths resulting from ? contributions being in the order C-Cl > C-Br > C-I.
- Friedrich, Edwin C.,Abma, Charles B.
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p. 1367 - 1371
(2007/10/02)
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- Homosolvolysis
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Nitroxides, when used as solvents, promote the homolysis of a variety of weak bonds.Strong chemical evidence for the formation of free radicals is confirmed by e.s.r. studies in which the formation of free radicals has been monitored.This fission of single bonds of solute molecules dissolved in solvents with unpaired electrons is called homosolvolysis, in contrast to the common bond fission observed in polar solvents which is called heterosolvolysis.
- Scott, Alan C.,Tedder, John M.,Walton, John C.,Mhatre, Sushila
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p. 260 - 266
(2007/10/02)
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