Reactions of halobenzenes with methanol on the microporous solid acids hbeta, HZSM-5, and HSAPO-5: halogenation does not improve the hydrocarbon pool

The reactions of fluorobenzene, 3-fluorotoluene, and three isomers of difluorotoluene, chlorobenzene, and bromobenzene with excesses of methanol were investigated on the large-pore catalysts HBeta (*BEA) and HSAPO-5 (AFI), and on the medium-pore HZSM-5 (MFI). Flow reactor studies in pulse mode with GC-MS detection revealed that the fluorobenzene derivatives were readily methylated at, for example, 375 degrees C, but not even pentamethylfluorobenzene was obviously active as a reaction center for methanol-to-olefin (MTO) catalysis. Carbon-labeling studies revealed that small amounts of methylbenzenes were formed by defluorination, and these aromatic hydrocarbons seemed to account for the small yields of olefins (and their secondary reaction products) observed. Loss of one fluorine was also evident in the products for one of the difluorotoluene isomers. On HSAPO-5 the activity order for ring-methylation of halobenzenes was F > Cl > Br. On HZSM-5, chlorobenzene and especially bromobenzene lost halogen through a route forming halomethane. These largely negative results will nevertheless be useful in testing theoretical models of the detailed reaction steps in the hydrocarbon pool mechanism for MTO catalysis.     

Low-temperature reaction of magnesium with fluorobenzene

The low-temperature reaction of magnesium with fluorobenzene has been investigated. Joint condensation of magnesium and fluorobenzene vapours at low temperatures quantitatively gave phenylmagnesium fluoride in one stage.     

The Reaction of H2PtCl6 with aromatic compounds in CF3COOH/H2O affording the anionic σ-aryl complexes of platinum(IV) : IV. The synthesis of platinum(IV) complexes of fluorinated benzenes and the electronic influence of the platinum moiety

The reaction of H₂PtCl₆ with fluorobenzene, σ-chlorofluorobenzene and m-chlorofluorobenzene in CF₃COOH/H₂O affords anionic σ-aryl complexes of platinum(IV). The first two compounds give rise to mixtures of two isomers (meta and para), the latter forms only one isomer (1,3,5-substituted). The ¹⁹F NMR spectrum shows that [PtCl₄NH₃]^? group, when bound to fluorobenzene, is an electron donor in both the inductive and resonance senses.     

Theoretical study on the mechanism and kinetics of addition of hydroxyl radicals to fluorobenzene

Geometries, frequencies, reaction barriers, and reaction rates were calculated for the addition of OH radical to fluorobenzene using Möller–Plesset second‐order perturbation (MP2) and G3 methods. Four stationary points were found along each reaction path: reactants, prereaction complex, transition state, and product. A potential for association of OH radical and fluorobenzene into prereaction complex was calculated, and the associated transition state was determined for the first time. G3 calculations give higher reaction barriers than MP2, but also a significantly deeper prereaction complex minimum. The rate constants, calculated with Rice–Ramsperger–Kassel–Marcus (RRKM) theory using G3 energies, are much faster and in much better agreement with the experiment than those calculated with MP2 method, as the deeper well favors the formation of prereaction complex and also increases the final relative populations of adducts. The discrepancies between the experimental and calculated rate constants are attributed to the errors in calculated frequencies as well as to the overestimated G3 reaction barriers and underestimated prereaction complex well depth. It was possible to rectify those errors and to reproduce the experimental reaction rates in the temperature range 230–310 K by treating the relative translation of OH radical and fluorobenzene as a two‐dimensional particle‐in‐the‐box approximation and by downshifting the prereaction complex well and reaction barriers by 0.7 kcal mol^?1. The isomeric distribution of fluorohydroxycyclohexadienyl radicals is calculated from the reaction rates to be 30.9% ortho, 22.6% meta, 38.4% para, and 8.3% ipso. These results are in agreement with experiment that also shows dominance of ortho and para channels. © 2012 Wiley Periodicals, Inc.     

Suzuki cross-coupling reaction of fluorobenzene with heterogeneous palladium catalysts

In this work, we accomplished for the first time the Suzuki cross-coupling reaction between fluorobenzene and phenylboronic acid with different heterogeneous catalysts and bases. The conversion values obtained are similar to those provided by homogeneous catalysts and activated aryl fluorides.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part 12.[1] Additivity of fluorine substituent effects in methoxydefluorination

The rates of methoxydefluorination of all twelve polyfluorobenzenes in dimethyl sulphoxide-methanol mixtures (DMSO-MeOH; 9:1, v/v; 298.2 K) have been measured. Three substituent rate factors (f_o, 60; f_m, 180; f_p, 0.75) are sufficient to reproduce the effect of the fluorine substituent in this reaction upon each member of the series. The solvent effect, comparing these results with an earlier and more limited study in methanol is predominantly a simple acceleration. The effects of substituents upon the rate of methoxydefluorination of fluorobenzene itself are slightly greater (?^?, 6.9) than in the corresponding reaction of pentafluorobenzene derivatives (?^?, 5.8), but the change in sensitivity is much less than that found with nitrobenzene derivatives.     

Homolytic reactions of polyfluoroaromatic compounds V. The reaction of pentafluorophenyl radicals with fluorobenzene

The arylation of fluorobenzene with pentafluorophenyl radicals obtained by the reaction of the corresponding aniline with pentyl nitrite is described. The reaction involves attact at the 2t?-,3t?-and 4t?-positions. The composition of the mixture and the nature of its components were determined by ¹⁹F NMR spectroscopy and were confirmed by gas-liquid chromatography.     

Site of protonation in the reaction of gaseous Brønsted acids with halobenzene derivatives

The site of protonation in the reaction of gaseous Brønsted acids with chlorobenzene and fluorobenzene derivatives has been examined using deuterium labelling of chlorobenzene and deuterated reagent gases (D₂ and N₂/D₂). In the protonation of chlorobenzene by [H₃]⁺ ～30% of the [MH? HCl]⁺ fragment ions arise from a chlorine-protonated species while ～70% arise from a ring-protonated species in which complete hydrogen scrambling has occurred. In the reaction of [N₂H]⁺ with chlorobenzene ～75% of the fragment ions arise from the chlorine-protonated form with ～25% arising from the ring-protonated form of [MH]⁺. By contrast fluorobenzene fragments almost entirely from the fluorine-protonated form. Similar results are obtained for dihalobenzenes. The mechanistic implications are discussed.     

Halogenated arenes in the Duff reaction at high pressures

The reaction of fluorobenzene with urotropine in trifluoroacetic acid (TFAA) at high pressures and temperatures affords predominantly fluorobenzaldehydes andN-(fluorophenylmethyl)trifluoroacetamides. The yields of these products depend considerably on the reaction conditions. The rates of their formation have the maximum values at the momemt of the phase transition (PT) of TFAA. A new efficient cyclic (dynamic) regime is proposed for the synthesis at high pressures. The regime involves periodically occurring PT of the solvent. The change in the relative rate of product formation with the degree of fluorobenzene conversion is wave-like.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 319–323, February, 1995.     

Photoinduced reaction of dichloromaleimide with some aromatic compounds

Conclusions The photoreaction of dichloromaleimide with benzene, fluorobenzene, and anisole has been investigated. In the first two cases, the main process comprises the 1,2-addition of two dienophile molecules. The reaction with anisole proceeds exclusively by a scheme comprising substitution to form anisylmaleimides followed by photodimerization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 401–404, February, 1979.     

Influence of hydrogen bonding on hydrogen-atom abstraction reactions of dehydropyridinium cations in the gas phase

The reactions of several substituted, positively charged dehydropyridinium cations with cyclohexane, methanol, and tetrahydrofuran have been examined in a Fourier-transform ion cyclotron resonance mass spectrometer. All of the charged monoradicals react with the neutral reagents exclusively via hydrogen atom abstraction. For cyclohexane, there is a good correlation between the reaction efficiencies and the calculated electron affinities at the radical sites; that is, the greater the electron affinity of the charged monoradical at the radical site, the faster the reaction. The reaction efficiencies with methanol and tetrahydrofuran, however, do not correlate with the calculated electron affinities. Density functional theory (DFT) calculations indicate that for these reagents a stabilizing hydrogen bonding interaction exists in the hydrogen atom abstraction transition states for some of the charged monoradicals but not for others. At both the MPW1K and G3MP2B3 levels of theory, there is a good correlation between the calculated activation enthalpies and the observed reaction efficiencies, although the G3MP2B3 method provides a slightly better correlation than the MPW1K method. The extent of enhancement in the reaction efficiencies caused by the hydrogen bonding interactions parallels the calculated hydrogen bond lengths in the transition states.     

A novel Pt/Au/C cathode catalyst for direct methanol fuel cells with simultaneous methanol tolerance and oxygen promotion

A novel Pt/Au/C catalyst was prepared by depositing the Pt and Au nanoparticles on the carbon support. The synthesized catalysts were characterized by energy-dispersive X-ray (EDX) and transmission electron microscopy (TEM), and electrochemically analyzed for activity towards oxygen-reduction reaction and methanol oxidation reaction. EDX and TEM results reveal that Pt nanoparticles supported on carbon supports were separated by Au nanoparticles. The electrochemical analysis indicate that the novel catalyst showed the enhanced methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction, which could be attributed to the less methanol adsorption on Pt/Au/C catalyst.     

A novel type of nucleophilic substitution reactions on nonactivated aromatic compounds and benzene itself with trimethylsiliconide anions

[reaction: see text]. The reaction of fluorobenzene with Me3Si- anion (1) in HMPA at room temperature surprisingly affords o- and p-fluorotrimethylsilylbenzenes (substitution of aromatic H for TMS, 76% yield) 7a and 7b and also 14% of trimethylsilylbenzene (2). Benzene itself reacts at 50 degrees C to furnish 4 in 45% yield. Pyridine affords p-trimethylsilylpyridine quantitatively. Mechanistic studies are presented.     

New Activated Difluoroaromatic Compounds Containing Internal Acetylenic Moieties

New activated difluoroaromatic compounds having an internal acetylenic moiety were synthesized by reaction of trichloroacetaldehyde with fluorobenzene, followed by reaction with iodobenzene and cross coupling with acetylene in the presence of palladium complexes. According to the results of quantum-chemical calculations and ¹⁹F NMR data, the products are highly reactive compounds which can be used for the preparation of high-molecular-weight aromatic polyethers.     

石墨烯纳米片担载Pt-Pd双金属纳米球作为甲醇氧化的电催化剂(英文)

利用简便的无表面活性剂的方法合成了石墨烯担载的Pt-Pd双金属纳米球.首先由Na2PdCl4与氧化石墨烯发生氧化还原反应生成Pd晶种,然后诱导Pt纳米粒子的生长,得到Pt-Pd双金属纳米球.采用扫描电子显微镜、透射电子显微镜和X射线粉末衍射仪表征了合成的Pt-Pd/GR催化剂的结构,并测定了其作为甲醇氧化电催化剂的性能.结果表明,Pt-Pd/GR催化剂对甲醇氧化反应表现出高催化活性和稳定性,甲醇氧化电流密度为51.8mA·cm-2.     

Theoretical calculations of chemical interactions-111: The reaction of halonitrobenzenes with nucleophiles

Potential o-zwitterionic complexes formed between fluorobenzene, p- and o-nitrofluorobenzene with ammonia and amide ion where calculated by CNDU, INDO and MNDO semiempirical methods with a wide geometry optimization. Data for bond lengths, bond angles and charge densities are given. In the case of the complexes with ammonia the reaction coordinate was also calculated by the MNDO procedure. The obtained results show that theoretical calculations can provide useful data on these type of complexes and provide models for systems not amenable to experiment yet.     

Catalytic oxidation of fluorobenzene by molecular oxygen

Kinetic and thermal-desorption methods have been applied to the oxidation of fluorobenzene by molecular oxygen. The catalytic oxidation mechanism for fluorobenzene is similar to that for benzene. A suggestion is made on why there is no fluoromaleic anhydride in the oxidation products from fluorobenzene.Translated from, Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 1, pp. 116–119, January–February, 1989.     

The effect of including polarization functions on the geometrical parameters calculated for benzene,fluorobenzene and cyanobenzene

The geometrical parameters for benzene, fluorobenzene, and cyanobenzene have been calculated using the 6–31G*(5D) and 6–31G** basis sets, and, in addition, the 6–31 + G*(5D) basis set in the case of fluorobenzene. Compared to previous results obtained using the 6-31G basis set there are minor changes in the magnitude of the bond lengths and angles in the ring, but the relative values remain unaltered. The values for the ipso angles in fluorobenzene and cyanobenzene are again somewhat less than those reported from microwave and/or electron diffraction studies. The distortion of the ring is characterized as either an elongation or a flattening with respect to the F–C₁ ⃛C₄ and NC C₁C₄ axes, and the shape is characterized as either a broadening or a narrowing across the ring just below the F and Cn group, i.e., an increase or a decrease in the C₂ ⃛C₆ internuclear distance, relative of the C₃ ⃛C₅ distance.     

Catalytic effect of ammonium chloride on the synthesis of imidate esters

Preparation of imidate esters by reaction arylamines containing electron withdrawing groups with ethyl 3-ethoxy-3-imino-propionate in methanol is described. Evidence is presented for an orthoester intermediate. The unusual catalytic effect of ammonium chloride is discussed.