Superacidic and HUSY-zeolite activation of 1,3-indandione: reactions with benzene and cyclohexane

1,3-Indandione (1) readily condenses with benzene and undergoes selective ionic hydrogenation with cyclohexane when activated by superacids, such as CF₃SO₃H, AlCl₃ and AlBr₃ to give 3,3-diphenyl-1-indanone (4) and 1-indanone (7), respectively. Combination of these reactions in ‘one-pot’ yields 3-phenyl-1-indanone (5). In addition, similar reactions have been carried out using the regenerable solid acid, HUSY-zeolite, providing an effective excess of acidic sites. The mechanism of these reactions, with potential involvement of superelectrophilic dicationic intermediates, is discussed.     

The generation and reactions of some diaryl-dihalomethylcarbonium ions

Previously unknown diaryl-dihalomethylcarbonium ions, formed in high yield from the respective alkenes in trifluoromethanesulfonic acid (triflic acid) undergo facile rapid equilibration of aryl groups in triflic acid with a second added aryl component.     

Interaction of cyclopentane with benzene,carbon tetrachloride and cyclohexane

Heats of mixing cyclopentane + benzene, + carbon tetrachloride, + cyclohexane at 308.15 K and for cyclohexane + carbon tetrachloride at 298.15 K have been determined in an adiabatic calorimeter. The data have been examined for current theories (McGlashan, Flory and Barker) of solutions and show that McGlashan's theory predicts values for H^E and G^E that are in good agreement with their corresponding experimental values. Interaction energy between the components of these mixtures has also been determined.     

Comments on the electronic properties of cyclopropane,cyclobutane, and cyclohexane

Spectral quantities of cyclopropane, cyclobutane, cyclohexane, and of several derivatives, have been calculated by a semiempirical all-valence electron SCF-CI MO method. In cyclopropane, HOMO is practically localized in the carbon-frame, and LVMO is purely so. In cyclobutane, these two MO's are based on C-H bonds, while cyclohexane holds an intermediate position. Despite the overall similarity-experimental and computed-of the spectra of these molecules, assignments are non-parallel. Like cyclopropane, cyclobutane can extend conjugation, but to a diminished degree; cyclohexane behaves in this respect like an acyclic alkane. An interpretation of this gradation, in terms of the nature of high-lying MO's, is proposed.     

Pervaporation of benzene/cyclohexane mixtures using ion-exchange membrane containing copper ions

The sorption, diffusion, and pervaporation (PV) properties of benzene/cyclohexane (Bz/Cx) mixtures on cation-exchange membranes containing copper ions (Cu(II)) were investigated. The equilibrium sorption isotherms of pure vapors in the membranes and the partial solubility of binary solutions in the membranes were described using the UNIQUAC model. The τ_iM and τ_Mi values were 0.978 and 0.591 for Bz, and 0.922 and 0.475 for Cx. The transient regimes of vapor sorption were employed to calculate the concentration-dependent diffusion coefficients. Long’s model sufficiently explained the diffusivity of Bz and Cx in the membranes. The pre-exponential factors were 3×10⁻¹³ m²/s and the plasticization factors were 3.0 and 3.6 for Bz and Cx, respectively. Excellent agreement was found with the experimental results applying the solubility and diffusivity data to simulate the pervaporation performance (flux and selectivity) using the modified Maxwell–Stefan equation. The membrane containing Cu(II) demonstrates better facilitating capability for Bz transport than that with Na(I), mainly due to its preferential sorption property toward Bz. Replacing Na(I) with Cu(II) into a Neosepta membrane resulted in better separation efficiency and higher Bz flux throughout the entire Bz concentration range.     

Superacidic activation of quinoline and isoquinoline; their reactions with cyclohexane and benzene(1)

Quinoline (1) and isoquinoline (2), upon activation by strong acids, lead to intermediate N,C-diprotonated dications, which are involved in reactions with weak nucleophiles. Thus, 1 and 2 undergo selective ionic hydrogenation with cyclohexane in CF3SO3H-SbF5, HBr-AlBr3-CH2Br2, or HCl-AlCl3-CH2Cl2 acid systems to give their 5,6,7,8-tetrahydro derivatives. They also readily condense with benzene in the presence of HBr-AlBr3 or HCl-AlCl3 to provide 5,6,7,8-tetrahydro-5,7-diphenylquinoline (10) and 5,6,7,8-tetrahydro-6,8-diphenylisoquinoline (12), respectively.     

Charge separation reactions of doubly charged benzene ions

Photoion-photoion coincidence spectra of benzene and benzene-d₆ photoionized by He(II) light and synchrotron radiation show the existence of six major and eight minor charge-separation reactions of the [C₆H₆]²⁺ ion. Three main groups of ion pairs are related to [C₃H₃]⁺ + [C₃H₃]⁺, [C₂H₃]⁺ + [C₄H₃]⁺ and [CH₃]⁺ + [C₅H₃]⁺, with appearance energies of 32.2 ± 0.5 eV, 31.3 ± 0.5 eV and 28.4 ± 0.3 eV. The kinetic energy release is the same for all pairs within a group, irrespective of hydrogen number, but differs from group to group. Results are interpreted in terms of fast, direct charge separation of [C₆H₆]²⁺, and subsequent hydrogen loss by the singly charged fragments.     

The kinetics of hydroxyl radical reactions with cyclopropane and cyclobutane

A laser flash photolysis/resonance fluorescence investigation has been carried out to study the kinetics of the overall reactions OH + cyclopropane (1) and OH + cyclobutane (2) in the temperature range 298–490 K and at 298 K, respectively. The following kinetic parameters have been determined: k₁ =(3.9 ±0.6) 10⁻¹²exp- (2.2 ± 0.1)kcal mol⁻¹/RT molecule⁻¹cm³s⁻¹, k₂(298 K) = (17.5 ± 1.5)10⁻¹³molecule⁻¹ cm³s⁻¹.     

Analytical application of ion-molecule reactions. Reactions of various substituted cyclopropane molecular ions with ammonia

By ion cyclotron resonance it is found that various substituted cy clopropanes after ionization react with ammonia to give products which allow identification of the degree and kind ofsubstitution on the cyclopropl ring. For example, cyclopropyle reacts to give [CH₂NH₂]⁺ (m/e 30), methylcyclopropane gives [CH₂NH₂]⁺ (m/e 30) and the ethyl substituted [CH(C₂H₃)NH₂]⁺ (m/e 44) and ethylopropane gives [CH₂NH₂]⁺ (m/e 30) and the ethyl substituted [CH(C₂H₅)NH₂]⁺ (m/e 58). It is suggested that reactions of stable molecular ions with reagent neutrals may be a source of highly specific structural information for organic compounds.     

The reactions of some halogenated pyridines with methoxide and methanethiolate ions in dimethylformamide

The reactions of 2,6- and 2,5-dibromopyridines and of 2,3- and 3,5-dichloropyridines with sodium isopropanethiolate and methanethiolate afforded the products of mono- or of bis-substitution depending on the experimental conditions. The same pyridines reacted with sodium methoxide to give good yields of the mono-substituted products; bis-substitution occurred easily only in the case of the 2,6-dibromo- and of the 3,5-dichloropyridine. The syntheses of some methoxy thiomethoxypyridine, starting from the halogeno methoxypyridines or from the halogeno thiomethoxypyhdines are also described. The bis-(alkylthio)pyridines can be fragmented by sodium in HMPA to give the bis(mercapto)pyridines.     

Enthalphy of mixing of bromobenzene with n-alkanes,with cyclohexane,and with benzene

A dynamic flow microcalorimeter of the Picker design was used to measure enthalpies of mixing at 298.15 K and atmospheric pressure of the six binary systems bromobenzene + n-hexane, + n-heptane, + n-nonane, + n-tetradecane, + cyclohexane, and + benzene. Within the homologous series of n-alkane systems, the interaction parameter, h₁₂, calculated from rigid-lattice group contribution theory, decreases weakly with increasing chain length of the alkane. This behavior is quite analogous to that observed with chloro-derivatives of benzene + n-alkane.     

Multiply-charged ions and interstellar chemistry

Gaseous molecules and ions, and even dust grains, can accumulate charge in the interstellar medium (ISM) by harvesting the energy of UV photons, cosmic rays, helium ions and metastable atoms. This Perspective views the various modes of gas-phase formation of multiply-charged cations and the possible impact of their reactions on the chemical and ionization structure of the ISM, in the light of what is still very limited knowledge. Emphasis is given to gas-phase reactions of multiply-charged cations with atoms, molecules and electrons that lead to charge reduction, charge separation and chemical bond formation and these are examined for multiply-charged atoms, small molecules, hydrocarbons, polycyclic aromatic hydrocarbons and fullerenes, primarily as dications but also as a function of charge state. The increased electrostatic interaction due to multiple charge is seen to promote bonding to individual charge sites on large molecules (e.g. fullerenes) and allow ensuing "surface" chemistry under the influence of Coulomb repulsion. The unique ability of multiply charged cations to undergo charge separation reactions, either unimolecular or bimolecular, can feature in the production in the ISM of internally cold, but translationally hot, cations of lower charge state or hot atoms that may provide the driving force for subsequent chemical reactions in what is otherwise an ultracold environment. Available chemical kinetic models that account for the role of multiply-charged ions in the ISM are few and of limited scope and the observation of these ions in the ISM has remained elusive.     

Microheterogeneity of benzene solutions of cyclohexane, 1,4-dioxane,and morpholine

Data obtained in molecular light scattering, adiabatic compressibility, and molar volume studies of benzene solutions of cyclohexane, 1,4-dioxane, and morpholine were used to suggest a model of the structure of these solutions and show that microheterogeneity of solutions was caused by the presence of agglomerates comprising benzene molecules in the benzene-cyclohexane system and conglomerates including heteromolecular interactions in the other systems.     

A computational investigation of the reactions of methylene, chlorocarbene, and dichlorocarbene with cyclopropane

The reactions of CH(2), CHCl, and CCl(2) with cyclopropane, 1, have been examined computationally. In all cases the lowest energy reaction between the carbene and 1 is predicted to be C-H insertion. In the reaction of CH(2) with 1, the transition state for C-C insertion leading to cyclobutane is 1.7 kcal/mol higher in enthalpy than the transition state for C-H insertion at the G3B3 level. A pathway higher in energy than C-H insertion in the reactions of CHCl and CCl(2) with 1 involves two-bond cleavages generating ethylene along with chloro and dichloroethylene, respectively.     

Reactions of platinum cluster ions with benzene

In this work, the cation and anion products of the reactions between platinum clusters produced by laser ablation and the benzene molecules seeded in argon have been studied using a high-resolution reflectron time-of-flight mass spectrometer (RTOFMS). The dominant cation products are [C(6n)H(6n - k)](+) and [Pt(m)(C(6)H(6))(n)](+) complexes, while the dominant anion products are dehydrogenated species, [C(6)H(5)PtH](-), [PtC(12)H(k)](-) and [Pt(m)C(6)H(4) . . . (C(6)H(6))(n)](-), etc. Some important intermediate structures ([PtC(6)H(6)](+), [Pt(C(6)H(6))(2)](+), [Pt(2)(C(6)H(6))(3)](+), [C(6)H(5)PtH](-), [Pt(2)C(6)H(4)](-), [Pt(3)C(6)H(4)](-) and [Pt(4)C(6)H(4)](-)) have been analyzed using density functional theory (DFT) calculations. Different reaction mechanisms are proposed for platinum cluster cations and anions with benzene, respectively.     

Graph-theoretic study of certain interstellar reactions

Certain interstellar reactions have been studied through the graph-theoretic method using a Fortran-77 program. A plausible mechanism has been proposed for the reactions. The criterion of the conversion of edge to loop and vice versa proposed by the Bratislava group [Theor. Chim. Acta 79 , 65 (1991)] has been given a reasonable chemical insight. In the reaction scheme the nucleophilic/electrophilic/carbene (singlet, triplet) or biradical loops have been generated by the fragmentation of reactant. Subsequently, Pearson's hard and soft acids bases (HSAB) theory and frontier orbital (FO) theory have been applied to explain the reaction mechanism. Few possible reactions of the interstellar and circumstellar molecules have been investigated with illustrations involving carbene intermediate and Woodward-Hoffmann rule. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 495–508, 1997