Hydrogenation of cyclohexene on different types of catalysts

Hydrogenation of cyclohexene has been studied under pressure in a flow reactor on the following catalysts: Na- and H-forms of Y-type zeolites, erionite, magnesium and lanthanum oxides, palladium on silica and aluminum oxide. This reaction is accompanied by skeletal isomerization to give methylcyclopentane and methylcyclopentenes. The differences in activation energies for isomerization and hydrogenation reactions were estimated as 83–96 kJ/mole for NaY and Na,K-erionite, 33–50 kJ/mole for the H-forms of the zeolites, 33–37 kJ/mole on the Pd catalysts, and 25–33 kJ/mole on magnesium and lanthanum oxides. It is suggested that the cyclohexyl complex, formed as an intermediate during hydrogenation of cyclohexene on Na-forms of the zeolites, is neither a carbocation nor a radical.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 791–799, April, 1992.     

Liquid–liquid phase equilibria of the ternary system of water/1,4-dioxane/dihydromyrcene

Liquid–liquid phase equilibria (LLE) for the system of water/1,4-dioxane/dihydromyrene (DHM) were investigated experimentally at 343.15, 348.15, 353.15, 358.15 K and atmospheric pressure. The reliability of the experimental tie-lines has been confirmed by using Othmer–Tobias correlation. The NRTL and improved UNIQUAC models were used to correlate the phase equilibria in the system using the interaction parameters determined from experimental data. The root mean square deviation (RMSD) between the observed and calculated mole percents was 0.58%. It is found that NRTL and improved UNIQUAC used for LLE could provide a good correlation.     

Kinetics of the ionization of monoalkylbenzenes and nitroalkanes in polar solvents. 2. Calculation of the outer-sphere reorganization energy

Conclusions The outer-sphere reorganization energies have been calculated for the ionization of toluene (167 kJ/mole) and cumene (146 kJ/mole) in solutions of potassium tert-butoxide in DMSO.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 326–328, February, 1989.     

Heats of adsorption of CO2 on high-silicon zeolites ZSM-5 and silicalite

The heat of adsorption of C0₂on NaZSM-5 at zero occupancy is 50.0 kJ/mole. The differential heats have two linearly descending segments, corresponding to the formation of two types of adsorption complexes with one or two C0₂ molecules, on the average. The heat of adsorption on silicalite coincides with the heat of adsorption of CO₂ on the noncationic segment of the NaZSM-5 zeolite structure (28–29 kJ/mole). The adsorbate-adsorbate interaction forces are not evident on the zeolites up to 1.5 mmole/g occupancy. The isotherms for the adsorption of C0₂ on zeolite NaZSM-5 and silicalite at 303 K in the occupancy region of 0–1.5 and 0–0.5 mmole/g are completely described by VMOT equations.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2636–2638, November, 1989.     

Investigations of TsVM zeolite acidities with different degrees of exchange of Na+ by H+

The method of programmed thermal desorption of ammonia has been used to establish that on the surface of the sodium form of type TsVM zeolite having a modulus SiO₂/Al₂O₃= 34.5 there are two types of acidic centers having ammonia desorption activation energies E_d equal to 40–45 and 80–100 kJ/mole. Replacement of Na⁺ by H⁺ leads to the appearance of a third type of center with a value E_D=130–150 kJ/mole. In this case in the IR spectra of specimens saturated with ammonia a band appears at 1410 cm_–1, which is evidence for the presence of NH ₄ ⁺ ions. Increasing the degree of Na⁺ replacement by H⁺ leads to a nonproportional rapid increase in the concentration of highly energetic centers, which may be explained by the partial transfer of aluminum into cationic positions with the formation of additional acidic centers.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 752–755, November–December, 1986.     

A thermochemical study of cesium and nitrile perchloratozirconates

Measurements were carried out for the solution enthalpies of zirconium perchlorate, nitrile perchlorate, nitrile perchloratozirconate, and cesium perchloratozirconate in concentrated nitric acid. A thermochemical reaction cycle was established and the enthalpies of formation H_f ⁰ at 298.15 K were found for Zr(ClO₄)₄(s) (–745.5±2.7 kJ/mole), (NO₂)₂[Zr(ClO₄)₆](s) (–714.2±4.4 kJ/mole), and Cs₂[Zr(ClO₄)₆](s) (–1656.3±4.5 kJ/mole).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 910–913, April, 1990.     

Effect of chemical modification of clinoptilolite on the adsorption energy of dipolar and quadrupolar molecules

Adsorbents can be made by chemical modification of clinoptilolite for which the characteristic adsorption energies of H₂O, CO₂, H₂S and SO₂ differ from those of the initial zeolite by 9–12 kJ/mole (cation exchange) and 16–21 kJ/mole (dealuminated). The characteristic adsorption energies of the molecules on modified clinoptilolite increased in the order SO₂ > H₂S > C0₂ > H₂O.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 5, pp. 324–328, September–October, 1995.     

Study of the reactivity of ammonium carboxylates in the synthesis of amides under high-pressure deformation conditions

On deformation under pressures up to 10 GPa the ammonium salts of aliphatic and aromatic acids, as well as mixtures of a free carboxylic acid with the ammonium salts of strong mineral acids, are converted into the corresponding amides. The amide yields increase with pressure, the magnitude of shearing deformation, and temperature. The temperature and pressure coefficients for amide formation are low and have values of 2.5–4 kJ/mole and –1 to –2 cm³/mole, respectively. The reactivity of ammonium salts in the synthesis of amides alternates in the homologous series of aliphatic acids in a similar way to the shear stress of these salts. The reactivity of the ammonium salts of aliphatic acids increases when the reaction is conducted in a matrix of an ammonium salt which possesses plasticity and a high shear stress.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2289–2292, October, 1989.     

Sorption of cesium on montmorillonite and effects of salt concentration

The sorption behavior of cesium on montmorillonite type clay was studied by using radioactivity measurements. Concentrations of Cs⁺ ions ranged from 10^–6 to 10^–2M. Cesium retention reduced with increasing salt concentration which was varied between 10^–4 and 10^–1M. Selectivity coefficients K_Cs–Na for the exchange between Cs and Na were calculated for different equivalent fractions of Cs on the solid phase. Using theK _Cs–Na values, free energy change was found to be 7.8 kJ/mol. The data could be fitted to a Freundlich isotherm, and empirical Freundlich parameters enabled the generation of a site distribution function. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm, a mean energy of sorption of 8.6 kJ/mole was calculated which corresponds to the energy of ion exchange reactions. The values of energy changes calculated by using two different methods were in good agreement.     

Kinetics of colloid formation during the preparation of sol-gel zirconia

The formation of zirconia colloids by hydrolysing zirconium n-propoxide in n-propanol has been investigated by simultaneous, multi-angle static and dynamic light scattering, and vibrational spectroscopy, as a function of reactant concentration, water-to-alkoxide mole ratio and temperature.The overall hydrolysis/condensation reaction followed pseudo 2nd-order kinetics at 303 K, with an induction period of <1 to 24 hours. The induction period could be substantially reduced by increasing the temperature to 348 K. For hydrolysis with 3.6 moles of water per mole of alkoxide, the apparent activation energy was 24 kJ mol^–1. Such a low activation energy implies that hydrolysis occurs readily over the temperature range investigated (303–348 K). During the induction period, processing with stoichiometric, or excess, water produced oxy-hydroxides, while hydrated oxides formed under water-deficient conditions.The hydrolysis reactions yielded zirconia colloids with equivalent spherical, z-averaged diameters of <200 nm. The colloids exhibited fractal dimensions of 3.0, with a low size-polydispersity, inferring the formation of dense, monodispersed spherical particles. SEM observations confirmed these results.     

Radical hydroxylation of aromatic hydrocarbons examined by MINDO/3 methods

MINDO/3 calculations have been made on the potential-energy surfaces for the attachment of OH^. radicals to benzene (1) and naphthalene (2) in the vapor state. The activation energies of these reactions are calculated as 88 and 58 kJ/mole. while the enthalpies at 298K are calculated as –211 and –199 kJ/mol. The transition states in (1) and (2) lie closer to the reagents than the products on the reaction coordinate, while (1) has an earlier transition state than does (2). The transition states in these reactions have high dipole moments: 3.1 and 3.6 D, respectively, which are due to charge transfer from the hydrocarbons to the OH^.. Quantum-chemical calculations and kinetic data on the reactions of aromatic hydrocarbons with OH^. in aqueous solution indicate that the mechanism is probably not one involving electron transfer and a rate-limiting stage in the attachment. These processes are of high performance because the radicals are of high stability, while polar effects determine the selectivity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 20–26, January–February, 1986.     

Motion of protons in the central opening of porphyrins

The distribution of the electrostatic potential of the molecule of porphine (P) and the anions formed by the successive elimination of one and two central protons from it has been studied by the SCF-MO-LCAO method in the all-valence-electron CNDO/2 approximation. The electrostatic potential of the potential of the (P-2HO^2– dianion is characterized by the presence of four minima located at a distance of about 1 Å from the nitrogen atoms. The potential in them is equal to –991 kJ/mole. The value of the potential at the center of the opening is –978 kJ/mole. The distribution of the electrostatic potential of the (P-H)^– anion with a fixed position of the proton near one of the nitrogen atoms is characterized by the presence of a deep valley situated at the oppositely lying nitrogen atom perpendicularly to the N-H bond. The potential of the molecule of P in the plane of the ring does not have negative values, attesting to the energetic unfavorability of the planar conformations of the (P+H)⁺ cation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 216–220, March–April, 1986.     

Conditions for the formation of ions with strong quasisymmetric hydrogen bonds

The conditions necessary for the formation of ions with strong hydrogen bonding (B...H...OH₂)⁺ are determined: 1) acid-base interaction achieves the stage of ion formation; 2) the base molecules contain atoms with unshared electron pairs; and, 3) the heat of protonization of a base molecule in the gas phase is not less than the heat of protonization of a water molecule (711 kJ/mole), but not more than the value determined by the difference between the energy of breaking the strong hydrogen bond in H₅O₂ ⁺ and the heat of the hydrogen bond in a dimer of water, i.e., –836 kJ/mole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 32–35, January, 1990.     

Creep study of high-esterified pectin gels.

Summary A creep study has been made of pectin gels concentrated to 0.5–2.5% in the temperature interval 25 to 50°C. In the region of linear viscoelasticity the pectin gels are capable of being strained both reversibly and irreversibly. The shape of the reversible strain relaxation curves corresponds to the transition region between the glassy and highly elastic states. The temperature dependence of the largest Newtonian viscosity is described by de Guzmán-Arrhenius equation. The break-down enthalpy of the gel cross-links is between 51 and 74 kJ/mole, showing an increase with concentration.With 10 figures and 1 table     

Energy of rehydration of natural clinoptilolite and its lithium form as a function of the dehydration temperature

Natural clinoptilolite (CL) is practically reversibly rehydrated below (350±50)°C, and is only 10% sintered at 500°C. LiCL is reversibly dehydrated up to (250±20)°C, and is sintered much more rapidly than CL at higher temperatures (by 50% at 400°C, for example). The heats of rehydration pass through maxima as a function of the calcination temperature: for CL (250±10) J/g at 300–400°C, and for LiCL (300±15) J/g at 250°C. The corresponding half-widths of the maxima are >500 and (330±20)°C. The maximum values of the average molecular integral heats of adsorption of water vapors are (73±3) kJ/mole on CL and (76±3) kJ/mole in LiCL.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2407–2409, November, 1989.We would like to thank T. M. Guliev for assisting in the measurements.     

X-ray crystallographic and quantum-chemical investigation of tert-butyl hydroperoxide

An MNDO calculation and an x-ray crystallographic investigation of tert-butyl hydroperoxide (I) were undertaken. The two symmetrically independent molecules of (I), which in fact have identical geometric parameters, form infinite chains along the y axis through staggered hydrogen bonds. The chains have local symmetry, described by a noncrystallographic slip plane. The difference between the experimental value of the COOH dihedral angle (average 100°) and the calculated value (128.5°) is most likely due to the formation of intermolecular hydrogen bonds in the crystal, the energies of which (30 kJ/mole) are considerably larger than the calculated excess energy of the conformers observed in the crystal (3.4 and 1.9 kJ/ mole).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 1, pp. 82–87, January–February, 1989.     

The oxidation of organic compounds

In a study of the behavior of tris(hydroxymethyl)-4-picoline (I) under the conditions of vapor-phase oxidation on a vanadium-tin oxide catalyst, it was found that with the addition of 150–250 mole of water and 125–200 mole of O₂ per mole of I and a contact time of 0.35–0.45 sec, the main reaction product was isonicotinic acid (II), the yield of which amounted to 60–65% of theoretical, calculated on the I passed.For part XLVIII, see [1].     

Adsorption energetics of hydrocarbons on silicalite

The differential adsorption heat curves for hydrocarbons on silicalite feature Langmuir invariance without apparent interaction for heptane, a linear increase with increasing occupancy for pentane, and great complexity with both minima and maxima for benzene. The adsorption heat increment per CH₂ group is 10.0 kJ/mole from the adsorption heat data for ethane, butane, pentane, and heptane, while the free regression term corresponding to the adsorption of 2H or H ₂ is 11.5 kJ/mole. The mean molar entropies of pentane and heptane is less than the entropies of the liquids by -60 J/mole · K, while the state of normal alkanes in silicalite channels is solidlike. The isotherms for the adsorption of hydrocarbons on silicalite are described completely by the volumetricmicropore occupancy theory equations. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2333–2335, October, 1989.     

A new chemiluminescence emitter in the hydroquinone-inhibited reaction of cumene oxidation by oxygen

A new chemiluminescence emitter was detected in the hydroquinone-inhibited reaction of homolytic oxidation of cumene by oxygen. The emission band lies in the range (22-18)·10³ cm^–1, which corresponds to an energy of 230 kJ/mole between levels. It is suggested that this emitter is p-benzoquinone, formed in the reaction between the phenoxyl and peroxy radicals.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 2, pp. 103–107, March–April, 1994.     

State of the structural hydroxyl groups in minerals of the kaolinite group according to infrared spectroscopic data

An interpretation of the IR spectra of kaolinite, dickite, and nacrite is proposed, based on the concept of resonance interaction of two intrasurface hydroxyl groups, and their manifestation in the spectrum as a split doublet 30 cm^–1 and by the individual vibration of a third intrasurface OH-group. The structural identification of each band in the IR spectra of the kaolinite minerals is given. It was demonstrated that thermal dehydroxylation under vacuum of kaolinite occurred in two stages with activation energies of 43 and 84 kJ/mole. The activation energy of proton delocalization of the structural hydroxyl groups of kaolinite has been evaluated (E 13 kJ/mole). The contribution of the energy of the interlayer hydrogen bonds (AH 28 kJ/mole) to the total cohesion energy of adjoining layers of kaolinite (E_c 165 kJ/mole) was calculated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 73–81, January–February, 1985.