Sorption studies of the interaction of water and 2-propanol with catalysts based on kaolinite

The interaction of water and 2-propanol with monocation-substituted crystalline and metaforms of Glukhovskoe kaolinite was investigated. It was shown that the nature of the exchange complex and the structure of the surface affect both the distribution of absorbed molecules of water on various segments of the surface in the first stages of its rehydration and the orientation of adsorbed molecules of 2-propanol. On crystalline forms of kaolinite a part of the alcohol molecules is oriented perpendicular to the surface, while on metaforms planar orientation of molecules is predominant.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 209–214, March–April, 1990.     

Study of intermolecular interactions in the equilibrium catalytic transesterification of esters

The interaction of alcohols ROH with esters PhCOOR (R = Me,n-Bu,n-C₇H₁₅) in binary mixtures and in solutions in non-polar solvents (CCl₄, cyclohexane) was studied over a wide temperature range by Fourier IR spectroscopy. Even with a great excess of alcohol (up to 3000-fold molar excess), two bands are observed in the region ofv(CO) vibrations. The low-frequency band, which is down-shifted by 15–20 cm^–1 with respect to thev(CO) band in the absence of alcohol, corresponds to ester molecules bonded by hydrogen bonds of the C=O...HO type. The high-frequency band is up-shifted by 3–5 cm^–1 with respect to the esterv(CO) band. The discreteness of the shift, which is confirmed by the appearance of an isobestic point, indicates that an H-complex of yet another type is formed between the alcohol and the ester. The analysis of the data available allows one to conclude that complex formation involves the alkoxyl oxygen atom of the ester. The enthalpies of formation were determined forn-BuOH H-bonds with the esters and with the transesterification catalysts, i.e., As(OBu)₃, B(OBu)₃, and Ti(OBu)₄.Part 3 — see ref.1Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–713, April, 1993.     

Influence of the temperature on the fluorescence quenching of pheophytin α by toluquinone

The influence of the temperature on the constant for the fluorescence quenching of pheophytin a by toluquinone in various solvents has been investigated. It has been shown that the quenching occurs in alcohols according to both static and dynamic mechanisms. The static quenching is caused by the formation of complexes of two types: charge-transfer complexes of ordinary structure and more stable complexes, in which the donor and acceptor are bound to one another by the alcohol molecules.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 115–118, January–February, 1985.     

Influence of viscosity of medium on processes of oxygen quenching of excited states of mesoporphyrin

The oxygen quenching rate constants for singlet and triplet excited states of the dimethyl ester of mesoporphyrin IX increase with decreasing viscosity of the medium and reach a maximum at a viscosity of approximately 0.4 mPa·sec, after which the rate constants begin to decrease. The drop in rate constant with increasing fluidity of the medium may be related to a nonequilibrium character of the elementary act in the interaction of the reactants in the solvent cage. In viscous media such as isopropyl alcohol, isobutyl alcohol, and isoamyl alcohol, the reaction radius is greater than the sum of the radii of the reacting particles. The long-range character of these processes is due to the relatively weak dependence of the quenching probability on distance.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 161–167, March–April, 1989.     

Methylsilylation of highly dispersed graphite surfaces

The chemisorption of hexamethyldisilazane on the surface of a highly dispersed graphite has been studied. It was shown that with increase in the reaction temperature, the amount of the grafted trimethysilyl groups increases. The characteristic features of the formation of the trimethylsilyl coating have been discussed on the basis of the data on the thermodesorption of water, carbon oxides and methane from graphite surfaces with mass-spectrometric monitoring.Deceased.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 184–186, March–April, 1992.     

Investigation of the interaction of benzene with vanadium-molybdenum oxide catalysts by programmed thermal desorption

Programmed thermal desorption was used to investigate the interaction of benzene with vanadium-molybdenum oxide catalysts. It was established that the amount of maleic anhydride desorbed from the catalyst surface depends on the catalyst composition and that it varies with its activity and selectivity.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 21, No. 2, pp. 252–255, March–April, 1985.     

Photocatalytic liberation of hydrogen from C1-C4 alcohols with the participation of titanium complexes

It was established that in UV irradiation of solutions of TiCl₄ in methanol, ethanol, isopropanol, and butanol, alcohol-chloride complexes of titanium(III) are formed. The quantum yields of the formation of coordination compounds of titanium(III) depend on the nature of the alcohol: 0.08 (methanol); 0.13 (ethanol); 0.20 (butanol); 0.22 (isopropanol). As complexes of titanium(III) accumulate in solution, there is a liberation of molecular hydrogen. The quantum yields of the formation of hydrogen, determined in a steady-state process, are correlated with the values of the C-H bond energy at the -carbon atom of the alcohol and are equal to 2·10^–3, 3.4·10^–3, 4.3·10^–3 and 1·10^–2 for solutions in methanol, butanol, ethanol, and isopropanol, respectively. A substantial increase in the quantum yield of the formation of molecular hydrogen was detected when a heterogeneous catalyst (palladium on silica gel) was used, and the possible mechanism of the process of photocatalytic liberation of hydrogen from alcohols with the participation of titanium complexes is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 3, No. 2, pp. 181–186, March–April, 1987.The authors would like to thank V. M. Granchak for his participation in the discussion of the results.     

Kinetics and mechanism of the reaction of organosiloxanes with the surface of pyrogenic silica

Infrared spectroscopy and gravimetry were used to study chemisorption kinetics and adsorption equilibrium in the reaction of hexamethyldisiloxane (HMDS), hexamethylcyclotrisiloxane (HMTS), octamethylcyclotetrasiloxane (OMTS), and 1,3,5 trivinyl-1,3,5-trimethylcyclotrisiloxane (MVCTS) with the surface of pyrogenic silica. It was determined that the electron-donor ability of the siloxanes in the formation of hydrogen bonds with surface hydroxyl groups decreases in the series HMDS > HMTS > OMTS > MVCTS. A reaction scheme is proposed, which includes electrophilic substitution of hydrogen of the surface silanol group in the limiting stage. It was found that the chemisorption kinetics is described by an equation of an inhomogeneous-surface model with allowance for interaction between species in a neutral-field approximation. The relative reactivity of the siloxanes in these transformations is governed mainly by the difference of the energies of the reactant siloxane bonds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 167–172, March–April, 1992.     

Dependence of the reactivity of allophanates on the conformation of the main chain

The CNDO/2 method was used to investigate the conformation and structure of alkylsubstituted allophanates. The possibility of the existence of isomers both with coplanar and with noncoplanar main chains NCNC was studied. It was shown that the formation of conformers with a cis-structure of the ester group is more probable. On the basis of an analysis of the dependence of the reactivity on the structure of the main chain, hypotheses were advanced on the role of the more stable conformers in various channels of polyaddition of isocyanates.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 360–363, May–June, 1986.     

Molecular Structure of γ-Apienes. Crystal and Molecular Structure of Ferocin

The molecular structure of the sesquiterpene humulene ester ferocin isolated from plants of the Ferula genus was determined by x-ray structure analysis. The conformation of the 11-membered γ-humulene ring was analyzed by molecular mechanics. It was found that four energetically similar macrocycle conformations are characteristic of γ-apienes.__________Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 125–128, March–April, 2005.     

Current status and prospects for development of research on the hydrophilicity of disperse systems

The current status of research on the hydrophilicity of disperse systems was discussed. The criterial values of the surface pressure of the adsorbed water film, heat and contact angle of wetting with water which separate the hydrophilic and hydrophobic surfaces were determined. An analysis of the thermodynamic characteristics showed that the boundary layers of water are more ordered near a hydrophilic surface (mica, kaolinite) and less ordered near a hydrophobic surface (organokaolinite, graphite) in comparison to liquid water. The biexponential character of the change in the structural component of the disjoining pressure with the thickness of the water film was demonstrated for disperse materials with a hydrophilic surface (kaolinite). The classification of the forms of water bound by hydrophilic disperse materials was discussed. The changes in the thermodynamic functions of vermiculite in adsorption of water were found with complex adsorptioncalorimetric and dilatometric measurements. This adsorbent undergoes a first-order phase transition during adsorption. The prospects for use of the adsorption-calorimetric method for determining the amount and energy characteristics of hydrophilic sites was demonstrated for ZSM-5 hydrophobic zeolite.Presented to the meeting of the Chemistry Section of the Academy of Sciences of the Ukraine on October 27–29, 1992.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 29, No. 2, pp. 100–115, March–April, 1993.     

Structure of the surface of synthetic titanosilica

X-ray photoelectron spectroscopy (ESCA), high-resolution NMR (on ²⁹Si nuclei), and mass spectrometry have been used to investigate a synthetic titanosilica (TS) containing 28–37% titanium dioxide. It has been found that titanium siloxane bonds can form in synthetic TS, regardless of the fact that silicon-oxygen polyhedra predominate in the surface layer. The presence of titanium ions in the surface layer of TS leads to its significant rearrangement; this reduces significantly the concentration of centers for the strong adsorption of water.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 240–243, March–April, 1986.     

Interaction of sodium dodecylsulfate (SDS) with homoionic montmorillonites: adsorption isotherms and metal-ion release

The interaction of dodecylsulfate anions (DS^–) with homoionic Ca-, Mg-, Ni-, Cu-, Cd-, Pb- and Fe-montmorillonites were investigated. Mg- and Cd-montmorillonite do not adsorb DS^–, and an anion exchange at the edges of the clay mineral does not take place. Three different adsorption processes are identified on the other montmorillonites: i) Fe-montmorillonite is covered with amorphous iron hydroxide, and DS^–-anions are bound at positively charged sites. ii) On Ca- and Pb-montmorillonite DS^– is precipitated as Me(DS)₂. iii) On Ni- and Cu-montmorillonite DS^– forms ion pairs with the cations on the surface. In all cases DS^– is not bound above the CMC but the metal ions are mobilized from the surface either by solubilization of the precipitates or by formation of mixed micelles.     

Influence of solvation and adsorption on acid-base properties of o-nitrophenol

Transmission spectra were obtained of o-nitrophenol in aqueous solutions at various pH values and in the adsorbed state on the surface of monocation-substituted forms of kaolinite. An interpretation of the electronic spectra of the adsorbed indicator was carried out using quantum-chemical calculations by the CNDO/2 and PPP SCF MO LCAO methods, taking into account the disturbing effect of cations within a point charge model. It was found that the mechanism of the interaction of the dye molecules with active centers on a solid suface differs from its behavior in solution, and this results in changes in the acid-base properties of o-nitrophenol due to changes in the phase composition of the medium. It was concluded that the indicator molecules are adsorbed simultaneously on electron-acceptor and electron-donor centers of the aluminosilicate surface.Translated from Teoreticheskaya i Éksperimental'naya, Khimiya, Vol. 25, No. 2, pp. 226–230, March–April, 1989.     

The most favorable condition for lipid hydrolysis by Rhizopus delemar lipase in combination with a sugar–ester and alcohol W/O microemulsion system

The hydrophobic interfacial characterization of sugar–ester alcohol W/O microemulsion was investigated in order to develop a suitable design for reaction media. A W/O microemulsion system was prepared as a combination of sugar–ester, DK-ester-F-110 with alcohol as a cosolvent. The diameter of the sub-micron-sized water pool, the hydrophobicity of the water pool, and the fluidity of the micro-interface were studied to analyze the reactivity of Rhizopus delemar lipase in lipid hydrolysis. The diameter of the sub-micron sized water pool was measured by dynamic laser light scattering. It was proportional to the 0.33 power of W_soln and decayed with increasing alcohol concentration. The initial reaction rate of the hydrolysis of triolein in W/O microemulsion depended on the solubilized water content. The hydrophilic character of the micro-water pool was estimated from the fluorescence wavelength indicated by Coumarin 343. The maximum initial reaction rate appeared at 450–460 nm. The fluidity of the micro-interface was investigated by fluorescence anisotropy using TMA-DPH. A suitable physicochemical reaction condition for high reactivity to occur was found, satisfying both the hydrophilicity and the fluidity of the micro-interface.     

Complexation of nitrogen-containing pharmaceutical preparations from the calcium antagonists group with phosphatidylcholine and calcium ions

The complexation of calcium antagonists with phosphatidylcholine and calcium cations in binary and ternary systems was studied by UV spectrophotometry and NMR spectroscopy. It was found that the stability constants of the complexes of the preparations studied with phospholipids increase in the series of verapamil < sensite < nifedipine. Introduction of Cal^{2 +} cations into the preparation — phospholipid system leads to the formation of more stable ternary complexes.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 27, No. 2, pp. 249–251, March–April, 1991.     

Forms of adsorption of methanol on anatase and directions of their transformation

The adsorption of methanol on titanium(IV) oxide in the anatase crystalline modification was investigated by IR spectroscopy and thermal desorption. It was established that coordinationally bonded alcohol and two types of methoxides are formed on the surface of the titanium dioxide (anatase). The adsorption centers of the methanol were found. The thermal stability and the degree of particípation in oxidation were determined for the surface structures of the adsorbed alcohol. The possibility of the conversion of the coordinationally bonded alcohol and the weakly bonded methoxyl into partial oxidation products and the strongly bonded methoxyl into total oxidation products was demonstrated. In the investigated system formate complexes at concentrations sufficient for detection by IR spectroscopy were only formed with the participation of the oxygen of the gas phase through further oxidation of the strongly bonded methoxyls.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 707–712, November–December, 1988.The authors thank V. A. Gerasimova and S. K. Anan'in for assistance in the production of the experimental results.     

Three-dimensional structures in oscillating reactions of oxidation of nickel and copper tetraazamacrocyclic complexes and influence of surface on their course

The formation on three-dimensional structures in systems containing a bromate and nickel and copper tetraazamacrocyclic complexes has been described. The reasons influencing their formation and course of oscillating chemical reactions with the participation of macrocyclic complexes is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 234–236, March–April, 1987.     

Investigation of the reactivities and tautomerism of azolidines. 40. 2-iminothiazolidin-4-one in the mannich reaction

It is shown that the aminomethylation of 2-iminothiazolidin-4-one and its 5-methyl and 5-arylidene derivatives in an alcohol medium leads to the formation of 6-oxo-2,3,4,5,6,7-hexahydrothiazolo [3,2-a]-1,3,5-triazines. The structures of the compounds obtained were confirmed by their IR, PMR, and UV spectra.See [1] for Communication 39.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 477–480, April, 1981.     

Mechanism and kinetics of vapor-phase hydrogenation of acetone to propane

The kinetics of hydrogenation of acetone to propane on a complex palladium-containing catalyst was studied at elevated temperatures when equilibrium was established in the accompanying reaction of isopropanol formation. The kinetic equation resulting from the proposed mechanism of the complex process agrees with the experimental data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 250–252, March–April, 1987.