Alkylaromatic carbene ions on H-TsVK zeolites

Conclusions The adsorption of styrene (298 K), triphenylcarbinol (298 K), and of propylene with toluene (473 K) on H-TsVK zeolite leads to the formation of alkylaromatic carbocations which are stable up to 473–573 K and are characterized by bands in DRS at 320–330 and 400–440 nm and in IR by vC=C of the aromatic ring in the regions 1500 and 1610–1620 cm^–1. In the adsorption of benzene, toluene, isopropylbenzene, and 1,3-dimethylnaphthalene at 298 K, only weakly bonded surface complexes are formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1486–1490, July, 1989.     

Volumetric Properties of Toluene with Ethyl Acrylate, Butyl Acrylate, Methyl Methacrylate, and Styrene at 25°C

Densities of the binary systems of toluene with ethyl acrylate, butyl acrylate, methyl methacrylate, and styrene have been measured as a function of the composition, at 25°C and atmospheric pressure, using an Anton Paar DMA 5000 oscillating U-tube densitometer. The calculated excess volumes were correlated with the Redlich–Kister equation and with a series of Legendre polynomials. The excess volumes are negative for systems toluene + (ethyl acrylate, butyl acrylate, and styrene) and positive for the system toluene + methyl methacrylate.     

A rapid HPLC method for the determination of carboxylic acids in human urine using a monolithic column

A rapid HPLC method for the determination of carboxylic acids in urine samples using a Chromolith Performance RP/18e 100/4.6 with Chromolith Guard Cartridge RP/18e 10/4.6 (Merck KgaA, Darmstadt, Germany) was developed. The method facilitates the simultaneous determination of aromatic hydrocarbon metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA) from styrene and ethylbenzene, hippuric acid (HA) from toluene and 2-, 3-, 4-methylhippuric acids (MHA) from xylene. 3-Hydroxybenzoic acid (3-HBA) was used as internal standard. A chromatographic run is completed within less than 5 min for styrene, ethylbenzene and toluene metabolites, and within 10 min for xylene metabolites. The detection limits are 9 mg L^–1 urine for MA, 1.25 mg L^–1 urine for PGA, 4.9 mg L^–1 urine for HA, 22 mg L^–1 urine for 2-MHA, and 18.5 mg L^–1 urine for 3-MHA.No significant differences of the MA, PGA and HA concentrations in human urine samples obtained by HPLC chromatography on LiChrosorb RP 18 and on Chromolith RP/18e columns were found. The results were evaluated by using ANOVA.Abbreviations MA mandelic acid - PGA phenylglyoxylic acid - HA hippuric acid - MHA methylhippuric acid - 3-HBA 3-hydroxybenzoic acid - ANOVA analyses of variance - GC gas chromatography - HPLC high-performance liquid chromatography     

Electrochemical Studies of the Benzoate Adsorption on Au (111) Electrode

Cyclic voltammetry (CV), differential capacity (DC), and charge densitymeasurements have been employed to study the benzoate (BZ) adsorption at the Au(111)electrode surface. Thermodynamic analysis of charge density (_M) data has beenperformed to describe the properties of the adsorbed benzoate ion. The Gibbsexcess , Gibbs energy of adsorption G, and the number of electrons flowingto the interface per adsorbed benzoate ion at a constant potential (electrosorptionvalency) and at a constant bulk concentration of the benzoate (reciprocal of theEsin—Markov coefficient) have been determined. The results demonstrate thatalthough benzoate adsorption starts at negative charge densities, it takes placepredominantly at a positively charged surface. At the most positive potentials,the surface concentration of benzoate attains a limiting value of about 7.3×10^–10mol-cm^–2, which is independent of the bulk benzoate concentration. This valueis consistent with packing density corresponding to a closed-packed monolayerof vertically adsorbed benzoate molecules. At negative charge densities, benzoateassumes a flat (-bonded) surface coordination. The surface coordination ofbenzoate changes, by moving from a negatively to positively charged surface.At the negatively charged surface, the electrosorption bond is quite polar. Thepolarity of the chemisorption bond is significantly reduced due either to a chargetransfer or a screening of the charge on the anion by the charge on the metal.     

Mechanism of byproduct formation in oxidative dehydrogenation of ethylbenzene to styrene on magnesium ferrite-containing catalyst

Conclusions It has been shown by application of the kinetic isotope method that in the oxidative dehydrogenation of ethylbenzene to styrene on a magnesium ferrite catalyst, benzene and toluene are formed from ethylbenzene and also from styrene. Carbon dioxide appears mainly as a result of exhaustive oxidation of the side chain of the aromatic hydrocarbon.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 778–781, April, 1986.     

Photochemical oxidation of hydrocarbons by atmospheric oxygen in acetonitrile catalyzed by cyclopentadienyliron complexes

[(-ArH)Fe(-C₅H₅)]⁺BF₄ ^–, where ArH is benzene or toluene, catalyzes the photochemical oxidation of hydrocarbons by oxygen in acetonitrile. Cyclohexane and ethylbenzene are oxidized to the alcohol and ketone derivatives, which are formed in different amounts (after gas-liquid chromatography); benzaldehyde is obtained from styrene. The proposed mechanism involves the formation of a peroxide radical from the organometallic complex, which is capable of hydrogen atom abstraction from the alkane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1680–1683, July, 1991.     

Anionic graft polymerization of vinyl monomers initiated by metallized aromatic rings of graphite powder

Anionic graft polymerizations of methyl methacrylate (MMA) and styrene from graphite powder initiated by metallized aromatic rings on the surface were investigated. Metalation of the surface was achieved by the reaction of polycondensed aromatic rings of graphite withn-butyllithium (BuLi) in N,N,N,N-tetramethylethylenediamine (TMEDA) or hexamethylphosphorous triamide (HMPT) at 0 °C., Anionic polymerizations of MMA and styrene were initiated by metallized graphite, and these polymers were grafted onto the surface. The conversion and percentage of grafting increased by increasing the amount of BuLi used for metalation. When 0.20 g of graphite was treated with 0.4–0.5 mmol of BuLi in TMEDA, the percentage of grafting of PMMA and polystyrene reached the maximum value: PMMA 52.8% (PMMA/graphite =0.528 g/1.0 g) and polystyrene 37.2% (polystyrene/graphite=0.372 g/1.0 g). Grafting of polymers was also confirmed by infrared spectra. Although no metalation of graphite proceeded in toluene, graphite could be metallized even in toluene by the addition of crown ether as a complexing cation agent. The stability of graphite powder in organic solvent dispersion was found to be improved remarkably by grafting of polymer onto the surface.     

Nature of the centers on the surface of oxide catalysts and the forms of adsorbed toluene

IR spectroscopy has been used to analyze the forms of toluene adsorbed on various oxides, differing in the nature of their surface centers: TiO₂, CuO, V₂O₅/Al₂O₃, V₂O₅. The form of adsorption is found to depend on the nature of the surface centers of the oxide. When coordinationally saturated cations are involved complexes of toluene are formed, while if surface oxygen is involved benzoate structures are produced. The temperature at which the latter begin to be formed depends on the strength of the bond between oxygen and the surface. It was shown that the presence of acidic hydroxyl groups on the surface of the oxide leads to proton transfer to the aromatic compound to give carbonium ions. The nature of the interaction is then determined by the mobility of the proton on the surface and the basic strength of the adsorbed molecule. The possibility of identifying such compounds spectroscopically is discussed.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 710–715, November–December, 1990.     

Thermal transformations of divinyl sulfone in the gas phase

Conclusions The main products of the gas-phase pyrolysis (580–600°) of divinyl sulfone are SO₂, acetylene, and ethylene; butadiene, benzene, toluene, isomeric xylenes, styrene, and benzothiophene are also formed in smaller amounts. In an H₂S atmosphere the pyrolysis of divinyl sulfone is apparently accompanied by a partial reduction of the latter to divinyl sulfoxide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 931–932, April, 1983.     

Spectrophotometric determination of uranium in sea water with thiocyanate and rhodamine B

Summary Spectrophotometric Determination of Uranium in Sea-Water with Thiocyanate and Rhodamine B In the presence of a large excess of thiocyanate uranium(VI) forms a violet colour with Rhodamine B. The complex can be stabilized by addition of poly (vinyl alcohol). The calibration graph for measurement at 600 nm is linear in the range 0.5–10g of uranium per 25ml, the molar absorptivity being 3.56×10⁵1-mole^–1·cm^–1. The effect of foreign ions has been studied and the method can be applied to the determination of uranium in sea-water, with reliable results. Uranium is preconcentrated from sea-water by a flotation procedure with toluene in presence of benzoate and Safranine T, with nitrilotriacetic acid as masking agent. The method is highly selective for uranium, with a recovery of 97.9–99.2%.     

Synthesis and properties of stable aromatic bis(nitrile oxides)

A number of stable bis(nitrile oxides) based on dimesitylmethane and didurylmethane and their analogs in which two aromatic rings are joined by various bridging groups were synthesized. The thermal isomerization of the bis(nitrile oxides) to diisocyanates and the relative reactivities of the bis(nitrile oxides) in 1,3-dipolar cycloaddition to styrene were studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1398–1403, June, 1991.     

Effect of Cathode Potential on Electrosynthesis and Physicochemical Properties of Styrene and Methyl Methacrylate Copolymers

The voltammetry, ESR and UV spectroscopy methods and quantum chemical calculations (PPDP/2) are used to determine the nature of active centers, the anionic mechanism of electrochemical copolymerization (ECP) of styrene (St) and methyl methacrylate (M) at the cathode surface, and the radical-anion mechanism in aprotic solvents. The composition, microstructure, and dielectric properties of copolymers are determined by the cathode potential, which is due to a change in the nature of inducing species (M°^–, °M–M^–, ^–M–M^–, St^2–) and in the ratio of their concentrations during ECP.     

Effect of preparative conditions of a porous surface layer on the hydrogen permeability of palladium/ruthenium alloy membranes

The possibility of producing a porous surface layer on membranes formed from palladium alloys with mercury and lanthanum has been investigated. Membranes with the highest permeability to hdyrogen produced at temperatues in the range 500–550 K with zinc and 560–570 K with copper had maximum surface porosity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1308–1312, June, 1991.     

Determination of styrene in olive oil by an automatic purge-and-trap system coupled to gas chromatography-mass spectrometry

Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg^–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg^–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg^–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market.     

Heats of xenon adsorption on Nax zeolite at high pressures and various temperatures

The heats of xenon adsorption on zeolite NaX at 299–467 K and 0–21 MPa were measured on a Tian-Calvet differential calorimeter. A significant temperature dependence of the heats measured at high occupancies of the adsorption surface was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 223–226, January, 1991.     

Certain aspects of heterophase ion exchange

Ion exchange between an aqueous solution of KCl and a solution of tetraoctylammonium bromide in toluene has been studied at 20–70°C. Equilibrium exchange constants were measured. The free energy of the ion exchange is determined to a large extent by Coulombic interaction, which increases with decrease in the radius of the ion. The strength of the Q⁺X^– bond is weakened on passing from the normal onium salt to the hydrate and the rate of ion exchange increases. The position of equilibrium during approach to it from different sides may be affected by different formation processes of complexes with low activity in respect to exchange.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1773–1776, August, 1991.     

Selectivity limitations in the heterogeneous epoxidation of olefins: branching reactions of the oxametallacycle intermediate in the partial oxidation of styrene

The partial oxidation of olefins on Ag surfaces has been a long standing problem in surface science and is of great commercial interest. We present a temperature-programmed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS) study of the partial oxidation of styrene on Ag(111). The reaction products are CO2, water, styrene oxide, benzene, and benzoic acid. XPS gives evidence for two different reaction intermediates that we assign to an oxametallacycle and to benzoate. The oxametallacycle seems to be the precursor for both the formation of styrene oxide and the formation of benzoate, and thus, in addition to leading to styrene oxide, also leads to undesired byproducts. The benzoate reacts further to form CO2, benzene, and benzoic acid.     

Synthesis and structure of diethyl 2-oxo-1-oxaspiro[4,5]decane-3,4-dicarboxylate

Ethyl 1-oxaspiro[2,5]octane-2-carboxylate reacts with diethyl sodiomalonate in toluene to give diethyl 2-oxo-1-oxaspiro[4,5]decane-3,4-dicarboxylate, which on distillation under goes partial de-ethoxycarbonylation to give ethyl 2-oxo-1-oxaspiro[4,5]decane-4-carboxylate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 28–32, January, 1991.     

Benzoate ion-selective electrode with improved selectivity and reproducibility for benzoate determination in medicinal syrups

This paper describes the construction and evaluation of a benzoate anion selective electrode with enhanced working characteristics, namely reproducibility and selectivity, to be used in medicinal syrups analysis by direct potentiometry. The electrode, without an internal reference solution, was prepared with a PVC membrane, based onbis(triphenylphosphoranylidene) ammonium benzoate as ion-exchanger, dissolved in 2-nitrophenyl octyl ether as mediator solvent and 4-t-octylphenol as additive. The characteristics of the electrodes were evaluated in sodium benzoate solutions with adjusted ionic strength and showed a linear response in the range 10^–2–2 × 10^–4 mol dm^–3 with a slope of 54.7 ± 0.5 mV/decade and a reproducibility of ±0.2 mV/day for solutions with pH 6.3. The potentiometric selectivity coefficients were determined for some possible interfering species and showed that the electrodes prepared with the additive had good selectivity, especially over iodide and nitrate, when compared with those without any additive. The electrodes were used for benzoate determinations in several medicinal syrups by direct potentiometry. The results gave recovery values in the range 98.3–104.6%.     

1H NMR studies on intermolecular association of amphiphilic cationic polyelectrolyte micelles induced by hydrophobic counteranions in water

Interactions of a series of amphiphilic cationic polyelectrolytes with various kinds of organic counteranions have been investigated in water by one- and two-dimensional ¹H NMR spectroscopy at 20 °C. The cationic polyelectrolytes were prepared by micellar homopolymerization of tail-type cationic surface-active monomers with a cationic charge with -end, (ST–C_m–AB, m=5, 7, and 9, where ST is a styrenic group, C_m, an alkylene chain at the 4-position of styrene, and AB, alkyltrimethylammonium bromide). Aliphatic monosodium salt of maleic acid (MAS) and its stereoisomer, fumaric acid (FAS), sodium benzoate (NaB), potassium hydrogen phthalate (PHK), and sodium salicylate (NaSal) were added to a salt-free aqueous solution of the polyelectrolytes and ¹H NMR measurements were carried out. Amphiphilic P(ST–C_m–AB) polyelectrolytes act as efficient hosts to strongly capture the hydrophobic counteranions B^–, PH^–, and Sal^–, but not MA^– and FA^–. The ¹H NMR signals of these hydrophobic counteranions remarkably shift upfield and broaden in water in the presence of the amphiphilic polyelectrolytes. The nuclear Overhauser effect (NOE) signals between the cationic group of the polymer and aromatic benzoate counteranion protons are clearly observed to imply cation– interaction. The capturing of hydrophobic counterions by the polyelectrolytes is likely due to electrostatic, hydrophobic, and cation– interactions between them. The reduced viscosity, _sp/C_p, for the solution at [PHK]/[P(ST–C₇–AB)]=1.0 steeply increases with increasing polymer concentration (C_p) above ca. 0.9 g/dL to show pronounced viscoelasticity.