Features of the Tautomerism of Some α-Substituted Pyridines

The AM1 quantum-chemical semi-empirical method was used to calculate the values of the enthalpy of activation (H^#), the heats of reaction (H), and the tautomeric equilibrium constants (K_T) for several -substituted pyridines. It was found that the keto-enol tautomeric conversion in -pyridone occurs more readily than the amino-imino conversion in 2-aminopyridine but in 2-methylpyridine the tautomeric equilibrium does not exist at all.     

XPS and chemisorption studies of the surface layer of Pd?Ag catalysts for CO oxidation

XPS and chemisorption studies of the surface composition of a Pd–Ag alloy (5% Pd) before and after its application in CO oxidation have been performed. It is shown that in a freshly prepared sample the bulk and surface layer compositions are the same. High-temperature treatment of the catalyst in the reaction medium leads to a thermodynamic equilibrium between surface and bulk.

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Pd–Ag Pd 5% CO . , . .

     

Determination of sucrose content of cariogenic diets by thermal analysis

The sucrose content of cariogenic diets was determined by thermal analysis. The thermal characteristics of various cariogenic diets were examined up to 700 °C. A linear correlation was found between the sucrose content of the sample and the mass loss in the range 180–240 °C.The values determined by thermogravimetry were compared with those obtained by photometry as reference values.

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Zusammenfassung Mittels Thermoanalyse wurde der Saccharosegehalt von Karies verursachenden Diäten bestimmt. Die thermischen Eigenschaften verschiedener kariogener Diäten wurden bis 700 °C untersucht. Zwischen Saccharosegehalt der Probe und Massenverlust bei 180–240 °C konnte ein linearer Zusammenhang festgestellt werden. Die thermogravimetrisch erhaltenen Werte wurden mit den durch Fotometrie erhaltenen Werten als Referenzwerte vergliche.

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. 700°. 180–240°. , , , .

     

Isomeric composition of pyrazolines obtained from unsaturated carbonyl compounds and hydrazine

The ²-pyrazolines synthesized under the usual conditions from unsaturated aldehydes and hydrazine contain from 2 to 3% of the ¹-isomers and considerable amounts of the isomeric 3-alkyl-²-pyrazolines, which are formed as a consequence of migration of the double bond. Mixtures of the stereoisomeric ²-pyrazolines are formed from ,-dialkyl-substituted acroleins. Migration of the double bond does not occur in the condensation of unsaturated ketones with hydrazine, and ²-pyrazolines that are free from admixtures of the structural isomers are obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1225–1229, September, 1971.     

Activity in CO oxidation of manganese dioxide for batteries

The low temperature oxidation of CO over MnO₂ containing samples for batteries has been investigated. It is found that the samples contain compositional and hydrate water and Mn⁴⁺, Mn³⁺, Mn²⁺ ions. The high efficiency is due to Mn⁴⁺ content.

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CO MnO₂, . , Mn⁴⁺, Mn³⁺, Mn²⁺. Mn⁴⁺.

     

FTIR investigation of the structure of vanadium oxides on ZrO2 and oxidation of toluene on it

The oxidation of toluene has been studied on V₂O₅/ZrO₂ by both FTIR spectroscopy and pulse method. The results suggest that Lewis-acidic sites play a significant role in the formation of benzaldehyde from toluene.

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V₂O₅/ZrO₂ - , . .

     

Catalytic autooxidation of hydroquinone in the presence of chelate complexes of transition metals

Autooxidation of hydroquinone was studied in the presence of Co and Cu complexes with salene, decamethyl-octadehydrocorrine, corrine and o-phenanthroline as ligands in aqueous solution and in protic and aprotic solvents. A possible mechanism of the catalytic action of some active complexes is discussed.

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, Co, Cu , , - . .

     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXIX. Solvent Effects on the Activation Parameters of Heterolysis of tert-Butyl Chloride

The kinetics of heterolysis of t-BuCl in sulfolane, PhCN, PhNO₂, acetophenone, cyclohexanone, chloroform, and 1,2-dichloroethane at 30-50°C were studied by the verdazyl method. Quantitative analysis of the effect of solvent parameters on the G , H , S , and log k _{2 5} values for heterolysis of t-BuCl in a set of 15 protic and 16 aprotic solvents and separately in either group of solvents was performed. In the above set of solvents, three H -S compensation effects are observed, associated with jump changes in the potential energy of the reaction.     

Thermodynamic behavior of mixed benzodiazepines by a new liquid chromatographic method

Summary Using a rapid chemometric methodology to determine the separation factor, , at different temperatures, Gibbs Helmholtz parameters ( (H), (S), (G)) of two adjacent benodiazepines on a chromatogram were obtained from ln versus T^–1 plots. A temperature dependent reversal of the elution order was studied and the mobile phase composition and column temperature were optimized to obtain the best separation. A flow rate of 0.80 ml min^–1 with 52.6% methanol in the methanol-water mixture and a column temperature of 48°C gave the most efficient separation of ten benzodiazepines.     

Reaction of methylmagnesium iodide with steroid keto oxides

Summary The reaction of the 3-acetate of the 20-ketal of 16,17-oxido-⁵-pregnenol-3-one-20 with methylmagnesium iodide and subsequent hydrolysis of the reaction product yielded 16-methyl-⁵-pregnenediol-3 –17-one –20. 18-Nor-17-methyl-17-iso-^5.11-pregnadienediol-3,16-one-20 was formed as a by-product.     

Charge control in the formation of complexes of phenol with ethylene derivatives containing organoelemental group IVB substituants

The v(OH) frequency shifts of phenol and the v_R resonance components of these shifts in the IR spectra of phenol H-complexes with ethylene derivatives containing various substituents including organosilicon, organogermanium, and organotin groups have been studied. The relationship between v and v_R and the values that characterize the influence of substituents on the effective charges of the double bonded carbon atoms was established; the latter values have been calculated previously usingab initio quantum chemical methods. The effective charges for the compounds with organoelemental substituents have been calculated. It has been elucidated that of the two types of possible interactions, charge controlled and orbital controlled, occurring in the formation of a complex of a hard acid, phenol, with the studied ethylene derivatives, the former is predominant.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1383–1387, August, 1993.     

The influence of solvent structure on the solvolysis oftrans-dichlorotetra (4-ethylpyridine) cobalt(III) perchlorate

Summary The solvolysis oftrans-[Co(4-Etpy)₄Cl₂]ClO₄, was followed spectrophotometrically in water/isopropanol at different temperatures. The activation energy varied nonlinearly with the mole fraction of the co-solvent, ₂. The plot of logk versus D _s ^–1 was also non-linear. These features were attributed to the differential solvation of the initial and transition states. On plotting H versus S, the points fall very close to straight line. The isokinetic temperature was found to be 334K, indicating that the solvolysis reaction is controlled by S and not H. The change in H and S with the mole fraction of the cosolvent shows extrema at the composition range where changes in solvent structure occur. The influence of the solvent structure on the complex ion in the transition state dominates over that in the initial state, where –G _t ⁰ [Co(4-Etpy)₄Cl]²⁺>–G _t ⁰ [Co(4-Etpy)₄Cl₂]⁺.     

Simulation of adsorption dynamics in adsorbent layers of short length. Estimation of the concentration region of validity of Zeldovich"s equality

The frontal adsorption dynamics with the convex adsorption isotherm at a stage of parallel transfer, was numerically simulated. The change with time in the mean adsorption values a _c in the adsorbent layers of short length L and corresponding concentrations c _L at the outlet from L was calculated. Zeldovich"s equality, which suggests that the ratio of c _L to a _c is equal to the ratio of the inlet fluid phase concentration to the amount adsorbed at equilibrium, is fulfilled at L 0 over the interval of relative concentrations from 10^–4 to 1. This indicates that Zeldovich"s equality is fulfilled as local at any limiting stage of mass transfer. The nonequilibrium dynamics of adsorption always has the finite L value at which the calculated c _L and a _c values approximately coincide with the a and c values of the equilibrium adsorption isotherm.     

Determination of enthalpy of ionization of water from 250 to 350° C

The enthalpy changes at zero ionic strength (H°) for the ionization of water (H₂O=H⁺+OH^–) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of H values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, H°, S°, C _p ^° and V°) for the ionization of water using the H° values determined in this study from 250 to 350°C and literature log K and H° values from 0 to 225°C. Smoothed values of log K, H°, S°, C _p ^° , and V° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.     

Four types of relaxation in chemical kinetics (linear case)

According to results obtained previously for the linear equations of chemical kinetics, the relation between the steady-state reaction rate and the relaxation time has been studied.

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, , .

     

Studies of molybdenum in Mo?Ti oxide catalysts

ESR studies indicate that in Mo–Ti oxide catalysts prepared via the addition of ammonium paramolybdate to pasted titanium hydroxide, Mo⁵⁺ ions are observed in three states: in heteropoly blue, disperse MoO₃ and a solid substitutional solution in TiO₂.

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, , - , - Mo⁵⁺— , MoO₃ TiO₂.

     

The conductance of lithium-7 fluoride in dioxane-water mixtures at 25°C

Conductance data for lithium-7 fluoride in dioxane-water mixtures covering the range 78.35>D>36 in dielectric constant are presented. These data and other previous data on lithium-7 chloride and lithium-7 iodide were analyzed by the Fuoss 1980 conductance equation in order to find the limiting conductance _o, the pairing distance R and the conductometric association constant K. Setting K_a=K/V_M (where V_M is the molar volume of the solvent), the thermodynamic pairing constant and the corresponding change of the free energy g were calculated. Correlation among the values found for R and g=h–Ts and the properties characteristic of the ions and solvents are discussed.R. M. Fuoss died on 1^st December 1987 before this work was completed. A D'Aprano and F. Accascina dedicate this paper to him with respect and affection.     

Conductance of iron(III) laurate solutions in binary liquid mixtures

Summary The specific conductivity of iron(III) laurate solutions in binary liquid mixtures shows that the soap aggregates into micelles and CMC is found to be independent of temperature and concentration of benzene, acetone and tetrachloromethane in 1-butanol. The variation of molecular conductance,, with soap concentration, C, is expressed by the equation: = 10^AC^B. Both constants A and B vary with solvent composition but B remains constant with increase in temperature. Several parameters such as molecular conductance at infinite dilution, , dissociation constant, K, heat of dissociation, H, entropy, S and free energy, G of dissociation of soap have been evaluated and the effect of the nature of solvents has been discussed.     

Oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82− and by IO4− in binary aqueous solvent mixtures at pressures up to 1.25 kbar

Second order rate constants and activation parameters H, S, and V have been measured for the oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82– and by IO4– in highly aqueous H2O – t-BuOH mixtures. The changes in solvation on going from the initial to the transition state are discussed on the basis of the transfer functions Gto, Hto and Sto. Whereas Gt changes smoothly as the proportion of t-BuOH increases, the plots of Ht and TSt exhibit mirror behaviour and pass through extrema located around x2(t- BuOH)=0.038. Information on the role of solvation is complemented by the determination of activation volumes. These are discussed in terms of intrinsic and solvational contributions. It is proposed that changes in hydrophobic hydration are of principal importance in determining the response of H, S, and V to changes in solvent composition in H2O – t-BuOH mixtures.