Volume 225, Issue 2 -

Proper reduction of available literature data on the heterogeneous CO + O 2 reaction on Pt group metals allows one to describe the parallel process of CO desorption, in extended intervals of temperature and gas composition, both in the High-Rate regime of an oxygen rich surface and in the Low-Rate regime of a CO rich surface. The outcome of this analysis is the determination of “apparent” as well as of “true” activation energies for both CO oxidation and desorption and their dependence on surface coverage by O or by CO-adspecies. The conclusion is reached that non-equilibrium conditions of vibrational excitation of the adlayers prevail in the HR regions, while Boltzmann equilibrium characterizes LR regimes in extended temperature and pressure intervals. These results have been discussed in the framework of a theoretical model that predicts hyperthermal vibrational states of the adlayer, which depend on the efficiency of energy dissipation into the metal.

The effect of particle size on the thermal decomposition of potassium titanium oxalate (PTO) has been studied using TG-DTA-DTG techniques in nitrogen atmosphere at different heating rates. The thermal decomposition of PTO undergoes through five stages, finally forming the stable potassium titanate. The theoretical mass loss data agree very well with experimental data for all stages of the thermal decomposition of PTO. The third thermal decomposition stage of PTO, the combined elimination of carbon monoxide and carbon dioxide, were subjected to kinetic analyses by a model free method, which is based on the isoconversional principle. We observed that both the onset and peak temperatures in DTA and DTG and the apparent activation energy are independent of particle size. The kinetic results indicate that the third thermal decomposition stage of PTO, the combined elimination of carbon monoxide and carbon dioxide, undergoes through a single step.

The title unsubstituted (normal) ( E )-2-hydroxyimino-2-cyanoacetic acid ethyl ester (the abbreviated name: ( E )-2-cyanoethyl ester-2-oxime or 2-oxime) and its 2-deuterated analogue have been prepared and characterized using infrared, Raman and inelastic, incoherent neutron scattering (IINS) spectroscopy. Molecular structures (molecular conformations) of the compounds are proposed for the vapour state. Four molecular conformers, namely two pairs of the s-cis, s-trans rotational isomers (rotamers) from six lower energetic conformations of E -2-hydroxyimino-2-cyanoacetic ethyl ester, are predominating for the single molecule of the compound. They amount together to almost 100% of the conformational populations of both rotational isomers as it was theoretically calculated using DFT (B3LYP) method with 6-311G++(d,p) basis set. Additionally dimers of 2-oxime were considered using B3LYP/6-31G * method in order to improve the results obtained for single molecule. In both parent (=N–OH) and deuterated (=N–O–D) molecules of the ( E )-2-ethylcyano ester-2-oxime respectively, extra bands corresponding primarily to hydrogen (deuterium) bond vibrations ( γ –bending out of plane of hydrogen bond, σ –stretching of hydrogen bond bridge, δ –bending in plane of hydrogen bond, λ –bending of hydrogen bond bridge have been identified, namely σ (N–O–H···O) at 132.8, 212.5, 279, 358.7, 424, 448, 523.6, 872, γ (N–O–H···O) at 334, 564, 592, 745, 820, δ (N–OH···O) at 1461, 1600, 1862cm −1 in the low temperature IINS spectrum, whereas the frequency at 365cm −1 has been assigned as the out of plane (o.o.p.) ( γ O–D···O ) vibrational mode. Formation of the O–H···O hydrogen bridge is reflected in shifting of the bands of the stretching and bending vibrations of OH group as well as arising of the bridge vibrations in the low frequency range. Moreover, equilibrium geometries and all harmonic vibrational frequencies of the ( E )-2-cyano ethyl ester-2-oxime molecules with potential energy distribution (PED) were also calculated by means of the above mentioned theoretical programs.

The general redox behaviour of phthalocyanines bearing N-benzyl-4-phenyloxyacetamide moieties (H 2 Pc, ZnPc, NiPc, CuPc, and CoPc) has been identified by cyclic voltammetry and differential pulse voltammetry on Pt in dimethylsulfoxide/tetrabutylammonium perchlorate. These measurements showed that the complexes indicate subsequent one-electron reduction and oxidation processes. Although the voltammetric measurements implied the association of the redox processes of some complexes with aggregation phenomenon, the complete evaluation of the aggregation effects by only these measurements was not possible. In situ UV-Vis spectroelectrochemical measurements enabled us to assign the ligand- and metal-based redox processes, and identify if the aggregation affects these processes. These measurements suggested that the redox processes of H 2 Pc, NiPc, and CuPc are coupled by aggregation phenomenon, while those of ZnPc and especially CoPc are not, probably due to the difference in their axial coordinating properties.

Base-catalyzed hydrolysis of 6-nitro-2H-chromen-2-one (NC) and 6-nitro-2H-chromen-2-one-3-carboxylic acid (NCC) in binary water/methanol and water/acetone mixtures were studied kinetically at 298 K. The changes in the activation barrier of the investigated compounds from water to water/methanol and water/acetone mixtures were estimated from the kinetic data. Solvent effects on the reactivity trends were analyzed into initial state and transition state components. These were determined from the transfer chemical potentials of the reactants and the kinetic data. The transfer chemical potentials δ m μ θ for NC were derived from its solubilities in water/methanol and water/acetone mixtures, and the transfer chemical potentials for NCC − anion were derived from solubility data for its calcium, cerium and lanthanum salts. Base-catalyzed hydrolysis of NC and NCC in water/methanol and water/acetone mixtures follow a rate law with k obs = k 2 · c (HO − ) and k obs = k 1 +k 2 · c (HO − ), respectively. The decrease in the rate constants of base-catalyzed hydrolysis of NC as methanol% or acetone% increases is dominated by the initial state (IS), while the decrease in the rate constants of base-catalyzed hydrolysis of NCC as methanol% or acetone% increases is dominated by the transition state (TS).

Tetraethylammonium bromochromate (TEABC) oxidation of 18 meta - and para -substituted benzyl alcohols (BnOH) in dimethylsulphoxide (DMSO) leads to the formation of corresponding aldehydes. The reaction is first order each in TEABC and the alcohols. The reaction is catalyzed by hydrogen ions. The hydrogen ion dependence has the form: k obs = a + b [H + ]. The oxidation of αα ´ -dideuterio benzyl alcohol exhibited a substantial primary kinetic isotope effect ( k H / k D =5.71 at 303 K). Oxidation of benzyl alcohol was studied in 17 different organic solvents. The solvent effect has been analyzed using Kamlet's and Swain's multi parametric equation. A correlation of data with Kamlet–Taft solvatochromic parameters ( α , β , π * ) suggests that the specific solute-solvent interactions play a major role in governing the reactivity. A mechanism involving a hydride ion transfer via chromate ester is proposed.

From extraction experiments and γ -activity measurements, the extraction constant corresponding to the equilibrium H 3 O + (aq) + 1·Na + (nb)⇌1·H 3 O + (nb) + Na + (aq) taking place in the two-phase water-nitrobenzene system (1 = benzo-18-crown-6, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (H 3 O + , 1·Na + )=-0.8±0.1. Further, the stability constant of the 1·H 3 O + complex in water-saturated nitrobenzene was calculated for a temperature of 25°C as log β nb (1·H 3 O + )=6.3±0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1·H 3 O + cationic complex species was derived. In this complex, the hydroxonium ion H 3 O + is bound by three strong linear hydrogen bonds to one (Ar–O–CH 2 ) ethereal oxygen and two (CH 2 –O–CH 2 ) ethereal oxygen atoms of the parent crown ligand 1. The interaction energy was found to be -401.4kJ/mol, confirming the formation of the considered complex 1·H 3 O + .

From extraction experiments and γ -activity measurements, the exchange extraction constants corresponding to the general equilibrium M + (aq)+NaL + (nb)⇔ML + (nb)+Na + (aq) taking place in the two-phase water-nitrobenzene system (M + =Li + , Ag + , Rb + , Tl + , Cs + ; L= p-tert -butylcalix[4]arene-tetrakis( N,N -diethylacetamide); aq=aqueous phase, nb=nitrobenzene phase) were determined. Moreover, the stability constants of the ML + complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Cs + < Rb + < Tl + < Ag + < Li + .