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  • Author or Editor: G. Perez x
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Abstract  

Radiolytically formed O2H+, N2H+, and CO2H+ ions were allowed to react with gaseous p-cymene. Dealkylation and isomerization reactions were observed with O2H+ and N2H+ ions, while only the first process occurred when CO2H+ ions were employed. The results show that dealkylation is favored with respect to isomerization as the protonation exothermicity decreases.

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Abstract  

Unsolvated methyl cations, generated by spontaneous -decay of multitritiated methane, have been allowed to react with some aliphatic ethers. The reaction mixtures contain various products, mainly aliphatic ethers, that have been separated by gaschromatography and continuously counted in an ionization chamber. A mechanism involving different reaction channels can provide an explanation of the results.

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Abstract  

D3 + ions, produced by deuterium -radiolysis, were allowed to react with gaseous p-tert-butyltoluene. The excited arenium ions formed, if not collisionally stabilized, underwent predominantly dealkylation to form toluene and, to a minor extent, isomerization. The dependence of reaction product yields on the substrate pressure is discussed.

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Abstract  

The -radiolysis of solutions of benzene and naphthalene in carbon tetrachloride has been studied to obtain information about chlorination reactions. The position of naphthalene showed a reactivity 2.5 higher with respect to benzene, while the absence of 2-chloronaphthalene among the products confirmed the relatively high activation energy required for the attack in position.

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Abstract  

The radiolysis of aqueous benzene solutions was carried out at 35 °C, 45 °C, 55 °C, and 65 °C. The results, obtained by coupling HPLC and GC separations, showed that the yields of all the radiolysis products increased with temperature. However, the comparison of the results must be limited to those compounds that are formed exclusively in aqueous solutions. It was found that the increase of the relative concentrations of the products with the temperature followed the order: nitrobenzene>phenol>o-nitrophenol >p-nitrophenol.

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Abstract  

The complex [Pd(2-Phpy)(-Cl)]2 reacts with pyridines (L=pyridine, α-picoline and γ-picoline), amines (L=isopropylamine, tert-butylamine) and ammonia to form the corresponding ortho-palladatedderivatives [Pd(2-Phpy)ClL]. The compounds have been characterized by C, H and Nanalyses and spectroscopic methods (IR and 1H and 13C NMR).TG, DTG and DSC studies of the complexes were carried out in dynamic nitrogen atmosphere. From DSC analyses the heats of decomposition were calculated. The kinetics ofthe first step of thermal decomposition were evaluated from TG data by isothermal methods for L=pyridine and isopropylamine. The activation energies obtained are in the range 90–100 kJ mol-1. The best fitting for data was observed for R2 and A1.5 kinetic models.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: M. R. Granados-Uribe, F. J. Lona-Ramírez, C. Pérez-Pérez, J. Barajas-Fernández, V. Rico Ramírez, and G. González-Alatorre

Abstract

The nitrosation of 1,3-dialkylureas was carried out in the presence of carboxylic acids and halides in an aqueous perchloric medium. The aim of this work was to validate the proposed mechanism for the nitrosation of such substrates. In accordance with the rate limiting step of the proposed mechanism, the protonic transfer to the solvent, basic catalysis and an absence of catalysis by halides should be observed. The Br⊘nsted parameters were determined by basic general catalysis.

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The glass transition temperatures of sorbitol and fructose were characterized by four points determined on DSC heating thermograms (onset, mid-point, peak and end-point), plus the limit fictive temperature. The variations of these temperature values, observed as functions of cooling and heating rates, were used to determine the fragility parameter, as defined by Angell [1] to characterize the temperature dependence of the dynamic behavior of glass-forming liquids in the temperature range above the glass transition.

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Abstract  

Discontinuous isoperibolic thermal analysis (ΔITA) is a phase diagram investigation technique applicable to organic components systems (with at least one liquid phase). The elementary signal is composed by the evolution of the temperature of the system vs. time after a composition shift. A theoretical analysis and a mathematical modeling of this signal show that the overall enthalpy exchanged multiplied by a proportional factor can be obtained. From different experiments, evidence is given that this semi-quantitative calorimetric measurement is reliable. Thus, ΔITA allows consistent and accurate descriptions of phase diagrams and is a real relative calorimetric measurement technique.

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Abstract  

We report results obtained on the separation of lanthanum, cerium, and samarium from synthetic and natural uranium samples by means of solvent extraction and ion exchange. Quantitative determinations of these elements were performed using X-ray fluorescence, polarography, and chemical or neutron activation analysis.

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