Francisco J. Hoyuelos

Shear viscosities of binary mixtures of pyrrolidin-2-one with C6–C10n-alkan-1-ols

Excess viscosities and excess Gibbs energies of activation for viscous flow at five temperatures have been calculated for binary liquid mixtures of pyrrolidin-2-one with (C6–C10) alkan-1-ols from the experimental densities and viscosities of the mixed fluids. The excess viscosities and excess Gibbs energies of activation were negative, and increased with increasing temperature. The fitting of viscosities to the one-parameter (d) Nissan–Grunberg equation, and the two-parameter (ν12 and ν21) McAllister equation was extended to the C1–C5 alkanols using earlier results, and examined in terms of interactions between unlike molecules. The ν12 and ν21 parameters were positive and increased with increasing temperature. A minimum in the excess Gibbs energies and d values at equimolar concentrations of the two components has been observed for the pyrrolidin-2-one–pentan-1-ol system.

Preferential Solvation in Alkan-1-ol/Alkylbenzoate Binary Mixtures by Solvatochromic Probes

The binary mixtures of methanol with (C(1)-C(4)) alkylbenzoates and of (C(1), C(3), C(5), C(7), C(9), C(11)) alkan-1-ols with methylbenzoate were used as solvents to look into the preferential solvation and intermolecular interactions of the solvatochromic indicators 2-nitroanisole, 4-nitroaniline, 4-nitrophenol, and Reichardts dye by UV-vis measurements. The experimental data at 298.15 K have served to deduce the corresponding Reichardt and Kamlet-Taft parameters of the mixed solvents. The solvation effects exerted on the solvatochromic probes by the solvents used, either pure or binary mixed, were analyzed by means of the preferential solvation model. Likewise, the (1)H NMR, (13)C NMR, and IR spectroscopic parameters measured for the mixed solvents corroborate the structural effects. The sets of experimental data gathered shed abundant light on the underlying solute-solvent and solvent-solvent interactions. The alkanol/methylbenzoate mixtures display stronger solvation ability than the pure solvents.

Heat Capacity Behavior and Structure of Alkan-1-ol/Alkylbenzoate Binary Solvents

Heat capacities for the binary mixtures of methanol with (C(1)-C(4)) alkylbenzoates and methylbenzoate with (C(1)-C(11)) alkan-1-ols have been measured over the whole composition range at 298.15 K under atmospheric pressure. From the experimental measurements, the derived excess molar heat capacities and partial excess molar heat capacities at infinite dilution have been calculated. A Redlich-Kister-type equation was fitted to these data, and the fitting parameters and standard deviations have been evaluated. Likewise, the IR spectra for the same systems have been recorded as a function of composition. The sets of experimental data gathered contribute to shed light onto the solvent structure and the underlying molecular interactions between the mixture constituents. The conclusions drawn have been established in terms of solute-solvent and solvent-solvent interactions and the ensuing structural effects between the solvent constituents.

Acid–base behaviour of organopalladium complexes [Pd(CNN)R]BF4

Protonation of the orthopalladated carbon of the cyclometallated complex [Pd(CNN)L]+, where L = P(OMe)3 and HCNN is the C-deprotonated form of the tricoordinated chelant donor ligand 2-acetylpyridinephenylhydrazone, has been studied at 25, 35, 40 and 45 °C in highly acidic 10% v∶v ethanol–water, and at 25 °C in 30% and 50% v∶v ethanol–water. The acidity constants pKSH2+ remained essentially constant with temperature, whereas these values noticeably increased with decreasing water content. Likewise, the complexes with L = P(OPh)3, PPh3, and SC4H8 were also studied at 25 °C in 10% v∶v ethanol–water. Under such conditions the pKSH2+ values were more negative in the order SC4H8 < PPh3 < P(OMe)3 < P(OPh)3; in the case of phosphines, this feature can be attributed to the substituent π-acceptor ability. These complexes behave as very weak bases and the reactions occur in sulfuric acid stronger than 1.3 M; the medium effects observed in the spectral curves were corrected to reliably determine the pKSH2+ values. The observed difference in the solvation parameter m* can be related to the differing hardness of the ligands bound to Pd.

Hydrolysis Mechanisms for the Organopalladium Complex [Pd(CNN)P(OMe)3]BF4 in Sulfuric Acid

The acid-catalyzed hydrolysis of the organopalladium complex [Pd(CNN)P(OMe)3]BF4 species was monitored spectrophotometrically at different sulfuric acid concentrations (3.9 and 11.0 M) in 10% v:v ethanol-water over the 25-45 degrees C temperature range and in 30% and 50% (v/v) ethanol-water at 25 degrees C. Two acidity regions (I and II) could be differentiated. In each of the two regions the kinetic data pairs yielded two different rate constants, k(1obs) and k(2obs), the former being faster. These constants were fitted by an Excess Acidity analysis to different hydrolyses mechanisms: A-1, A-2, and A-SE2. In region I ([H2SO4] < 7.0 M), the k(1obs) values remained constant k(1obs)(av) = 1.6 x 10(-3) s(-1) and the set of k(2obs) values nicely matched an A-SE2 mechanism, yielding a rate-determining constant k(0,ASE2) = 2.4 x 10(-7) M(-1) s(-1). In region II ([H2SO4] > 7.0 M), a switchover was observed from an A-1 mechanism (k(0,A1) = 1.3 x 10(-4) s(-1)) to an A-2 mechanism (k(0,A2) = 3.6 x 10(-3) M(-1) s(-1)). The temperature effect on the rate constants in 10% (v/v) ethanol-water yielded positive DeltaH and negative DeltaS values, except for the A-1 mechanism, where DeltaS adopted positive values throughout. The solvent permittivity effect, epsilonr, revealed that k(1obs)(av) and k(0,A2) dropped with a fall in epsilonr, whereas the k(0,ASE2) value remained unaffected. The set of results deduced is in line with the schemes put forward.

Microwave dielectric relaxation spectroscopy study of alkan-1-ol/alkylbenzoate binary solvents.

The structure and dynamics of alkan-1-ol/alkylbenzoate binary mixtures have been studied by microwave dielectric relaxation spectroscopy in the 200 MHz to 20 GHz frequency range. The binary mixtures of methanol, ethanol, propan-1-ol, butan-1-ol, and pentan-1-ol with methyl, ethyl, propyl, and butyl benzoates were studied at 298.15 K. The relaxational response of the pure alcohols, pure esters, and their binary mixtures over the full composition range is properly described by the Havriliak-Negami model. The alcohol content, alcohol length, and alkyl side-chain effects on the relaxational properties have been studied for these mixtures over the whole composition range. From the experimental readings, the effective and the corrective Kirkwood and Bruggeman correlation factors have been calculated. The data gathered have been interpreted in terms of the alkyl side-chain effect and their reliance on the mixture composition.

Phosphine and thiophene cyclopalladated complexes: hydrolysis reactions in strong acidic media.

The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF(4) (R=P(OPh)(3), PPh(3), and SC(4)H(8)) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3-11.7 M range. In all cases, a biphasic behavior was observed with rate constants k(1obs), which corresponds to the initial step of the hydrolysis reaction, and k(2obs), where k(1obs)>k(2obs). The plots of k(1obs) and k(2obs) versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k(1obs) value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh(3), P(OPh)(3), and SC(4)H(8), respectively. Regarding k(2obs), the change occurred in all cases at about 6.5 M H(2)SO(4) and matched up with the results reported for the hydrolysis of the 2-acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of k(i),(obs) (i=1,2) versus cH+. The rate-determining constants, k(0,A-1), k(0,A-2), and k(0,A-SE2) were evaluated in all cases. The R=P(OPh)(3) complex was most reactive due to its π-acid character, which favors the rupture of the trans nitrogen-palladium bond in the A-2 mechanism and also that of the pyridine nitrogen-palladium bond in the A-1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent.