Juan Z. Dávalos

Evaluation of poultry litter as a feasible fuel

Caloric values (massic energy of combustion) of poultry litter coming from the chicken farm “Cantos Blancos” (Guadalajara– Spain) were determined by static bomb calorimetry. These values correspond to samples treated in different conditions of drying-up. The massic energy of combustion of the “dry samples” was 14 447 kJ/kg and for “wet samples” decreased linearly with increasing water content. The optimum conditions to use these waste product as an economic fuel were also established.

The ever-surprising chemistry of boron: enhanced acidity of phosphine.boranes.

The acidity-enhancing effect of BH(3) in gas-phase phosphineboranes compared to the corresponding free phosphines is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. Thus, the enhancement of the acidity of protic acids by Lewis acids usually observed in solution is also observed in the gas phase. For example, the gas-phase acidities (GA) of MePH(2) and MePH(2)BH(3) differ by about 118 kJ mol(-1) (see picture).The gas-phase acidity of a series of phosphines and their corresponding phosphineborane derivatives was measured by FT-ICR techniques. BH(3) attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol(-1)). This acidity-enhancing effect of BH(3) is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High-level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH(3) association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH(3) group is present. Our study also shows that deprotonation of ClCH(2)PH(2) and ClCH(2)PH(2)BH(3) is followed by chloride departure. For the latter compound deprotonation at the BH(3) group is found to be more favorable than PH(2) deprotonation, and the subsequent loss of Cl(-) is kinetically favored with respect to loss of Cl(-) in a typical S(N)2 process. Hence, ClCH(2)PH(2)BH(3) is the only phosphineborane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.

Mössbauer study of the corrosion behaviour of pure iron and weathering steel under a wet-dry cycle

Mossbauer spectroscopy (MBS) and X-ray diffraction (XRD) have been used to establish the composition of the rust layer formed on weathering steel and pure iron under several wet-dry cycles in a SO2-polluted atmosphere. FeSO3−3H2O, FeSO4−4H2O, and poorly crystalline ferrihydrite were identified as the only corrosion products. The Mossbauer spectrum of FeSO3−3H2O is reported.

The design, construction and testing of a microcombustion calorimeter suitable for organic compounds containing C, H and O

To obtain reliable standard energies of combustion with small amounts of C, H, O compounds, a new microcombustion calorimetry system has been set up. The design, construction, calibration and measurement experiments are described. The system includes a commercial combustion bomb with an internal volume of 22 cm3. Samples of around 80 mg are suitable if one wants to retain the same levels of accuracy and reproducibility as those in macrocombustion experiments. Calibration of the calorimeter was performed using benzoic acid. e(calorimeter) = 2083.74±0.48JK-1 was obtained. Combustion measurements using m-methoxybenzoic acid were made in order to verify the chemistry of the combustion process involved in the corresponding analysis of results and the accuracy of the measurement of combustion energy. The uncertainty of the results shows that the instrument described and the experimental procedure used for the determination of enthalpies of formation of compounds containing C, H and O provide a high reliability.

Thermodynamic Stabilities of Carbocations

Publisher Summary This chapter addresses the quantification of the concept of “stability”. Thermodynamic criteria have been applied to rank carbenium ions on the basis of their intrinsic stabilities—that is, stabilities in the absence of solvent. Both experimental and computational data have been used. It discusses the relationship between the intrinsic thermodynamic stability of these species and their reactivity in solution, from both the thermodynamic and the kinetic points of view. Relevant structural features of these species, as revealed by experimental or computational methods data, have been reviewed. Quantum mechanical calculations at the highest possible levels (within our computational capabilities) have been performed on most of the species. The scope of this chapter is limited to a relatively small number of ions that illustrate some representative examples of structural effects. The “low resolution” overview of the gas-phase stabilities of a variety of carbenium ions shows that they are by no means exotic data unrelated to solution reactivity. On the contrary, they are the fundamental factor determining the relative stabilities of the same species in solution.

Gas-Phase Basicities Around and Below Water Revisited

This work employs Fourier transform ion cyclotron resonance (FT-ICR) and the Gaussian quantum chemistry composite methods W1 and G2 to experimentally and computationally analyze gas-phase basicities (GB) for a series of weak bases in the basicity region around and below water. The study aims to clarify the long-standing discrepancy between reported GB values for weak bases obtained via high-pressure mass spectrometry (HPMS) and ICR; the ICR scale is observed to be more than 2 times contracted compared to the HPMS scale. The computational results of this work support published HPMS data. This agreement improves with increasing sophistication of the computational method and is excellent at the W1 level. Several equilibria were also re-examined experimentally using FT-ICR. In the experiments with some polyfluorinated weak bases (hexafluoro-2-propanol and nonafluoro-2-methyl-2-propanol), it was found that two protonation processes compete in the gas phase: protonation on oxygen and protonation on fluorine. In these species, protonation on fluorine proceeds faster and is statistically favored over protonation on oxygen but leads to cations that are thermodynamically less stable than oxygen-protonated cations. The process may also lead to the irreversible loss of HF. The rearrangement of fluorine-protonated cations to oxygen-protonated cations is very slow and is further suppressed by the process of HF abstraction. These results at least partially explain the discrepancy between published HPMS data and earlier FT-ICR findings and call for the utmost care in using FT-ICR for gas-phase basicity measurements of heavily fluorinated compounds. The narrower dynamic range of ICR necessitates the measurement of several problematic bases and produces some differences between the ICR results in the present work and the published HPMS data; the wider dynamic range allows HPMS to overcome these difficulties in connecting the ladder.

Corrosion of weathering steel and iron under wet-dry cycling conditions: Influence of the rise of temperature during the dry period

The effect of a dry-hot period on the SO2 corrosion of weatherig steel and pure iron under wet-dry cycling was investigated. Corrosion products were identified by Mössbauer spectroscopy and X-ray powder diffraction. The formation of an intermediate corrosion layer of spm α-FeOOH only on weathering steel was the most significant result.

Computational Thermochemistry of Six Ureas, Imidazolidin-2-one, N,N '-Trimethyleneurea, Benzimidazolinone, Parabanic Acid, Barbital (5,5 '-Diethylbarbituric Acid), and 3,4,4 '-Trichlorocarbanilide, with an Extension to Related Compounds

A computational study of the structural and thermochemical properties of N-phenyl (open) and N-alkyl (cyclic) ureas, through the use of M05-2X and B3LYP density functional theory calculations has been carried out. The consistency of the literature experimental results has been confirmed, and using mainly isodesmic reactions, the unknown Delta(f)H(0)(g) of the other urea derivatives were estimated. The experimental results together with the theoretical information have permitted the study of the effect of phenyl, p- and m-chlorophenyl, alkyl, and carbonyl substitutions on the thermodynamical stability of urea and its cyclic derivatives. The peculiar behavior of the N-tert-butyl substituent in cyclic ureas has been related to geometric deformations.

Impact of glutathione-enriched inactive dry yeast preparations on the stability of terpenes during model wine aging.

The impact of the addition of glutathione-enriched Inactive dry yeast preparations (g-IDYs) on the stability of some typical wine terpenes (linalool, α-terpineol, β-citronellol, and nerol) stored under accelerated oxidative conditions was evaluated in model wines. Additionally, the effects of a second type of IDY preparation with a different claim (fermentative nutrient) and the sole addition of commercial glutathione into the model wines were also assessed. Model wines were spiked with the low molecular weight fraction (<3 kDa permeate) isolated from the IDYs, avoiding the interaction of aroma compounds with other yeast components. An exhaustive chemical characterization of both IDY permeates was carried out by using targeted and nontargeted metabolomics approaches using CE-MS and FT-ICR-MS analytical platforms. The findings suggest that the addition of <3 kDa permeate isolated from any of the IDYs employed decreases the loss of typical wine terpenes in model wines submitted to accelerated aging conditions. The g-IDY preparation did indeed release reduced GSH into the model wines, although this compound did not seem exclusively related to the protective effect on some aroma compounds determined in both model wines. The presence of other sulfur-containing compounds from yeast origin in g-IDY, and also the presence of small yeast peptides, such as methionine/tryptophan/tyrosine-containing tripeptide in both types of IDYs, seemed to be related to the antioxidant activity determined in the two permeates and to the minor loss of some terpenes in the model wines spiked with them.

Energetics and Structural Properties, in the Gas Phase, of trans-Hydroxycinnamic Acids

We have studied the energetics and structural properties of trans-cinnamic acid (CA), o-, m-, and p-coumaric acids (2-, 3-, and 4-hydroxycinnamic acids), caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), iso-ferulic acid (3-hydroxy-4-methoxycinnamic acid), and sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid). The experimental values of Δ(f)H(m)°(g), determined (in kJ·mol(-1)) for CA (-229.8 ± 1.9), p-coumaric acid (-408.0 ± 4.4), caffeic acid (-580.0 ± 5.9), and ferulic acid (-566.4 ± 5.7), allowed us to derive Δ(f)H(m)°(g) of o-coumaric acid (-405.6 ± 4.4), m-coumaric acid (-406.4 ± 4.4), iso-ferulic acid (-565.2 ± 5.7), and sinapic acid (-698.8 ± 4.1). From these values and by use of isodesmic/homodesmotic reactions, we studied the energetic effects of π-donor substituents (-OH and -OCH(3)) in cinnamic acid derivatives and in the respective benzene analogues. Our results indicate that the interaction between -OCH(3) and/or -OH groups in hydroxycinnamic acids takes place without significant influence of the propenoic fragment.