Atmospheric chemistry of isopropyl formate and tert‐butyl formate

Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH₃)₂, and tert‐butyl formate, HC(O)OC(CH₃)₃. Product distributions are reported from both Cl‐ and OH‐initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the α‐ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15–20%). The OH radical initiated oxidation of tert‐butyl formate gives acetone, formaldehyde, and CO₂ as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10^?12, and with Cl (1.75 ± 0.35) × 10^?11, and for tert‐butyl formate with Cl (1.45 ± 0.30) × 10^?11 cm³ molecule^?1 s^?1. Simple group additivity rules fail to explain the observed distribution of sites of H‐atom abstraction for simple formates. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 479–498, 2010     

Sorption kinetics for the removal of aldehydes from aqueous streams with extractant impregnated resins

The sorption kinetics for the removal aldehydes from aqueous solutions with Amberlite XAD-16 and MPP particles impregnated with Primene JM-T was investigated. A model, accounting for the simultaneous mass transfer and chemical reaction, is developed to describe the process. It is based on the analogy to the diffusion and reaction in a stagnant liquid sphere, but corrected for the porosity and particle properties influencing the diffusion. The developed model describes the kinetic behavior of the process in the low concentration region rather well. However, in the high concentration region, larger discrepancies are observed. Initially, the influence of the flow rate was investigated to eliminate the effect of the external mass transfer. The influence of the particle morphology was investigated for both physical and reactive sorption. Physical sorption experiments were used to determine the factor τ that takes the particle properties influencing the diffusion into account. It was shown that the diffusion is faster in XAD-16 than in MPP impregnated systems. Reaction rate constant k _x was determined by fitting the model to the experimental data. Sorption of benzaldehyde appears to be significantly slower (k _x ∼10⁻⁴ l/mol s) than the sorption of pentanal (k _x ∼10⁻³ l/mol s) due to the slower chemical reaction. The influence of the particle size was investigated for the sorption of pentanal with XAD-16. It was observed that the particle size does influence the diffusion term, but does not have an effect on the reaction rate. On the other hand, the extractant loading influences the reaction rate slightly in the low concentration region, whereas the initial concentration of the solute has more pronounced effect.     

Industrial photochemistry XIV: Light distribution around an external source made of a fluorescent relay

The principle of the use of a fluorescent relay is described. Its aims is to transform undesirable wavelengths into active photons for a specific photoreaction and to improve the use of commercial mercury vapour lamps in photochemistry. The light profile in the photoreactor in the presence of a fluorescent relay has been established, using a sensor made of an optical fibre with a small integrating sphere; the experimental values are compared with the model (the lamp is assumed to be a quasi-linear source). The determination of a semi-empirical model for the light distribution, which considers the partial transmission of fluorescent light through the lamp (shadow effect), leads to the calculation of the extinction coefficient μ_O of the fluorescent solution corresponding to the best efficiency of the fluorescent relay.     

ChemInform Abstract: Crystal Structures and Hydrogenation Properties of Palladium‐Rich Compounds with Elements from Groups 12—16.

Crystal structures based on powder XRD and hydrogenation properties of 24 Pd‐rich intermetallics are presented.     

Liquid densities of THF and excess volumes for the mixture with water in a wide temperature and pressure range

In this paper densities for THF (tetrahydrofuran) and THF + water mixtures measured with the help of the Anton Paar DMA HPM vibrating tube densimeter are reported. The pure component densities of tetrahydrofuran measured in the temperature range from 278 to 437 K and pressures up to 130 MPa were correlated with the TRIDEN-System. Additionally densities of the binary mixture tetrahydrofuran + water were measured for 6 different concentrations in a temperature range from 288 to 338 K and up to 130 MPa. Excess volumes (vE)$(v^E)$ of the mixture were determined using the own correlation of the tetrahydrofuran densities and the equation of state (EoS) for water by Wagner and Pruß. Redlich–Kister polynomials were used to fit the vE-data$v^E\text{-data}$. Additionally in this work it was checked if the vibrating tube densimeter allows the determination of the miscibility gap for the system THF–water as a function of temperature and pressure.     

Transition from the ballistic to the diffusive regime in a turbid medium

By varying the absorption coefficient and width of an intralipid-India ink solution in a quasi-one-dimensional experiment, we investigate the transition between the ballistic and the diffusive regimes. The medium's attenuation coefficient changes abruptly between two different values within a single mean free path. This problem is analyzed both experimentally and theoretically, and it is demonstrated that the transition location depends on the scattering coefficient as well as on the measuring solid angle.     

An entropy-based approach to automatic image segmentation of satellite images

An entropy-based image segmentation approach is introduced and applied to color images obtained from Google Earth. Segmentation refers to the process of partitioning a digital image in order to locate different objects and regions of interest. The application to satellite images paves the way to automated monitoring of ecological catastrophes, urban growth, agricultural activity, maritime pollution, climate changing and general surveillance. Regions representing aquatic, rural and urban areas are identified and the accuracy of the proposed segmentation methodology is evaluated. The comparison with gray level images revealed that the color information is fundamental to obtain an accurate segmentation.