Speciation of 30 % tri-n-butyl phosphate solvent during extraction of nitric acid

Several solutions of 30 % TBP/n-dodecane were equilibrated with different concentrations of aqueous nitric acid solutions at 298.15 K at a phase ratio of unity. The resultant equilibrated aqueous and organic solutions were analyzed for acidity. A three-solvate model with molecular HNO₃ based mechanism was assumed for nitric acid extraction by TBP. With nonlinear chemometric methods, the coefficients were evaluated. With the set of optimized coefficients, derived on the basis of experiments reported in this work, the estimated solvate species and free-TBP species in the TBP containing organic phase were found to be in good agreement with the reported concentrations in the literature.     

Thermal studies of hypervalent iodine reagents

The use of unconventional synthesis methods in the formation of CaO·2Al₂O₃ (CA₂) is justified because it reduces the formation temperature of the compound. CA₂ is formed by classical method at temperatures above 1,400 °C. The polymeric precursor method allows a significant temperature decrease in CA₂ synthesis reaching temperatures of 1,000 °C. This paper deals with CA₂ synthesis by “citrate” method which is often presented as Pechini method, starting from a mixture of citric acid, ethylene glycol and calcium, and aluminum nitrates. A method based on the formation of a polymeric precursor was also used, starting from a mixture of acrylic acid and nitrates of calcium and aluminum. The results showed a net difference in favor of samples obtained from acrylic acid, which by annealing at 800 °C for 1 h, contain pure CA₂. The samples obtained from citric acid, after annealing at 800 °C are amorphous. After annealing at 900 °C in all samples CA₂ is single phase.     

Functionalized Organotellurium Halides: Synthesis,Characterization, and Observation of Intra- and Intermolecular Secondary Bonding

Abstract

Activated tellurium, but not selenium, reacts with para-substituted benzoylmethyl bromides as well as with iodoacetamide at their melting points in absence of a solvent to give bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC₆H₄COCH₂)₂TeBr₂, (Y = H, Me, and MeO) and bis(acetamido)tellurium diiodide, (H₂NCOCH₂)₂TeI₂, respectively. Quick reduction of (p-YC₆H₄COCH₂)₂TeBr₂, with sodium metabisulphite in a two-phase system yields crystalline (p-YC₆H₄COCH₂)₂Te. These tellurides undergo smooth oxidative addition of halogens, interhalogen ICl or a pseudohalogen (SCN)₂. Intramolecular coordination of the carbonyl group in these functionalized diorganotellurium dihalides is evident from IR spectra and shorter Te···O (carbonyl) distances in comparison to the sum of van der Waals radii and completes six coordination around Te atom. Not unexpectedly, therefore, intermolecular secondary bonding effects of the type Te…O, Te···X and X···X are missing in (PhCOCH₂)₂TeBr₂, (p-MeOC₆H₄COCH₂)TeBr₂ and (PhCOCH₂)₂TeI₂. Instead, these compounds provide rare examples, among organotellurium compounds, of supramolecular architecture, where C–H···Br and C–H···O hydrogen bonds and π-π (phenyl ring) interactions appear to be the noncovalent intermolecular associative forces that dominate the crystal packing.     

Handling uncertainties in toxicity modelling using a fuzzy filter

A fundamental concern in the Quantitative Structure-Activity Relationship approach to toxicity evaluation is the generalization of the model over a wide range of compounds. The data driven modelling of toxicity, due to the complex and ill-defined nature of eco-toxicological systems, is an uncertain process. The development of a toxicity predicting model without considering uncertainties may produce a model with a low generalization performance. This study presents a novel approach to toxicity modelling that handles the involved uncertainties using a fuzzy filter, and thus improves the generalization capability of the model. The method is illustrated by considering a data set dealing with the fathead minnow (Pimephales promelas) toxicity of 568 organic compounds.     

Lanthanum Trifluoromethane-sulfonate‐Catalyzed Facile Synthesis of Per‐O‐acetylated Sugars and Their One‐Pot Conversion to S‐Aryl and O‐Alkyl/Aryl Glycosides†

Lanthanum trifluoromethanesulfonate‐catalyzed solvent‐free per‐O‐acetylation with stoichiometric acetic anhydride proceeds in high yield (95%–99%) to afford exclusively pyranose products as anomeric mixtures. Subsequent anomeric substitution employing borontrifluoride etherate and thiols or alcohols furnished the corresponding 1,2‐trans‐linked thioglycosides and O‐glycosides, respectively, in good to excellent overall yield (75%–85%). Alternatively, reaction of free sugars in neat alcohol employing the same catalyst at elevated temperature gives the corresponding 1,2‐cis‐linked O‐glycosides (along with 1,2‐trans‐linked glycosides as minor product) in good yield (73%–80%). Anomeric mixtures of compounds thus produced were characterized as their per‐O‐acetylated derivatives.      

Liquid-phase dehydration of sorbitol under microwave irradiation in the presence of acidic resin catalysts

Liquid-phase dehydration of sorbitol has been investigated in wide reaction conditions especially under microwave irradiation in the presence of acidic resin catalysts. From the selectivity for sorbitan and isosorbide, it can be understood that the dehydration is a consecutive reaction (sorbitol to sorbitan, and finally to isosorbide) and that the sorbitan is an intermediate of the dehydration. By using microwave irradiation, the dehydration can be accelerated by around 20?C34 times compared with the rate by conventional electric heating at the same temperature, or the reaction temperature can be decreased by around 40 °C for the comparable conversion in a similar reaction time. However, the microwaves do not have noticeable effects on the selectivity for isosorbide or sorbitan. The accelerated dehydration under microwaves is mainly due to decreased activation energy.     

Synthesis and α‐glucosidase inhibitory,DPPH scavenging activity of substituted 2‐oxo‐2H‐chromen‐7‐yl‐dihydrogen phosphate derivatives

Series of phosphorylated coumarin derivatives ( 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j ) were synthesized by Pechmann condensation, phosphorylation, and debenzylation reactions in very good yields. Thus, synthesized compounds ( 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j ) were evaluated for their α‐glucosidase and 1,1‐diphenyl‐2‐picrylhydrazyl scavenging activities; few compounds showed moderate to good activity. J. Heterocyclic Chem., 00 , 00 (2011).     

Kinetic studies on saponification of ethyl acetate using an innovative conductivity‐monitoring instrument with a pulsating sensor

An innovative conductometric measurement technique using a nonconventional but high‐performance (high‐precision, high‐resolution, rapid response features for online graphic display) in house–built pulsating conductivity monitoring instrument has been deployed to study the kinetic behavior during the reaction of ethyl acetate and NaOH. A laboratory‐made constant temperature reaction bath with the facility of continuous stirring of solution for homogeneous mixing was used to carry out experiments at desired solution temperatures. Rate constants of the saponification reaction in the temperature range at various temperatures (30–55°C) were determined, and the results were compared with the reported values. Although the reported data exhibit wide scatter, our data are in agreement with some of the literature data. From these data, thermodynamic parameters such as activation energy, activation enthalpy, activation entropy, and activation free energy have been evaluated. With the introduction of this novel conductometric measurement technique, the determination of rate constants at various solution temperatures becomes much simpler and faster. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 648–656, 2011     

Competition between hydrogen bonding and dispersion interactions in the indole···pyridine dimer and (indole)2···pyridine trimer studied in a supersonic jet

Structures of the indole···pyridine dimer and (indole)2···pyridine trimer have been investigated in a supersonic jet using resonant two-photon ionization (R2PI) and IR-UV double resonance spectroscopic techniques combined with quantum chemistry calculations. R2PI spectra of the dimer and the trimer recorded by electronic excitation of the indole moiety show that the red-shift in the band origin of the dimer with respect to the 0(0)(0) band of the monomer is larger compared to that of the trimer. The presence of only one conformer in the case of both the dimer and the trimer has been confirmed from IR-UV hole-burning spectroscopy. The structures of the dimer and the trimer have been determined from resonant ion dip infrared (RIDIR) spectra combined with ab initio as well as DFT/M05-2X and DFT/M06-2X calculations. It has been found that the dimer, observed in the experiment, has a V-shaped geometry stabilized by N–H···N and C–H···N hydrogen bonding interactions, as well as C–H···π and π···π dispersion interactions. The geometry of the trimer has been found to be a cyclic one stabilized by N–H···N, N–H···π, C–H···π, and C–H···N interactions. The most important finding of this current study is the observation of the mixed dimer and trimer, which are stabilized by hydrogen bonding as well as dispersion interactions.