Asymmetric Synthesis of Alkyl and Aryl Sulfinates of DAG: An Improved and General Route to Both Enantiomerically Pure Sulfoxides

Abstract

A short, efficient and general route for the preparation of o.p. alkyl and aryl sulfinates is described. Both epimers at sulfur can be obtained using DAG as unique inductor of chirality and, only by choosing the adequate base (Py or i-Pr₂NEt), the configuration at sulfur can be predicted. The efficiency of this methodology has been demonstrated by the synthesis of o.a. alkyl aryl and dialkyl sulfoxides with high e.e. (up to 100%).     

Electrogenerated Base-Promoted Synthesis of Dithiocarbamate Acid Esters and 3-(N-Substituted-amino)-2-cyanodithiocrotonates from Primary or Secondary Amines and Carbon Disulfide

Electrogenerated cyanomethyl anion promotes the reaction between primary or secondary amines, carbon disulfide, and alkyl or benzyl halide. Secondary amines are converted to alkyl or benzyl dithiocarbamates, whereas primary amines give N-substituted alkyl or benzyl 3-amino-2-cyanodithiocrotonates. The mechanisms are discussed.     

Experimental study of a smart foam sound absorber

This article presents the experimental implementation and results of a hybrid passive/active absorber (smart foam) made up from the combination of a passive absorbent (foam) and a curved polyvinylidene fluoride (PVDF) film actuator bonded to the rear surface of the foam. Various smart foam prototypes were built and tested in active absorption experiments conducted in an impedance tube under plane wave propagation condition at frequencies between 100 and 1500 Hz. Three control cases were tested. The first case used a fixed controller derived in the frequency domain from estimations of the primary disturbance at a directive microphone position in the tube and the transfer function between the control PVDF and the directive microphone. The two other cases used an adaptive time-domain feedforward controller to absorb either a single-frequency incident wave or a broadband incident wave. The non-linearity of the smart foams and the causality constraint were identified to be important factors influencing active control performance. The effectiveness of the various smart foam prototypes is discussed in terms of the active and passive absorption coefficients as well as the control voltage of the PVDF actuator normalized by the incident sound pressure.     

Photoluminescence quenching of porous silicon in organic solvents: evidence for dielectric effects

Photoluminescence (PL) intensity of porous silicon has been recorded in a selected set of organic solvents. PL stability has been systematically examined on the time scale of the measurements in order to carefully exclude any interfering chemical effects. A three-order-of-magnitude drop is found by increasing the value of the dielectric constant of the solvent from 2 to 20. This spectacular result can be quantitatively accounted for in terms of a geminate recombination mechanism and of the variation of the Onsager length with the dielectric constant of the embedding medium. For values of the dielectric constant larger than 20, the Onsager length becomes of the order of the nanostructure size, and no further quenching is observed. These results show that materials of low-dielectric constant should be chosen for encapsulating porous silicon without affecting its PL.     

Speech enhancement in dual-microphone mobile phones using Kalman filter

In this paper, a dual-microphone speech enhancement algorithm for the mobile phones is proposed. The adopted method exploits the coherence function algorithm and the Kalman filter. This algorithm has a simple implementation that does not need a prediction of interfering signals statistics. In addition, this algorithm can be used in small devices with so closely distance between the two microphones. Moreover, the use of such algorithm allows reducing multiple noise sources at many azimuths positions. Finally, the new algorithm proves its performances referring to the perceptual evaluation of speech quality and the time domain waveforms.     

C2-symmetric bissulfoxides as organocatalysts in the allylation of benzoyl hydrazones: spacer and concentration effects

A comparative study on the allylation of a benzoyl hydrazone with allyl trichlorosilane using monosulfoxides, methylene-bridged C2-symmetric bissulfoxides, and ethylene-bridged C2-symmetric bissulfoxides shows that the enantioselectivity of the process is highly dependent on the spacer between the two sulfinyl sulfurs and the concentration of the reaction.     

One-pot green synthesis,study of fluorescence properties,and biological activity of pyrano[3,2-c]chromenes derivatives via mesoporous materials MgO/SBA-15

This current work describes the preparation of MgO-SBA-15 catalysts by ultrasonic method, and it is characterized by the different analysis techniques of XRD, BET, SEM, and IRTF. In order to find out an application for this mesoporous material, MgO/SBA-15 was used as a heterogeneous catalyst in the one-pot synthesis of pyrano[3,2-c]chromenes derivatives isolated at room temperature reaction according to green chemistry criteria. To enhance these derivatives, a spectroscopic study of molecular fluorescence properties was carried out as well as an identification analysis by nuclear magnetic resonance and FTIR was used. Furthermore, biological activity experiment is also carried out, from where the obtained test results were satisfactory for AC09 , AC05 , and AC10 compounds and they are checked after computation by molecular modeling.     

Influence of specimen-reconstituting method on the undrained response of loose granular soil under static loading

This paper describes the results of an experimental study on the undrained shear behaviour of loose sand collected from the location close to the epicenter of the recent Chlef (Algeria) Earthquake (October 10,1980).The study focuses on the effects of the mode of the soil deposition on the liquefaction resistance of the Chlef sand.For this purpose,the results of undrained monotonic triaxial compression tests performed on samples with initial density of 0.29 under initial confining pressures ranged from 50 kPa to 200 kPa are presented.The specimens were prepared by two depositional methods namely dry funnel pluviation and wet deposition.It was found that there was a marked difference in the undrained behaviour of sand in terms of maximal deviatoric stress,peak strength,residual strength and excess pore water pressure,even though the density and stress conditions were identical.The conclusion was that the soil fabric was responsible for this result.The results indicated also that at low confining pressures,the specimens reconstituted by the wet deposition method exhibited complete static liquefaction (zero effective confining pressure and zero stress difference).     

Theoretical study of hydrogen and deuterium bond in glutaric acid crystal dimer

In the spirit of the work of Blaise et al. [J Chem Phys, 2005, 122, 64306], we have extended their quantum theoretical approach by accounting for the intrinsic anharmonicity of the slow frequency mode, which is described by a Morse potential to reproduce the polarized infrared line shapes of glutaric acid dimer and its deuterium derivative at different temperatures. In this approach, the adiabatic approximation is performed for each separate H‐bond bridge of the dimer, and a strong nonadiabatic correction is introduced into the model via the resonant exchange between the fast mode excited states of the two moieties. Working within the strong anharmonic coupling theory, according to which the high‐frequency mode is anharmonically coupled to the H‐bond bridge, this approach incorporated the Davydov coupling between the excited states of the two moieties, the quantum direct and indirect dampings and the intrinsic anharmonicity of the H‐bond bridge. The spectral density was obtained within the linear response theory by Fourier transform of the damped autocorrelation functions. The numerical results show that the theoretical line shapes of the glutaric acid dimer are in fairly good agreement with the experimental ones. Using a minimum number of independent parameters, this theoretical approach fits correctly the experimental line shapes of the glutaric acid dimer. The effects of deuteration and temperature have been successfully reproduced by our calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012