Comparison of merging zones,injection of reagent and single-line manifolds for enthalpimetric flow injection analysis

A flow enthalpimeter suitable for all flow injection manifolds is described. The apparatus includes the injection valve immersed in an equilibration water bath which improves sensitivity and sampling rate. Detection limits for quantitation of hydrochloric acid range from 0.4 to 0.07 mM at 80–90 samples per hour.     

Effets de cryptands et activation de bases—II: Genese d'enolates et essais d'activation de LiH,NaH et KH dans l'ether,le THF et le benzene

The generation of the lithium, sodium and potassium enolates of cyclohexanone using LiH, NaH and KH has been investigated. The utilization of macrocyclic ligands (which selectively complex the metal cation) activated the alkaline hydride reagent. However, the most dramatic effect was the activation of the enolate, enabling proton abstraction from the solvent.     

A novel ditopic zinc-salophen macrocycle: a potential two-stationed wheel for [2]-pseudorotaxanes

Crown ether macrocycle 1 including a zinc-salophen unit is obtained via a de novo synthetic design to give a potential pH-driven two-stationed wheel component of [2]-pseudorotaxane systems.     

A new approach to flow-batch titration. A monosegmented flow titrator with coulometric reagent generation and potentiometric or biamperometric detection

Monosegmented flow analysis (MSFA) has been used as a flow-batch system to produce a simple, robust, and mechanized titrator that enables true titrations to be performed without the use of standards. This paper also introduces the use of coulometry with monosegmented titration by proposing a versatile flow cell. Coulometric generation of the titrand is attractive for titrations performed in monosegmented systems, because the reagent can be added without increasing the volume of sample injected. Also, biamperomeric and potentiometric detection of titration end-points can increase the versatility of the monosegmented titrator. The cell integrates coulometric generation of the titrand with detection of end-point by potentiometry or biamperometry. The resulting titrator is a flow-batch system in which the liquid monosegment, constrained by the interfaces of the gaseous carrier stream, plays the role of a sample of known volume to be titrated. The system has been used for determination of ascorbic acid, by coulometric generation of I₂ with biamperometric detection, and for determination of Fe(II), by coulometric generation of Ce(IV) with potentiometric detection of the end-point, both in feed supplements.     

Near infrared emission spectroscopy induced by ultrasonic irradiation

Near infrared emission caused by ultrasonic excitation is demonstrated for the first time in this work. The instrument is constituted of an acousto-optical tunable filter-based spectrometer, an ultrasonic processor connected to a titanium alloy ultrasonic probe and a cylindrical borosilicate flask containing the sample to be excited. The radiation emitted by the sample is collected by a concave mirror and sent to the spectrometer. The effects of the position of the probe extremity in relation to a lateral entrance of the borosilicate flask and of the ultrasonic power on the emission signal were studied. The best results were obtained by positioning the probe extremity up to 2mm from the reflexive body (lateral entrance) using 30% of the full ultrasonic incident power and acquiring spectra after 5 min of sonication. The NIR emission spectra resulting from the ultrasonic excitation were in agreement with that obtained by thermal excitation. The proposed technique was utilized to study different poly(dimethylsiloxane) samples having different viscosities.     

Evaluation of the Mooney Viscosity of Natural Rubber by Near‐Infrared Spectroscopy

Abstract

The direct near‐infrared spectroscopic reflectance measurements of prevulcanized natural rubber (brown crepe) was employed for determination of its Mooney viscosity. NIR reflectance spectra were obtained for a total of 100 samples whose Mooney viscosity (VM in the range 68–95 units) have been determined by the standard reference procedure using a commercial computerized Mooney viscometer. These samples were employed as the raw material or were treated to achieve better homogenization. A Fourier transform near infrared (FT‐NIR) spectrophotometer was employed, and the reflectance spectra were obtained with resolution of 4 cm^?1 in the range 4000–10,000 cm^?1 as an average of 75 scans. The samples were split in a calibration set containing 70 samples and in an external validation set consisting of the remaining 30 samples. The calibration and validation spectra sets were treated to correct for baseline shift, further transformed by first derivative and finally modeled by partial least squares (PLS) employing four latent variables. The model was evaluated with the external sample test set, and a RMSEP of 3.6 and 3.9 units of Mooney viscosity were obtained for homogenized and nonhomogenized samples, respectively. The NIR method is capable of determining the Mooney viscosity in few minutes in the non‐pretreated sample with an error that is satisfactory for quality control of natural rubber destined for automobile tire manufacturing.     

γ-Valerolactone (GVL) as a green and efficient dipolar aprotic reaction medium

The great challenge for modern research is to define the most efficient tools to make more sustainable the industrial production and manufacturing. Among the different aspects that require attention the replacement of toxic and/or non-renewable solvents it is certainly playing a crucial role. Dealing with widely used dipolar aprotic solvents, among the different alternatives proposed in the literature γ-valerolactone (GVL) plays a pivotal role covering different application area. In this contribution, the benefits derived from the use of GVL as a circular, safe, biomass-derived reaction medium are highlighted covering most recent publications (2021). The presentation has been divided into three major sections: (i) biomass valorization, (ii) materials synthesis, manufacturing and recycle and (iii) new synthetic methodologies.     

A quantum mechanical strategy to investigate the structure of liquids: the cases of acetonitrile, formamide, and their mixture

A computational strategy based on quantum mechanical (QM) calculations and continuum solvation models is used to investigate the structure of liquids (either neat liquids or mixtures). The strategy is based on the comparison of calculated and experimental spectroscopic properties (IR-Raman vibrational frequencies and Raman intensities). In particular, neat formamide, neat acetonitrile, and their equimolar mixture are studied comparing isolated and solvated clusters of different nature and size. In all cases, the study seems to indicate that liquids, even when strongly associated, can be effectively modeled in terms of a shell-like system in which clusters of strongly interacting molecules (the microenvironments) are solvated by a polarizable macroenvironment represented by the rest of the molecules. Only taking into proper account both these effects can a correct picture of the liquid structure be achieved.