A high temperature and high sensitivity micro-thermobalance

A thermobalance which ensures a sensivity of 1 × 10^?6 g and an excellent stability up to 1500 C has been developed. A sample, which is suspended from one end of the beam of the balance, is heated in a compact furnace with a small heat capacity. Temperature is measured by a Pt-PtRh (10%) thermocouple placed close to the sample. Use of an alumina mantle ensures easy control of atmosphere: at room temperature, the evacuation can be done to 1 × 10^?4 Torr, and stable operation can be done up to 1500 C in air inert gas at a flow-rate smaller than 50 ml min^?1. It is also possible to use a corrosive gas as atmosphere. In a blank test with platinum cell support (6.5 mm diam. and 0.1 mm thick) suspended in an air stream of 50 ml min^?1 and heated up to 1500 C at 10 C min^?1, the drift was smaller than 20 × 10^?6 g and the reproducibility was better than 10×10^?6 g. This paper refers to the construction of the thermobalance, and its performances. And some examples of high temperature thermogravimetry through the results of analyses of CaCO₃, quick lime and byproduct lime are also reported.     

A new synthesis of symmetrical 2,5-diaryl-1,3,4-thiadiazoles

Treatment of aromatic aldehydes with sulfur and hydrazine hydrate in the ratio 1:2:3, respectively, under the Willgerodt conditions affords the title compounds in excellent yields and in a good state of purity. Under the same conditions 2-chloro and 2,6-dichlorobenzaldehyde yield 3H-1,2-benzodithiole-3-thione and bis-(2,6-dichlorobenzyl)tetrasulfide, respectively.     

A new synthesis of symmetrical 2,5-disubstituted 1,3,4-oxadiazoles

Several new 2,5-disubstituted 1,3,4-oxadiazoles have been synthesized in good yields by reaction of aromatic acids with hydrazine dihydrochloride in a mixture of orthophosphoric acid, phosphorus pentoxide and, in general, with addition of phosphorus oxychloride to the reaction mixture. The structures of new oxadiazoles derivatives were confirmed by analytical and spectral data.     

A new protocol for the one-pot synthesis of symmetrical biaryls

Biaryls play an important role in modern organic chemistry. Although a large number of protocols for the synthesis of symmetrical and unsymmetrical biaryls already exist, most of them are not generally applicable. In our studies toward the total synthesis of the secalonic acids, we were interested in bis(pinacolato)diboron as a reagent for transforming haloarenes into arylboronic esters. By optimizing the reaction conditions, we were able to obtain biaryls containing various functional groups in good to excellent yields.     

A new catalytic and enantioselective desymmetrization of symmetrical methylidene cycloalkene oxides

Chiral copper complexes of C2-symmetrical phosphoroamidites were found to be highly effective catalysts for both kinetic resolution and novel desymmetrization reactions of new methylidene epoxycycloalkanes.     

A new feature selection method based on symmetrical uncertainty and interaction gain

Defining important information from complex biological data is of great significance in biological study. It is known that the physiological and pathological changes in an organism are usually influenced by molecule interactions. Analyzing biological data by fusing the evaluation of the individual molecules and molecule interactions could induce a more accurate and comprehensive understanding of the organism. This study proposes an Interaction Gain - Recursive Feature Elimination (IG-RFE) method which evaluates the feature importance by combining the relevance between feature and class label and the interaction among features. Symmetrical uncertainty is adopted to measure the relevance between feature and the class label. The average normalized interaction gain of feature f, every other features and the class label is calculated to reflect the interaction of feature f with other features in the feature set F. Based on the combination of symmetrical uncertainty and normalized interaction gain, less important features are removed iteratively. To show the performance of IG-RFE, it was compared with seven efficient feature selection methods, MIFS, mRMR, CMIM, ReliefF, FCBF, PGVNS and SVM-RFE, on eleven public datasets. The experiment results showed the superiority of IG-RFE in accuracy, sensitivity, specificity and stability. Hence, integrating feature individual discriminative ability and the interaction among features could better evaluate feature importance in biological data analysis.     

Introduction of a new simultanous symmetrical and digital TG-DTA thermoanalyzer

A completely new simultaneous digital and symmetrical TG-DTA thermoanalyzer, called TAG 24, has been designed.The instrument is built around a very sensitive microbalance and one or two high-temperature furnaces (maximum limit: 2400 °C). When the TAG 24 is used in the symmetrical version (two furnaces), the buoyancy effect is eliminated and more sensitive thermogravimetric measurements can be achieved.The controller controls the furnace temperature, the positions of 8 electrovalves for vacuum and gas sweeping, and the taring of the balance, calculates the DTG value, and also amplifies and processes the analog signals (temperature, TG and DTA). Still higher performance is produced by coupling the controller with a scientific computer through a serial interface.

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Zusammenfassung Ein völlig neues, digitalisiertes und symmetrisches Gerät TAG 24 wurde für simultane TG-DTA entwickelt. Es enthält eine sehr empfindliche Mikrowaage und einen oder zwei Öfen (Temperaturgrenze 2400 °C). Wenn es in der symmetrischen Version (mit 2 Öfen) benutzt wird, wird der Auftriebseffekt unwirksam, so dass empfindlichere TG-Messungen möglich sind. Der Regler steuert die Ofentemperatur, die Stellung von 8 elektrischen Ventilen für Vakuum und Gasspülung und die Waagentarierung, er berechnet das DTG-Signal und verstärkt und verarbeitet die analogen Signale von Temperatur, TG und DTA. Über ein serielles Interface kann ein wissenschaftlicher Rechner zur Erhöhung der Leistungsfähigkeit angeschlossen werden.

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Synthesis of new siloxane or sulfur containing symmetrical monomers based on carvone

Abstract

We demonstrated, that based on carvone, new symmetrical AA-type monomers with double bonds can be easily prepared by thiol-ene or Michael addition of dithiols. Moreover, hydrosilylation reaction with difunctional telehelic siloxane, containing Si-H groups was also studied. Obtained monomers are suitable for further polymerization by thiol-ene or hydrosilylation polyaddition.     

A facile synthesis of symmetrical 1,1-disubstituted ethylenes

The reaction of ethyl trimethylsilylacetate with two equivalents of a Grignard reagent in ether followed by treatment with acid gives 1,1-disubstituted ethylenes in excellent yield.     

由酮合成对称二烃基二硒醚的新方法

在正丁胺的催化下, 酮与硒氢化钠, 二硒化钠乙醇溶液通过"一锅"法反应得到了中等产率的二硒醚.     

Synthesis with silicon derivatives: non symmetrical derivatization of symmetrical diamines

The conversion of symmetrical diamines to monoamides via the use of cyclic silicon-nitrogen compounds as intermediates is described.     

A new concise strategy for synthesis of dibenzo[b,f]thiepins and related fused symmetrical thiepin derivatives

A new strategy for preparation of dibenzo[b,f]thiepins and related fused systems in good overall yields is described, featuring ortho-metalation of aromatic or heterocyclic aldehyde acetals followed by treatment with bis(phenylsulfonyl) sulfide for construction of the required bis(aryl)- or bis(heteroaryl) sulfide precursors, which were thereafter subjected to deacetalization, and finally McMurry coupling as the ring-forming step.     

A very simple method for the preparation of symmetrical disulfides

A serendipitiously discovered, extremely simple, fast and previously unreported method for the preparation of symmetrical aliphatic, aromatic and heteroaromatic disulfides is reported. Addition of sulfuryl chloride to an alkyl- or arylthiol in a 1:2 ratio under solvent free conditions or in dichloromethane solution produces the corresponding disulfides in nearly quantitative yields with the concomitant elimination of gaseous SO₂ and 2 equiv of HCl. Thus, optimally the reaction needs no work-up at all leaving the disulfide as the sole product in excellent yield. In dichloromethane solution, the reaction is conveniently carried out in a rotary evaporator by mixing the solvent, thiol and SO₂Cl₂ in a round-bottomed flask followed by evaporation of the volatiles.     

A one-step procedure for the monoacylation of symmetrical 1,2-diols

A series of lanthanide (III) salts have been shown to catalyze the monoacylation of symmetrical 1,2-diols by carboxylic acid anhydrides with surprisingly high selectivity.     

Molecular symmetry and biological activities of new symmetrical tris(2-aminoethyl)amine derivatives

In terms of molecular symmetry and bioactivity, new C3- and CS-symmetrical derivatives based on the tris(2-aminoethyl)amine scaffold were designed and synthesized. The synthesized compounds were evaluated for antiviral activity with herpes simplex virus type 1 (HSV-1) by a plaque reduction assay and for cytotoxic activity with Vero cells. Most of the compounds showed no significant anti-HSV-1 activity, but some of the symmetrical derivatives showed high levels of cytotoxic activitiy.     

A simple preparation of symmetrical and unsymmetrical diarylsulfides from arenediazonium tetrafluoroborates

The reaction between arenediazonium tetrafluoroborates and arenethiolates in Me₂SO represents a mild, efficient, and safe alternative to the Ziegler synthesis of diaryl sulfides.