Excess enthalpies,heat capacities,and excess heat capacities as a function of temperature in liquid mixtures of ethanol + toluene,ethanol + hexamethyldisiloxane,and hexamethyldisiloxane + toluene

The heat capacities of liquid ethanol, toluene, and hexamethyldisiloxane, and of 14 binary mixtures of these were measured at atmospheric pressure at a series of temperatures between 298 and 348 K. In addition, the excess enthalpy was measured for each of the 14 mixtures at room temperature and corrected with the aid of the heat capacities to 298.15 K. The results were represented by empirical equations of a polynomial form. From these equations, the excess heat capacity was derived and the excess enthalpy was calculated, and fitted to equations, as a function of composition at temperatures between 298 and 348 K. All the mixtures are non-ideal as evidenced by the substantial excess enthalpy. The excess enthalpy for the mixtures containing ethanol showed a strong positive temperature dependence, while the variation of temperature between 298 and 348 K had little effect on the excess enthalpy of toluene + hexamethyldisiloxane.     

Long-term deactivation of Pt/alumina catalyst by organosilicons in the total oxidation of hydrocarbons

The deactivation of a supported platinum catalyst by long-term exposure to hexamethyldisiloxane was investigated. Ethyl acetate containing several tenfold excess of organosilicon relative to the real application was fed to the reactor. Three sets of catalyst and the blank support were aged for 350, 650, and 1000 h. The ex situ activity measurements on the aged pellets showed that all samples were deactivated as they were exposed to hexamethyldisiloxane. Silicon species were found at the surfaces of both the catalyst and the blank support. The quantitative analysis of silicon loading showed a linear profile versus poison exposure time and axial position in the bed. The radial silicon distribution in an individual pellet revealed an eggshell distribution of silicon residues, which is an indication of a diffusion-limited mechanism of silicon deposition. The deactivation was attributed to deposition of thin layer of silicon residues, which blocks the surface sites. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 6, pp. 918–928. The text was submitted by the authors in English.     

Thionation with the reagent combination of phosphorus pentasulfide and hexamethyldisiloxane

The combination of P4S10 and hexamethyldisiloxane efficiently converts esters, lactones, amides, lactams, and ketones to their corresponding thiono derivatives. In the presence of elemental sulfur, 3-oxoesters are converted to dithiolethiones by this reagent. Yields are comparable to or superior to those obtained with Lawesson's reagent. The method has the advantage that reagent-derived byproducts may be removed by a simple hydrolytic workup or by filtration through silica gel, rather than by chromatography, as required for Lawesson's reagent.     

Gas-Phase Reaction of Free Diethylsilylium Ions with Hexamethyldisiloxane

The gas-phase reaction of diethylsilylium ions with hexamethyldisiloxane was studied by the radiochemical procedure. As in reactions with other nucleophiles, the degree of rearrangement of the diethylsilylium ion in the reaction with hexamethyldisiloxane correlates with the condensation energy. In contrast to the reaction of Et₂SiT⁺ with dibutyl ether, in the reaction with hexamethyldisiloxane the labeled substrate is formed, which is due to isomerization of the trimethylsilyl substituent giving rise to a labile hydrogen atom.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 751–753.Original Russian Text Copyright © 2005 by Kochina, Vrazhnov, Sinotova, Ignat’ev.     

含巯基MTQ树脂的合成及对丙烯酸酯体系光固化性能的影响

以六甲基二硅氧烷、γ-巯丙基三乙氧基硅烷（KH-580）和正硅酸乙酯为原料,在酸性条件下通过水解共聚反应合成了含巯基MTQ树脂（SH-MTQ）。通过傅里叶红外光谱、核磁共振氢谱（¹HNMR）、凝胶渗透色谱和热重,对所合成的树脂进行了表征和分析。以1-羟基环己基苯基甲酮（184）为光引发剂,考察了含巯基MTQ树脂对三丙二醇二丙烯酸酯（TPGDA）光固化过程和材料性能的影响,发现含巯基MTQ树脂的加入使得TPGDA的光固化速率和双键转化率有所提高,并且固化膜硬度、热稳定性、透过率和接触角等材料性能也有所提高。     

Synthesis and characterization of oligocyclosiloxanes via the hydrosilation of vinylsilanes and vinylsiloxanes with heptamethylcyclotetrasiloxane

The preparation of oligocyclosiloxanes via hydrosilation reactions has been investigated. Hydrosilation reactions employing heptamethylcyclotetrasiloxane and vinyl-containing silanes and siloxanes yielded a variety of oligocyclosiloxanes with various numbers of cyclosiloxane rings connected through tri-, tetra-, penta-, hexa-, hepta-, or octafunctional junctions. The oligocyclosiloxanes were characterized by gas chromatography, IR spectroscopy, ²⁹Si-, ¹H-, and ¹³C-NMR spectroscopy, elemental analysis, and vapor phase osmometry. The polycyclics were redistributed with hexamethyldisiloxane and the resulting fragments analyzed by gas chromatography. All results were consistent with the formation of isomeric oligocyclosiloxanes due to a lack of absolute regioselectivity of the hydrosilation reaction. © 1993 John Wiley & Sons, Inc.     

^1HNMR双内标法测定2,4-DNT标准物质中的有机杂质

利用^1HNMR确定了2,4-DNT标准物质中的有机杂质为乙醇,根据化合物的核载量定义,采用不含四甲基硅烷（TMS）的氘代丙酮为溶剂,将1,1,2,2-四氯乙烷与六甲基二硅醚的四氯化碳标准溶液加入待测液中作为双内标,用乙醇的甲基质子峰为定量峰对其含量进行了测定。双内标法测定结果分别为O．075％,0．074％,标准偏差分别为0．005,0．006,t检验证实该结果与色谱法定值结果一致。该方法专属、准确、简便、快速,适用于标准物质中有机杂质的测定。     

The mixing properties of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) cyclotrisiloxane with various organosilicon compounds at different temperatures

The density and refractive index were determined for four binary mixtures of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) cyclotrisiloxane with octamethyl-cyclotetrasiloxane, hexamethyldisiloxane, 2,4,6,8-tetramethyl-cyclotetrasiloxane and 2,4,6,8-tetramethyl-2,4,6,8-tetraethenylcyclotetrasiloxane at different temperatures T = (308.15, 313.15, 318.15, 323.15 and 328.15) K and atmospheric pressure using a DMA4500/RXA170 combined system. The excess molar volume, partial excess volume at infinite dilution, isobaric coefficient of thermal expansion, excess refraction indices, Lorentz–Lorenz molar refraction and the deviation in molar refraction have been calculated using this data. The results have been incorporated into the Redlich–Kister equation and used to estimate the binary interaction parameters and standard deviation. The values of partial excess volume at infinite dilution and excess refraction indices for the four binary systems at different temperatures were calculated using the adjustable parameters of the Redlich–Kister smoothing equation. The factors that affect these excess quantities are discussed.     

Analyse von organosiliciumverbindungen

Zusammenfassung Bei der Analyse von technischem Hexamethyldisiloxan wurden in den höhersiedenden Destillationsanteilen eine Reihe von bisher wenig bekannten niedermolekularen Organosiliciumverbindungen mit siloxanartiger Struktur gefunden. Die Trennung und Identifizierung der Komponenten der Gemische von verzweigten Methyl- und Methylhydroxiloxanen erfolgte durch gas-chromatographische Methoden in Verbindung mit der Massenspektrometrie.

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Analysis of organosilicon compounds VII separation and identification of branched low molecular weight methyl-and methylhydrosiloxanes by GC/MS

Summary A series of unusual, low molecular weight organosilicon compounds with the siloxane structure has been found as a result of the analysis of hexamethyldisiloxane by gas chromatography. The components of the mixture of branched, low molecular weight methyl- and methylhydrosiloxanes have been identified by gas chromatography and mass spectrometry.

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VI. Mitteilung: Coll. Czech. Chem. Comm.36, 3497 (1971).     

Breathable rubbery skin protectors: Design,synthesis, characterization,and properties of cyanoacrylated silicone rubber networks

We extended our investigations of rubbery wound closure adhesives and created novel flexible networks by crosslinking cyanoacrylated silicone rubbers (i.e., commercial methylhydrosiloxane‐dimethylsiloxane copolymers, PMHS‐co‐PDMS) with N,N‐dimethyl‐p‐toluidine in tetrahydrofuran and hexamethyldisiloxane solvents at room temperature. Cyanoacrylation was achieved by hydrosilating (anthracene‐protected) allyl cyanoacrylate with PMHS‐co‐PDMS. Steric hindrance and the molecular weight of the copolymer strongly affect the extent of hydrosilation. The rate of crosslinking is proportional with the number of cyanoacrylate groups in the copolymer and networks form in seconds with appropriate amounts of initiator. Networks on porcine skin yield well‐adhering flexible optically‐transparent colorless conformal coatings of good “feel” appropriate for clinically useful non‐occlusive “breathable” skin or wound protectors. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1367‐1372     

Gaseous Nitrogen Dioxide for Sustainable Oxidative Deprotection of Trimethylsilyl Ethers

Abstract

In this study, trialkylsilyl ethers of indispensable protected alcohols are oxidatively deprotected in neat form with gaseous nitrogen dioxide (NO₂). Quantitative yields of aldehydes or ketones are obtained without the necessity of chromatography. The byproducts, nitrogen monoxide, anhydrous nitric acid, and hexamethyldisiloxane, can be quantitatively separated by evaporation and distillation in closed systems for recycling or further use. The direct new method supersedes the previous techniques that produce dangerous wastes and require chromatographic workup, while the atmospheric gas NO₂ and its gaseous reduction products are easily kept in closed systems until further use.     

Solvent-free thionation of γ-lactones under microwave irradiation

A series of γ-thionolactones was synthesized, with good yields, using a new combination of Lawesson's reagent (LR) and hexamethyldisiloxane (HMDO) in solvent-free conditions under microwave irradiation.     

Enantiomer-Differentiation Induced by an Enantiomeric Excess during Chromatography with Achiral Phases

It is shown, in the case of the diketone 2 , that chromatography with achiral phases of a non-racemic mixture of enantiomers can furnish fractions which differ in enantiomeric excess. Such chromatography may, therefore, be used to further enrich a sample in one enantiomer. By the same token, chromatography is not a generally safe method for the purification of the product of an enantio-differentiating process, if the enantiomeric excess of a purified portion of that product is taken to be a measure of the efficiency of the process. The described effect represents an enantiomer differentiation induced solely by an alredy existing enantiomeric excess during chromatography. It thus belongs to a class of effects where the relative amounts of two enantiomers induce an observable difference between them. Such effects are called EE effects. The common principle underlying EE effects is explained by a simple symmetry argument. Since EE effects can also occur during reactions with achiral reagents, further transformations of an enantiomer-enriched product may furnish false information on its enantiomeric excess.     

快速测定酶法动力学拆分中转化率和ee值的新方法

在动力学拆分反应中 ,转化率和对映体过量值( ee值 )是经常需要测量的两个重要参数 .传统的测定转化率的方法包括色谱法、分光光度法和滴定法等 .而测定 ee值主要应用手性色谱柱、手性毛细管电泳、核磁以及旋光法等 .在动力学拆分过程中 ,需要对反应进程进行监测 ,而应用传统的方法进行监测需要同时测定两个量 (转化率和 ee值 ) ,工作量较大 ,且使用手性色谱柱进行监测成本也较高 ,不适合大量实验数据的常规分析 .为此 ,需要发展一种快速、灵活、经济的测量方法 ,用以实验前期筛选条件时的常规分析 .基于此思路 ,我们借助于自己编制的计算机…     

Evolution of the surface polar character of pyrogenic silicas, with their grafting ratios by dimethylchlorosilane, studied by microcalorimetry

The interactions of water, hexamethyldisiloxane, and dodecane with pyrogenic silica samples, modified by a controlled partial silylation with dimethyldichlorosilane, were studied by microcalorimetry and wettability measurements. The samples, having a coverage ratio lower than dimethylsilyl (DMS) monolayer capacity ( approximately 2.6 DMS/nm(2)), show a regular and linear decrease of their heat of immersion into water with the coverage ratio and correlate with the increase of residual silanol groups. Two critical coverage ratios were evidenced at about 25 and 50% of the DMS monolayer capacity, the grafted silica remaining hydrophilic, below 25% being strongly hydrophobic beyond. The heat of immersion into hexamethyldisiloxane decreases until 50% of the DMS monolayer whereas that of dodecane remains independent of the grafting ratio. This study demonstrates that the water/residual free silica surface plays the main role in the stabilization of the W/O Pickering's emulsions.     

Reaction of the Dioxane Complex of Dichlorogermylene with Siloxanes

The major organogermanium compounds formed by reactions of the dioxane complex of dichlorogermylene with hexamethyldisiloxane, octamethyltrisiloxane, and hexamethyltricyclotrisiloxane are bis(trimethylsiloxy)dichlorogermane, 3,3-dichloro-1,1,1,5,5,7,7,7-octamethyl-3-germa-2,4,6-trioxa-1,5,7-trisilaheptane, and a cyclic germatetrasiloxane.     

Group transfer polymerization in the bulk: linear polymers and randomly cross-linked networks

Linear homopolymers and randomly cross-linked homopolymer networks of 2-(dimethylamino)ethyl methacrylate of various molecular weights (MWs) were synthesized by group transfer polymerization in the bulk. 1-methoxy-1-(trimethylsiloxy)-2-methyl propene was used as the initiator, while tetrabutylammonium bibenzoate served as the catalyst. Ethylene glycol dimethacrylate was the cross-linker used for the network synthesis at an 8-fold molar excess with respect to the initiator. Gel permeation chromatography in tetrahydrofuran was used to characterize the linear homopolymers in terms of their MW and molecular weight distribution (MWD). Although the experimental MWs did not match the theoretical MWs, they were reasonably close to them. The MWDs were rather broad with polydispersity indices ranging between 1.5 and 1.9. The monomer conversion was relatively high, ranging from 97% to 74% for theoretical degrees of polymerization (DPs) from 5 to 500. No polymerization was observed for an attempted DP of 1000. Networks with molar ratios of monomer to initiator (nominal DPs) from 5 to 200 were prepared, while an attempted synthesis with a nominal DP of 500 did not yield a network. The networks were characterized in terms of their degree of swelling in water and the effects of DP, pH, salt concentration and temperature were investigated.     

Prediction of enantiomeric excess in a combinatorial library of catalytic enantioselective reactions

A quantitative structure-enantioselectivity relationship was established for a combinatorial library of enantioselective reactions performed by addition of diethyl zinc to benzaldehyde. Chiral catalysts and additives were encoded by their chirality codes and presented as input to neural networks. The networks were trained to predict the enantiomeric excess. With independent test sets, predictions of enantiomeric excess could be made with an average error as low as 6% ee. Multilinear regression, perceptrons, and support vector machines were also evaluated as modeling tools. The method is of interest for the computer-aided design of combinatorial libraries involving chiral compounds or enantioselective reactions. This is the first example of a quantitative structure-property relationship based on chirality codes.     

人工神经网络用于交流示波计时电位法的研究

提出了交流示波计时电位法的人工神经网络校正方法,并对其可行性和适用性进行了探讨,用此方法分别解析了大量Ｔｌ＾＋存在时Ｐｂ＾２＋和大量Ｉｎ＾２＋存在时Ｃｄ＾２＋的交流地波计时电位法的ｄＥ／ｄｔ－Ｅ曲线,结果表明,对Ｐｂ＾２＋和Ｃｄ＾２＋和Ｃｄ２＋的预测最大相对误差不超过５％,其性能良好。     

Preparation and properties of dimethyl phosphonomethyl methylsiloxane dimethylsiloxane copolymers

Dimethyl phosphonomethylheptamethylcyclotetrasiloxane (II) and 1, 3-bis(dimethyl phosphonomethyl)tetramethyldisiloxane (III) have been prepared by Arbuzov reaction of trimethyl phosphite with bromomethylheptamethylcyclotetrasiloxane (I) and 1, 3-bis(bromomethyl)tetramethyldisiloxane, respectively. Dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymers have been prepared by acid-catalyzed ring-opening polymerization of II with hexamethyldisiloxane (MM) as an end-capping reagent and by reaction of II with III as an end-capping reagent. Dimethylsiloxane polymers with dimethyl phosphonomethyldimethylsiloxy end groups have been prepared by acid-catalyzed polymerization of octamethylcyclotetrasiloxane (D₄) and III. Under these conditions hydrolysis of the dimethyl phosphonate ester groups was a problem. On the other hand Arbuzov reaction of trimethyl phosphite with bromomethylmethylsiloxane dimethylsiloxane copolymer gave a dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymer with uniform properties. These polymers have been characterized by ¹H-, ¹³C-, ²⁹Si-, and ³¹P-NMR spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC) and their thermal stability measured by TGA.