- NMR DETERMINATION OF ABSOLUTE SITE-SPECIFIC NATURAL ISOTOPE RATIOS OF HYDROGEN IN ORGANIC MOLECULES. ANALYTICAL AND MECHANISTIC APPLICATIONS
-
It has been shown that the "internal" isotope distribution within a given molecular species at the natural abundance level is accessible by a new method, SNIF-nmr, which is based on deuterium NMR.Relative internal factors, Ri/j, have been defined which enable the isotope content of a given site, i, to be compared to that of another molecular site, j, taken as a reference.Several referencing methods intended to provide direct access to relative externals, Ti, and absolute, (D/H), site-specific parameters, are now discussed from both the theoretical and the experimental points of wiev.In the intramolecular referencing method, which involves a time-consuming chemical transformation of the sample, the risk exists of more or less systematic errors resulting from discriminating fractionation effects.However this technique offers, conversely, an interesting way of investigating kinetic isotope effects without the need for specific labelling.In spite of its lower spectral precision the external referencing method has the advantage of being fast and less sensitive to systemetic errors and may be used for direct rough routine determinations of the site-specific isotope contents.More precise results can be obtained, at the price of contaminating the sample, when an intermolecular reference is added and signal heights are used, remembering however that the intensity parameters then have no strict physical meaning in terms of absolute isotope contents.The site-specific parameters, Ti and (D/H)i thus accessible, provide new information on the mechanisms of the fractionation effects occuring in natural conditions and exaples are considered.
- Martin, G. J.,Sun, X. Y.,Guillou, C.,Martin, M. L.
-
-
Read Online
- Synthesis and thermal transformations of polyphosphosiloxane based on trimethyl phosphate and (3-aminopropyl)triethoxysilane
-
A method for the synthesis of polyphosphosiloxane by the thermal condensation of an equimolar mixture of trimethyl phosphate and (3-aminopropyl)triethoxysilane at 200 °C was developed. The reaction affords ethanol and polyphosphosiloxane-{Si(OEt)[(CH
- Klement'eva,Cherepennikova,Semenov,Kirillov,Lopatin,Kuznetsova,Kurskii,Zaitsev,Klapshina,Duglas,Domrachev
-
-
Read Online
- Unimolecular Decomposition of Ethoxytrimethylsilane
-
A study of the metastable spectra from ethoxytrimethylsilane and the mass shifts of the deuterium-labeled species permitted the rationalization of the fragmentation mechanism for forming all major ions in the mass spectrum.A new mechanistic pathway for th
- Herold, David A.,Furtell, Jean H.
-
-
Read Online
- Catalytic Enantioselective Strecker Reaction of Isatin-Derived N-Unsubstituted Ketimines
-
A catalytic enantioselective Strecker reaction of isatin-derived N-unsubstituted ketimines directly afforded the N-unprotected α-aminonitriles with a tetrasubstituted carbon stereocenter in up to 99% ee without requiring protection/deprotection steps. One-pot Strecker reactions from the parent carbonyl compounds were also realized with comparable yields and enantioselectivities. Direct transformations of the N-unprotected α-aminonitrile products streamlined the synthesis of unnatural amino acid derivatives and achieved the shortest one-pot stereoselective routes to a biologically active compound reported to date.
- Kadota, Tetsuya,Sawa, Masanao,Kondo, Yuta,Morimoto, Hiroyuki,Ohshima, Takashi
-
supporting information
p. 4553 - 4558
(2021/06/28)
-
- Sustainable Catalytic Synthesis of Diethyl Carbonate
-
New sustainable approaches should be developed to overcome equilibrium limitation of dialkyl carbonate synthesis from CO2 and alcohols. Using tetraethyl orthosilicate (TEOS) and CO2 with Zr catalysts, we report the first example of sustainable catalytic synthesis of diethyl carbonate (DEC). The disiloxane byproduct can be reverted to TEOS. Under the same conditions, DEC can be synthesized using a wide range of alkoxysilane substrates by investigating the effects of the number of ethoxy substituent in alkoxysilane substrates, alkyl chain, and unsaturated moiety on the fundamental property of this reaction. Mechanistic insights obtained by kinetic studies, labeling experiments, and spectroscopic investigations reveal that DEC is generated via nucleophilic ethoxylation of a CO2-inserted Zr catalyst and catalyst regeneration by TEOS. The unprecedented transformation offers a new approach toward a cleaner route for DEC synthesis using recyclable alkoxysilane.
- Putro, Wahyu S.,Ikeda, Akira,Shigeyasu, Shinji,Hamura, Satoshi,Matsumoto, Seiji,Lee, Vladimir Ya.,Choi, Jun-Chul,Fukaya, Norihisa
-
p. 842 - 846
(2020/12/07)
-
- Application of a novel nano-immobilization of ionic liquid on an MCM-41 system for trimethylsilylation of alcohols and phenols with hexamethyldisilazane
-
3-[(3-(Trisilyloxy)propyl)chloride]-1-methylimidazolium tribromide ionic liquid supported on MCM-41 [nano-MCM-41@(CH2)3-1-methylimidazole]Br3 as a novel heterogeneous nano-catalyst was easily prepared and characterized usi
- Zolfigol, Mohammad Ali,Sajjadifar, Sami,Ghorbani-Choghamarani, Arash,Tami, Farzaneh
-
p. 7093 - 7106
(2018/08/17)
-
- Metal-Free Catalytic Reductive Cleavage of Enol Ethers
-
In contrast to the well-known reductive cleavage of the alkyl-O bond, the cleavage of the alkenyl-O bond is much more challenging especially using metal-free approaches. Unexpectedly, alkenyl-O bonds were reductively cleaved when enol ethers were reacted with Et3SiH and a catalytic amount of B(C6F5)3. Supposedly, this reaction is the result of a B(C6F5)3-catalyzed tandem hydrosilylation reaction and a silicon-assisted β-elimination. A mechanism for this cleavage reaction is proposed based on experiments and density functional theory (DFT) calculations.
- Chulsky, Karina,Dobrovetsky, Roman
-
supporting information
p. 6804 - 6807
(2018/11/02)
-
- Preparation of tetrafluoroethylene from the pyrolysis of pentafluoropropionate salts
-
The use of tetrafluoroethylene (TFE) in academic institutions beyond a few millimoles has often been inhibited by the compound's inherent danger and general lack of commercial availability. On the other hand, TFE is prepared industrially on a rather large scale by a number of major fluorochemical companies via the pyrolysis of chlorodifluoromethane at high temperatures, yielding TFE and HCl. For a few years at The University of Alabama and Clemson University, we have been preparing TFE on a 100+-gram scale by the pyrolysis under dynamic vacuum of pentafluoropropionate salts, which can be obtained from the neutralization of pentafluoropropionic acid with a M(OH)n (where M?=?Li, Na, K, and Cs for n?=?1 and Mg, Ca, and Ba for n?=?2). Additionally, potassium pentafluoropropionate can be prepared from the reaction of potassium trimethylsilanolate and ethyl pentafluoropropionate. The pentafluoropropionate salts and their decomposition products have been characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, Fourier transform-infrared (FTIR) spectrophotometry, scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDAX), X-ray diffraction (XRD), and single-crystal X-ray crystallography, where applicable. Typical yields of TFE obtained from pyrolysis of potassium pentafluoropropionate obtained from the acid-base neutralization method are >98%, while yields of TFE from the same salt prepared by the silanolate method from ethyl pentafluoropropionate are ca. 80%.
- Hercules, Daniel A.,Parrish, Cameron A.,Sayler, Todd S.,Tice, Kevin T.,Williams, Shane M.,Lowery, Lauren E.,Brady, Michael E.,Coward, Robert B.,Murphy, Justin A.,Hey, Trevyn A.,Scavuzzo, Anthony R.,Rummler, Lucy M.,Burns, Emory G.,Matsnev, Andrej V.,Fernandez, Richard E.,McMillen, Colin D.,Thrasher, Joseph S.
-
p. 107 - 116
(2017/04/18)
-
- One-Step Synthesis of Siloxanes from the Direct Process Disilane Residue
-
The well-established Müller–Rochow Direct Process for the chloromethylsilane synthesis produces a disilane residue (DPR) consisting of compounds MenSi2Cl6?n(n=1–6) in thousands of tons annually. Technologically, much effort is made to retransfer the disilanes into monosilanes suitable for introduction into the siloxane production chain for increase in economic value. Here, we report on a single step reaction to directly form cyclic, linear, and cage-like siloxanes upon treatment of the DPR with a 5 m HCl in Et2O solution at about 120 °C for 60 h. For simplification of the Si?Si bond cleavage and aiming on product selectivity the grade of methylation at the silicon backbone is increased to n≥4. Moreover, the HCl/Et2O reagent is also suitable to produce siloxanes from the corresponding monosilanes under comparable conditions.
- Neumeyer, Felix,Auner, Norbert
-
supporting information
p. 17165 - 17168
(2016/11/23)
-
- ELECTROLYTE FORMULATIONS CONTAINING CYANO-ALKOXY-BORATE ANIONS
-
The present invention relates to electrolyte formulations containing cyano-alkoxy-borate anions, their preparation and their use, in particular as part of electrolyte formulations for electrochemical or optoelectronic devices and special compounds containing cyano-alkoxy-borate anions.
- -
-
Page/Page column 59-60
(2012/04/17)
-
- Tetrabutylammonium phthalimide-N-oxyl: An efficient organocatalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane
-
Tetrabutylammonium phthalimide-N-oxyl (TBAPINO) was found to be an effective organocatalyst for rapid, simple and chemoselective protection of the hydroxyl group of alcohols and phenols using hexamethyldisilazane (HMDS) under mild conditions. The low catalyst loading, high to quantitative yields and simple removal of the catalyst from the reaction mixture illustrate the other attractive features of this protocol.
- Dekamin,Yazdaninia,Mokhtari,Naimi-Jamal
-
experimental part
p. 537 - 544
(2012/06/18)
-
- Synthesis of new types of N,N-disubstituted aminomethylspirophosphoranes
-
Aminomethylation of several hydrospirophosphoranes and their derivatives, using chloro-, alkoxy-, and amino-substituted methylamines of various structures, is proposed as the convenient method for the synthesis of new N,N-disubstituted aminomethylspiropho
- Prishchenko, Andrey A.,Livantsov, Mikhail V.,Novikova, Olga P.,Livantsova, Ludmila I.,Petrosyan, Valery S.
-
experimental part
p. 515 - 520
(2011/07/09)
-
- CYCLIC AMINO COMPOUNDS FOR LOW-K SILYLATION
-
Disclosed herein are mono-functional silylating compounds that may exhibit enhanced silylating capabilities. Also disclosed are method of synthesizing and using these compounds. Finally methods to determine effective silylation are also disclosed.
- -
-
-
- Acyl iodides in organic synthesis. Reaction of acyl iodides with triphenylethoxy- and triphenylhydroxysilane
-
The reaction of triphenylethoxysilane with acetyl or benzoyl iodide led to the formation of triphenyliodosilane and ethyl ester of the corresponding carboxylic acid. Triphenyliodosilane formed also in the reaction of triphenylsilanol with benzoyl iodide.
- Voronkov,Tsyrendorzhieva,Rakhlin
-
experimental part
p. 1621 - 1622
(2010/04/27)
-
- Monosodiumoxyorganoalkoxysilanes: Synthesis and properties
-
The reaction of organoalkoxysilanes with sodium hydroxide was studied in detail. Studies indicate that this reaction involves more than one stage and involves rather complex multistep process, which leads to the formation of both monosodiumoxyorganoalkoxysilanes (MSOAS) and several secondary products. Analysis of experimental evidence makes it possible to advance the mechanism behind this phenomenon and to define the optimum conditions for the preparation of pure MSOAS with high yields. Different MSOAS were synthesized and their basic physicochemical properties were studied. MSOAS are shown to constitute multifunctional reagents with chemically independent functional groups, and their reaction with trimethylchlorosilane selectively proceeds via - ONa groups, whereas their interaction with triethylesilanol and higher alcohols proceeds exclusively via - OAlk groups. Exchange interaction between MSOAS and organoalkoxysilanes via - ONa and - OAlk groups was found and studied in detail. Temperature corresponding to the onset of thermal degradation of MSOAS was estimated to be equal to ～ 180-190°C.
- Rebrov,Muzafarov
-
p. 514 - 541
(2007/10/03)
-
- Method for preparing a regenerated cellulose fibre or yarn
-
A method has been developed for making regenerated cellulose yarn. The method includes the steps of spinning a solution derived from cellulose or a cellulose derivative in a molten state through at least one extrusion die, then regenerating the cellulose by treating the resulting yarn, wherein a silylated cellulose derivative is prepared by reaction with a silylating agent; the silylated cellulose is extracted from the synthesis reaction medium; then spun through at least an extrusion die; and the resultant yarn treated with a desilylation agent to regenerate the cellulose and a siloxane. The resulting cellulose yarns or fibers may be used for making woven or knitted textile surfaces or non-woven surfaces. Said yarns or fibers are also useful as reinforcing fibers in elastomeric materials and more particularly, in tires.
- -
-
-
- Effect of substituents on the silicon atom on etherification of organochlorosilanes with ethanol
-
The kinetics of etherification of organochlorosilanes with various substituents on the silicon atom with ethanol were studied. The etherification rate is mostly controlled by the inductive constants of the substituents and increases as the electron-acceptor power of the substituents increases. The ρ* value in the Taft equation for etherification of organochlorosilanes with ethanol was determined.
- Chernyshev,Belyakova,Komarov,Bykovchenko
-
p. 1038 - 1040
(2007/10/03)
-
- Substituent effects on the reactivity of the silicon-carbon double bond. Resonance, inductive, and steric effects of substituents at silicon on the reactivity of simple 1-methylsilenes
-
The reactivities of a series of substituted 1-methylsilenes RMeSi=CH2 (R = H, methyl, ethyl, t-butyl, vinyl, ethynyl, phenyl, trimethylsilyl, and trimethylsilymethyl) in hydrocarbon solvents have been investigated by far- UV (193-nm) laser flash photolysis techniques, using the corresponding 1- methylsilacyclobutane derivatives as silene precursors. Each of these silacyclobutanes yields ethylene and the corresponding silene, which can be trapped as the alkoxysilane RSiMe2OR' cleanly upon 193- or 214-nm photolysis in solution in the presence of aliphatic alcohols. UV absorption spectra and absolute rate constants for reaction of the silenes with methanol, ethanol, and t-butyl alcohol have been determined in hexane solution at 23°C. The rate constants vary from a low 3 x 107 M-1 s-1 for reaction of 1- methyl-1-trimethylsilylsilene with t-BuOH to a high of 1 x 1010 M-1 s- 1 for reaction of 1-ethynyl-1-methylsilene with MeOH. In several cases, rate constants have been determined for addition of the deuterated alcohols, and for addition of methanol over the 0-55°C range. Invariably, small primary deuterium kinetic isotope effects and negative Arrhenius activation energies are observed. These characteristics are consistent with a mechanism involving reversible formation of a silene-alcohol complex which collapses to alkoxysilane by unimolecular proton transfer from oxygen to carbon. Silene reactivity increases with increasing resonance electron-donating and inductive electron-withdrawing ability of the substituents at silicon and is significantly affected by steric effects within this series of compounds. This is suggested to be due to a combination of effects on both the degree of electrophilicity at silicon (affecting the rate constants for formation and reversion of the complex) and nucleophilicity at carbon (affecting the partitioning of the complex between product and free reactants). Two 1- methyl-1-alkoxysilacyclobutanes were also investigated, but proved to be inert to 193-nm photolysis.
- Leigh, William J.,Boukherroub, Rabah,Kerst, Corinna
-
p. 9504 - 9512
(2007/10/03)
-
- Silicon-29 NMR spectra of trimethylsilylated alcohols
-
29Si NMR spectra of trimethylsilyl (TMS) derivatives of 26 simple alcohols were measured under standardized conditions (i.e., in sufficiently diluted deuteriochloroform solutions). Due to association with the solvent the chemical shifts are in almost all cases larger than those reported earlier for different solutions. This observation is in agreement with the proposed mechanism of steric effects as being due to sterically controlled association with the solvent. The use of chloroform as a solvent enhances steric effects hut at the same time it can reduce small differences due to polar effects in closely related compounds. In the studied class of compounds the gross dependence of the chemical shift on polar effects is not substantially affected by the change of the solvent.
- Kvicalova, Magdalena,Cermak, Jan,Blechta, Vratislav,Schraml, Jan
-
p. 816 - 820
(2007/10/03)
-
- Far-UV laser flash photolysis in solution. A time-resolved spectroscopic study of the chemistry of 1,1-dimethyl-1,3-(1-sila)- butadiene
-
Laser flash photolysis (193 nm) of 1,1-dimethyl-(1-sila)cyclobut-2-ene in hexane solution leads to the formation of a transient species (τ ～ 1.5 μs at 23°C) assigned to 1,1-dimethyl-1,3-(1-sila)butadiene on the basis of its UV absorption spectrum (λm
- Kerst, Corinna,Byloos, Martin,Leigh, William J.
-
p. 975 - 982
(2007/10/03)
-
- NEW TYPES OF AMINOMETHYL ORGANOPHOSPHORUS COMPOUNDS
-
We studied aminomethylation of various PH acids their derivatives containing highly reactive PH, PSi, POSi and PC(O) fragments: tris(trimethylsilyl)phosphine, trimethylsilyl esters of phosphorus(III) acids, pivaloylphosphonite, and hydrospirophosphoranes.Chloro-, alkoxy- or dialkylaminomethylamines, dialkylformamide acetals, azomethines, and enamines were used as aminomethylating reagents.Convenient methods for synthesizing previously unknown or difficult-to-obtain organic compounds of two-, three-, four, and five-coordinate phosphorus containing a P-C-N fragment were proposed.
- Prishchenko, A.A.,Livantsov, M.V.,Petrosyan, V.S.
-
p. 1181 - 1193
(2007/10/02)
-
- DIALKYL TRIMETHYLSILYL TETRATHIOPHOSPHATES. SYNTHESIS AND TRANSFORMATIONS
-
We have developed an efficient method for synthesizing dialkyl trimethylsilyl tetrathiophosphates, which react with aldehydes, acetals, ortho esters, thioacetals, bis(thiocyanato)methane, diethyl disulfide, and alkyl halides to give a number of new tetrathiophosphate derivatives.
- Nizamov, I.S.,Kuznetsov, V.A.,Batyeva, E.S.,Al'fonsov, V.A.
-
p. 1196 - 1198
(2007/10/02)
-
- DIALKYL(TRIMETHYLSILYL)TETRATHIOPHOSPHATES IN SYNTHESIS OF SUBSTITUTED TETRATHIOPHOSPHATES
-
Reactions of S,S'-dialkyl-S''-trimethylsilyl tetrathiophosphates with aldehydes, acetals, ortho ethers, aminals, thioacetals, bis(thiocyanato)methane, disulfides and alkyl halides resulted in the products of tetrathiophosphate structure.Key words: S,S'-Dialkyl-S''-trimethylsilyl tetrathiophosphates; organic substances; substituted tetrathiophosphates.
- Nizamov, Il'Yas S.,Kuznetzov, Vladislav A.,Batyeva, Elvira S.
-
p. 249 - 258
(2007/10/02)
-
- Laser-powered homogeneous pyrolysis of 1,1-dimethyl-1-silacyclobutane in the presence of some common monomers
-
Laser-induced homogeneous pyrolysis of 1,1-dimethyl-1-silacyclobutane yields 1,1,3,3-tetramethyl-1,3-disilacyclobutane and ethene as major products.In the presence of vinyl acetate, allyl methyl ether, acrolein, methyl vinyl ether, methyl acrylate or meth
- Pola, Josef,Cukanova, Dana,Minarik, Milan,Lycka, Antonin,Tlaskal, Jaroslav
-
-
- REACTION OF SILYLPHOSPHITES WITH SECONDARY AMINES
-
The reaction of dialkylsilylphosphites with linear and cyclic secondary amines leads to the formation of acid alkoxydialkylamidophosphites and dialkyl phosphites.Aminolysis of pyrocatecholsilylphosphite was accomplished with retention of the phosphorus atom and formation of the corresponding amidophosphites.
- Pudovik, M. A.,Kibardina, L. K.,Pudovik, A. N.
-
p. 217 - 218
(2007/10/02)
-
- Mechanism of Thermal Eliminations. Part 29. The Effect of Different Silyl groups upon Thermal Elimination of Ketene from Ethyl Silylacetates
-
A series of ethyl silylacetates, R3SiCH2CO2Et where R3 = Me3, Me2Ph, MePh2, Ph3, have been prepared and their rates of gas-phase thermal elimination to ketene and the corresponding ethyl silyl ether measured, each over 50 deg C temperature range.Activation energies are in the range of 136-144 kJ mol-1, and log(A/s-1) values 10.1-10.8.Increase in the electrophilicity of silicon through replacement of one methyl group by phenyl produces a minor increase in reactivity, but further similar replacements eventually produce a rate decrease, which is attributed to steric hinderance.Overall the kinetic data indicate that the strength of the silicon-oxygen bond formed is sufficiently important that alteration in the ester structure is incapable of producing substantial variation in the rate of ketene formation.
- Chapman, Sara E.,Taylor, Roger
-
p. 1119 - 1120
(2007/10/02)
-
- Reaction Rates of Trimethylethoxysilane and Trimethylmethoxysilane in Alkaline Alcohol Solutions
-
The kinetics of the reaction (CH3)3SiOC2H5 + CH3O- (CH3)3SiOCH3 + C2H5O- have been investigated in both directions by means of FTIR spectroscopy.To obtain k1, trimethylethoxysilane was reacted with methoxide in a metha
- Jaeglid, Ulf,Lindqvist, Oliver
-
p. 887 - 891
(2007/10/02)
-
- SILICON DERIVATIVES OF CARBAZIC ACIDS. SYNTHESIS, PREPARATIVE SEPARATION, CONFORMATION, AND SOME PROPERTIES OF PERSILYLATED HYDRAZINO-N,N'-DICARBOXYLIC ACID TAUTOMERS
-
The ratio of persilylated hydrazino-N,N'-dicarboxylic acid tautomers formed in the reaction of hydrazine salts with (Me3Si)2NH and CO2 is a function of the degree of dilution of the reaction mixture.The tautomers can be separated by preparative GLC and ex
- Sheludyakov, V. D.,Lebedeva, A. B.,Kirilin, A. D.,Turkel'taub, G. N.,Kisin, A. V.,et al.
-
p. 1093 - 1097
(2007/10/02)
-
- Reactions of Trialkylsilyl Trifluoromethanesulfonates, IX. - Electrophilic Silylation of Electron-Rich Alkenes
-
Ketene O,O-, O,S-, and O,N-acetals 1, 7, and 9 are converted into the C-silylated derivatives 4, 8, and 11, respectively, by reaction with trimethylsilyl triflate (2a)/tertiary amine or sodium hydride.The ambident character of the ketene O,O-acetals 1 in
- Schulz, Dieter,Simchen, Gerhard
-
p. 745 - 750
(2007/10/02)
-
- REACTION OF HEXAMETHYLDISILOXANE WITH 2-ETHOXY-1,3-DIOXOLANE
-
The reaction of hexamethyldisiloxane with 2-ethoxy-1,3-dioxolane is described.It is shown that cleavage of the endo- and exocyclic carbon-oxygen bonds of the ortho ester occurs under mild condition (16 - 20 deg C) in the presence of acidic catalysts with
- Zhurkina, I. P.,Nedogrei, E. P.,Musavirov, R. S.,Kondrat'eva, I. A.,Rakhmankulov, D. L.
-
p. 1338 - 1342
(2007/10/02)
-
- Facile Reduction of Organometallic Halides with Bis(pentamethylcyclopentadienyl)ytterbium and the X-Ray Structure of (C5Me5)2YbCl(THF)
-
Reduction of (C5H5)2MCl2 (M=Ti, Zr) and TiCl4 with one equiv. of (C5Me5)2Yb(THF)2 gave rise to the formation of 2 and TiCl3(THF)3, respectively, together with (C5Me5)2YbCl(THF).The molecular structure of (C5Me5)2YbCl(THF) has been determined by the X-ray analysis.The reaction of (C5Me5)2Yb(THF)2 with Me3SiCl yielded a mixture composed of n and C5Me5(CH2)4OSiMe3.
- Yasuda, Hajime,Yamamoto, Hitoshi,Yokota, Kiyohiko,Nakamura, Akira
-
p. 1309 - 1312
(2007/10/02)
-
- Organometallic substrates of enzymes: lipase catalysed transesterifications in organic solvents via O-stannyl ethers
-
Lipases from pig pancreas and from Chromobacterium viscosum (but not from Candida cylindracea) catalyze transesterification reactions between ethyl esters of carboxylic acids and tributylstannyl ethers of primary and secondary alcohols.At concentrations 1M or higher in anhydrous hydrocarbons, use of these nucleophilic derivatives of alcohols gives reaction rates ca. three times higher than those for the corresponding alcohols.
- Therisod, Michel
-
-
- CRYPTATE ACIDITY SCALES. V. EQUILIBRIUM ACIDITY OF INDICATOR CH-ACIDS IN TETRAHYDROFURAN
-
A scale of equilibrium cryptate acidity in tetrahydrofuran is constructed.Its distinguishing feature is the constancy of the contribution from ionic association.A method is proposed for determination of the constants for the association of the ions into ion pairs in dimethyl sulfoxide.
- Antipin, I. S.,Gareev, R. F.,Vedernikov, A. N.,Konovalov, A. I.
-
p. 1039 - 1044
(2007/10/02)
-
- Generation of Organic Cations from Group 14 Organometallic Compounds via Photoinduced Electron Transfer in the Presence of Cu(II) Salt
-
Irradiations of acetonitrile-alcohol (3:1) solutions of arylmethyl silanes, germane, or stannanes in the presence of Cu(BF4)2 gave alkyl arylmethyl ethers in good yields via arylmethyl cations, The efficiency of this photoreaction increased in the order of Si- Ge- Sn-compounds.
- Mizuno, Kazuhiko,Yasueda, Masahiro,Otsuji, Yoshio
-
p. 229 - 232
(2007/10/02)
-
- Method of preparing trialkyl organo-oxysilanes
-
A method for the continuous or batch preparation of trialkyl organo-oxysilanes by reaction of organic hydroxy compounds with trialkyl halogen silanes in the absence of acid-binding substances is disclosed. The organic hydroxy compound is added directly to the trialkoxy halogen silane in an amount which corresponds to no more than the stoichiometrically necessary amount. The trialkyl halogen silane, or the resultant mixture is always at the boiling temperature or above the boiling temperature in the gaseous state. The reaction mixture is subjected, no later than toward the end of the reaction, to a column distillation in which the column temperature is held such that the reaction is carried to the end within the column. In continuous operation, the trialkyl halogen silane is introduced in gaseous form into the bottom of a column and either kept under reflux or introduced into a reactor into which corresponding stoichiometric amounts of organic hydroxy compound are simultaneously introduced. In the column, either a raw product or freshly introduced organic hydroxy compound in liquid form flows against the gaseous trialkyl halogen silane, and the desired trailkyl organo-oxysilane collects at ebullition on the floor of the column and is continuously removed.
- -
-
-
- Synthesis of Hydroxy-Substituted 4-Phenyl-1,2,4-triazoline-3,5-diones
-
Starting from 4-aminophenol, 4-(4-hydroxyphenyl)-1,2,4-triazoline-3,5-dione (4) and 4-(4-hydroxy-3-nitrophenyl)-1,2,4-triazoline-3,5-dione (11) are synthesized.Contrary to the base-catalyzed formation of the unsubstiuted phenyl derivative 1, the heterocycle 9 is formed by heating of 1-(ethoxycarbonyl)-4-semicarbazide (8).By treatment of 4-(4-hydroxyphenyl)urazole (9) with NO2 nitration of the aromatic ring and oxidation occur simultaneously with formation of 11.Oxidation by tert-butyl hypochlorite gives 4.First investigations on polybutadienes modified with 1, 4, 11 show the influence of the additional hydroxy group to the mechanical properties.
- Burgert, Josef,Stadler, Reimund
-
p. 691 - 694
(2007/10/02)
-
- The Thermal Elimination of Ketene from Alkyl Trimethylsilylacetates
-
Alkyl trimethylsilylacetates readily undergo thermal elimination to give ketene and trimethylsilyl alkyl ethers; Arrhenius data have been obtained for this new unimolecular first-order reaction which involves a semi-concerted four-centre process.
- Taylor, Roger
-
p. 741 - 742
(2007/10/02)
-
- Reactivity of the Labile Silaethene Me2Si=C(SiMe3)2, Stored as Ph2C=NSiMe3 Adducts
-
Silaethene Me2Si=C(SiMe3)2 (1), stored as Ph2C=NSiMe3 adducts and regenerated from the adducts at about 100 deg C as a reaction intermediate, combines with reactants a-b (e.g.HO-H, RO-H, RCOO-H, RS-H, RHN-H, Ph2CN-H, RO-SiR3, R2N-SiR3, Ph2CN-SiR3, Cl-GeR3, Cl-SnR3) with insertion into the a-b bond, with a=b (e.g.O=CPh2, Me3SiN=CPh2, CH2=CHOMe, cis-piperylene), a=b=c (e.g.RN=N=N, O=N=N), a=b-c=d (e.g. butadiene, isoprene, trans-piperylene, 2,3-dimethylbutadiene, cyclopentadiene, anthracene, benzophenone, N-trimethylsilylbenzophenoneimine) under -, - as well as -c ycloaddition and with a=b-c-H (e.g. propene, butenes, isoprene, 2,3-dimethylbutadiene, acetone) under ene reaction.According to relative reaction rates, insertion and -cycloadditions seem to proceed in two reaction steps, whereas -cycloadditions and ene reactions with organic dienes and enes obviously are one step reactions.For reactivities cf.Table I. - Key words: Silaethene Me2Si=C(SiMe3)2, Insertions, Cycloadditions, Relative Reactivities
- Wiberg, N.,Preiner, G.,Wagner, G.,Koepf, H.
-
p. 1062 - 1074
(2007/10/02)
-
- A New Four-centre Reaction of Alkanol-Alkoxide Negative Ions. The Reaction of with Alkoxysilanes. An Ion Cyclotron Resonance Study
-
Alkanol-alkoxide negative ions 1O...H...OR2>(-) react with alkoxysilanes Me3SiOR3 to produce both 1O(-)> and 2O(-)> ions of trigonal bipyramidal geometry.When R1 2 and either R1 or R2 >= Pr, the four-center reaction 1O...H...OR2>(-) + Me3SiOR3 -> 2O...H...OR3>(-) + Me3SiOR1 is observed.Addition of 1O...H...OR2>(-) in the reverse direction is not detected.Analogous reactions do not occur between Me3SiX and 1O...H...OR2>(-) when X = F, NHR, NR2, SiMe3, alkyl, allyl, propargyl, benzyl, or aryl, but 1O...H...X>(-) ions of small abundance are formed when X = HO, OCOMe, OCN, and SR.Cyclic ethers react with alkanol-alkoxyde negative ions by reaction (i;n = 2-4).
- Hayes, Roger N.,Bowie, John H.,Klass, Gunter
-
p. 1167 - 1174
(2007/10/02)
-
