141-62-8Relevant articles and documents
Cyclic phosphonitrilic compounds bearing -N=PCL3 group as homogenous catalyst towards the silanol condensation
Vaugeois, Yann,Mazzah, Ahmed,De Jaeger, Roger,Habimana, Jean
, p. 1819 - 1840 (2004)
Condensation reactions of 1,1,3,3,3 pentamethyldisiloxane-ol (MDH), in toluene catalysed by two types of phosphonitrilic catalyst bearing a phosphazene -N=PCl3, were studied using sampling and gas chromatographic analysis method. The condensation kinetics reactions were compared for both phosphazene compounds. The process is selective, leading to linear decamethyltetrasiloxane MD2M, (where D denotes the dimethylsiloxane unit and M denotes the trimethyloxysilane unit) as almost the exclusive primary product. The mechanisms of the MDH condensation are discussed using the 31P NMR sampling technique.
Kinetics and mechanism of oligosiloxanol condensation and oligosiloxane rearrangement catalysed with model phosphonitrile chloride catalysts
Chojnowski,Fortuniak,Habimana,Taylor
, p. 105 - 115 (1997)
The condensation kinetics of 1,1,3,3,3-pentamethyldisiloxanol (MDH) in n-heptane solution were compared for two types of phosphonitrilic catalyst, hexachloro-1 λ-diphosphaza-1-enium hexachloroantimonate salt, [Cl3PNPCl3]+[SbCl6]-, 1, and P-trichloro-N- dichlorophosphoryle phosphazene, [Cl3PNP(O)Cl2], 2. The kinetic law of reaction is not changed when 1 is replaced by 2. The process is selective leading to linear decamethyltetrasiloxane (MD2M, where D denotes the dimethylsiloxane unit, and M denotes the trimethylsiloxane unit) as almost the exclusive primary product. Other oligomers of the MDnM series are formed as a result of the MD2M rearrangement. The MD2M rearrangement was studied in separate experiments in the absence of the siloxanol and water. Both catalysts 1 and 2 gave similar rate-concentration behaviour. Some of the kinetic features of the process resemble those of chain reactions and mechanisms of the MDH condensation, and the MD2M rearrangement are discussed.
Condensation of model linear siloxane oligomers possessing silanol and silyl chloride end groups. The mechanism of silanol silylation by a chlorosilane in the presence of neutral nucleophiles
Rubinsztajn, S.,Cypryc, M.,Chojnowski, J.
, p. 27 - 38 (1989)
The condensation of pentamethyldisiloxane-1-ol (1) with 1-chloro-1-isopropyltetramethyldisiloxane (2) in methylene chloride solution has been studied as model of the polyheterocondensation of functional oligosiloxanes.The process catalysed by triethylamine, hexamethylphosphoroamide (HMPA) or some nitrogen heterocycles showed a high selectivity towards heterocondensation.Triethylamine promotes the reaction by acting as the base bonding to the incipient proton on the silanol group entering into the condensation.This mechnism of the catalysis by Et3N was demostrated by kinetic studies involving use of gas-liquid chromatography in conjunction with study of the hydrogen bonding by IR spectroscopy.In contrast, the kinetic data and the reactivity pattern indicate that N-heterocycles and HMPA catalyse the reaction by fuctioning as nucleophiles to form a transient complex with the chloride substrate.A mixture containing a highly nucleophilic N-heterocycle, triethylamine has no effect on the rate of the reaction, acting only as a HCl acceptor.
Silylating Disulfides and Thiols with Hydrosilicones Catalyzed by B(C6F5)3
Brook, Michael A.,Liao, Mengchen,Zheng, Sijia
supporting information, p. 2694 - 2700 (2021/06/25)
Hydrosilanes and silicones, catalyzed with B(C6F5)3, may be used to silylate thiols or cleave disulfides giving silyl thio ethers. Alcohols were found to react faster than thiols or disulfides, while alkoxysilanes (the Piers-Rubinsztajn reaction) were slower such that the overall order of reactivity was found to be HO>HS>SS>SiOEt. The resulting silane and silicone-protected thio ethers produced from the sulfur-based functional groups could be cleaved to thiols using alcohols or mild acid with rates that depend on the steric bulk of the siloxane.
One-Step Synthesis of Siloxanes from the Direct Process Disilane Residue
Neumeyer, Felix,Auner, Norbert
supporting information, p. 17165 - 17168 (2016/11/23)
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.
(Me3N)Mo(CO)5-catalyzed reduction of DMF by disiloxane and disilane moieties: Fate of the silicon-containing fragments
Sharma, Hemant K.,Arias-Ugarte, Renzo,Tomlinson, David,Gappa, Rie,Metta-Magana, Alejandro J.,Ito, Haruhiko,Pannell, Keith H.
, p. 3788 - 3794 (2013/08/23)
The use of HSiMe2OSiMe2H (1) and various hydrodisilanes, R3SiSiMe2H (2; R = alkyl, aryl), as reductants for N,N-dimethylformamide (DMF) in the presence of (Me 3N)Mo(CO)5 as a catalyst led to the formation of a series of novel and structurally interesting siloxanes as well as trimethylamine. In the case of 1 the cyclic poly(dimethylsiloxanes) D4 and D6 are obtained, and for 2 the products are bis(disilyl) ethers, (R 3SiSiMe2)2O. Siloxymethylamine intermediates resulting from an initial hydrosilylation of DMF, (Me2NCH 2OSiMe2)2O (3) and R3SiSiMe 2OCH2NMe2 (4; R = Me, Ph), from the reactions of 1 and 2, respectively, can be observed and, in the case of 3, isolated and purified. In the presence of the respective starting silanes and the catalyst the intermediates readily react to form the appropriate siloxane materials and trimethylamine. Compound 3 was functionalized by reaction with R3ECl (E = Si, Ge, R = Me, Ph) to provide group 14 containing products (R 3EOSiMe2)2O (R = Me, E = Si (5a), Ge (6a); R = Ph, E = Si (5b), Ge (6b)). Reactions of Me3SiSiMe2OCH 2NMe2 (4a) with R3ECl produced Me 3SiSiMe2OER3 (R = Me, E = Si (7), R = Ph, E = Ge, 8). The crystal structure of (Ph3SiSiMe2)2O (9c) is reported and exhibits an Si-O-Si angle of 165 and the longest Si-Si bond length (2.376(2) A) for such bis(disilyl) ethers. The new (Ph 3EOSiMe2)2O derivatives 5b and 6b have been structurally characterized and exhibit distinct conformations about the central SiOSi fragment. In the case of the Ph3Si compound 5b the dihedral angle between the two end groups is 180 with completely staggered SiMe groups on the central Si atoms, whereas for the Ge congener it is 55.7 and the structure exhibits eclipsed SiMe groups. The distinction seems to be due to both intra- and intermolecular phenyl group π stacking in 6b stabilizing this formally higher energy conformation.
Monosodiumoxyorganoalkoxysilanes: Synthesis and properties
Rebrov,Muzafarov
, p. 514 - 541 (2007/10/03)
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.
Reaction of organylchlorosilanes with dimethyl sulfoxide in the presence of octamethyltrisiloxane
Basenko,Gebel',Boyarkina,Voronkov
, p. 882 - 884 (2007/10/03)
Dichloro(methyl)(vinyl)silane reacts with DMSO in the presence of octamethyltrisiloxane to form cyclooligomethyl(vinyl)siloxanes(MeViSiO) n (n = 3-6). The reaction involves disproportionation of octamethyltrisiloxane into hexamethyldisiloxane and decamethyltetrasiloxane. Along with the latter two products, insertion products of methyl vinyl silanone into both permethyloligosiloxanes were identified. Alkyltrichlorosilanes RSiCl3 (R = Me, Et) react with DMSO in the presence of octamethyltrisiloxane to form cyclic oligoalkyltrichlorosiloxanes (RClSiO) m (m = 3-6).
Polycondensation and disproportionation of an oligosiloxanol in the presence of a superbase
Grzelka, Agnieszka,Chojnowski, Julian,Cypryk, Marek,Fortuniak, Witold,Hupfield, Peter C.,Taylor, Richard G.
, p. 14 - 26 (2007/10/03)
Kinetics of reactions of model oligosiloxanols, 1,1,3,3,3-pentamethyldisiloxane-1-ol (MDH) and 1,1,3,3,5,5,5-heptamethyltrisiloxane-1-ol (MD2H), which occur in the presence of phosphazenium superbase, hexapyrrolidine-diphosphazenium hydroxide, in an acid-base inert solvent, toluene, was studied using sampling and gas chromatographic analysis method. In addition, kinetics of reactions of MDH and MD2H with trimethylsilanol (MH) was studied. In the MDH and MD2H systems the oligosiloxanol condensation competes with the oligosiloxanol disproportionation, the latter being the dominating process. The disproportionation products, i.e. MDn+1H and MDn-1H, n=1, 2, ? undergo analogous consecutive disproportionation and condensation reactions. The kinetic law was derived and rate parameters determined from initial rates and by computer simulation to the best agreement with experimental data. Both competing reactions, the disproportionation and the condensation, conform to the same general kinetic law being first internal order in substrate and first order in catalyst. Activation parameters of these reactions were determined. The results were interpreted in terms of a bimolecular mechanism in which nucleophilic attack of the silanolate anion directed to silicon of the silanol group causes the cleavage of one of its geminal bonds to oxygen, either the one to hydroxyl leading to condensation or the one to siloxane which leads to disproportionation. The latter is faster as the silanolate is a better leaving group compared with OH-. Moreover, in the pentacoordinate silicon transition state (or intermediate) the siloxane substituent preferentially enters the apical position, thus driving the OH substituent into the unreactive equatorial position.