- Cyclic phosphonitrilic compounds bearing -N=PCL3 group as homogenous catalyst towards the silanol condensation
-
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.
- Vaugeois, Yann,Mazzah, Ahmed,De Jaeger, Roger,Habimana, Jean
-
-
Read Online
- Kinetics and mechanism of oligosiloxanol condensation and oligosiloxane rearrangement catalysed with model phosphonitrile chloride catalysts
-
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.
- Chojnowski,Fortuniak,Habimana,Taylor
-
-
Read Online
- 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
-
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.
- Rubinsztajn, S.,Cypryc, M.,Chojnowski, J.
-
-
Read Online
- Silylating Disulfides and Thiols with Hydrosilicones Catalyzed by B(C6F5)3
-
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.
- Brook, Michael A.,Liao, Mengchen,Zheng, Sijia
-
supporting information
p. 2694 - 2700
(2021/06/25)
-
- 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)
-
- (Me3N)Mo(CO)5-catalyzed reduction of DMF by disiloxane and disilane moieties: Fate of the silicon-containing fragments
-
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.
- 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)
-
- 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)
-
- Reaction of organylchlorosilanes with dimethyl sulfoxide in the presence of octamethyltrisiloxane
-
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).
- Basenko,Gebel',Boyarkina,Voronkov
-
p. 882 - 884
(2007/10/03)
-
- Polycondensation and disproportionation of an oligosiloxanol in the presence of a superbase
-
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.
- Grzelka, Agnieszka,Chojnowski, Julian,Cypryk, Marek,Fortuniak, Witold,Hupfield, Peter C.,Taylor, Richard G.
-
-
- Siloxanes as sources of silanones
-
Pyrolysis of hexamethyldisiloxane (HMDS) and its copyrolysis with chlorotrimethylsilane and tetrachlorosilane were studied. Based on the data of GLC analysis and on the mass spectrum of the condensate obtained after the pyrolysis of HMDS, it was concluded that HMDS acts as a source of dimethylsilanone. The results of the copyrolysis of HMDS with chlorotrimethylsilane used as a trapping reagent indicate that the dimethylsilanone generated from HMDS can be inserted into the Si-Cl and Si-O bonds. In the copyrolysis of HMDS with tetrachlorosilane serving as a trapping reagent for dimethylsilanone, both dimethylsilanone and dichlorosilanone are generated.
- Chernyshev,Krasnova,Sergeev,Abramova
-
p. 1586 - 1589
(2007/10/03)
-
- Interactions of hexachlorodiphosphazenium ion with an alcohol and with some silicon-oxygen reagents and their role in the catalysis of polycondensation in silanol-alkoxysilane systems
-
Condensation reactions of trimethylethoxysilane (MOEt) and pentamethyldisiloxanol in n-heptane catalysed by hexachloro-1λ-diphosphaza-1-enium salts were studied. Although the substrate conversion vs. time dependences point to domination by heterofunctional condensation, the process is more complex. Homofunctional condensation as well as fast consecutive hydrolysis and ethanolysis strongly contribute to the overall process. Results of kinetic studies point to inhibition of these component reactions by an excess of MOEt. Interactions of the hexachloro-1λ-diphosphaza-1-enium salts with MOEt, ethanol and silanol were studied by 31P NMR. It was demonstrated that a fast substitution reaction of chloride by ethoxy group takes place when ethanol or ethoxysilane is introduced into solutions of hexachlorodiphosphazenium salts. This process is responsible for the decrease in condensation activity of the catalyst.
- Chojnowski, Julian,Cypryk, Marek,Fortuniak, Witold,Kazmierski, Krzysztof,Taylor, Richard G.
-
p. 351 - 361
(2007/10/03)
-
- FEATURES OF INFLUENCE OF HCl ON HYDROLYTIC COPOLYCONDENSATION OF BIFUNCTIONAL ORGANOCHLOROSILANES WITH TRIMETHYLCHLOROSILANE
-
The hydrogen chloride that is formed in the hydrolytic copolycondensation of R'RSiCl2 with Me3SiCl affects the composition of the reaction products only at cocentrations above 30-35percent, where it is responsible for splitting out the terminal trimethylsiloxy group.The stability of the terminal groups increases with increasing size of the substituents on the silicon atom in the R'RSiCl2.The total yield of Me3SiO(R'RSiO)mSiMe3 with m = 1-4 also increases with increasing size of the substituents on the silicon atom in the R'RSiCl2.The total yield of p with p = 3-5 increases with decreasing tendency of the R'RSiCl2 to form rings by hydrolytic polycondensation, and with increasing sensitivity of the terminal trimethylsiloxy group in the cocondensation products to the action of HCl and its activity with respect to the siloxane bond.
- Kopylov, V. M.,Agashkov, S. P.,Sunkovich, G. V.,Prikhod'ko, P. L.
-
p. 1257 - 1261
(2007/10/02)
-
- MUTUAL EFFECT OF SOLUTIONS OF SALTS AND HCl ON COHYDROLYSIS OF METHYLCHLOROSILANES
-
In hydrolytic polycondensation of Me2SiCl2, the combined effect of salts and HCl causes a decrease in the yield of 4, and this effect increases with an increase in the binding strength of the water with the salt in hydrate complexes and the concentration of HCl.The combined effect of salts and HCl on the composition of the products of the reaction in hydrolytic copolycondensation of Me2SiCl2 with Me3SiCl and MeSiCl3 with Me3SiCl increases with an increase in the degree of binding of water in hydrate complexes, caused by competition in the formation of hydrate complexes between the salt and HCl.
- Kopylov, V. M.,Agashkov, S. P.,Sunkovich, G. V.,Prikhod'ko, P. L.
-
p. 692 - 697
(2007/10/02)
-
- Siloxane basicity toward strong acid in nonpolar solution
-
The relative basicities of ten siloxanes and an ether were studied in benzene by determining from visible spectroscopic measurements the thermodynamic constants for the competition between the substrate and a reference base (4-chloro-2-nitroaniline) for acid (trifluoromethanesulfonic acid): RB-HA + S ? RB + S·HA. The Keq values were considered as a measure of basicity with the following order established and explained by inductive effects in the protonated species: permethyl linear siloxanes (Me3Si(OSiMe2)nOSiMe3, n = 0-3) > dibutyl ether > HMe2SiOSiMe2H > branched siloxanes ((Me3SiO)3SiMe, (Me3SiO)4Si) > cyclic siloxanes ((Me2SiO)n, n = 3-5). The ΔH and ΔS values were positive and increased with higher basicity; this behavior was attributed to differential solvation of ion pairs.
- Shepherd, Brian D.
-
p. 5581 - 5583
(2007/10/02)
-
- Cleavage of poly(diorganosiloxanes) by trimethyialuminum
-
The interaction of AlMe3 at elevated temperatures with poly(diorganosiloxanes), (RMeSiO)x (R = Me, n-C18H37, -CH2CH2CF3, Ph), leads to rupture of the silicon-oxygen framework and yields the dimeric aluminum siloxides [Me2Al(OSiMe2R)]2. The molecular structure of [Me2Al(OSiMe2Ph)]2 has been confirmed by X-ray crystallography. The compound [Me2Al(OSiMe2Ph)]2 crystallizes in the monoclinic space group P21/n with unit cell dimensions a = 7.970 (3) ?, b = 24.563 (10) ?, c = 13.322 (4) ?, β= 105 05 (3)° Z = 4, 2754 observed data, R = 0.0478, and Rw = 0.0639. At ambient temperatures the cyclic trisiloxane (Me2SiO)3 forms a highly fluxional 1:1 Lewis acid-base adduct with AlMe3.
- Apblett, Allen W.,Barron, Andrew R.
-
p. 2137 - 2141
(2008/10/08)
-
- Reaction of O(3P) with Hexamethyldisilane
-
The title reaction has been investigated at room temperature in a discharge flow system and also by stationary Hg(3P1)-sensitized N2O photolysis experiments.By far the most important reaction is the insertion of O(3P) atoms into the Si-Si bond yielding a vibrationally excited hexamethyldisiloxane.The rate constant for this reaction has been measured to be (1.3 +/- 0.3) x 10-13 cm3 s-1.The vibrationally excited hexamethyldisiloxane could not be stabilized at pressures up to 1 bar, decomposing mainly by Si-C bond cleavage.A reaction mechanism is proposed to account for the observed products.
- Hoffmeyer, H.,Potzinger, P.,Reimann, B.
-
p. 4829 - 4831
(2007/10/02)
-
- OXIDATION OF n-DECAMETHYLTETRASILANE WITH PEROXYBENZOIC ACID
-
It is shown, that the first stage of the reaction of n-decamethyltetrasilane with peroxybenzoic acid is oxidation of one of the two terminal Si-Si bonds, rather than oxidation of a central Si-Si bond.
- Razuvaev, G. A.,Semenov, V. V.,Brevnova, T. N.,Kornev, A. N.
-
p. C31 - C33
(2007/10/02)
-
- METAL COMPLEX-CATALYZED REDISTRIBUTION REACTIONS OF ORGANOSILANES. IV. REDISTRIBUTION REACTIONS OF METHYLSILOXANES CATALYZED BY TRANSITION METAL COMPLEXES
-
Redistribution reactions of a variety of hydrogen-substituted siloxanes are catalyzed by various transition metal complexes of iridium and rhodium.The products arise from breaking and remaking of Si-C, Si-H, and Si-O bonds.Siloxanes not possessing a Si-H bond are inert under the conditions studied.The most favored reaction pathway appears to scramble preferentially the groups directly attached to the silicon bearing the hydrogen atom.A new cyclo-iridiadisiloxane, (L = Ph3P; R = Me3SiO) is reported.This compound exists in three isomeric forms as a consequence of the spatial arrangements of the R and Me groups on the ring.
- Gustavson, Wayne A.,Epstein, Paul S.,Curtis, M.D.
-
-