- One-Step Synthesis of Siloxanes from the Direct Process Disilane Residue
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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
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supporting information
p. 17165 - 17168
(2016/11/23)
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- Monosodiumoxyorganoalkoxysilanes: Synthesis and properties
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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
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p. 514 - 541
(2007/10/03)
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- PROCESS FOR STABILIZATION OF SILOXANE COMPOUNDS
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A method for stabilizing silicone dry cleaning solvents containing impurities, comprising contacting the silicone solvent with an adsorbent, neutralizing agent or combination thereof to purify the solvent and prevent reequilibration and polymerization, and separating the silicone solvent.
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- Kinetics and mechanism of the reaction between oligosiloxanes and P-trichloro-N-dichlorophosphoryl monophosphazene (Cl3P=N-POCl2)
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31P NMR investigation has been made of the action of Cl3P=N-POCl2 (I) first on hexamethyldisiloxane (Me3Si)2O and then on oligosiloxanes Me3Si-(OSiMe2)n-OSiMe3 n = 2 and n=3. The reactions were carried out in bulk or in solution with molar ratios siloxane/(I) varying from 1 to 5. It was demonstrated that only the monosubstitution of a chlorine atom by the -(OSiMe2)n-OSiMe3 species n = 0, 2, 3 with elimination of trimethylchlorosilane occurred leading to the derivatives Cl2OP-N=PCl2O-(SiMe2-O)nSiMe 3 (II). For n=2, 3 the siloxane redistribution reactions were observed by 29Si NMR analysis. A two steps mechanism is proposed, consisting in a nucleophilic substitution, involving a tricoordinate phosphazenium intermediate, followed by the formation of an active ionic centre probably an oxonium ion, arising from the solvatation by the siloxane of this phosphazenium ion and /or of (II) leading to the redistribution reactions. The influences of the solvent, of trimethylchlorosilane, of the temperature, and of the addition of a protonated species (MDH) were investigated.
- Meliani, Abdeslam,Vaugeois, Yann,Bali, Hamza,Mazzah, Ahmed,De Jaeger, Roger,Habimana, Jean
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p. 283 - 301
(2007/10/03)
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- FEATURES OF INFLUENCE OF HCl ON HYDROLYTIC COPOLYCONDENSATION OF BIFUNCTIONAL ORGANOCHLOROSILANES WITH TRIMETHYLCHLOROSILANE
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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.
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p. 1257 - 1261
(2007/10/02)
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- Siloxane basicity toward strong acid in nonpolar solution
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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.
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p. 5581 - 5583
(2007/10/02)
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