- 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)
-
- Hydrogenolysis of Polysilanes Catalyzed by Low-Valent Nickel Complexes
-
The dehydrogenation of organosilanes (RxSiH4?x) under the formation of Si?Si bonds is an intensively investigated process leading to oligo- or polysilanes. The reverse reaction is little studied. To date, the hydrogenolysis of Si?Si bonds requires very harsh conditions and is very unselective, leading to multiple side products. Herein, we describe a new catalytic hydrogenation of oligo- and polysilanes that is highly selective and proceeds under mild conditions. New low-valent nickel hydride complexes are used as catalysts and secondary silanes, RR′SiH2, are obtained as products in high purity.
- Comas-Vives, Aleix,Eiler, Frederik,Grützmacher, Hansj?rg,Pribanic, Bruno,Trincado, Monica,Vogt, Matthias
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supporting information
p. 15603 - 15609
(2020/04/29)
-
- Heterocyclization and solvent interception upon oxidative triflamidation of allyl ethers, amines and silanes
-
The reactions of triflamide with a series of mono- and diallyl heteroatomic compounds have been studied in the presence of various oxidants (t-BuOI, NBS, NIS). The reaction course was found to be strongly dependent on the oxidant leading to the products of bis(triflamidation) or heterocyclization in the system (t-BuOCl + NaI), or amidines – the Ritter-type solvent interception halosulfamidation products – with N-bromo- or N-iodosuccinimide. The amidines were converted to imidazolines in high yield via the base-induced heterocyclization.
- Ganin, Anton S.,Moskalik, Mikhail Yu.,Astakhova, Vera V.,Sterkhova, Irina V.,Shainyan, Bagrat A.
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-
- METHOD FOR PRODUCING SILOXANE OLIGOMER
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PROBLEM TO BE SOLVED: To provide a production method capable of simply producing a siloxane oligomer in a high yield when producing a siloxane oligomer by hydrolysis of a silicon halide compound and to provide a production method capable of selectively producing a linear or cyclic siloxane oligomer in particular. SOLUTION: The siloxane oligomer can be efficiently produced without performing any special agitation by providing two electrospray nozzles to oppose to each other in a medium liquid and in the medium liquid, electrostatically spraying in an electric field a first liquid sample containing a silicon halide compound from one nozzle and electrostatically spraying in an electric field a second liquid sample containing water from the other nozzle and allowing the liquid samples to collide and fuse with each other. SELECTED DRAWING: None COPYRIGHT: (C)2017,JPO&INPIT
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-
Paragraph 0034; 0045
(2017/07/23)
-
- Tris(pentafluorophenyl)borane-Catalyzed Reactions of Siloxanes: A Combined Experimental and Computational Study
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The reaction of 1,1,3,3-tetramethyldisiloxane with 1-octene as a model reaction of silicone curing catalyzed by B(C6F5)3 resulted in the redistribution of the disiloxane into dimethylsilane and cyclic oligosiloxanes, and the subsequent hydrosilylation reaction of dimethylsilane afforded dimethyldioctylsilane. To obtain insights into the reaction mechanism and possibility alter the reaction pathway to favor the hydrosilylation over the redistribution, mechanistic analysis of the reaction between a hydrosiloxane (1,1,3,3-tetramethyldisiloxane, silox-H) and a vinylsiloxane (1,1,3,3-tetramethyl-1,3-divinyldisiloxane, silox-vin) in the presence of B(C6F5)3 was performed through density functional theory calculations. The results of the calculations indicate that the activation of a Si–H bond in silox-H by B(C6F5)3 initiates the reaction to form the B(C6F5)3–silox-H complex with a Lewis acidic silicon atom and a hydridic hydrogen atom. The B(C6F5)3–silox-H complex can undergo two different reaction pathways, that is, trisiloxane formation and the hydrosilylation of silox-vin by silox-H. The trisiloxane formation involves trisilyloxonium ions as intermediates and can lead to either the homotrisiloxane of silox-H or a mixed trisiloxane of silox-H and silox-vin. The energetics of the reaction pathways predict the preference of trisiloxane formation over hydrosilylation, and the fine tuning of the steric and electronic natures of the substrates could alter the thermodynamic and kinetic favorability.
- Mathew, Jomon,Eguchi, Katsuya,Nakajima, Yumiko,Sato, Kazuhiko,Shimada, Shigeru,Choe, Yoong-Kee
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p. 4922 - 4927
(2017/09/13)
-
- Selective Formation of Alkoxychlorosilanes and Organotrialkoxysilane with Four Different Substituents by Intermolecular Exchange Reaction
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Alkoxychlorosilanes are scientifically and industrially important toward preparing silicone and silica as well as preparation of siloxane-based nanomaterials by stepwise reactions of Si?OR (R=alkyl) and Si?Cl groups. Intermolecular exchange of alkoxy and chloro groups between alkoxysilanes and chlorosilanes (functional group exchange reaction) provides an efficient and environmentally benign route to alkoxychlorosilanes. BiCl3 as a Lewis acid catalyst can promote the functional group exchange reactions more efficiently than conventional acid catalysts. Higher reactivity has been observed for chlorosilanes with smaller numbers of Si?CH3 groups and for alkoxysilanes with larger numbers of Si?CH3 groups. The reaction mechanism is proposed and selective syntheses of alkoxychlorosilanes are demonstrated. These findings also enable us to synthesize an organotrialkoxysilane with four different substituents.
- Komata, Yuma,Yoshikawa, Masashi,Tamura, Yasuhiro,Wada, Hiroaki,Shimojima, Atsushi,Kuroda, Kazuyuki
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p. 3225 - 3233
(2016/11/29)
-
- A dimethyl dichloro silane hydrolysate cracking method
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The invention discloses a method for splitting dimethyl dichlorosilane hydrolysate. The method comprises the following steps: carrying out load reaction onto strong-basicity macroporous anion exchange resin, potassium hydroxide, potassium trimethylsilanolate and [bmim]BF4 ionic liquid to obtain a composite catalyst after the reaction is ended; adding dimethyl dichlorosilane hydrolysate into a splitting kettle to obtain a ring-body mixture by splitting and re-arranging solvent oil, the composite catalyst and the hydrolysate; and washing with water to remove high-boiling point residues and low-boiling point residues to obtain products such as octamethylcyclotetrasiloxane D4, hexamethylcyclotrisiloxane and decamethylcyclopentasiloxane.
- -
-
Paragraph 0026; 0028
(2017/02/24)
-
- 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
-
supporting information
p. 17165 - 17168
(2016/11/23)
-
- Depolymerization of end-of-life poly(dimethylsilazane) with boron trifluoride diethyl etherate to produce difluorodimethylsilane as useful commodity
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A straightforward protocol for the depolymerization of end-of-life poly(dimethylsilazane) using boron trifluoride diethyl etherate as depolymerization reagent to convert the Si-N to Si-F bonds was set-up. The application of the depolymerization reagent affords difluorodimethylsilane as major products, which can be a suitable synthon for the synthesis of new polymers (e.g., poly(dimethylsiloxanes) and allow an overall recycling of the [Me2Si]-unit.
- D?hlert, Peter,Pfrommer, Johannes,Enthaler, Stephan
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p. 1189 - 1193
(2016/08/31)
-
- Method for preparing hybrid cyclo-boron siloxane
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The invention relates to the field of chemistry and chemical engineering, provides a cheap and efficient cyclo-boron siloxane intermediate in order to prepare high-performance boracic polysiloxane, and particularly provides a method for preparing hybrid cyclo-boron siloxane. Under inert gas shielding, a mixture of alkyl boric acid and an organic solvent A is dropwise added to dialkyl dichloro-slane, stirring and reacting are carried out for 3 h to 8 h at the temperature of -20 DEG C to 80 DEG C, then the mixture is added into a mixture of an organic solvent B and metallic oxide, filtering and washing are carried out after reacting is carried out for 6 h to 18 h, the organic solvent A and the organic solvent B are evaporated out, and hybrid cyclo-boron siloxane is obtained. The method has the advantages that the raw materials can be obtained easily, and cost is low, and the compound can be used for synthesizing boron-silicon rubber, a heat-resisting adhesive, a heat-resisting coating and other boracic polysiloxane products, and can be widely applied to aerospace, electronics, chemical engineering, machinery and other industries.
- -
-
Paragraph 0032; 0033; 0034; 0035; 0036; 0037; 0038
(2016/10/10)
-
- Platinum-catalyzed reduction of DMF by 1,1,3,3-tetramethyldisiloxane, HMeSi2OSiMe2H: New intermediates HSiMe 2OSiMe2OCH2NMe2 and HSiMe 2(OSiMe2)3OCH2
-
The use of Karstedt's catalyst to study the reduction of Me2NCHO (DMF) by the popular "dual SiH"-containing tetramethyldisiloxane, HMe2SiOSiMe2H (1), has revealed that the first step in the process involves an initial sing
- Martinez, Jorge L.,Sharma, Hemant K.,Arias-Ugarte, Renzo,Pannell, Keith H.
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supporting information
p. 2964 - 2967
(2014/07/08)
-
- (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.
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p. 3788 - 3794
(2013/08/23)
-
- Silicone-Organic Hybrid Emulsions In Personal Care Applications
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Personal care compositions containing silicone polymer and organic polymer containing alloy and/or hybrid emulsions are disclosed. The silicone organic hybrid emulsions are particularly useful in hair care formulations to simultaneously provide conditioning and styling benefits. The silicone organic hybrid emulsions are also useful in color cosmetic formulations to provide shine and wash-off resistance benefits.
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- Silanones and silanethiones from the reactions of transient silylenes with oxiranes and thiiranes in solution. The direct detection of diphenylsilanethione
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The transient silylenes SiMe2 and SiPh2 react with cyclohexene oxide (CHO), propylene oxide (PrO), and propylene sulfide (PrS) in hydrocarbon solvents to form products consistent with the formation of the corresponding transient silanones and silanethiones, respectively. Laser flash photolysis studies show that these reactions proceed via multistep sequences involving the intermediacy of the corresponding silylene-oxirane or -thiirane complexes, which are formed with rate constants close to the diffusion limit in all cases and exhibit UV absorption spectra similar to those of the corresponding complexes with the nonreactive O- and S-donors, tetrahydrofuran and tetrahydrothiophene. The SiMe2-PrO and SiPh2-PrO complexes both exhibit lifetimes of ca. 300 ns, and are longer-lived than the corresponding complexes with CHO, which are both in the range of 230-240 ns. On the other hand, the silylene-PrS complexes are considerably shorter-lived and vary with silyl substituent; the SiMe2-PrS complex decays with the excitation laser pulse (i.e., τ ≥ 25 ns), while the SiPh2-PrS complex exhibits τ = 48 ± 3 ns. The decay of the SiPh2-PrS complex affords a long-lived transient product exhibiting λ max ≈ 275 nm, which has been assigned to diphenylsilanethione (Ph2Si=S) on the basis of its second order decay kinetics and absolute rate constants for reaction with methanol, tert-butanol, acetic acid, and n-butyl amine, for which values in the range of 1.4 × 108 to 3.2 × 109 M-1 s-1 are reported. The experimental rate constants for decay of the SiMe2-epoxide and -PrS complexes indicate free energy barriers (ΔG?) of ca. 8.5 and ≥7.1 kcal mol-1 for the rate-determining steps leading to dimethylsilanone and -silanethione, respectively, which are compared to the results of DFT (B3LYP/6-311+G(d,p)) calculations of the reactions of SiH 2 and SiMe2 with oxirane and thiirane. The calculations predict a stepwise C-O cleavage mechanism involving singlet biradical intermediates for the silylene-oxirane complexes, and a concerted mechanism for silanethione formation from the silylene-thiirane complexes, in agreement with earlier ab initio studies of the SiH2-oxirane and -thiirane systems.
- Kostina, Svetlana S.,Leigh, William J.
-
supporting information; experimental part
p. 4377 - 4388
(2011/06/11)
-
- Effect of catalyst structure on the reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane
-
Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place. In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that leads to formation of long chain linear and cyclic siloxanes of general formula HMe2Si(OSiMe2) n H and (-OSiMe2-)m (n = 2-6, m = 3-7), respectively. Platinum catalysts promotes formation of linear siloxanes, while both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate metallocomplexes is studied.
- De Vekki,Skvortsov
-
body text
p. 762 - 777
(2009/09/26)
-
- SYNTHESIS OF CATIONIC SILOXANE PREPOLYMERS
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This application is directed toward an improved method of synthesizing cationic siloxane prepolymers as well as a specific cationic siloxane prepolymer having improved compatibility with monofunctional siloxanyl methacrylate monomers and medical devices containing the cationic siloxane prepolymer.
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- METHOD FOR THE PRODUCTION OF CYCLIC POLYSILOXANES
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A process for producing cyclic polysiloxanes is disclosed. The first step of the process comprises combining a poiysiloxane, a cafaiyst and a high boiling endblocker, wherein the catalyst is selected from the group consisting of a phosphazene base and a carborane acid. The second step of the process comprises heating said poiysiloxane, catalyst and high boiling endblocker, and the third step of the process comprising recovering the cyclic poiysiloxane,
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Page/Page column 19-21
(2009/01/23)
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- Phototransformation of perchlorate to chloride in the presence of polysilanes
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Perchlorate is a uniquely stable chemical described as an emerging thyroid disrupting agent that is presently detected in several terrestrial and aquatic matrices. The present study was undertaken to deoxygenate perchlorate to the chloride anion photolytically in the presence of dodecamethylcyclohexasilane (Me2Si)6 1. It is found that photolysis of 1 in the presence of dry NaClO4 in tetrahydrofuran (THF) at 254 nm leads to the disappearance of the salt. The removal of ClO4? occurred with the concurrent formation of ClO3? and ClO2?, which disappear to eventually produce the chloride anion quantitatively. The two cyclic silanes (Me2Si)5 3 and (Me2Si)4 4 in addition to several other siloxanes that include (Me2SiO)3, (Me2SiO)4, and (Me2Si)xO2 (x ≤ 4 and 5) were also detected. When the reaction was repeated using uniformly labelled 18O- [ClO4?] it was found that oxygen incorporated in the siloxane products was derived from perchlorate. Mixing 1 with perchlorate in THF in the dark or adding the salt to 1 after the latter being photolyzed in THF did not deoxygenate ClO4?. Based on experimental evidence gathered thus far it is concluded that dimethylsilylene, Me2Si: 2, a reactive intermediate produced by the photolysis of 1, is in part responsible for the deoxygenation of perchlorate. Direct oxygen transfer from ClO 4? to the silanes during photolysis is also suggested as a potential route of deoxygenating ClO4?. CSIRO 2007.
- Lazar, Carmen,Halasz, Annamaria,Beaulieu, Chantale,Thiboutot, Sonia,Ampleman, Guy,Hawari, Jalal
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p. 857 - 861
(2008/09/19)
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- Novel direct process
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The invention relates to continuous processes for making cyclic dimethylsiloxane oligomers by reacting in situ methyl bromide, dimethyl ether and activated silicon particles in a direct process reaction zone to produce methylsiloxanes, wherein the proportion of dimethylsiloxane produced in said reaction zone is greater than 75 mole % of the methylsiloxanes produced and recovering the dimethylsiloxane from the reactions zone. The invention favors making cyclic dimethylsiloxane oligomers by this in situ direct reaction.
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Page/Page column 19-20
(2008/06/13)
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- SILICONE CONDENSATION REACTION
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A new silicone condensation reaction, the condensation between an alkoxy silane or siloxane or a dihydric phenol and an organo-hydrosilane or siloxane and catalysts therefore is described and claimed.
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Page/Page column 20-21
(2010/10/20)
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- REACTIVE DISTILLATION OF CHLOROSILANES
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Chlorosilanes such as dimethyldichlorosilane are hydrolyzed in a first super-azeotropic hydrochloric acid distillation column A to produce cyclosiloxanes, chlorosiloxanes, and hydrogen chloride gas. The cyclosiloxanes and the chlorosiloxanes are washed and separated according to their volatility in a second sub-azeotropic hydrochloric acid distillation column B, to produce a substantially chloride free volatile cyclosiloxane stream and a substantially chloride free non- volatile siloxane stream. The process is substantially chloride efficient.
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Page/Page column 7-8
(2008/06/13)
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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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- A facile and efficient synthesis of organocyclosiloxanes
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A new facile preparative method for the synthesis of organocyclosiloxanes is reported. Ring closure of the dichlorosilanes with NaHCO3 and pyridine gave mixture of organocyclosiloxanes with cyclotrisiloxane as a main product.
- Zuev, Vjacheslav V.,Kalinin, Alexei V.
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p. 1289 - 1294
(2007/10/03)
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- Anionic and cationic ring-opening polymerization of 2,2,4,4,6,6-hexamethyl-8,8-divinylcyclotetrasiloxane
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Ring-opening polymerization (ROP) of 2,2,4,4,6,6-hexamethyl-8,8-divinylcyclotetrasiloxane (I) initiated by both l-fert-butyl-4,4,4-tris(dimetnylamino)-2,2-bis[tris(dimethylamino)phosphoran-yli denamino]-2λ5,4λ5-catenadi(phosphazene) (C22H63N13P4, P4-t-Bu Superbase) and trifluoromethanesulfonic acid (CF3SO3H, triflic acid) has been studied. Both reactions lead to mixtures of linear copolymer, low molecular weight co-oligomers and monomeric cyclosiloxanes. The composition, molecular weight distribution, microstructure, and thermal properties of the copolymers have been determined. The copolymer microstructure has been determined by 29Si NMR spectroscopy. Monomeric cyclosiloxanes have been identified by GC/MS. Both copolymer microstructure and cyclosiloxanes formed depend on the particular catalyst system utilized. P4-t-Bu superbase-initiated anionic ROP of I leads to a copolymer with a random microstructure and to a series of monomeric cyclotetra-, cyclopenta-, and cyclohexasiloxanes formed by random combination of dimethylsiloxane (D) and divinylsiloxane (V) units. On the other hand, triflic acid-initiated ROP of I occurs in a chemoselective manner. This leads to a copolymer with a more ordered microstructure. In this case, I is the only monomeric cyclosiloxane found.
- Teng, Conan J.,Weber, William P.,Cai, Guoping
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p. 5126 - 5130
(2007/10/03)
-
- Reaction of the dioxane complex of dichlorogermylene with siloxanes
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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-o
- Shcherbinin,Pushkina,Krivolapova,Bykovchenko,Khromykh,Komalenkova,Chernyshev
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p. 1907 - 1910
(2007/10/03)
-
- New route to permethylcyclosiloxanes
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A new method for preparing permethylcyclosiloxanes, based on reaction of 1,1,3,3-tetramethyldisiloxane with iodine (molar ratio 1:1) in inert organic solvents (alkanes, alkyl halides, benzene) is proposed. The products of the reaction react with ethoxytrimethylsilane and tetramethoxysilane in hexamethyldisiloxane to give respectively pentamethyldisiloxane and products of successive substitution of the methoxy groups in Si(OMe)4 by Me2SiHO. A probable scheme of their formation is discussed.
- Basenko,Klyba,Voronkov
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p. 1368 - 1370
(2007/10/03)
-
- FTIR study of thermally induced transformations of trimethylsilylmethyl acetate in the temperature range 623-813 K
-
The chemistry of trimethylsilylmethyl acetate in the gas phase in the temperature range 623-813 K has been investigated under static conditions using Fourier transform IR spectroscopy. Little change occurs at temperatures lower than 623 K, at which temperature a thermally induced isomerization to form ethyldimethylsilyl acetate occurs. Some ethanoic acid is also produced at this temperature. The ethyldimethylsilyl acetate produced undergoes thermolysis at temperatures > 723 K giving methane, ethene, carbon monoxide, carbon dioxide, ethanoic acid, 1,3-diethyl-1,1,3,3-tetramethyldisiloxane, cyclohexamethyltrisiloxane, and cyclooctamethyltetrasiloxane as products. Loss of ethyldimethylsilyl acetate is first order over the whole temperature range, and first-order rate constants vary from 4.87 × 10-5 s-1 at 723 K to 33.5 × 10-5 s-1 at 813 K, respectively, leading to an activation energy, Ea,, of 110(4) kJ mol-1. An intramolecular five-centre process is proposed for the isomerization reaction. The thermolysis is interpreted in terms of principally radical reactions involving initial homolytic dissociation of the EtMe2SiO-C(O)CH3 bond.
- Ball, Ian K.,Harrison, Philip G.,Torr, Ashley
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p. 185 - 194
(2007/10/03)
-
- Electrochemical oxygenation of diorganyldichlorosilanes: A novel route to generation of diorganylsilanones
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Interaction of diorganyldichlorosilanes R2SiCl2 (R = Me, Et, Ph) with superoxide or peroxide anions, produced in situ by electroreduction of molecular oxygen, provides short-living diorganylsilanones R2Si=O. The latter undergo cyclization to give lower perorganylcyclosiloxanes (R2SiO)n, n = 3 or 4 and then insert to the molecules of these primary products to form higher cyclic oligomers. When the process is carried out in the presence of a reagent-trap for silanones (hexamethyldisiloxane, hexamethylcyclotrisiloxane), the products of insertion of diorganylsilanones into the molecule-traps (Me3Si(OSiR2)nOSiMe3 with n ≥ 1, and (Me2SiO)3(R2SiO)m with m ≥ 1, respectively) were obtained.
- Fattakhova,Jouikov,Voronkov
-
p. 170 - 176
(2007/10/03)
-
- Synthesis of 14C-labeled cyclic and linear siloxanes
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Simple procedures to synthesize a variety of 14C-labeled monomeric and polymeric siloxanes are described. Specifically, the synthesis of the following siloxanes, some of which are of significant commercial importance are provided: 14C-octamethylcyclotetrasiloxane (D4), 14C-decamethylcyclopentasiloxane (D5), 14C-hexamethyldisiloxane (MM), 14C-dimethyldimethoxysilane and 14C-dimethylsilanediol (DMSD) are examples of discrete monomeric species. 14C-350 and 1000 cSt polydimethylsiloxanes (PDMS) are examples of polymeric species. Synthesis of the monomeric species with the exception of dimethylsilanediol involve reactions of Grignard reagents with the appropriate chlorosilanes, while the polymeric materials were synthesized via acid catalyzed equilibration reaction of 14C-D4 with dodecamethylpentasiloxane (MD3M). The compound 14C-DMSD was obtained by the hydrolysis of 14C-dimethyldimethoxysilane. The labeled materials listed here were synthesized for their utility as tracers in several of the ongoing environmental fate and effects studies as well as toxicological investigations.
- Varaprath, Sudarsanan
-
-
- Siloxanes as sources of silanones
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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
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p. 1586 - 1589
(2007/10/03)
-
- The hydroxyl radical reaction rate constants and atmospheric reaction products of three siloxanes
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The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of hexamethyldisiloxane (MM, (CH3)3Si-O-Si(CH3)3), octamethyltrisiloxane (MDM, (CH3)3Si-O-Si(CH3)2-O-Si(CH 3)3), and decamethyltetrasiloxane (MD2M, (CH3)3Si-O-Si(CH3)2-O-Si(CH 3)2-O-Si(CH3)3). Hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane react with OH with bimolecular rate constants of 1.32 ± 0.05 × 10-12 cm3molecule-1s-1, 1.83 ± 0.09 × 10-12 cm3 molecule-1, and 2.66 ±0.13 × 10-12 cm3molecule-1s-1, respectively. Investigation of the OH + siloxane reaction products yielded trimethylsilanol, pentamethyldisiloxanol, heptamethyltetrasiloxanol, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and other compounds. Several of these products have not been reported before because these siloxanes and the proposed reaction mechanisms yielding these products are complicated. Some unusual cyclic siloxane products were observed and their formation pathways are discussed in light of current understanding of siloxane atmospheric chemistry.
- Markgraf, Stewart J.,Wells
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p. 445 - 451
(2007/10/03)
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- Hydrolysis of oligodimethylsiloxane-α,ω-diols and the position of hydrolytic equilibrium
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The hydrolysis of tetramethyldisiloxane-1,3-diol and hexamethyltrisiloxane-1,5-diol in aqueous solutions has been studied. The position of equilibrium of the system including these compounds, dimethylsilanediol, and water has been determined. Concentrations of these compounds in dilute aqueous solutions were determined by coupling HPLC to ICP analysis for Si and also by extraction into ethyl acetate followed by triethylsilylation and GC analysis. It was found that the siloxanediols hydrolyze to the equilibrium mixture at environmentally significant rates and that dimethylsilanediol dominates the equilibrium in dilute aqueous solution, even at concentrations orders of magnitude above that expected in the environment. The hydrolysis of tetramethyldisiloxane-1,3-diol in water was found to be first order in [H+] and in [phosphate buffer] by studying the rates at pH 3 and 6. The hydrolysis of a mixture of higher oligodimethylsiloxane-α,ω-diols as a suspension in water is also described. The first observation of dimethylsilanediol in an environmental sample is reported. The hydrolysis of tetramethyldisiloxane-1,3-diol and hexamethyltrisiloxane-1,5-diol in aqueous solutions has been studied. The position of equilibrium of the system including these compounds, dimethylsilanediol, and water has been determined. Concentrations of these compounds in dilute aqueous solutions were determined by coupling HPLC to ICP analysis for Si and also by extraction into ethyl acetate followed by triethylsilylation and GC analysis. It was found that the siloxanediols hydrolyze to the equilibrium mixture at environmentally significant rates and that dimethylsilanediol dominates the equilibrium in dilute aqueous solution, even at concentrations orders of magnitude above that expected in the environment. The hydrolysis of tetramethyldisiloxane-1,3-diol in water was found to be first order in [H+] and in [phosphate buffer] by studying the rates at pH 3 and 6. The hydrolysis of a mixture of higher oligodimethylsiloxane-α,ω-diols as a suspension in water is also described. The first observation of dimethylsilanediol in an environmental sample is reported.
- Spivack,Dorn
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p. 2345 - 2352
(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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- MUTUAL EFFECT OF SOLUTIONS OF SALTS AND HCl ON COHYDROLYSIS OF METHYLCHLOROSILANES
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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.
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p. 692 - 697
(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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- Cleavage of poly(diorganosiloxanes) by trimethyialuminum
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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.
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p. 2137 - 2141
(2008/10/08)
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- Nonaqueous method for making silicone oligomers
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A nonaqueous method is provided for making silicone oligomers by using stoichiometric amounts of formic acid to effect the condensation of polyalkoxysilanes or polayminosilanes. Reaction can be effected under ambient conditions.
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- On the Problem of the Intermediate Formation of Silanone R2Si=O by Reactions of Silenes with Dinitrogen Oxide
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The silaethene Me2Si=C(SiMe3)2 (1a; unstable; from 1a * Ph2C=MSiMe3 = 4) forms with N2O an unstable cycloadduct, which decomposes under isomerization or cleavage.It was not possible to decide clearly, whether the last reaction, which leads to (Me3Si)2CN2 and polymers with (Me2SiO)n groups, proceeds with intermediate formation of silanone Me2Si=O or not (no trapping product with Et3SiH, but with Me3SiCl).The silanimines Me2Si=NSitBu3 (2a; unstable; from 2a * tBu3SiN3 = 7) and tBu2Si=NSitBu3 (2b; metastable) form with N2O unstable cycloadducts, which, under participation of the silanimines, react into products (10) being composed of a molecular silanone and a molecule silanimine.As has been shown by trapping experiments with Et3SiH, Me3SiCl, or Me3SiOMe, latter reaction involves unstable free silanones Me2Si=O (3a) or tBuSi=O (3b) as intermediates. 3b, generated in benzene from 2b/NO2 in the presence of equimolar amounts of tetrahydrofuran (THF), obviously forms an adduct 3b*THF, which is trapped by excess 2b.When 3b is produced in THF as solvent, the silanone starts THF polymerization, indicating a high Lewis acidity of silanones.
- Wiberg, Nils,Preiner, Gerhard,Schurz, Klaus
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p. 1407 - 1412
(2007/10/02)
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- Reaction of 6-Oxa-3-silabicyclohexanes with Phosphinimines. Synthesis of 6-Vinyl-1,3-dioxa-2,4-disilacyclohexanes
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Reaction of 3,3-dimethyl-6-oxa-3-silabicyclohexane with N-benzyltriphenylphosphinimine yields 1,3-butadiene and 2,2,4,4-tetramethyl-6-vinyl-1,3-dioxa-2,4-disilacyclohexane (3).A mechanism for the formation of (3) which involves the reaction of dimethylsilanone with 2,2-dimethyl-4-vinylsilaoxetane is proposed.
- Baceiredo, Antoine,Juengst, Clifford D.,Manuel, Georges,Weber, William P.
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p. 237 - 240
(2007/10/02)
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