1066-40-6Relevant articles and documents
High-speed living polymerization of polar vinyl monomers by self-healing silylium catalysts
Zhang, Yuetao,Lay, Frank,Garcia-Garcia, Pilar,List, Benjamin,Chen, Eugene Y.-X.
, p. 10462 - 10473 (2010)
This contribution describes the development and demonstration of the ambient-temperature, high-speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (RSKA) initiator (I) with a strong Bryonsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near-precise polymer number-average molecular weight (Mn, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain-termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well-defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst self-repair involved in this living polymerization system have been elucidated, chiefly featuring a propagation catalysis cycle consisting of a rate-limiting C-C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et2O)2] + [B(C 6F5)4]- is the most effective activator, which spontaneously delivers the most active R3Si +, reaching a high catalyst turn-over frequency (TOF) of 6.0 x 103 h-1 for methyl methacrylate polymerization by Me 3Si+ or an exceptionally high TOF of 2.4 x 105 h-1 for n-butyl acrylate polymerization by iBu3Si +, in addition to its high (>90%) to quantitative efficiencies and a high degree of control over Mn, and MWD (1.07-1.12). An intriguing catalyst self-repair feature has also been demonstrated for the current living polymerization system.
Reaction of O(3P) with Hexamethyldisilane
Hoffmeyer, H.,Potzinger, P.,Reimann, B.
, p. 4829 - 4831 (1985)
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.
The role of the phase quasiequilibrium in the reaction system chlorotriorganosilane-water-acetone
Ivanov, P. V.,Maslova, V. I.,Mlakhovskaya, O. V.,Chernyshev, E. A.
, p. 1156 - 1160 (1994)
On the basis of analysis of product composition in the hydrolytic polycondensation (HPC) of chlorotriorganosilanes, the parameters of the kinetic and the diffusion field, the zone of the reaction, and the region of the conodes of the phase diagrams are determined.It is suggested that the conodes correspond to a phase quasiequilibrium, which defines the composition of the reaction products.The results of this investigation confirm the previously discovered features of HPC of dichloromethylphenylsilanes: the formation of the siloxane bond during the hydrolysis of chloroorganosilanes by water mainly occurs in the organic phase of the system and proceeds as the heterofunctional polycondensation of the reaction products with the starting chloroorganosilanes.The role of the phase quasiequilibrium consists of the creation of a field of reagent concentration, based on which one can control the composition of the reaction products. - Key words: quasiequilibrium; conodes; Gibbs phase diagram; hydrolysis; chloroorganosilanes; silanols; field of the reaction.
CONDENSATION REACTIONS OF α-AMINO-ZINCENAMINES WITH ALDEHYDES; APPLICATION TO INDOLIZINES
Wissing, Elmo,Havenith, Remco W. A.,Boersma, Jaap,Koten, Gerard van
, p. 7933 - 7936 (1992)
The zinc-enamine 1 is easy accessible via the reaction of Et2Zn with t-BuN=CHCH=Nt-Bu and is reactive towards aldehydes.The condensation reaction of 1 with 2-pyridine-carboxaldehyde results in the thermally instable zinc-aldolate 2b that subsequently rearranges to the indolizine 4.
Reaction of O(3P) with Trimethylsilane
Hoffmeyer, H.,Horie, O.,Potzinger, P.,Reimann, B.
, p. 2901 - 2905 (1985)
The title reaction has been investigated at room temperature in a discharge flow system as well as by stationary Hg(3P1) sensitized N2O photolysis experiments.O(3P) atoms abstract hydrogen from the silicon center with a rate constant of k(1) = (2.6 +/= 0.3)E-12 cm3s-1.Hydroxyl radicals formed in the primary step react in a second abstraction reaction to yield H2O with a rate constant larger than k(1) by a factor of about 20.The fate of trimethylsilyl radical, the other primary product, depends on the experimental conditions.In the flow system they combine with O and OH; the combination products decompose unimolecularly, yielding CH3 and CH4, respectively, and the common product (CH3)2SiO.In stationary photolyses they mainly abstract O from N2O to ultimately form (CH3)3SiOSi(CH3)3.In a separate static experiment a ratio of k(14)/k1/2(7) = 2.5E-12 cm3/2s-1/2 has been determined for oxygen abstraction of trimethylsilyl radicals from N2O vs. combination of two trimethylsilyl radicals.The rate constant of N(4S) with trimethylsilane has been measured in the flow system to be k(2) = (2.6 +/= 0.8)E-14 cm3s-1.
Trimethylsilyl group migration in the Criegee intermediate of gas-phase ozonolysis of trimethylsilylethenes
Fajgar, Radek,Pola, Josef
, p. 2435 - 2438 (2000)
GC, GC/MIS and GC/FTIR analyses of the final products of ozonolysis of trimethylsilylethene and trans-1,3-bis(trimethylsilyl)ethene reveal that the ester channel of decomposition of the Criegee intermediate takes place exclusively via migration of Me
Enzyme mediated silicon-oxygen bond formation; The use of Rhizopus oryzae lipase, lysozyme and phytase under mild conditions
Abbate, Vincenzo,Bassindale, Alan R.,Brandstadt, Kurt F.,Lawson, Rachel,Taylor, Peter G.
, p. 9361 - 9368 (2010)
The potential for expanding the variety of enzymic methods for siloxane bond formation is explored. Three enzymes, Rhizopus oryzae lipase (ROL), lysozyme and phytase are reported to catalyse the condensation of the model compound, trimethylsilanol, formed in situ from trimethylethoxysilane, to produce hexamethyldisiloxane in aqueous media at 25 °C and pH 7. Thermal denaturation and reactant inhibition experiments were conducted to better understand the catalytic role of these enzyme candidates. It was found that enzyme activities were significantly reduced following thermal treatment, suggesting a potential key-role of the enzyme active sites in the catalysis. Similarly, residue-specific modification of the key-amino acids believed to participate in the ROL catalysis also had a significant effect on the silicon bio-catalysis, indicating that the catalytic triad of the lipase may be involved during the enzyme-mediated formation of the silicon-oxygen bond. E. coli phytase was found to be particularly effective at catalysing the condensation of trimethylsilanol in a predominantly organic medium consisting of 95% acetonitrile and 5% water. Whereas the use of enzymes in silicon chemistry is still very much a developing and frontier activity, the results presented herein give some grounds for optimism that the variety of enzyme mediated reactions will continue to increase and may one day become a routine element in the portfolio of the synthetic silicon chemist. The Royal Society of Chemistry.
DEOXYMETALATION REACTIONS. THE MECHANISMS OF DEOXYSILYLATION OF MONO-TRIMETHYLSILYL-AND BIS-TRIMETHYLSILYL-SUBSTITUTED ALCOHOLS AND A COMPARISON TO THE MECHANISM OF DEOXYSTANNYLATION AND DEOXYPLUMBYLATION
Davis, Dennis D.,Jacocks, Henry M.
, p. 33 - 47 (1981)
The relative rates of acid-catalyzed deoxysilylation of 2-trimethylsilyl-1-hydroxyethane, 4, 1-trimethylsilyl-2-hydroxypropane, 5, 1,3-bis(trimethylsilyl)-2-hydroxypropane, 6, and 1-trimethylsilyl-2-methyl-2-hydroxypropane, 7, were found to be 1 : 103.30 : 105.92 : 106.77, respectively, in 9 vol percent aqueous-methanol at 40 deg C.These rates are directly proportional to the sum of the ?+ constants of the substituents on the carbon bearing the nucleofuge (ρ+ = -11).The additive rate-accelerating effect of two trimethylsilyl groups requires equal conjugativen bystabilization by each trimethylsilyl group, and a mechanism involving a hyperconjugatively-stabilized carbocation intermediate is proposed.In contrast, the deoxymetalation reactions of the triphenyltin-, triphenyllead-, and iodomercury-analogs exhibit very different structure-reactivity relationships and have been described as proceeding through concerted E2-like or bridged-ion mechanisms.These mechanistic regimes are reconciled by considering the conjugative interactions, electrofugalities and nucleophilic solvent assistance at the organometal-leaving groups in terms of Thornton's Reacting Bond Rules.This analysis suggests a spectrum of merging mechanisms, the acid-catalyzed deoxysilylation representing one extreme, the E1M (carbocation intermediate) mechanism and the other Group IV deoxymetalation reactions more nearly concerted E2M-paths.
A Quantitative Scale for the Structural Effect on Reactivity toward Nucleophilic Displacement at Silicon
Shimizu, Nobujiro,Takesue, Naohide,Yamamoto, Akiko,Tsutsumi, Toru,Yasuhara, Sigefumi,Tsuno, Yuho
, p. 1263 - 1266 (1992)
The rates of solvolysis for forty different triorganochlorosilanes have been measured in 89 molpercent aqueous dioxane at 25 deg C; the logarithmic rates relative to that for trimethylchlorosilane, log krel = log 1R2R3SiCl)/k(Me3SiCl)>, provide a quantitative scale for the structural effect of various silyl groups on the reactivity toward nucleophilic displacement at silicon, ranging from 1.99 for HSiMe2 to -6.89 for t-BuSiPh2 groups.
Sodiumoxy(aminopropyl)alkoxysilanes - AB2 type monomers for the synthesis of hyperbranched poly(aminopropyl)alkoxysiloxanes and their derivatives
Migulin, Dmitry,Milenin, Sergey,Cherkaev, Georgy,Svidchenko, Evgeniya,Surin, Nikolay,Muzafarov, Aziz
, p. 24 - 32 (2018)
Based on commercially available aminopropyltrialkoxysilanes, new monosodium salts of organoalkoxysilanes (sodiumoxoaminopropyldialkoxysilanes) with two types of chemically independent functional -ONa and -OAlk groups at the silicon atom were synthesized and characterized. The sodiumoxoaminopropyldialkoxysilanes obtained can be regarded as AB2-type monomers - promising reagents for providing controlled polycondensation and production of functional organosilicon polymers with controlled molecular architectures. Subsequently, polyaminopropylsiloxanes with hyperbranched molecular architectures were obtained by heterofunctional polycondensation of the corresponding AB2-type monosodiumoxoorganodialkoxysilanes. The structures synthesized were characterized using 29Si NMR, 1H NMR, GPC and elemental analyses. The hyperbranched polymer matrices obtained containing aminopropyl organic radicals showed the ability to stabilize silver nanoparticles.
