Peculiarities Of Hydrosilylation Of Unsaturated Organic Compounds On A Surface Of Hydride Silica
Peculiarities of hydrosilylation of UNSATURATED ORGANIC COMPOUNDS ON a SURFACE of hydride silica
L.A. Belyakova, A.M. Varvarin
Institute of Surface Chemistry, Ukrainian National Academy of Sciences, General Naumov st. 17, 03164 Kiev, Ukraine
The change of disperse silicas properties as a result of chemical modifying of a surface may be used for synthesis of specific adsorbents, selective catalysts, biologically active compound supports, composite materials.
The efficiency of use of modified silicas depends on hydrolytic and thermal stability of surface chemical compounds, namely, strength of chemical bonds formed between a silica surface and grafted organic radicals:
]Si-O-C
Therefore the formation of bond Si-C as a result of chemical interactions of silica surface with manifold organic or organosilicon compounds is more preferable.
The formation of chemical bond Si-C on a surface of silica is possible as a result of interaction of previously chlorinated silicon dioxide with:
– lithium- or magnesium organic compounds;
– aromatic hydrocarbons at the presence of aluminum chloride as the catalytic agent (analog of Fridel-Krafts reaction);
– halogensubstituted organic compounds at the presence of metallic sodium (analog of Vurts synthesis).
We experimentally prove the formation of chemical bond Si-C on the silica surface as a result of interaction of hydride silica (silica with Si-H functional groups on the surface) with:
– organic chlorosubstituted reagents (analog of the reaction of high-temperature condensation of hydrosilanes with chlorine-containing organic compounds);
– benzene (analog of the reaction of high-temperature reduction);
– unsaturated organic or organosilicon compounds (analog of the hydrosilylation reaction).
We have studied the reaction of hydrosilylation between a surface of hydride silicas and unsaturated organic compounds of various classes (primary terminal olefines with C6–C18, vinyltrichloro- and vinyltrimethylsilanes, acrylamide, vinyl acetate, acetylacetone, ethylene carboxylic acid, N-vinyl-2-pyrrolidone) at the liquid-phase catalytic conditions (solid-phase catalytic hydrosilylation) and at the gas-phase mode without a solvent and catalyst (solid-phase thermal hydrosilylation) in detail.
It was established that solid-phase hydrosilylation of primary terminal olefines, and also functional olefines with C=C unsaturated bonds only runs with high yield at the presence of Speier catalyst and without it.
The reaction of hydrosilylation for functional olefines with C=C and C=O unsaturated bonds in a molecule is carried out with participation of both functional groups. The preferable direction of solid-phase hydrosilylation is connected with distribution of electronic density in a molecule of unsaturated compound. So, in case of ethylene carboxylic acid the reaction of hydrosilylation proceeds mainly on carbonyl group of organic acid with the formation of a surface organosilicon ether (1,4-hydrosilylation). For all other investigated functional olefines the reaction of solid-phase hydrosilylation is carried out on С=С bonds with formation of chemical bonds Si-C between a silica surface and modifier.
The side reactions are found which run on a hydride silica surface simultaneously to reaction of solid-phase catalytic hydrosilylation:
– acid hydrolysis of Si-H groups of a hydride silica surface;
– etherification of silanol groups formed as a result of hydrolysis of Si-H groups of hydride silica;
– formation of finely disperse metallic platinum reduced from the solution of Speier catalyst - H2PtCl6.6 H2O by molecular hydrogen, which appeared at hydrolysis or etherification of silicon-hydride groups.
In case of reaction of solid-phase thermal hydrosilylation at elevated temperatures there can be a thermal polymerization of olefines as a side reaction.
The obtained results have confirmed the advantages of thermal solid-phase hydrosilylation in comparison with solid-phase catalytic hydrosilylation of olefines on a surface of hydride silicas.
Related articles::