One‐Step Synthesis of Siloxanes from the Direct Process Disilane Residue

Abstract

The well-established Müller-Rochow Direct Process for the chloromethylsilane synthesis produces a disilane residue (DPR) consisting of compounds Me Si Cl (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 Et O 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/Et O reagent is also suitable to produce siloxanes from the corresponding monosilanes under comparable conditions.

Lewis Base Catalyzed Selective Chlorination of Monosilanes

“…Turning to the influence of different ethers on the reaction rate, we note that in previous work Et 2 O cleavage was observed only upon heating of a 5 m HCl/Et 2 O solution above 100 °C resulting in formation of EtCl, EtOH, and H 2 O . Accordingly, in our experiments alkoxysilane and siloxane formation set in only at temperatures of 100 °C and above.…”

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts

“…Bifunctional monosilanes represent fundamentally important building blocks in silicone technology. Utilizing 1) the Si−H functionality for hydrosilylation reactions to create silicon–carbon bonds and 2) the Si−Cl functions for hydrolysis or alcoholysis provides access to the corresponding silanols or alkoxysilanes employed in condensation reactions to form the siloxane Si−O−Si bonding motif . For the synthesis of bifunctional monosilanes, some preparative protocols have been reported: As shown by D′Errico and Sharp for a variety of halosilanes, the selective reduction of a single Si−Cl bond is possible by using alkyltin hydrides .…”

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes

“…Some of us recently reported the quantitative DPR conversion into siloxanes by reaction with HCl/ether solutions at elevated temperatures . The results implied intermediate formation of monosilanes which were, however, not isolable under the reaction conditions.…”

“…[3,5] Some of us recently reported the quantitativeD PR conversion into siloxanes by reactionw ith HCl/ether solutions at elevated temperatures. [6] The results implied intermediate forma-tion of monosilanes which were, however,n ot isolable under the reaction conditions. Among the presumed reaction intermediates,t he bifunctional monosilanes Me 2 SiHCl and MeSiHCl 2 are particularly valuable compounds [7] whoset argeted synthesis traditionally represents af undamental challenge, despite the seeming simplicity of the compounds.…”