Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic, Green, and Sustainable Sources. Issue 3 (3rd December 2015)

• Record Type: Journal Article
• Authors: Laine, Richard M.; Furgal, Joseph C.; Doan, Phi; Pan, David; Popova, Vera; Zhang, Xingwen
• Is Part Of: Angewandte Chemie international edition. Volume 55:Issue 3(2016)
• Page Start: 1065
• Page End: 1069
• Publication Date: 2015-12-03
• Subjects: depolymerization -- materials science -- silicon -- sustainable chemistry; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201506838
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: The direct depolymerization of SiO2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Simet, followed by treatment with ROH. We report herein the base‐catalyzed depolymerization of SiO2 with diols to form distillable spirocyclic alkoxysilanes and Si(OEt)4 . Thus, 2‐methyl‐2, 4‐pentanediol, 2, 2, 4‐trimethyl‐1, 3‐pentanediol, or ethylene glycol (EGH2 ) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H2 O and distillable spirocyclic alkoxysilanes [bis(2‐methyl‐2, 4‐pentanediolato) silicate, bis(2, 2, 4‐trimethyl‐1, 3‐pentanediolato) silicate or Si(eg)2 polymer with 5–98 % conversion, as governed by surface area/crystallinity. Si(eg)2 or bis(2‐methyl‐2, 4‐pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt)4 in 60 % yield, thus providing inexpensive routes to high‐purity precipitated or fumed silica and compounds with single Si−C bonds. Abstract : No detours : The base‐catalyzed depolymerization of SiO2 from different sources with diols led directly to distillable alkoxysilanes, including spirocyclic compounds, thus providing inexpensive routes to high‐purity silica and compounds with single Si−C bonds (see scheme): The alkoxysilanes could be converted either into Si(OEt)4 by treatment with EtOH and a catalytic amount of acid or into high‐purity precipitated (ppt) or fumed silica.