Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic, Green, and Sustainable Sources

The direct depolymerization of SiO 2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Si met , followed by treatment with ROH. We report herein the base‐catalyzed depolymerization of SiO 2 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 (EGH 2 ) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H 2 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.