High-temperature reaction of SiO2 with methanol: Nucleophilic assistance of some N-unsubstituted benzazoles

Authors: Andrey M. Chibiryaev, Ivan V. Kozhevnikov, Oleg N. Martyanov

Abstract:
SiO₂-containing materials (quartz, Pyrex glass, silica gel, and H-Y zeolite) react slowly with methanol at 350 ^◦C under both supercritical and gas-phase conditions. The amount of SiO₂ reacted with supercritical methanol depends on the kind of the material and is varied from 0.05 wt% for quartz sand to 4.0 wt% for wide-porous silica gel for 5 h of the reaction. The main products of the reaction are methyl orthosilicates, mainly tetramethyl orthosilicate. N-Unsubstituted 1H-indole, 1H-benzimidazole, and 1H-indazole additives considerably increase the amount of reacted SiO₂-containing material. Noteworthy, quartz sand “solubility” is increased ca 14-fold when indole is used at the same reaction conditions. These benzazoles provide a nucleophilic assistance to the reaction between SiO₂ and methanol. During the assistance, the azole ring is methylated by methanol, and the participation of SiO₂-surface or tetramethyl orthosilicate molecule facilitates the alkylation reaction of benzazole used.

Keywords:
SiO₂-containing materials
Supercritical methanol
Tetramethyl orthosilicate
Benzazole methylation catalyst
Nucleophilic assistance

Published in: Applied catalysis A: General  (Volume 456, Pages 1-248, 10 April 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

High-temperature reaction of SiO2 with methanol: Nucleophilic assistance of some N-unsubstituted benzazoles

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