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

Paper ID Volume ID Publish Year Pages File Format Full-Text
40530 45857 2013 9 PDF Available
Title
High-temperature reaction of SiO2 with methanol: Nucleophilic assistance of some N-unsubstituted benzazoles
Abstract

•Different forms of SiO2 react slowly with methanol at 350 °C to give mainly TMOS.•Some N-unsubstituted benzazoles increase considerably the amount of reacted SiO2.•The key role of heterocycles is nucleophilic assistance to the reaction.•Azole ring of heterocycles is methylated by MeOH during the reaction.•Both SiO2-surface and TMOS catalyze the methylation of benzazole.

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.

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Keywords
SiO2-containing materials; Supercritical methanol; Tetramethyl orthosilicate; Benzazole methylation catalyst; Nucleophilic assistance
First Page Preview
High-temperature reaction of SiO2 with methanol: Nucleophilic assistance of some N-unsubstituted benzazoles
Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 456, 10 April 2013, Pages 159–167
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis