Manifestation of zeolitic pore characteristics of modified montmorillonite in oxazole synthesis by propargylation and cycloisomerization reactions
•Zeolitic pore formation in montmorillonite upon PDSA treatment.•Cycloisomerization of alkynylamide to oxazole is enhanced by zeolitic pore.•There is a good correlation between VAF and oxazole formed.•VAF is a term which is a product of acidity and micropore volume.
Zeolitic micropores are found to be developed on montmorillonite clay by treatment with phenoldisulphonic acid (PDSA). The micropores developed have the ability to enhance the cycloisomerization of the alkynylamide to form oxazole product. Pore characteristics by surface measurement techniques and acidity by pyridine adsorption using FT-IR were evaluated. Surface measurements showed significant increase in the surface area, acidity and the micropore volume but neither of them correlated well with the cycloisomerization activity. Variation in Brønsted and Lewis acidity and pore volume by surface coverage using Brønsted (B) and Lewis (L) acid compounds, caused variation in cycloisomerization activity. Best correlation with the amount of oxazole formed was observed when volume accessibility factor (VAF), a product of micropore volume and ratio of B to L acidity were considered. Based on this, a reaction scheme for cycloisomerization is proposed involving both B and L sites within the micropores.
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Journal: Applied Catalysis A: General - Volume 496, 25 April 2015, Pages 51–57