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Ionone synthesis by cyclization of pseudoionone on silica-supported heteropolyacid catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
42933 45947 2009 8 PDF Available
Title
Ionone synthesis by cyclization of pseudoionone on silica-supported heteropolyacid catalysts
Abstract

The liquid-phase cyclization of pseudoionone to ionones (α, β and γ isomers) was studied on silica-supported heteropolyacid (HPA) catalysts containing between 18.8 and 58.5% HPA. The HPA used was tungstophosphoric acid (H3PW12O40). The catalyst surface and structural properties were thoroughly characterized by several techniques. The density, chemical nature and strength distribution of the surface acid sites were determined by adsorbing and monitoring by temperature-programmed desorption and infrared spectroscopy probe molecules such as NH3 and pyridine. The pseudoionone conversion to ionones increased linearly with the Brønsted acid site density until the HPA loading approached to the monolayer saturation coverage. For higher HPA contents, the pseudoionone adsorption and conversion were hampered because of spatial constraints that diminished the reactant accessibility to the proton active sites. The highest ionone yield, 79%, was obtained on a 58.5 wt% HPA/SiO2 catalyst at 383 K and is comparable to the best values reported in literature for the homogeneously catalyzed reaction using sulfuric acid. The ionone isomer distribution was modified by varying both the temperature and the reaction time. A reaction mechanism was postulated in which ionone isomers (α, β and γ) are primary products, but γ-ionone is isomerized to α-ionone while β-ionone is not converted in the other isomers.

Graphical abstractThe liquid-phase cyclization of pseudoionone to ionones (α, β and γ isomers) is studied on silica-supported heteropolyacid (HPA) catalysts. The reaction is promoted on strong Brønsted acid sites. The pseudoionone conversion to ionones increases with HPA loading and reaction temperature. The latter also affects the isomer distribution. The α isomer is mainly obtained.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Ionone; Heteropolyacid; Acid catalysis; Tungstophosphoric acid; HPA
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Ionone synthesis by cyclization of pseudoionone on silica-supported heteropolyacid catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 358, Issue 1, 30 April 2009, Pages 95–102
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
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Full-text PDF Download
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