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Aromatization of para-menthenic terpenes by aerobic oxidative dehydrogenation catalyzed by p-benzoquinone

Paper ID Volume ID Publish Year Pages File Format Full-Text
43244 45959 2008 5 PDF Available
Title
Aromatization of para-menthenic terpenes by aerobic oxidative dehydrogenation catalyzed by p-benzoquinone
Abstract

The aerobic dehydrogenation of cheaply available para-menthenic terpenes, i.e., γ-terpinene, α-terpinene, limonene, and terpinolene, to commercially more valuable p-cymene has been developed. The reaction is catalyzed by p-benzoquinone and occurs in acetic acid solutions under relatively mild conditions (80–100 °C, 5–10 atm). In the presence of Cu(OAc)2 as co-catalyst which accelerates the re-oxidation of p-hydroquinone to p-benzoquinone by molecular oxygen, the aerobic dehydrogenation can be performed even under atmospheric pressure. The reaction with γ-terpinene, the most reactive isomer, gives p-cymene in near quantitative yield and shows high turnover numbers (up to 1000). A solvent scope for this reaction can be extended to more friendly non-acidic alcoholic or amidic solvents. α-Terpinene also undergoes aromatization under similar conditions giving p-cymene in excellent yield (95%). On the other hand, the dehydrogenation of limonene and terpinolene, the substrates containing an exocyclic double bond, seems to be preceded by the double bond isomerization; so that these reactions require the presence of acid co-catalysts and give p-cymene in lower yields (ca. 60%).

Graphical abstractThe aerobic dehydrogenation of cheaply available para-menthenic terpenes, i.e., γ-terpinene, α-terpinene, limonene, and terpinolene, to commercially more valuable p-cymene has been developed. The reaction is catalyzed by p-benzoquinone (BQ) and occurs under relatively mild conditions. The addition of Cu(OAc)2, which catalyzes the re-oxidation of p-hydroquinone to BQ by molecular oxygen, significantly accelerates the reaction and allows to work under atmospheric pressure.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Aromatization; Oxidative dehydrogenation; Dioxygen; Monoterpenes; Benzoquinone
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Aromatization of para-menthenic terpenes by aerobic oxidative dehydrogenation catalyzed by p-benzoquinone
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 351, Issue 2, 30 December 2008, Pages 226–230
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
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Price was $35.95
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