STUDY OF CATALYTIC CYCLISATION OF (+)-CITRONELLAL WITH Zn/γ-ALUMINA AS CATALYST

https://doi.org/10.22146/ijc.21852

Elvina Dhiaul Iftitah(1*), Hardjono Sastrohamidjojo(2), M. Muchalal(3)

(1) Chemistry Department, Faculty of Mathematics and Natural Sciences Brawijaya University, Malang
(2) Chemistry Department, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Yogyakarta
(3) Chemistry Department, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada, Yogyakarta
(*) Corresponding Author

Abstract


The reaction of catalytic cyclisation of (+)-citronellal has been done using g-alumina and Zn/γ-alumina as catalysts. Zn/γ-alumina catalyst was prepared by impregnation of ZnBr2 into solid of γ-alumina in methanol as a solvent. The calcination process is performed on Muchalal reactor at 400 oC. The reactions were carried out under nitrogen gas atmosphere by mixing 5 mL sample and 1.0 g catalyst at 90-95 oC for 3 hours. The product of reaction was analyzed using GC, FT-IR and GC-MS. The reaction of cyclization of (+)-citronellal with γ-alumina catalyst did not give targeted product as well as reaction with Zn/g-alumina catalyst. Whereas, the reactions with Zn/γ-alumina catalyst gave four compounds of isopulegol stereoisomer. Conversion of (-)-Isopulegol, (+)-Neoisopulegol, (+)-Isoisopulegol and (+)-Neoisoisopulegol  were 64,29%, 18,80%, 9,20% and 3,32% respectively. For that reason, the transformation of (+)-sitronelal using Zn/γ-alumina was considered to be the best catalyst. A reaction mechanism is proposed where the (+)-citronellal molecule binds to a catalyst Lewis acid site via the aldehyde oxygen and the π-electrons of the double bond. Subsequent protonation of the aldehyde via a neighbouring Bronsted acid site initiates the cyclisation to isopulegol.


Keywords


catalytic cyclisation; impregnation; (+)-isopulegol

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References

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DOI: https://doi.org/10.22146/ijc.21852

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Indonesian Journal of Chemistry (ISSN 1411-9420 / 2460-1578) - Chemistry Department, Universitas Gadjah Mada, Indonesia.

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