The effects of temperature, time of reaction, and the reactants mole ratio on the cyclizationacetylation of (R)-(+)-citronellal with FeCl 3 /acetic anhydride were studied. Isopulegyl acetate (IPA) and neoisopulegyl acetate (NIPA) were obtained as the main products at room temperature (mole ratio of citronellal: acetic anhydride: FeCl 3 = 6:12:1). Both products are relatively fixed after the 30th minute. The average concentration of IPA at 30-180 minutes was 44.71%, while the average concentration of NIPA was 28.47%. Increasing temperature (80 o C) and the amount of acetic anhydride (mol ratio 2:6:1) gave p-cymene (17.53%) and citronellyl acetate (11.31%). Autoredoks reaction on the transformation of citronellal into pcymene and citronellyl acetate was studied with the carbon oxidation number concept.
Citronellal 97,3% has been isolated from Java citronella oil (Cymbopogon winterianus) from Yogyakarta Indonesia by fractional distillation under reduced pressure (5 cmHg, 110-120 oC). Citronellal has two optical isomerics that can be separated by capillary column of chiral GC phase. Enantioselective capillary GC with heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin (β-DEX-225) as stationary phase has been used for analysis of the enantiomers ratio of citronellal. The analysis of enantiomer ratio showed that citronellal contain of 88.21% ee of (R)-(+)-citronellal. Physical properties of isolated citronellal showed that the compound was (+) enantiomer. Structure identification of citronellal was carried out by GC-MS, IR, and 1H NMR, resulted identical fragment and spectra with standard citronellal. Theoretical study with semiempirical-AM1 method showed that energy of (R)-(+)-citronellal on the β-DEX 225 was lower than its (S)-(-)-citronellal.
Kinetic in cyclisation-acetylation of (R)-(+)-citronellal with acetic anhydride was investigated over Zn2+-Natural zeolite (Zn2+-Natzeo) as a catalyst. (R)-(+)-citronellal has been isolated from citronella oil by fractional distillation under reducing pressure. Enantioselective capillary GC on a Supelco β-DEX 225 column has been used for analysis the enantiomers ratio of citronellal. Catalyst Zn2+-Natzeo has prepared through acid activation of natural zeolite from Malang using HF 1% and HCl 6 M, followed by ion-exchange with 3 M NH4Cl and calcination at 450 °C for 1 h under nitrogen to obtained H-natural zeolite (H-Natzeo). H-Natzeo was modified to Zn2+-Natzeo by ion exchange with 0.1 M ZnCl2. Cyclisation-acetylation reaction was carried out by heating (R)-(+)-citronellal (CIT), acetic anhydride (AA), and 1 g catalyst in glass batch reactor with vigorous stirring at 80 °C. Molar ratio CIT/AA that used, i.e. 0.25; 0.5; 1.0; 1.2 and 1.5. As the reaction proceeded, 1 mL sample was taken off at 10; 20; 30; 60; 120; 180 min and extracted using n-hexane for every molar ratio. Structure analysis of product was conducted by GC-MS. Kinetic of the cyclisation-acetylation reaction was analyzed according to the Langmuir-Hinshelwood mechanism. Increasing molar ratio of CIT/AA will decrease the isopulegyl acetate (IPA) and neo-isopulegyl acetate (NIPA) formation. Rate constant of cyclisation-acetylation reaction catalyzed by Zn2+-Natzeo was 30.964-47.619 mmol(min. g cat)-1 at 80 °C, 30 min and the ratio adsorption equilibrium constant KCIT/KAA was 7.09. Keywords: Cyclisation-acetylation, (R)-(+)-citronellal, Zn2+-natural zeolite, kinetic
An investigation on characterisation and catalytic ativities of modified natural zeolite on cyclisationacetylation reaction of (R)-(+)-citronellal was performed. The experimental works involved the isolation of (R)-(+)-citronellal from Javanese citronella (Cymbopogon winterianus) oil by vacuum fractional distillation, the determination of its enantiomers, and the preparation and characterisation of different catalysts i.e. H-natural zeolite (H-Za), Fe 3+ -natural zeolite (Fe 3+ -Za), and Zn 2+ -natural zeolite (Zn 2+ -Za), followed by the examination of their activity and selectivity on cyclisation-acetylation reaction of (R)-(+)-citronellal. The isolated citronellal contained 88.21 ee.% of (R)-(+)-citronellal. The crystallinity and the morphology of the modified zeolites showed that the natural zeolite from Malang Indonesia has the main component of mordenite-type zeolite. The main products of cyclisation-acetylation of (R)-(+)-citronellal were isopulegyl acetate (IPA) and neo-isopulegyl acetate (NIPA). Fe 3+ -Za catalyst showed the highest activity towards IPA and NIPA production but its stereoselectivity was slightly lower than that of Zn 2+ -Za catalyst. It is shown that Lewis acidity plays the role in the formation of acetyl ionic from acetic anhydride.
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