LAPORAN HASIL PENELITIAN
HIBAH PENELITIAN STRATEGIS NASIONAL
DIPA UNIVERSITAS BRAWIJAYA
TAHUN 2010
Judul : KONVERSI SATU TAHAP SENYAWA SITRONELAL
DARI MINYAK SEREH MENJADI MENTOL
MENGGUNAKAN KATALIS MULTIFUNGSI Ni-ZnBr2/γ-ALUMINA (Sebagai Upaya Biodiversifikasi Minyak Atsiri Tanaman Sereh Menjadi Produk Senyawa Farmasetikal)
Ketua : Elvina Dhiaul Iftitah, S.Si, M.Si Anggota : Dra. Sri Wardhani, M.Si
Dibiayai oleh Direktorat Jenderal Pendidikan Tinggi, Departemen Pendidikan Nasional Melalui DIPA Universitas Brawijaya berdasarkan
No.0114/023-04.2/XV/2010, Tanggal 31 Desember 2009 dan Berdasarkan SK Rektor Nomor : 035A/SK/2010 Tanggal 12 Februari 2010
UNIVERSITAS BRAWIJAYA
MALANG
2010
RINGKASAN
Telah dilakukan sintesis mentol dari sitronelal melalui satu tahap reaksi menggunakan katalis ganda ZnBr2/γ-alumina dan Ni/γ-alumina dan studi katalis multifungsi Ni-ZnBr2/γ- lumina. Pengaruh temperatur, durasi reaksi, dan perbandingan durasi aliran gas N2 dan H2 terhadap konversi, selektivitas dan stereoselektivitas mentol dipelajari untuk memperoleh kondisi optimal sintesis sitronelal menjadi mentol. Sintesis dalam dua tahap reaksi juga dilakukan untuk membandingkan selektivitas dan stereoselektivitas produk mentol.
Penelitian dilakukan dengan terlebih dahulu mengisolasi sitronelal dari minyak sereh dengan distilasi fraksinasi pengurangan tekanan. Sitronelal diperoleh pada temperatur 110-120 °C dan tekanan 3 cmHg. Preparasi katalis dilakukan melalui tahap impregnasi prekursor logam (garam dari logam) terhadap pengemban γ-alumina dalam pelarut metanol, penguapan pelarut, pengeringan, kalsinasi dan reduksi (hanya untuk Ni/γ-alumina. Karakterisasi katalis dilakukan dengan XRF, XRD, dan uji keasaman melalui metode gravimetri dengan adsorpsi piridin. Katalis yang diperoleh diaplikasikan pada sintesis mentol dari sitronelal dengan variasi perbandingan lama aliran gas N2 terhadap H2 adalah 1 jam N2 : 5 jam H2, 2 jam N2 : 4 jam H2, 3 jam N2 : 3 jam H2, 4 jam N2 : 2 jam H2 dan 5 jam N2 : 1 jam H2, pada temperatur 150 dan 200 °C. Produk reaksi dianalisis menggunakan GC, GC-MS, dan FT-IR.
Hasil penelitian menunjukkan bahwa katalis ganda ZnBr2/γ-alumina dan Ni/γ-alumina mampu mengkatalisis sintesis mentol melalui satu tahap reaksi. Kondisi optimal reaksi dengan katalis ganda tersebut diperoleh dengan perbandingan durasi aliran gas 1 jam N2 : 5 jam H2, pada temperatur 200 oC, dan durasi reaksi 6 jam. Pada kondisi optimal tersebut, konversi sitronelal menjadi mentol sebesar 74,82%, selektivitas mentol adalah 13,57%, dengan stereoselektivitas terhadap (-)-mentol sebesar 68,90%. Perbandingan persen relatif masing-masing produk isomer (-)-mentol, (+)-neomentol, (+)-isomentol, (+)-neoisomentol berturut-turut adalah 8,04 : 2,08 : 0,92 : 0,63; dengan perbandingan stereoselektivitas masing-masing produk isomer berturut-turut sebesar 68,9 : 17,85 : 7,86 : 5,38. Sintesis dalam dua tahap reaksi, produk siklisasi terbaik diperoleh pada temperatur 150 oC dan durasi reaksi 240 menit. ZnBr2/γ-alumina aktif dan selektif terhadap (+)-sitronelal menghasilkan produk isopulegol dengan selektivitas sebesar 72,54%. Sedangkan produk hidrogenasi terbaik diperoleh pada temperatur 180 oC dan durasi reaksi 240 menit yang memberikan selektivitas produk mentol sebesar 86,46%, dan perbandingan masing-masing isomer untuk (-)-mentol : (+)-neo-mentol : (+)-iso-mentol : (+)-neoiso-mentol sebesar 74,24 : 15,26 : 9,80 : 9,62.
Kata kunci : siklisasi, hidrogenasi, sitronelal, isopulegol, katalis Ni/alumina, katalis ZnBr2/ γ-alumina
SUMMARRY
Synthesis of menthol from citronellal through one-step reaction was investigated over ZnBr2/γ-alumina and Ni/γ-alumina as catalyst. The effects of temperature, time reaction, and ratio of gas flow duration of N2 to H2 over conversion, selectivity, and stereoselectivity of menthols were studied to obtain optimum condition of the synthesis.
The research was done by isolating the citronellal from the citronella oil by fractional distillation at reduced pressure. Citronellal was obtained at 110 - 120 °C and 3 cmHg. The catalysts were prepared through several steps prior to characterization. The catalyst preparation consists of metal precursor impregnation to γ-alumina support in a methanol solution, solvent evaporation, drying, calcination, and reduction as an additional step for Ni/γ-alumina. The quantitative determination of total acid was done by gravimetric method with pyridine as probe molecule. The characterization of ZnBr2/γ-alumina and Ni/γ-alumina crystallinity was carried out by XRD. The quantitative determination of metal absorbed both Zn and Ni was conducted by XRF. The catalysts were applied to synthesis of menthol from citronellal through one-step reaction by varying the ratio of gas flow duration of N2 to H2. The reaction was conducted at 150 dan 200 °C for six hours. The products were analyzed by GC, GC-MS, and FT-IR.
The result shows that dual catalyst system of ZnBr2/γ-alumina and Ni/γ- alumina was able to catalyze synthesis of menthol through one-step reaction. The optimum condition obtained at 200 °C for six hours with the ratio of gas flow duration of N2 to H2 obtained at an hour of N2 and five hours of H2. The conversion of citronellal to menthol at those conditions was 74,82% and the selectivity to menthols was 13,57%. The ratio of relative concentration between isomer products, (-)-menthol : (+)-neomenthol : (+)-isomenthol : (+)-neoisomenthol, was 8.04 : 2.08 : 0.92 : 0.63 respectively. While, the ratio of stereoselectivity between them was 68.9 : 17.85 : 7.86 : 5.38 respectively.
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