SINTESIS DIMETIL ASETAL SITRONELAL DENGAN KATALIS GAS HCL

E Cahyono

Abstract


Perlindungan gugus aldehida melalui pembentukan asetal umumnya dilakukan dengan metanol atau etanol terkatalis asam. Sitronelal memiliki gugus aldehida dan gugus alkena. Dalam lingkungan asam, sitronelal mudah mengalami siklisasi membentuk isopulegol dan isomernya. Penelitian ini bertujuan untuk mensintesis dimetil asetal sitronelal dengan katalis gas HCl. Penggunaan gas HCl secara terbatas dimaksudkan untuk menghindari siklisasi sitronelal. Dalam suatu reaktor, 10 mL sitronelal ditambah dengan 20 mL metanol absolut dan 2 g CaCl2 pada labu leher tiga. Gas HCl dialirkan dengan laju alir 12 mL/menit pada temperatur ruang hingga pH campuran menjadi 2-3. Kemudian dilakukan pengadukan pada 30C selama 48 jam dan diambil sampel pada durasi reaksi 12, 24 dan 48 jam. Dalam penelitian ini dilakukan variasi temperatur dan jumlah CaCl2. Dimetil asetal sitronelal yang dihasilkan diisolasi dengan distilasi fraksinasi pengurangan tekanan dan diuji strukturnya dengan GC-MS, IR dan 1H-NMR. Peningkatan temperatur dan jumlah CaCl2 meningkatkan konversi sitronelal. Setelah 48 jam kuantitas dimetil asetal sitronelal mencapai 48,65%. Distilasi fraksinasi pengurangan tekanan (5 cmHg) terbukti meningkatkan kemurnian dimetil asetal sitronelal menjadi 86,39% terhadap produk kasarnya. Elusidasi struktur dengan spektrofotometer infra merah (IR) dan resonansi magnetik inti (1H-NMR) pada hasil distilasi fraksinasi membuktikan adanya struktur asetal sitronelal.

Aldehyde group protection through acetal formation is generally performed by acid catalyzed methanol or ethanol. Citronellal that has aldehyde and alkene groups. In acidic environment, it is prone to do cyclization to form isopulegol and its isomers. This study aims to synthesize dimethyl acetal of citronellal with HCl gas catalysts. The limitation of HCl using gas was intended to avoid the citronellal cyclization. In a reactor, 10 mL citronellal was added with 20 mL of absolute methanol and 2 g CaCl2 in the three-neck flask. HCl gas was flowed at 12 mL/minute at room temperature until the mixture pH reached the scale of 2-3. The stirring was done at 30?C for 48 hours and the samples was taken with the reaction duration of 12, 24 and 48 hours then the effect of temperature and the CaCl2 amount was investigated. Dimethyl acetal citronellal was isolated by fractional distillation by reducing the pressure and its structure was analyzed by GC-MS, IR and 1H-NMR. The increasing of temperature and amount of CaCl2 increased the citronellal conversion, then After 48 hours the quantity of dimethyl acetal of citronellal reached 48.65%. Fractional distillation by pressure reduction (5 cmHg) was proven to be able to improve the purity of dimethyl acetal citronellal up to 86.39% towards its crude product. Structure elucidation with IR and 1H-NMR in distilled fractionation product have proven the presence of citronellal acetal structure.

Keywords


citronellal; dimethyl acetal citronellal; HCl gas

Full Text:

PDF

References


Hassner A, Bandi CR & Panchgalle S. 2012. A mild, room-temperature protection of ketones and aldehydes as1,3-dioxolanes under basic conditions. Synlett 23: 2773-2776

Hebert' J & Gravel D. 1974. o-Nitrophenylethylene Glycol: a Photosensitive Protecting Group for Aldehydes and Ketones. Can J Chem 52: 187-189

Iwasaki H, Kitayama M & Onishi T. 2002. Process for producing acetals. European Patent Specification

Iwata T, Yoji H, & Yoshiki O. 2002. Process for producing isopulegol. European Patent Application

Leonard NM, Oswald MC, Freiberg DA, Nattier BA, Smith RC & Mohan RS. 2002. A simple and versatile method for the synthesis of acetals from aldehydes and ketones using bismuth triflate. J Org Chem 67: 52025207

The Lipid Library. 2007. http://lipidlibrary .aocs.org /ms/ms21/index.htm. diakses 11 Oktober 2009

Uemura M, Yagi K, Iwasaki M, Nomura K, Yorimitsu K & Oshima K. 2006. Pentamethylcyclo-pentadienide in organic synthesis: nucleophilic addition of lithium pentamethylcyclo-pentadienide to carbonyl compounds and carboncarbon bond cleavage of the adducts yielding the parent carbonyl compounds. Tetrahedron 62: 3523-3535

Ziyaei-Halimjani A, Azizi N & Saidi MR. 2005. Solid lithium perchlorate, a highly efficient and chemoselective catalyst for the acetalyzation of aldehydes. J Sci Islamic Republic of Iran. 16: 37-41


Refbacks

  • There are currently no refbacks.