Heterogeneous Catalytic Transformation of Citronellal to Menthol in a Single Step on Ir-Beta Zeolite Catalysts

Abstract

The synthesis of menthol from citronellal was studied on bifunctional Ir/Beta zeolite catalysts, prepared via impregnation of Beta zeolite with different concentrations of Ir. The results show that Beta zeolites, impregnated with Ir, catalyze the one-pot full conversion of citronellal to menthol by consecutive acid-catalyzed cyclization and Ir-catalyzed hydrogenation. The best results (95% selectivity for the menthol isomers, of which 75% is the desired (±)-menthol) were recorded on 3% Ir/Beta zeolite catalyst. In contrast with earlier studies, 0.05 g Ir/Beta catalyst per mL of substrate leads to complete and selective substrate transformation. The textural properties, acidity and hydrogenation function were studied by liquid N 2 adsorption-desorption, FT-IR, XPS and hydrogen chemisorption techniques. To clarify the mechanism of the cyclization of citronellal, tests were also performed using zeolites with different acidity and loaded with other metals (Pt, Pd, Rh, Ru).

MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst

“…To afford citronellal transformation into menthol in a one-pot, a bifunctional catalyst bearing acid and metal sites can be used. Jacobs et al 23,24 have reported that a 3% Ir-impregnated H-BEA zeolite catalyzes the one-pot synthesis of menthol from citronellal in two steps. First, the cyclization step was carried out under N 2 atmosphere, and then H 2 was added to carry out the hydrogenation.…”

MOFs vs. zeolites: carbonyl activation with M(iv) catalytic sites

“…Ir(III), in the Beta zeolite (entry 11) clearly increases the reaction rate. 11 Therefore, the presence of strong Lewis acid sites in a hydrophobic environment is decisive for the high catalytic activity of these Sn o Zr Beta zeolites, compared to MOFs, as will be confirmed in the following section.…”

Konversi Sitronelal Menjadi Senyawa Isopulegol dengan Katalis ZnBr2/β-Zeolit

“…Hal tersebut mendorong para peneliti melakukan upaya penggantian situs asam Bronsted dengan situs asam Lewis dengan cara mengembankan logam aktif. Penelitian sebelumnya mengenai katalis berbasis pengemban β-zeolit untuk konversi sitronelal telah banyak dilaporkan, antara lain adalah Ni/Zr-beta (Nie et al 2007), katalis Pt/H-beta yang dapat berperan sebagai katalis dwi fungsi (Mertens et al 2006), katalis Sn/β-zeolit yang memberikan stereoselektivitas 85% (Kang et al 2013), dan katalis Ir/ β-zeolit yang memberikan produk mentol yang tinggi (93%) dalam reaksi satu tahap (Dirk dan Jacobs 2009).…”