One pot menthol synthesis via hydrogenations of citral and citronellal over montmorillonite-supported Pd/Ni-heteropoly acid bifunctional catalysts

Cascade transformations of (±)-citronellal to menthol over extruded Ru-MCM-41 catalysts in a continuous reactor

“…Menthol is a fine chemical, one of the most common aroma compounds with a worldwide demand of more than 25 000-30 000 metric tons per year. [1][2][3][4][5] Three asymmetric carbon atoms in the cyclohexane ring lead to a chiral compound exhibiting four diastereoisomeric pairs, namely (±)-menthol, (±)-neomenthol, (±)-isomenthol and (±)-neoisomenthol. Only (−)-menthol has a strong physiological cooling effect and the characteristic odour worthy to be commercially used in i.e.…”

“…The other seven isomers are typically considered less valuable. [1][2][3][5][6][7][8][9] Synthetic (−)-menthol is mainly obtained by the industrial Takasago five step process with myrcene as the main reactant. 7,[10][11][12] The last two steps in this process are the 'ene' cyclization of (+)-citronellal to (−)-isopulegol in the presence of Lewis acid aqueous ZnBr 2 catalyst.…”

“…1) over heterogeneous catalyst represents a more attractive alternative due to an easy separation and reuse of the catalysts in one step. 10 Various heterogeneous bifunctional powder catalysts, such as Pt, Pd, Cu, Zr on H-MCM-41; 9,16 Pt, Pd, Cu on SBA-15; 16 ZnBr 2 , Ni on γ-Al 2 O 3 ; 17 ZnX 2 (X = Cl, Br, NO 3 ), Ru, Pd, Cu on SiO 2 ; [18][19][20] Ni on ZrS; 12 Ni, Pd on MM, HPA-MM; 5 Pt, Pd, Ni, Ir, Ru, Zr, Ni/Zr, Pd/Zr on H-Beta zeolite, 2,3,8,9,11,18,21,22 have been tested in a batch operation mode. These studies revealed that the active metal has a significant effect on the side reactions such as hydrogenation of citronellal, dimerization of citronellal or isopulegol, and defunctionalisation.…”

Unraveling the Role of Metal Oxide Catalysts in the CO2 Desorption Process from Nonaqueous Sorbents: An Experimental Study Carried out with 13C NMR

“…The obtained spectra are shown in Figure S1. The pyridine molecules can interact with the uncoordinated metal atoms to show peaks at around 1440 and 1590 cm –1 , indicating the presence of Lewis acid sites . The pyridine molecules can also interact with the surface hydroxyl groups and generate a peak at around 1540 cm –1 corresponding to the Brønsted acid sites .…”

“…The pyridine molecules can interact with the uncoordinated metal atoms to show peaks at around 1440 and 1590 cm −1 , indicating the presence of Lewis acid sites. 45 The pyridine molecules can also interact with the surface hydroxyl groups and generate a peak at around 1540 cm −1 corresponding to the Brønsted acid sites. 29 The peak appearing at 1490 cm −1 is attributed to the combination of Lewis acid sites and Brønsted acid sites.…”