Abstract: The acid catalyzed Prins cyclization reaction of (-)-isopulegol with aldehydes containing electron-donating and electron–withdrawing substituents is widely used for the synthesis of a variety of octahydro-2H-chromen-4-ols which possess biological activity. In this work, the effects of textural properties and Brønsted acidity on the catalytic performance in Reaction (1) of acid–activated clays with different structures, such as the montmorillonite from Mukhortala (Buryatia, Russia) (HCl-MM), the kaolin from Kampanovsk (Krasnoyarsk, Russia) (HCl-K), and a metakaolin obtained by calcination of kaolin at 650 ºC for 4 h (HCl-MK) were investigated. Special attention will be paid to the relation between the structure of the clays and the distribution of the products of the reaction, particularly the selectivity of isomers IIIa and IIIb [1,2]. (1) Textural and physicochemical properties of these materials were investigated by X-ray diffraction, N2 adsorption/desorption, chemical analysis and FT-IR spectroscopy using pyridine as probe molecule. Physicochemical methods point out that acid activation leads to the beginning of leaching of Al from the solids, which favours the change in textural and acidic properties. According to IR spectroscopy results, the amount of Brønsted acid sites (BAS) in the acid modified natural clays rises with increasing HCl concentration, while the strength of BAS varied negligibly. The type of clay affects the amount and strength of BAS. Amount of BAS in clays modified by 0.5M HCl decreases in the order: HCl-MM > HCl-K > HCl-MK. The effect of the structural properties and Brønsted acidity on the catalytic properties of these acid modified natural clays was investigated in reaction (1). All samples were activated at 150 ºC for 2 h for the removal of the water adsorbed onto the solids. Molar ratio of (I)/(II) was 1.0/1.0. It was demonstrated that in the presence of acid-treated MM the reaction proceeded at 35 ºC, while it was necessary to carry out the reaction at 50 ºC in the presence of acid-treated K and MK. The main products of the reaction were the isomers (IIIa-b). Selectivity towards (III) decreases in the order HCl-MK > HCl-K > HCl-M. The low selectivity towards (III) in the presence of acid-treated MM is related with the dehydration of isomers (III) to (IV). According to experimental data the concentration of HCl used for the acid activation of the clays strongly affects the reaction rate and the yield of isomers (IIIa-b) (Fig. 1). Figure 1. Effect of the HCl concentration and amount of BAS on the reaction rate and yield of (III) in the reaction of synthesis of octahydro-2H-chromen-4-ol from vanillin and (-)-isopulegol over samples of montmorillonite (MM), kaolin and metakaolin modified by HCl (Experimental conditions: 100 mg catalyst, 0.65 mmol (I), 0.65 mmol (II) in 4 mL toluene. MM - 35 oC, kaolin and metakaolin – 50 ºC) It was found that the amount of BAS in acid-activated clays is a key factor for the adjustment of the reaction rate and the selectivity of the reaction. An increase of the amount of BAS leads to a increase the reaction rate (Fig. 1). The nature of the clay affects the chemo- and stereo-selectivity, i.e. molar ratios of (III)/(IV) and (IIIa)/(IIIb). Stability of the most active 0.5M HCl-MM catalyst was investigated by using it in various successive catalytic tests. After each catalytic experiment, the catalyst was separated, washed with toluene, dried at room temperature and used in the next run. Experimental data points that 0.5M HCl-MM can be used repeatedly without significant loss of catalytic activity during at least three catalytic cycles due to the stability of the layer structure of montmorillonite, as confirmed by the XRD analysis of the catalyst after reaction. References: 1. M. N. Timofeeva, K. P.Volcho, O. S. Mikhalchenko, V. N. Panchenko, V. V. Krupskaya, S. V. Tsybulya, A. Gil, M. A. Vicente, N. F. Salakhutdinov, J. Mol. Catal. A: Chem., 2015, 398, 26. 2. M. N. Timofeeva, V. N. Panchenko, A. Gil, S. V. Zakusin, V. V. Krupskaya, K. P. Volcho, M. A. Vicente, Catal. Commun., 2015, 69, 234.

Cite: Timofeeva M.N. , Volcho K.P. , Panchenko V.N. , Gil A. , Vicente M.A.
Effect of Structure and Acidity of Acid Modified Clay Materials on Synthesis of Octahydro-2H-Chromen-4-ol from Vanillin and Isopulegol
In compilation The 5th Asian Symposium on Advanced Materials: Chemistry, Physics & Biomedicine of Functional and Novel Materials (ASAM-5) : Proceedings. 2015. – C.77-78.

Identifiers: No identifiers

Citing: Пока нет цитирований