Acid-activated clay as heterogeneous and reusable catalyst for the synthesis ofbioactive cyclic ketal derivatives

Abstract

A new heterogeneous acid catalyst based on a natural resource, Tunisian clay (Clay-H0.5), has been prepared and characterized by FT-IR, FE-SEM, and powder X-ray diffraction (XRD), as well as chemical composition, cation exchange capacity, specific surface area, and pore volume. Acid treatment for 0.5 h enlarged the surface area from 78.24 to 186.10 m 2 /g and pore volume (PV) from 0.186 to 0.281 cm 3 /g. The catalytic activity of this material was investigated in ketalization reaction under mild solvent-free conditions. This achieved up to 92% isolated yield for only 10 wt.% of the catalyst. This environmentally friendly method has advantages such as simple work-up procedure, avoidance of organic solvents, and good performance in ketalization reactions. Importantly, the Clay-H0.5 catalyst showed good recyclability where insignificant activity loss was exhibited even after six runs. Synthesized cyclic ketals were tested for their possible antileishmanial and antibacterial activities as well as antifungal activity. Biological screening showed that compound 11 had important antileishmanial activity against both L. major and L. infantum, while compound 14 also had significant antibacterial activity against four gram-positive and two gram-negative bacteria, and antifungal activity against Candida albicans, with minimal inhibitory concentration values ranging from 15.62 µg/mL to 125 µg/mL.

Green Production of Glycerol Ketals with a Clay-Based Heterogeneous Acid Catalyst

“…The evolution of r 0 between cycles indicates that the catalyst deactivates following an exponential trend towards a stable, but less active, catalytic species. Though less evident, it happens also in other ketalization systems, where the catalyst seems to be less prone to deactivation, but, again, a certain stabilization is observed after a few cycles [35]. This behavior is typical of a heterogeneous catalyst that contains two or more types of active centers with different stabilities or catalysts that are partially blocked during the reaction process [42,43].…”

“…The cation exchange capacity (CEC) was determined by elemental microanalysis. The adsorption process was conducted according to Hagui et al [35]. Briefly, 200 mg of sample were contacted with 20 mL of an aqueous solution of ammonium acetate (1 M) three times and was subsequently thoroughly washed with anhydrous methanol, firstly, and with Milli-Q water three times.…”

“…Finally, CEC of the raw or crude clay RC and the 1-h acid treated clay AC were assessed, to find that this property was reduced with the acid treatment from 74 ± 3 mequiv/100 g of solid to 32 ± 2 mequiv/100 g of solid, probably due to an ion-exchange process during the acid attack [35].…”

Removal of Cd(II), Cu(II), and Pb(II) by adsorption onto natural clay: a kinetic and thermodynamic study

“…The bands located at 693, 776, and 1005 cm -1 and the intense band located between 900 and 1200 cm -1 and centered at 1031 cm -1 correspond to the stretching vibrations of Si-O [9,[20][21][22][23][24]. Intense peaks were observed around 472 and 533 cm -1 attributable to the deformation of Si-O-Mg and Si-O-Al, respectively [25,26]. The band located at 912 cm -1 is attributed to the bending vibrations of the groups Al-Al-OH and Al-Mg-OH [27,28].…”

Valorization of natural clay as an ecological catalyst in the regioselective synthesis of some heterocyclic compounds based on 1,2,3-triazoles

“…Dioxolanes are heterocyclic acetal compounds with a cycle containing five atoms; two are oxygen. Several types of research report the synthesis of dioxolanes using activated clays as catalysts [3][4][5][6][7][8]. In contrast, triazoles are heterocyclic compounds with three nitrogen atoms placed in 1,2,3 or 1,2,4 positions of the cycle.…”