Brønsted and Lewis Solid Acid Catalysts in the Valorization of Citronellal

Terpenes are valuable starting materials for the synthesis of molecules that are of interest to the flavor, fragrance, and pharmaceutical industries. However, most processes involve the use of mineral acids or homogeneous Lewis acid catalysts. Here, we report results obtained in the liquid-phase reaction of citronellal with anilines under heterogeneous catalysis conditions to give tricyclic compounds with interesting pharmacological activity. The terpenic aldehyde could be converted into octahydroacridines with a 92% yield through an intramolecular imino Diels–Alder reaction of the imine initially formed in the presence of an acidic clay such as Montmorillonite KSF. Selectivity to the desired product strongly depended on the acid sites distribution, with Brønsted acids favoring selectivity to octahydroacridine and formation of the cis isomer. Pure Lewis acids such as silica–alumina with a very low amount of alumina gave excellent results with electron-rich anilines like toluidine and p-anisidine. This protocol can be applied starting directly from essential oils such as kaffir lime oil, which has a high citronellal content.

Heterogeneous catalytic synthesis of quinoline compounds from aniline and C1–C4 alcohols over zeolite-based catalysts

The synthesis of quinolines from aniline and a C₁–C₄ alcohol was conducted under gas-phase reaction conditions over a series of zeolite-based catalysts.

Synthesis of quinolines from aniline and propanol over modified USY zeolite: catalytic performance and mechanism evaluated by in situ Fourier transform infrared spectroscopy

Synthetic passway of quinolines from aniline and propanol over modified USY catalyst.

High-efficiency catalytic performance over mesoporous Ni/beta zeolite for the synthesis of quinoline from glycerol and aniline

Quinoline was synthesized via the typical Skraup approach with a vapor-phase process. The mesoporous Ni/beta zeolite catalyst exhibited high-efficiency catalytic activity and an enhanced ability of anti-deactivation.