Brønsted acid catalyzed Prins-Ritter reaction for selective synthesis of terpenoid-derived 4-amidotetrahydropyran compounds

A number of SO3H-functionalized solids (biochar, montmorillonites, carbon and halloysite nanotubes) has been studied as catalysts in the cascade Prins-Ritter reaction of (-)-isopulegol with benzaldehyde and acetonitrile for synthesis of octahydro-2H-chromene amides (as 4R- and 4S-isomers). A high selectivity to these products at 30 °C in the presence of H2O was observed on catalysts modified with chlorosulfonic acid (CSA) reaching 84% (4R/4S of 5.7) in the case of biochar, while a relatively large amount of octahydro-2H-chromenols (up to 31%), products of Prins condensation, was formed on the materials functionalized by 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSP). Although Prins condensation proceeds efficiently on weak acid sites, the Prins-Ritter reaction requires sulfated materials with strong (0.33 – 5.8 mmol/g) Brønsted acidity. Catalysts functionalized by CSP were stable, while for the materials modified with chlorosulfonic acid, leaching of -SO3H groups was observed. Nonetheless, on resistant Bioсhar-CSP, selectivity to the amides at 30 °C (67%) was higher than that with the commercial Amberlyst-15 (47%), and triflic acid at − 25 °C (62%). Similar selectivity to the desired products on Biochar-CSA (-SO3H groups) and H2SO4 (81–84%) as well as on Biochar-CSP (-PhSO3H) and with p-toluenesulfonic acid (67–70%) was observed. DFT calculations and experimental results showed that at 30 °C formation of 4S-amide thermodynamically is more beneficial than of alcohols and dehydration products. However, addition of water results in a sharp increase in the reaction rate and 4R-amide selectivity due to a change to the kinetic control, leading eventually to both high yields and stereoselectivity. The proposed reaction pathways also were confirmed by kinetic modelling.This work is part of the scientific activity of the Institute of Chemistry of New Materials, funded by the National Academy of Sciences of Belarus. Julián E. Sánchez thanks to Pontificia Universidad Javeriana for providing computational powder and to Universidad Jaume I (Pla de Promoció de la Investigació de la Universitat Jaume I) for the Post Doctoral Fellowship. Part of this work (synthesis and charaterization of sulfonic-acid catalysts presented in Fig. 2) was funded by the Portuguese funds through Fundação para a Ciência e a Tecnologia (FCT/MCTES) in the framework of the projects UIDB/50006/2020, UIDP/50006/2020. A.F.P. is also grateful to FCT for funding through the Individual Call to Scientific Employment Stimulus 2020.01614.CEECIND/CP1596/CT0007

Isomerization of ?-pinene over ion-exchanged natural zeolites

Catalysts prepared by ion exchange of clinoptilolite-based natural zeolite tuffs with NH4+, Ba2+ and Pb2+ were investigated in the isomerization reaction of ?-pinene at atmospheric pressure under nitrogen flow. Activity and selectivity to mono-, bi- and tricyclic products were correlated with acidity strength. © 2002 Elsevier Science B.V. All rights reserved.National Council for Scientific Research: MISAG-120 98 Muh 030Funding for this work from Turkish Scientific Research Council through Grant MISAG-120 and from Ege University Research Fund through Grant 98 Muh 030 is gratefully acknowledged. -

Diesel-like hydrocarbons from catalytic deoxygenation of stearic acid over supported pd nanoparticles on SBA-15 catalysts

Palladium catalysts with different loading on SBA-15 have been prepared using a direct synthesis method and characterized with X-ray diffraction, micrographimages, and X-ray photoelectron spectroscopy. Mesoporous Pd-SBA-15 was an active and selective catalyst for deoxygenation of stearic acid in dodecane as a solvent at 300 °C under 17 bar of 5 vol% H2 in argon as a carrier gas in a semibatch reactor