Microwave-assisted One-pot Synthesis of 2-Substituted Quinolines by Using Palladium Nanoparticles as a Catalyst developed from Green Alga Botryococcus braunii

Abstract

Background: Quinoline is a type of N-based organic heterocyclic biologically active compound. Quinolines have grasped the interest of scientists because of their wide scope of applications. Several methods have been developed for the synthesis of quinoline and its derivatives. In this study, a new, efficient, simple, one-pot synthesis of the substituted quinolines was developed by using palladium nanoparticles as a catalyst. Methods: Catalyst synthesized by algal extract of green alga Botryococcus braunii and palladium acetate solution, and characterized by different instrumental techniques like FTIR, SEM, and XRD. The synthesized palladium nanoparticles explored for the catalytic activity in the synthesis of quinoline derivatives by the use of 2-aminobenzyl alcohol in toluene with acetyl derivatives followed by the addition of potassium hydroxide. The formation of the product was confirmed by 1HNMR, 13C NMR, and electron ionization mass spectra. Results: The formation of palladium nanoparticles characterized by visual observation means the color change from light pale yellow to dark brown indicates the reduction of palladium ions into palladium nanoparticles. Synthesized palladium nanoparticles characterized by FTIR spectrum of the algal extract of green algae B. braunii for the presence of proteins, lipids, carbohydrates, carotenoids, vitamins and other secondary metabolites in algal extract, which function as active components for bioreduction. The morphology of the catalyst was confirmed by SEM and X-ray diffraction measurements for shape, crystalline nature and size. The synthesized palladium nanoparticles explored for the catalytic activity in the synthesis of quinoline derivatives by use of 2-aminobenzyl alcohol in toluene and added acetyl derivatives followed by the addition of potassium hydroxide. In order to establish the optimum heating method, a comparative study between conventional and microwave heating method was carried out in the presence of palladium nanoparticles as a catalyst. Conclusion: This protocol provides a convenient and practical procedure for the preparation of quinoline derivatives from 2-aminobenzyl alcohol, acetyl derivatives, potassium hydroxide and palladium nanoparticles as a catalyst. This protocol will be helpful in synthesizing other quinoline derivatives and several organic heterocycles which are used in different fields such as biological, industrial, pharmaceutical, chemical, medical, etc.