One pot green synthesis of Biginelli reaction catalysed by bio-waste metal-free super acid lignin sulphonate

Abstract

A Bio-waste metal-free super acid catalyst (BWC) has been synthesized at higher temperature and used as a catalyst for synthesis of 3,4-dihydropyrimidine-2-(1H)-ones (DHPMs) via one pot three component Biginelli reaction. The multicomponent reactions are very complex and involves more than two reagents. In the present study, sulfonated carbonaceous material called a green catalyst was utilized for three component reaction. Catalyst was synthesized from sodium lignosulfonate which is obtained from the wastage of paper-making industries from the sulfite pulping process. The synthesized green catalyst was characterized by FT-IR, Thermal Gravimetric Analysis (TGA) scanning electron microscopy (SEM), Thermal Electronic microscopy (TEM), and elemental analysis. The three component Biginelli synthesis the catalyst was optimized to 8 mol % quantity which was sufficient to complete the reaction within 1–4 hrs. The yield of reaction ranges from 70-90 %. Separation was easy and recycling ability of catalyst was also tested with good retention of catalytical activity. Catalytic activity was performed as an acid-catalyzed reaction in ethanol. The synthesis of all the compounds were confirmed by 1H NMR (Nuclear magnetic resonance), MS (Mass Spectra), FT-IR (Fourier Transform Infrared), CHNS (Carbo, Hydrogen, Nitrogen, Sulphur) analysis. The satisfactory results were obtained with good yields, shorter reaction time and simplicity in the experimental procedure. The catalysts could be recycled and reused three times without decrease in the catalytic activity significantly.