Comparison of classic and microwave-assisted synthesis of benzo-thio crown ethers, and investigation of their ion pair extractions

Abstract Macrocyclic benzo-thio crown ethers and benzo-oxo crown ethers were prepared using an esterification–ring closing method. These compounds were synthesised using 2,2′-dithiodibenzoyl chloride, and various glycols and dithiols, in the presence of pyridine base under a nitrogen atmosphere in chloroform. All reactions were performed under reflux condition with conventional heating and microwave (MW) irradiation. The synthesised macrocycles were characterised by FT-IR, 1 H NMR, 13 C NMR, LC-MS, and elemental analysis methods. Extraction studies have been performed on these original macrocycles using liquid-liquid ion-pair extraction with Li + , Na + , K + , Ni 2+ , Ca 2+ , Mg 2+ , Zn 2+ , Fe 2+ ,Fe 3+ , Co 3+ , Pb 2+ , Cr 3+ , Ag + , and Cd 2+ .The K D , ext.%, ΔG and log K Ext values were also calculated. While ( U1-U7 ) ligands exhibits selectivity for Zn 2+ , Ag + , Ca 2+ , Pb 2+ , Fe 3+ , Cr 3+ , Co 2+ , Mg 2+ , Cd 2+ , and Ni 2+ metal salts, they showed no selectivity for Li + , K + and Na + metal salts. Furthermore, Fe 3+ is the most selective cation for all ligands for competitive extraction. We also observed that microwave heating can have certain benefits over conventional ovens: reaction rate acceleration, milder reaction conditions, higher chemical yield, and lower energy usage. These ligands could be used as metal sensors, enzyme inhibitors, antimicrobial/antifungal agents, and in biological applications.