Ultrasound-Assisted Synthesis and DFT Studies of Novel Schiff Bases Derived from 3-Methyl-1,3-benzothiazol-2(3H)-one in an Ionic Liquid Medium

Abstract

A new series of Schiff bases have been prepared by the condensation between 3-methyl-2-oxo-2,3-dihydro-1,3-benzothiazole-6-carbaldehyde and primary aromatic amines using an eco-friendly method that employs the ionic liquid triethylammonium acetate [TEAA] as a solvent and catalyst at 80°C under ultrasonic irradiation. This protocol has a number of benefits, including short reaction times, direct isolation of the pure product, and high yield. The structures of the newly synthesized derivatives were established on the basis of IR, ¹H NMR, and ¹³C NMR spectroscopic techniques (including two-dimensional ¹H–¹³C HSQC and ¹H–¹³C HMBC experiments) and elemental analysis. A DFT theoretical study was carried out for the synthesized molecules in the gas phase using the B3LYP method with 6-311G(d,p) basis set; the HUMO and LUMO energies were calculated for the optimized geometries, which showed that compound 4e is the most stable with an energy gap of 4.05585 eV, as presented by the DOS spectrum. The reactivity of the compounds was studied by calculating some global reactivity descriptors, revealing that compound 4b is the most chemically reactive. In addition, molecular electrostatic potentials (MEP) was studied for the reaction centers of the synthesized compounds.