Synthesis, Characterization and Optimum Reaction Conditions of Oligo-N, N^′-bis (2-hydroxy-1-naphthalidene) Thiosemicarbazone

Abstract

The oxidative polycondenzation reaction conditions of N, N^′-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (HNTSC) using air oxygen, H₂O₂ and NaOCl were studied in an aqueous alkaline medium between 50–90 °C. Oligo-N, N^′-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was characterized by ¹H-NMR, FT-IR, UV-Vis, size exclusion chromatography (SEC) and elemental analysis techniques. Solubility testing of oligomer was investigated using organic solvents such as DMF, THF, DMSO, methanol, ethanol, CHCl₃, CCl₄, toluene acetonitrile, ethyl acetate, concentrated H₂SO₄ and an aqueous alkaline solution. Using NaOCl, H₂O₂ and air O₂ oxidants, conversion to oligo-N, N^′-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (OHNTSC) of N, N^′-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was found to be 85, 80 and 76%, respectively, in an aqueous alkaline medium. According to the SEC analyses, the number-average molecular weight, weight-average molecular weight and polydispersity index values of OHNTSC synthesized were found to be 1050 g mol⁻¹ 1715 g mol⁻¹ and 1.63, using NaOCl, and 2137, 2957 g mol⁻¹ and 1.38, using air O₂ and 2155 g mol⁻¹ 4164 g mol⁻¹ and 1.93, using air H₂O₂, respectively. Also, TG analysis was shown to be unstable of oligo-N, N^′-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone against thermo-oxidative decomposition. The weight loss of OHNTSC was found to be 97.29% at 900 °C.