Synthesis, Spectroscopic Studies and Keto-Enol Tautomerism of Novel 1,3,4-Thiadiazole Derivative Containing 3-Mercaptobutan-2-one and Quinazolin-4-one Moieties.

In this study, a novel 1,3,4-thiadiazole derivative containing 3-mercaptobutan-2-one and quinazolin-4-one moieties (Compound ) is synthesized by the coupling of 2-amino-1,3,4-thiadiazole-5-(3-mercaptobutan-2-one) (Compound ) with 2-Phenyl-4H-3,1-benzoxazin-4-one (Compound ) in one molecule moiety. Compound is found to exist as two types of intra-molecular hydrogen bonding with keto-enol tautomerism characters, which is further confirmed using FTIR, H-NMR, C-NMR, mass spectrometer, and UV-Visible spectra. The H-NMR and UV-Visible spectra of Compound are investigated in different solvents such as methanol, chloroform, and DMSO. Compound exhibits keto-enol tautomeric forms in solvents with different percentage ratios depending on the solvent polarity. The H-NMR and UV-Visible spectral results show that Compound favors the keto over the enol form in polar aprotic solvents such as DMSO and the enol over the keto form in non-polar solvents such as chloroform. The C-NMR spectrum gives two singles at δ 204.5 ppm, due to ketonic carbon, and δ 155.5 ppm, due to enolic carbon, confirming the keto-enol tautomerism of Compound . Furthermore, the molecular ion at 43 and 407 in the mass spectrum of Compound and fragmentation mechanisms proposed reveal the existence of the keto and enol forms, respectively.