Stepwise Synthesis and Mult spectroscopic Characterization of a 4-Hydroxyphenyl-Functionalized Benzimidazole Bis-Imine and Its Bis(thiazolidin-4-one) Derivative

Abstract

A para-hydroxyphenyl-functionalized benzimidazole sequence was prepared through two consecutive carbonyl–amine condensations followed by thioglycolic-acid-mediated cyclization. 4-(1H-Benzimidazol-2-yl)aniline (K1) was condensed with 4-aminoacetophenone to give the amino-ketimine K2, and the remaining para-amino group was subsequently reacted with 4-hydroxybenzaldehyde to furnish the unsymmetrical bis-imine K3. Treatment of K3 the corresponding bis(thiazolidin-4-one) compound was obtained by cyclization with thioglycolic acid using anhydrous ZnCl₂ as a catalyst derivative K4. For K3, FTIR showed the phenolic/benzimidazole stretching region, conjugated imine bands and an aryl C–O absorption, while the ¹H and ¹³C NMR spectra were consistent with the extended aromatic–imine framework. Cyclization to K4 was supported by the appearance of a strong thiazolidin-4-one C=O band at 1746 cm⁻¹, a carbonyl-carbon resonance at δ 170.19 ppm and new ¹H NMR resonances at δ 4.81 and 3.75 ppm. High-resolution mass measurements closely matched the calculated [M+H]⁺ values for K1–K4, and elemental analyses were consistent with the proposed molecular compositions. The combined analytical data establish a spectroscopically traceable para-hydroxy member of this benzimidazole bis-imine/thiazolidin-4-one series.