Synthesis, Structural Characterisation and Performance Evaluation of Symmetrical Para-Benzoylthiourea-Based Ligand as Colorimetric Chemosensors

Lye, Zhi Ying (2023) Synthesis, Structural Characterisation and Performance Evaluation of Symmetrical Para-Benzoylthiourea-Based Ligand as Colorimetric Chemosensors. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

In this work, three novel symmetrical para-substituted benzoylthiourea-based ligands, BT, p-Br BT and p-Me BT (where BT = benzoylthiourea) with different substituent bounded to the benzoylthiourea moiety have been synthesised and structurally characterized by CHNS elemental analysis, 1H NMR spectroscopy, 13C NMR spectroscopy and spectroscopic methods including FTIR spectroscopy and UV-Vis spectroscopy. Besides that, the melting point of the three synthesized ligands was investigated by using melting point apparatus and DSC to ascertain their purity. The melting point of the three ligands falls within the range of 254 – 256°C which were consistent with the melting point range obtained from melting point apparatus. The experimental result obtained from the CHNS elemental analysis was found to be consistent with the analytical calculated result. All the three ligands have displayed important functional groups including N-H, C=O, C-Naliphatic and C=S at the expected wavenumber range in the FTIR spectrum which are 3318 – 3329 cm-1, 1665 – 1670 cm-1, 1253 – 1258 cm-1, 1146 – 1148 cm-1, respectively. Besides, all ligands displayed transitions at the similar wavelengths ranging from 200 – 290 nm in acetonitrile. Both experimental FTIR and UV-Vis results obtained were well agreed with the calculated result. The origins of each electronic transition were well-interpreted through TD-DFT calculation using Gaussian 09 software. The 1H NMR displayed peaks for CONH, CSNH and aromatic rings (Ar-H) at approximately 12 ppm, 11 ppm and 7.3 – 8.0 ppm, respectively whereas 13C NMR displayed peaks for C=S, C=O and aromatic carbons at approximately 180 ppm, 169 ppm and 125.9 – 136.3 ppm, respectively. In addition. the total number of protons and carbons obtained from the integration of the peak’s height can confirmed the structure of the three ligands. After characterization, the three ligands were tested for their application as a sensitive colorimetric chemosensor for metal ion detection in aqueous media. The three novel ligands were tested for metal ions Cu2+, Cd2+, Ca2+, Co2+, Fe2+, Fe3+, Pb2+, Mn2+, Ni2+ and Zn2+ and only the metal ion Cu2+ showed a positive result. The colourless solution turned pale pink and an absorption peak was observed in the visible region at the 532.5 nm. Following that, the possible binding ratio and coordination mode of BT, p-Br BT and p-Me BT with Cu2+ ion was studied by Job’s method and FTIR spectroscopy, respectively. It was found that the ratio of ligand to Cu2+ was 2:1 ratio and the Cu2+ ion coordinate with the N of the -NH group next to the C=O group. The limit of detection of BT, p-Br BT and p-Me BT for Cu2+ ion was calculated to be as low as 3.10 × 10-5 M, 1.64 × 10-5 M and 1.97 × 10-5 M, respectively. The results indicates that all the three synthesized ligands may be applied as highly selective and sensitive colorimetric chemosensors for Cu2+ ion detection in the drinking water (3.15 × 10-5 M).