Synthesis of thiocarbonyl analogues of colourimetric coumarin-based chemosensors: altering the selectivity from Fe to Hg(ii) and Cu(ii) ions

Abstract

Lawesson's reagent is a thionating compound that can convert a carbonyl group into a thiocarbonyl analogue by replacing oxygen atoms with sulphur. Herein, ester-functionalised coumarin compounds S1a and S2a were successfully mono-substituted and disubstituted with sulphur atoms using Lawesson's reagent. It was noted that the lactone carbonyl was first substituted, resulting in the mono-substituted analogues S1b and S2b, followed by the formation of disubstituted derivatives S1c and S2c. The thionated compounds were separated using preparative TLC with a dichloromethane: petroleum ether mixture as the mobile phase. NMR and FT-IR spectroscopies were utilised to identify and confirm the compounds isolated from the thionation reaction. The thioanalogues were then tested as potential chemosensors for metal ion detection in an acetonitrile solvent system. The results showed unique selectivities, with the unsubstituted derivatives displaying selectivities for Fe²⁺ and Fe³⁺. In contrast, the mono-substituted and disubstituted derivatives were selective for Hg²⁺ and Cu²⁺, demonstrating the prospective applications of these compounds as chemosensors for these metal ions.