Oxidative properties of iodine-adducts of propylthiouracil and methimazole: Direct synthesis of mercury(ii) complexes from the reaction with liquid mercury

Abstract

The I₂-adducts of drugs propylthiouracil (PTU) and methimazole (MeImSH) oxidize liquid mercury in dichloromethane to separate in good yield the neutral complexes [HgI₂(PTU)₂·MeOH] (1), [HgI₂(PTU)₂·HgI₂] (2), and [Hg₂I₄(MeImSH)₂] (3). The single crystal X-ray diffraction analysis of 1–2 shows that the Hg(II) center is coordinated by two sulfur atoms and by two iodine atoms in a tetrahedral geometry. In complex 2 almost linear molecules of HgI₂ result encapsulated in the crystal packing enfolded by the hydrophobic propyl appendages of coordinated units of PTU. X-ray analysis of complex 3 shows the presence of dimeric [Hg₂I₄(MeImSH)₂] molecules to form Hg₂S₂I₄ cores. The intra- and intermolecular hydrogen bonds concerning PTU and MeImSH have been evaluated. The oxidation of Hg(0) to Hg(II) requires a two-electron transfer process accomplished by an oxidative addition from the “activated” iodine moiety. The oxidizing and complexing properties of PTU-I₂ and MeImSH-I₂ have been interpreted considering the S-donor to I₂ interaction that leads to a charge separation between the sulfur-bound iodine atom S–I and the terminal I atom. Compounds 1, 2, and 3 react with tetraethylammonium iodide to separate the compound (Et₄N)₂[HgI₄] with the release of free PTU and MeImSH, respectively. The reported dissolution technique could be applied to the recovery of mercury from waste electrical and electronic equipment (WEEE) scrap, the nature of complexes 1–3 makes it possible the easy separation of the mercury as tetraiodomercurate anion and the recycling of the donors.