Reactivity of di‐iodine toward thiol: Desulfuration reaction of 5‐nitro‐2‐mercapto‐benzimidazole upon reaction with di‐iodine

Abstract

Abstract The reaction of 2‐mercapto‐benzoic acid (H 2 MBA), 2‐mercato‐nicotinic acid (H 2 MNA), and 2‐mercapto‐pyrimidine (PMTH) with a twofold molar amount of di‐iodine (I 2 ) results in the isolation of crystals of the neutral disulfides of formulae: {(HMBA) 2 ·1/2(CH 3 CN)} ( 1 ), {(HMNA) 2 ·(H 2 O)} ( 2 ), and (PMT) 2 ( 3 ), respectively, when dichloromethane/acetonitrile/methanol ( 1 ) or dichloromethane ( 2,3 ) were used as solvents. The reaction of di‐iodine with thethiol PMTH and 2‐mercapto‐benzothiazole (MBZTH) yields the disulfide (PMT) 2 ( 3 ), and the di‐iodine adduct of formula {[MBZTH‐I 2 ]·[MBZTH] 2 } ( 4 ), respectively. The reaction of di‐iodine with 5‐nitro‐2‐mercapto‐benzimidazole (O 2 N‐MBZIMH) ( 5 ) in the presence of ferric trichloride hydrate (FeCl 3 ·6H 2 O), in a 6:3:1 (I 2 :thiol:FeCl 3 ·6H 2 O) molar ratio, results in cocrystal ( 6 ), which contain the desulfurated hydroxyl derivative O 2 N‐BZIMOH ( 6a ) and unreacted O 2 N‐MBZIMH ( 6b ) in a 3:1 molar ratio. The compounds were characterized by elemental analysis, FT‐IR, and 1 H NMR spectroscopy. The crystal structures of compounds 1 – 6 were also determined by X‐ray crystallography. Cyclic voltammetry measurements showed that thiols with low oxidation potentials (< 1.0 V) mainly form disulfides upon a reaction with di‐iodine, whereas those with higher oxidation potential form charge transfer (CT), resulting in desulfurated products, MBZIMH. However, in the case of O 2 N‐MBZIMH a desulfurated species was isolated. The formation of the final product also requires the presence of FeCl 3 . © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:498–511, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21042