Iodination of Organic Compounds with Elemental Iodine in the Presence of Hydrogen Peroxide in Ionic Liquid Media

Abstract

Iodo-transformations using the reagent system I2/H2O2 were studied in the water miscible ionic liquid (IL) 1-butyl-3-methyl imidazolium tetrafluoroborate (bmimBF4) and in water immiscible IL, 1-butyl-3-methyl imidazolium hexafluorophosphate (bmimPF6). Two different forms of H2O2 as mediators of iodination were investigated, namely 30% aq. H2O2 and urea-H2O2 (UHP) in solid form. The role of the oxidant during the course of a reaction could be distinguished based on the amount of reagent required for the most efficient transformation. Two types of iodo-functionalizations through an electrophilic process were observed depending on the structure of the substrates. Whereas ring iodination took place in the case of dimethoxy- and trimethoxy-benzenes, with arylalkyl ketones the alkyl group α to the carbonyl was regioselectively iodinated. The results were further evaluated in comparison with iodination using the reagent system I2/H2O2 in water as medium, and under solvent-free reaction conditions, in terms of efficiency, selectivity, mechanism, and the ‘green’ aspects. The reusability/recycling of water immiscible bmimPF6 was investigated for 1,3,5-trimethoxy benzene (1b), which required a 1/0.5/0.6 molar ratio of substrat/I2/oxidant, and for 1,2,3-trimethoxy benzene (1f), which required a 1/1/1 ratio for complete iodine introduction. In addition, the efficiency of iodination was tested by varying the substrates, and employing the recycled hydrophobic IL bmimPF6.