Spectrophotometric Exploration of the Mechanism of Dichloroiodate (ICl ₂ ^– ) Formation from NaI, NaOCl, and HCl

Benzyltriethylammonium dichloroiodate ([BTEA]-[ICl₂]) is a useful tool in organic synthesis, specifically for the iodination of aniline derivatives. While the mechanism of ICl₂ ^- formation from NaI, NaOCl, and HCl is not well studied, the vibrant colors involved in the reaction make UV-vis spectroscopy an excellent tool for monitoring the process. In this work, various conditions for preparing aqueous ICl₂ ^- were monitored spectrophotometrically, and observed intermediates were further characterized by Raman spectroscopy and mass spectrometry. The observed dependence of ICl₂ ^- formation on pH and Cl^- concentration, coupled with literature precedents, allowed a mechanism for the reaction to be proposed. Finally, preferred conditions for the bulk preparation of [BTEA]-[ICl₂] were recommended, after investigating the aqueous stability of [BTEA]-[ICl₂] and the persistent problem of undesirable I₂ formation.