[7790-99-0] · ClI · Iodine Monochloride · (MW 162.35)
Physical Data: mp 27.2 °C (a-form; black needles, ruby-red by transmitted light); mp 13.9 °C (b-form; black platelets, brownish-red by transmitted light); bp 97 °C (b-form, partial decomposition); d 3.10 g cm-3.
Solubility: sol alcohol, ether, CS2, acetic acid, acetone, pyridine; sol H2O, but hydrolyzes to HCl and IOH.
Form Supplied in: low melting black or brownish-red solid; widely available (usually 97-98% purity).
Handling, Storage, and Precautions: corrosive solid and vapor; readily absorbed through skin and mucous membranes; use in a fume hood and wear gloves and appropriate protective clothing; air-, moisture-, and light-sensitive; should be stored refrigerated (under N2) in a tightly sealed amber bottle. Explodes on contact with potassium metal; mixtures with sodium metal can explode if impacted. Reaction with PCl3 is extremely exothermic.
As a source of electrophilic iodine, iodine monochloride is an effective reagent for iodination of a wide variety of aromatic compounds,2 including heterocyclic aromatic compounds (eq 1).5 In a related mode of reactivity, uracil bases and protected nucleosides can be iodinated in excellent yield (eq 2).6 See also Iodine-Silver(I) Fluoride and Trifluoroacetyl Hypoiodite for iodination of aromatic compounds.
Formation of vicinal chloroiodoalkanes via iodine monochloride addition to alkenes generally occurs with high anti stereospecificity, implicating the intermediacy of an iodonium ion in the reaction sequence. Unsymmetrical alkenes typically undergo predominantly Markovnikov addition (e.g. reaction of 1-hexene produces a 66:34 mixture of 2-chloro-1-iodohexane and 1-chloro-2-iodohexane in 75% overall yield7). Regioselectivity and stereoselectivity in additions to alkynes are very dependent on the alkyne structure.
Except in the case of C-Fe and C-Co bonds, cleavage of carbon-metal bonds by iodine monochloride specifically produces the organic iodide and the metal chloride. Organosilicon8 (eq 3), organoboron9 (eq 4), and organoaluminum10 (eq 5) bond cleavage reactions are probably of greatest utility to synthetic organic chemists.
Iodine monochloride can function as a chlorinating agent because of its tendency to disproportionate to molecular iodine and molecular chlorine in nonpolar solvents.11 Oxidation of dioxolanes to esters has been reported to proceed in good to excellent yield.12 Also, a variety of conditions have been reported for the in situ generation of iodine monochloride, including t-Butyl Hypochlorite/Iodine,13 Antimony(V) Chloride/I2,14 and Iodine-Copper(II) Chloride.15
Ronald G. Brisbois & Randall A. Wanke
Hamline University, St. Paul, MN, USA