Hypoiodous acid, formation

A. J. Balard found mercury immediately decomposes hypochlorous acid without the disengagement of any gas, but mercury oxychloride is formed. P. Grouvelle reported previously that when chlorine acts on mercuric oxide suspended in water, mercury oxychloride, very slightly soluble in cold water, is formed. L. J. Thenard found that the liquid contained both chloride and chlorate of mercury, also in soln. A. J. Balard, however, believed that these bodies are formed consecutively, and that their existence was preceded by that of a mercuric hypochlorite, as takes place with the salts of silver, and, as previously indicated, he prepared hypochlorous acid by the action of chlorine on mercuric oxide suspended in water. No mercury hypobromite has yet been isolated. There is a possible formation of mercury hypoiodite, or more probably of hypoiodous acid, when iodine is shaken up with... 

Although the products differ considerably in these two reactions, presumably the mechanisms are not drastically different The negative hydroxide ion attacks the most positive atom in the organic iodide. In methyl iodide this is the carbon atom (, > jyc) and the iodide ion is displaced. In Ihe trifluoromethy) iodide the fluorine atoms induce a positive charge on the carbon which increases its electronegativity until it is greater than that of iodine and thus induces a positive charge on the iodine. The latter is thus attacked hy the hydroxide km with the formation of hypoiodous acid, which then loses an H+ in the alkaline medium to form IO . 

The rather fast reaction rate of halomethanes with Cl atoms suggests that this process may play a primary role in the removal of halomethanes from the troposphere and results in the formation of HC1 or 1C1 molecules. These degradation pathways do not lead to bromine or iodine atoms but to relatively stable molecules, which may initiate a different bromine and iodine cycles in the marine boundary layer. The atmospheric lifetime of IC1 is probably controlled by its sunlight photodissociation to iodine and chlorine atoms. Another possible degradation pathway of IC1 may be the hydrolysis to hypoiodous acid IOH, which may further be dissolved in seawater. 

A volatile iodine species, neither elemental nor organic, which has been found in steam/air atmospheres, has been identified as hypoiodous acid (HOI) (Cartan et al., 1968). In water-cooled power reactors, any fission products released from fuel will pass into hot alkaline water and thence to a steam-air mixture. These conditions are thought to favour the formation of HOI (Keller et al., 1970), but the evidence is indirect. For example, tests for elemental iodine or iodine with an oxidation state higher than that of HOI gave negative results. 

Hypoiodous acid deprotonates in alkaline solution (pKa = 11) furthermore, 10 is a well-characterized species in the gas phase (42), and it has been reported as an intermediate in the radiolysis and photolysis of HIO in aqueous solution (70). A value of 149.77 kJ/mol is reported in the NBS tables for the standard free energy of formation of IO in the gas... 

A. Skrabal has shown that in the case of hypoiodous acid in alkaline soln., ])robably an alhali hypotri-iodite, MI3O, is formed, which reacts like free iodine and the velocity of iodate formation is determined by the rate of reaction between the hypotri-iodite and the alkali by which iodide and iodate are formed. The kinetic equation, dx/(U k[)ll0Y[Vlf[01i ], based on these assumptions fits the observations of E. L. C. Forster. When the concentration of the iodine is small the reaction... 

The successful formation of the C-14,15 alkene was accomplished by oxidation of 51 with m-CPBA (Scheme 24), probably via an iodoso intermediate which undergoes syn-elimination of hypoiodous acid and hydrolysis of the sulfate to yield 52. The oxidative elimination is a procedure originally developed30 by Reich with obvious potential for complex molecule synthesis, although it is presently less popular than related sequences involving sulfoxides or selenoxides. 

Iodine can adopt a range of oxidation states, and various iodine species exist in an aqueous environment — 1 to -i 5, e.g., —1 (iodide, I ) + 1 (hypoiodous acid, HOI) -i5 (iodate, IO3 ). The oxidation of iodide by reactive oxygen species, such as H2O2, has been studied since the early 1920s. Two of the primary variables that determine the concentration and distribution of iodine species formed during the oxidation of iodide are pH and iodide. The effect of pH is dramatic the effect of iodide is nonlinear in that the rate of formation of Ij or hypoiodous acid (HOI) can increase or decrease as iodide is increased, depending on the precise experimental conditions (Gottardi, 1999). 

The mere presence of peroxidase, H2O2, and iodide are not necessarily sufficient to ensure formation of I2. Tissues must be capable of concentrating iodide at a sufficient threshold such that the iodide anion can itself compete for binding to the enzyme-bound hypoiodous acid intermediate to yield I2. Currently no evidence exists outside of thyroid and mammary tissue to support the formation of iodinated by-products, although both the salivary gland and ovaries concentrate iodide and express a peroxidase. 

Asensio and coworkers reported a low temperature oxidation of iodomethane with DMDO to afford a pale yellow precipitate of iodosylmethane (20, Scheme 2.10) [104]. Upon raising the temperature to -40 °C, in the presence of moisture iodosylmethane decomposes to form the unstable hypoiodous acid, HOI, which can be trapped in situ by an alkene to afford iodohydrins. The formation of MelO has also been detected in the photochemical reaction of iodomethane with ozone in an argon matrix at 17 K [105], A similar low-temperature reaction of trilluoroiodomethane affords the unstable CF3IO, which was identified by infrared spectroscopy [106]. 

The DMDO oxidation of iodocyclohexane affords lran5-2-iodocyclohexanol as the final product via intermediate formation of iodosylcyclohexane followed by elimination of hypoiodous acid, which then adds to the alkene generated in the elimination step [103]. The oxidative deiodination of iodoalkanes via conversion into iodosylalkanes followed by nucleophilic substitution of the iodosyl group has found some synthetic application, particularly in the synthesis of steroidal products (Section 3.1.19) [107]. 

Evans, G. J., Palson, A. S. ACE bench-scale studies of iodine volatility and interaction with epoxy painted surfaces. Proc. 3. CSNI Workshop on Iodine Chemistry in Reactor Safety, Tokai-mura, Japan, 1991 Report JAERI-M 92-012 (1992), p. 230-245 Fletcher, J. W., Miller, O. A. Radiolytic formation and reactivity of aqueous hypoiodous acid. Proc. Specialists Workshop on Iodine Chemistry in Reactor Safety, Harwell, UK, 1985 Report AERE-R-11974 (1986), p. 107-120 Fluke, R. J., Frescura, G. M., Sagert, N. H., Tennankore, K. N., Vlkis, A. C. The Canadian program on iodine chemistry in reactor safety. Proc. 3. CSNI Workshop on Iodine Chemistry in Reactor Safety, Tokai-mura, Japan, 1991 Report JAERI-M 92—012 (1992), p. 49-61... 

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