Iodine Acid: Properties and Uses

He Iodine acid Is a chemical compound of formula HIO2. Said acid, as well as its salts (known as iodites), are extremely unstable compounds that have been observed but never isolated.

It is a weak acid, which means that it does not dissociate completely. In the anion, the iodine is in the oxidation state III and has a structure analogous to chlorous acid or bromine acid, as illustrated in figure 1.

Structure of iodine acid Figure 1: Structure of iodine acid

Although the compound is unstable, iodine acid and its iodite salts have been detected as intermediaries in the conversion between iodides (I - ) And iodates (IO 3 - ).

Its instability is due to a dismutation reaction (or disproportion) to form hypoiodotic acid and iodic acid, which is analogous to chlorous and bromine acids as follows:

2HIO 2 -> HIO + HIO 3

In Naples in 1823, the scientist Luigi Sementini wrote a letter to E. Daniell, secretary of the Royal Institution of London, where he explained a method for obtaining iodine acid.

In the letter, he said that considering the formation of nitrous acid was by combining nitric acid with what he called nitrous gas (possibly N 2 O), the iodine acid could be formed in the same way by reacting the iodic acid with iodine oxide, a compound which he had discovered.

In doing so, it obtained a yellowish-yellow liquid that lost its color upon contact with the atmosphere (Sir David Brewster, 1902).

Subsequently, the scientist M. Wöhler discovered that Sementini's acid is a mixture of iodine chloride and molecular iodine, since the iodine oxide used in the reaction was prepared with potassium chlorate (Brande, 1828).

Physical and chemical properties of iodine

As mentioned previously, iodine acid is an unstable compound that has not been isolated, so its physical and chemical properties are theoretically obtained by calculations and computer simulations (Royal Society of Chemistry, 2015).

The iodine acid has a molecular weight of 175.91 g / mol, a density of 4.62 g / ml in the solid state, a melting point of 110 degrees centigrade (iodine acid, 2013-2016).

It also has a solubility in water of 269 g / 100 ml at 20 degrees centigrade (being a weak acid), has a pKa of 0.75, and has a magnetic susceptibility of -48.0 · 10-6 cm3 / mol (National Center for Biotechnology Information, sf).

Since iodine is an unstable compound that has not been isolated, there is no risk of its use. It has been found by theoretical calculations that iodine acid is not flammable.

Applications

1- Nucleophilic acylation

Iodine acid is used as a nucleophile in nucleophilic acylation reactions. The example is given with the acylation of trifluoroacetyls such as 2,2,2-trifluoroacetyl bromide, 2,2,2-trifluoroacetyl chloride, 2,2,2-trifluoroacetyl fluoride and 2,2,2-trifluoroacetyl iodide for Forming the iodosil 2,2,2-trifluoroacetate with or illustrated in Figure 2.1, 2.2, 2.3 and 2.4 respectively.

Iodine Acid: Properties and Uses Figure 2: formation reactions of iodosil 2,2,2-trifluoroacetate

Iodine acid is also used as a nucleophile for the formation of iodosyl acetate by reacting it with acetyl bromide, acetyl chloride, acetyl fluoride and acetyl iodide as shown in Figures 3.1, 3.2, 3.3 and 3.4 respectively (GNU Free Documentation, s.f.).

Iodine Acid: Properties and Uses 1 Figure 2: Yodosyl acetate formation reactions.

2- Dismutation Reactions

Dismutation or disproportionation reactions are a type of reduction oxide reaction, where the substance to be oxidized is the same which is reduced.

In the case of halogens, since they have oxidation states of -1, 1, 3, 5 and 7, different products of dismutation reactions can be obtained depending on the conditions employed.

In the case of iodine acid, the example of how it reacts to form hypoiodotic acid and iodic acid of the form was mentioned above.

2HIO 2 -> HIO + HIO 3

In recent studies the disodium reaction of iodine acid has been analyzed by measuring the proton concentrations (H + ), Iodine (10-3 - ) And the hypoiodite acid cation (H 2 IO + ) To better understand the mechanism of disodium of iodine acid (Smiljana Marković, 2015).

A solution containing the intermediate species I 3+ . A mixture of iodine (I) and iodine (III) species was prepared by dissolving iodine (I 2 ) And potassium iodate (KIO 3 ), In the ratio 1: 5, in concentrated sulfuric acid (96%). In this solution a complex reaction proceeds, which can be described by the reaction:

I 2 + 3IO 3 - + 8H + -> 510 + + H 2 OR

Species I 3+ Are stable only in the presence of excess iodate added. Iodine prevents the formation of I 3+ . The IO ion + Obtained as iodine sulfate (IO) 2 SW 4 ), Rapidly decomposes into aqueous acid solution and form I 3+ , Represented as the HIO 2 Or the ionic species IO3 - . Subsequently a spectroscopic analysis was performed to determine the value of the concentrations of the ions of interest.

This presented a procedure for the evaluation of pseudo-equilibrium concentrations of hydrogen, iodate and H ions 2 Hi + , Kinetic and catalytic species important in the process of disproportion of iodine acid, HIO 2 .

3- Reactions of Bray-Liebhafsky

A chemical clock or oscillation reaction is a complex mixture of reacting chemical compounds, in which the concentration of one or more components presents periodic changes, or when sudden changes of properties occur after a predictable induction time.

They are a class of reactions that serve as an example of non-equilibrium thermodynamics, resulting in the establishment of a non-linear oscillator. They are theoretically important because they show that chemical reactions do not have to be dominated by equilibrium thermodynamic behavior.

The Bray-Liebhafsky reaction is a chemical clock first described by William C. Bray in 1921 and is the first oscillation reaction in a stirred homogeneous solution.

Iodine acid is used experimentally for the study of this type of reactions when it is oxidized with hydrogen peroxide, finding a better agreement between the theoretical model and experimental observations (Ljiljana Kolar-Anić, 1992).

References

  1. Brande, W. T. (1828). A manual of chemistry, on the basis of Professor Brande's. Boston: University of Harvard.
  2. GNU Free Documentation. (S.f.). Iodine acid. Retrieved from chemsink.com: chemsink.com
  3. Iodine acid. (2013-2016). Retrieved from molbase.com: molbase.com
  4. Ljiljana Kolar-Anić, G. S. (1992). Mechanism of the Bray-Liebhafsky reaction: effect of the oxidation of iodine acid by hydrogen peroxide. Chem. Soc., Faraday Trans 1992, 88, 2343-2349. Http://pubs.rsc.org/en/content/articlelanding/1992/ft/ft9928802343#!divAbstract
  5. National Center for Biotechnology Information. (N.d.). PubChem Compound Database; CID = 166623. Retrieved from pubchem.com:pubchem.ncbi.nlm.nih.gov.
  6. Royal Society of Chemistry. (2015). Iodous acid ChemSpider ID145806. Retrieved from ChemSpider: chemspider.com
  7. Sir David Brewster, R. T. (1902). The London and Edinburgh Philosophical Magazine and Journal of Science. London: university of london.
  8. Smiljana Marković, R.K. (2015). Disproportionation reaction of iodine acid, HOIO. Determination of the concentrations of the relevant ionic species H +, H2OI +, and IO3 -.


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