He Bromo acid Is an inorganic compound of the formula HBrO2. This acid is one of bromine oxacid acids where it is found with oxidation state 3+.
The salts of this compound are known as bromitos. Brromic acid is an unstable compound that has not been isolated in the laboratory.
Figure 1: Structure of the bromous acid.
This instability, analogous to iodine acid, is due to a dismutation reaction (or disproportionation) to form hypobromous acid and bromic acid in the following manner:
2HBrO 2 → HBrO + HBrO 3
Bromic acid can act as an intermediary in different reactions in the oxidation of hypobromites (Ropp, 2013).
It can be obtained by chemical or electrochemical means where the hypobromite is oxidized to the bromide ion such as:
HBrO + HClO → HBrO 2 + HCl
HBrO + H 2 O + 2e - → HBrO 2 + H 2
Physical and chemical properties
As mentioned above, bromous acid is an unstable compound that has not been isolated, so its physical and chemical properties are obtained, with some exceptions, theoretically by computational calculations (National Center for Biotechnology Information, 2017).
The compound has a molecular weight of 112.91 g / mol, a melting point of 207.30 degrees Celsius and a boiling point of 522.29 degrees Celsius. Its solubility in water is estimated to be 1 x 106 mg / L (Royal Society of Chemistry, 2015).
There is no risk registered in the management of this compound, however, it has been found to be a weak acid.
The kinetics of the disproportionation reaction of bromine (III), 2Br (III) → Br (1) + Br (V), were studied in phosphate buffer in the pH range of 5.9-8.0, monitoring the optical absorbance at 294 nm using stopped flow.
The dependencies of [H + ] And [Br (III)] were of order 1 and 2 respectively, where no dependence of [Br-] was found. The reaction was also studied in acetate buffer, in the pH range of 3.9-5.6. Within the experimental error, no evidence was found for a direct reaction between two BrO2- ions. This study provides velocity constants 39.1 ± 2.6 M -1 For the reaction:
HBrO 2 + BrO 2 → HOBr + Br0 3 -
Speed constants 800 ± 100 M -1 For the reaction:
2HBr0 2 → HOBr + Br0 3 - + H +
And an equilibrium ratio of 3.7 ± 0.9 X 10 -4 For the reaction:
HBr02 ⇌ H + + BrO 2 -
An experimental pKa of 3.43 was obtained at an ionic strength of 0.06 M and 25.0 ° C (R.B. Faria, 1994).
Applications
Alkaline earth compounds
Brromic acid or sodium bromide is used to produce beryllium bromide according to the reaction:
Be (OH) 2 + HBrO 2 → Be (OH) BrO 2 + H 2 OR
The bromides are yellow in the solid state or in aqueous solutions. This compound is used industrially as an agent for the de-scaling of oxidative starches in textile refinement (Egon Wiberg, 2001).
Reducing agent
Brromic acid or bromides can be used to reduce the permanganate to manganate ion as follows:
2MnO 4 - + BrO 2 - + 2OH - → BrO 3 - + 2MnO 4 2- + H 2 OR
Which is convenient for the preparation of manganese (IV) solutions.
Reaction of Belousov-Zhabotinsky
Bromous acid acts as an important intermediary in the Belousov-Zhabotinski reaction (Stanley, 2000), which is an extremely visually striking demonstration.
In this reaction three solutions are mixed to form a green color, which turns blue, purple and red, and then returns to green and repeats.
The three solutions that are mixed are: a solution of KBrO 3 0.23 M, a solution of 0.31 M malonic acid with 0.059 M KBr and a solution of 0.019 M cerium (IV) ammonium nitrate and H 2 SW 4 2.7M.
During the presentation, a small amount of the indicator ferroin is introduced into the solution. Manganese ions may be used in place of cerium. The overall reaction B-Z is the cerium-catalyzed oxidation of malonic acid by bromate ions in dilute sulfuric acid as presented in the following equation:
3CH 2 (CO 2 H) 2 + 4 BrO 3 - → 4 Br - + 9 CO 2 + 6 H 2 O (1)
The mechanism of this reaction involves two processes. Process A involves ions and transfers of two electrons, while process B involves radicals and one-electron transfers.
The concentration of bromide ions determines which process is dominant. Process A is dominant when the concentration of bromide ions is high, while process B is dominant when the concentration of bromide ions is low.
Process A is the reduction of bromide ions by bromide ions in two electron transfers. It can be represented by this net reaction:
BrO 3 - + 5Br - + 6H + → 3Br 2 + 3H 2 O (2)
This occurs when solutions A and B are mixed together. This process occurs through the following three steps:
BrO 3 - + Br - +2 H + → HBrO 2 + HOBr (3)
HBrO 2 + Br - + H + → 2 HOBr (4)
HOBr + Br - + H + → Br 2 + H 2 O (5)
The bromine created from reaction 5 reacts with malonic acid as it slowly cools, as represented by the following equation:
Br 2 + CH 2 (CO 2 H) 2 → BrCH (CO 2 H) 2 + Br - + H (6)
These reactions work to reduce the concentration of bromide ions in the solution. This allows process B to become dominant. The overall reaction of process B is represented by the following equation:
2BrO3 - + 12H + + 10 Ce 3+ → Br 2 + 10Ce 4+ · 6H 2 O (7)
And it consists of the following steps:
BrO 3 - + HBrO 2 + H + → 2BrO 2 • + H 2 O (8)
BrO 2 • Ce 3+ + H + → HBrO 2 + Ce 4+ (9)
2 HBrO 2 → HOBr + BrO 3 - + H + (10)
2 HOBr → HBrO 2 + Br - + H + (eleven)
HOBr + Br - + H + → Br 2 + H 2 O (12)
The key elements of this sequence include the net result of equation 8 plus two times equation 9, which is shown below:
2Ce 3+ + BrO 3 - + HBrO 2 + 3H + → 2Ce 4+ + H 2 O + 2HBrO 2 (13)
This sequence produces self-catalytic bromine acid. Autocatalysis is an essential feature of this reaction, but does not continue until the reactants are depleted because there is a second order destruction of HBrO2, as seen in reaction 10.
Reactions 11 and 12 represent the disproportion of hyperbromous acid to bromine acid and Br2. Cerium (IV) ions and bromine oxidize malonic acid to form bromide ions. This causes an increase in the concentration of bromide ions, which reactivates process A.
The colors in this reaction are formed mainly by the oxidation and reduction of iron and cerium complexes.
Ferroin provides two of the colors seen in this reaction: as [Ce (IV)] increases, iron in the iron from red iron (II) oxidizes to blue iron (III). Cerium (III) is colorless and cerium (IV) is yellow. The combination of cerium (IV) and iron (III) makes the color green.
Under the right conditions, this cycle will be repeated several times. Glass cleaning is a concern because oscillations are interrupted by chloride ion contamination (Horst Dieter Foersterling, 1993).
References
- Bromous acid. (2007, October 28). Retrieved from ChEBI: ebi.ac.uk.
- Egon Wiberg, N.W. (2001). Inorganic Chemistry. London-san diego: academic press.
- Horst Dieter Foersterling, M. V. (1993). Bromous acid / cerium (4+): reaction and HBrO2 disproportionation measured in sulfuric acid solution at different acidities. Phys. Chem 97 (30), 7932-7938.
- Iodine acid. (2013-2016). Retrieved from molbase.com.
- National Center for Biotechnology Information. (2017, March 4). PubChem Compound Database; CID = 165616.
- B. Faria, I. R. (1994). Kinetics of Disproportionation and pKa of Bromous Acid. J. Phys. Chem., 98 (4), 1363-1367.
- Ropp, R.C. (2013). Encyclopedia of the Alkaline Earth Compounds. Oxford: Elsevier.
- Royal Society of Chemistry. (2015). Bromous acid. Retrieved from chemspider.com.
- Stanley, A.A. (2000, December 4). Advanced Inorganic Chemistry Demonstration Summary oscillating reaction.