The chlorous acid is an inorganic compound of formula HClO 2. Said acid is one of the oxacid acids of chlorine where it has a 3 + oxidation state. Although the acid is difficult to obtain in its pure substance, the conjugate base derived from these acids, the chlorite ion, is stable.
An example of a salt of this anion is the well-known sodium chlorite. This and other related salts are sometimes used in the production of chlorine dioxide.
Figure 1: Structure of chlorous acid.
Chlorous acid is a weak acid. The pure substance is unstable, disproportionate to hypochlorous acid (Cl +1 oxidation state) and chloric acid (Cl +5 oxidation state):
2HClO 2 → HClO + HClO 3
Chlorous acid is obtained, together with chloric acid, in the decomposition of the aqueous solution of chlorine dioxide.
The chlorous acid solution was obtained for the first time by reducing chloric acid with tartaric acid (AJ Downs, 1973), however, the main method of obtaining this acid is by treating a suspension of barium chloride with sulfuric acid:
Ba (ClO 2) 2 + H 2 SO 4 → BaSO 4 + 2HClO 2
Chlorous acid is a powerful oxidizing agent, although its tendency to dismutation or disproportion counteracts its oxidizing potential.
Chlorine is the only halogen that forms an isolable acid of formula HXO 2. Neither bromous acid nor iodine acid have been isolated. Some salts of bromous acid, bromites, are known, but, except as intermediates in reactions, there are no iodite salts.
Physical and chemical properties
Chlorous acid, when isolated, is a colorless liquid without a characteristic aroma (National Center for Biotechnology Information, 2017).
The compound has a molecular weight of 68.456 g / mol. It has a boiling point (calculated) of 502.07 ° C and a solubility in water (calculated) of 1 × 10 6 mg / l (Royal Society of Chemistry, 2015).
HClO 2 is unstable due to the dismutation (or disproportion) reaction to produce chloric and hypochlorous acid (CC Hong, 1968) similar to that of the analog bromine and iodine acids:
2HClO 2 → HClO + HClO 3
Chlorous acid is considered a weak acid although its dissociation constant is on the order of 1 x 10 -2, which does not make it as weak as other acids, having a pKa of 1.96.
Reactivity and hazards
Chlorous acid is an unstable compound and a strong oxidizing agent incompatible with reducing agents and alkalis.
Chlorous acid is irritating in case of contact with the skin and eyes, and is dangerous in cases of ingestion and inhalation.
In case of contact with the eyes, check whether you are wearing contact lenses and remove them immediately. Eyes should be flushed with running water for at least 15 minutes, keeping the eyelids open. Cold water can be used. Eye ointment should not be used.
If the chemical comes into contact with clothing, remove it as quickly as possible, protecting your own hands and body. Place the victim under a safety shower.
If the chemical accumulates on the victim's exposed skin, such as hands, the contaminated skin is gently and carefully washed with running water and non-abrasive soap.
Cold water can be used. If irritation persists, seek medical attention. Wash the contaminated clothing before using it again.
If the contact with the skin is severe, it should be washed with a disinfectant soap and cover the contaminated skin with an antibacterial cream.
In case of inhalation, the victim should be allowed to rest in a well-ventilated area. If inhalation is severe, the victim should be evacuated to a safe area as soon as possible. Loosen tight clothing such as a collar, belt, or tie.
If it is difficult for the victim to breathe, oxygen should be administered. If the victim is not breathing, mouth-to-mouth resuscitation is performed. Always keeping in mind that it can be dangerous for the person providing aid to give mouth-to-mouth resuscitation when the inhaled material is toxic, infectious or corrosive.
In case of ingestion, do not induce vomiting. Loosen tight clothing such as shirt collars, belts, or ties. If the victim is not breathing, perform mouth-to-mouth resuscitation. In all cases, immediate medical attention should be sought.
Applications
Studies have been conducted where meta-stable chlorous acid / chlorine oxide solutions are used as mouthwash for plaque reduction (Goultschin J, 1989).
The study was done on a group of 18 volunteers aged 20-27 years. Its effect on plaque development and salivary bacterial count was tested, obtaining a reduction of up to 34.5% reduction in dental plaque scores compared to a placebo group.
Chlorous acid is involved in the preparation of sodium acid chlorite which has antimicrobial properties and is intended to be used primarily as a spray or dipping solution for poultry, meats, vegetables, fruits, and seafood. It is also used in the cooling water of poultry.
Sodium acid chlorite is produced by adding a food-grade acid (for example, citric acid, phosphoric acid, hydrochloric acid, malic acid, or sodium hydrogen sulfate) to an aqueous solution of sodium chlorite (NaClO 2).
The combination of the acid with the sodium chlorite solution results in the conversion of chlorite to metastable chlorous acid (HClO 2).
NaClO 2 + H + ⇌ HClO 2 + Na +
This solution can subsequently form a mixture with chlorite (ClO 2 -), chlorine dioxide (ClO 2) and chloride (Cl¯). The reaction generates an oxidative solution with oxychlorinated species with antimicrobial properties.
Sodium Acid Chlorite is designed to be used as part of an integrated approach designed to control microbial loads in food.
Sodium acid chlorite solution acts to reduce the number of pathogens (eg, Escherichia coli, E. coli O157: H7, Salmonella spp., Campylobacter spp., And Listeria monocytogenes) (Rao, 2006).
References
- J. Downs, CJ (1973). The Chemistry of Chlorine, Bromine, Iodine and Astatine: Pergamon…, Volume 7. New York: Pergamon press.
- C. Hong, WH (1968). Kinetics of disproportionation of chlorous acid. Canadian Journal of Chemistry 46 (12):, 2053-2060. nrcresearchpress.com.
- EMBL-EBI. (2014, July 28). chlorous acid. Recovered from ChEBI: ebi.ac.uk.
- Goultschin J, GJ (1989). Use of a metastabilized chlorous acid / chlorine dioxide formulation as a mouthrinse for plaque reduction. Isr J Dent Sci. 2 (3), 142-147. ncbi.nlm.nih.gov.
- National Center for Biotechnology Information.. (2017, April 30). PubChem Compound Database CID = 24453. Retrieved from PubChem.
- Rao, MV (2006, December). ACIDIFIED SODIUM CHLORITE (ASC) Chemical and Technical Assessment. Recovered from fao.org.
- Royal Society of Chemistry. (2015). Chlorous acid. Recovered from chemspider.com.