Hypochlorous Acid - HOCl

What is Hypochlorous Acid?

Hypochlorous Acid is described as a weak acid having the chemical formula HOCl. It is also referred to as either Chlorine hydroxide or hypochloric acid or even as Hydrogen hypochlorite. In 1834, it was discovered by a French chemist named "Antoine Jerome Balard." It is also termed as an oxyacid of chlorine.

It also contains the monovalent chlorine that functions either as an oxidizing agent or a reducing agent. It functions as a human metabolite and is an unstable acid. It belongs to the reactive oxygen species family, and it is the conjugate acid of a hypochlorite.


Properties of Hypochlorous Acid – HOCl

IUPAC Name

Hypochlorous Acid

Chemical Formula

HOCl

Number of hydrogen bond acceptors

1

Number of hydrogen bond donors

1

The molecular weight of HOCl

52.457 g/mol

Monoisotopic mass of Hypochlorous Acid

51.972 g/mol


Hypochlorous Acid Structure – HOCl

(Image to be added soon)


Reactions

Reaction with the Protein Amino Groups

Hypochlorous acid readily reacts with the amino acids that contain amino group side-chains, with chlorine from HClO, with hydrogen displacement, resulting in an organic chloramine. The chlorinated amino acids decompose rapidly, but the protein chloramines are long-lived and retain a few oxidative capacities. A chemist named "Thomas et al." concluded from their results that several organic chloramines decayed by the internal rearrangement. The same fewer available NH2 groups promoted attack on the peptide bond, resulting in the protein's cleavage.

Davies and McKenna also found that 10 mM or greater HClO is required to fragment Vivo's proteins. With these consistent results, later, it was proposed that the chloramine encounters a molecular rearrangement, releasing ammonia and HCl to produce an aldehyde. Then, the aldehyde group can react further with the other amino group to produce a Schiff’s base, causing protein aggregation cross-linking.


Reaction with the Lipids

The hypochlorous acid reacts with the unsaturated bonds in lipids, but not on the saturated bonds. Moreover, the ClO− ion does not participate in this particular reaction. This reaction takes place by hydrolysis with the addition of chlorine to any of the carbons and one hydroxyl to the other.

Then, chlorohydrin is the resulting compound. The polar chlorine disrupts the lipid bilayers and could increase its permeability. When chlorohydrin formation occurs in lipid bilayers of red blood cells, the increased permeability occurs. Disruption could take place if necessary chlorohydrin is produced. Also, the addition of preformed chlorohydrin to the red blood cells will affect permeability. Cholesterol chlorohydrin has also been observed, but it does not affect permeability, and it is also believed that Cl2 is wholly responsible for this reaction.


Hypochlorites

Hypochlorites are the hypochlorous acid salts, and the commercially essential hypochlorites are sodium hypochlorite and calcium hypochlorite.


Production of Hypochlorites using Electrolysis

Solutions of the hypochlorites are formed by electrolysis of an aqueous solution of sodium chloride. The resulting solution's composition depends on the anode's pH. In acid conditions, the formed solution will have a high concentrated hypochlorous acid. However, it also contains dissolved gaseous chlorine, which is corrosive at a neutral pH; the solution will be nearly 25% hypochlorite and 75% hypochlorous acid. A few of the chlorine gas formed will dissolve, forming the hypochlorite ions. Also, hypochlorites can be produced by the chlorine gas disproportionation in alkaline solutions.


Formation of Hypochlorous Acid

When the acids are added to the hypochlorous acid's aqueous salts (like sodium hypochlorite in the commercial bleach solution), the resultant reaction is directed to the left and thus forms chlorine gas. Hence, the stable hypochlorite bleaches formation happened by dissolving chlorine gas into the basic water solutions, like sodium hydroxide.

The acid can also be prepared by dissolving the dichlorine monoxide with water; at standard aqueous conditions, where, currently, anhydrous hypochlorous acid is not possible to prepare because of the readily reversible equilibrium between it to its anhydride:

2 HOCl ⇌ Cl2O + H2O K (at 0 °C) = 3.55 10−3 dm3 mol−1

Either the presence of light or the transition metal oxides of nickel, copper, cobalt accelerates the exothermic decomposition into oxygen and hydrochloric acid:


Uses of Hypochlorous Acid

Let us know some of the important uses of hypochlorous acid as listed below.

  • HClO converts alkenes to chlorohydrins in organic synthesis.

  • Hypochlorous acid is generated in biology in activated neutrophils by the chloride ion’s myeloperoxidase mediated peroxidation and contributes to the bacteria's destruction.

  • In water distribution and food services, a specialized equipment to generate HClO weak solutions from salt and water is used at times to form adequate quantities of safe disinfectant to treat water supplies and food preparation surfaces.

  • Hypochlorous acid is an active sanitizer in water treatment in hypochlorite-based products, like in a swimming pool.

  • Similarly, in yachts and ships, the marine sanitation devices use electricity in converting seawater into hypochlorous acid to disinfect the macerated faecal waste prior to discharging into the sea.

FAQs (Frequently Asked Questions)

1. List some applications of hypochlorous acid?

A few of the applications of hypochlorous acid are listed below.

  • It can be used as a disinfectant. It means, for swimming pools and in bleaches (though the calcium and sodium salts are preferred), they are easier to make since their synthesis is not the equilibrium reactions).

  • It can also be used in small concentrations in skin cleaning products, which means cosmetics, especially those intended for infants, can clean the skin without drawing the water out and skin-drying (which, in turn, would irritate).

2. List the common uses of hypochlorous acid?

Some common uses of hypochlorous acid are listed as follows.

  • Hypochlorous has been investigated as a possible wound care agent. In early 2016, the U.S. FDA (Food& Drug Administration) has approved the products, whose primary active ingredient is hypochlorous acid for treating wounds and multiple infections in pets and humans.

  • It is also approved as a preservative for saline solutions by FDA.

3. What are hypochlorites?

Hypochlorites are defined as the salts of hypochlorous acid. At the same time, the commercially important hypochlorites are sodium hypochlorite and calcium hypochlorite.

4. How does the hypochlorous acid react with amino acids?

Hypochloric acid reacts rapidly with amino acids in the side chains of the amino group, with HClO chlorine displacing hydrogen resulting in organic chloramine. Chlorinated amino acids quickly decompose, but the protein chloramines last longer and retain a few oxidative abilities.