Гипохлористая кислота: свойства, применение и современные технологии получения.

Hypochlorous acid is an inorganic compound with the chemical formula |ClOH|auto=1, also written as HClO, HOCl, or ClHO. Its structure is |H\sO\sCl. It is an acid that forms when chlorine dissolves in water, and itself partially dissociates, forming hypochlorite anion, |ClO−. HClO and |ClO− are oxidizers, and the primary disinfection agents of chlorine solutions. HClO cannot be isolated from these solutions due to rapid equilibration with its precursor, chlorine. Because of its strong antimicrobial properties, the related compounds sodium hypochlorite (NaOCl) and calcium hypochlorite (|Ca(OCl)2) are ingredients in many commercial bleaches, deodorants, and disinfectants. The white blood cells of mammals, such as humans, also contain hypochlorous acid as a tool against foreign bodies. In living organisms, HOCl is generated by the reaction of hydrogen peroxide with chloride ions under the catalysis of the heme enzyme myeloperoxidase (MPO). Like many other disinfectants, hypochlorous acid solutions will destroy pathogens, such as COVID 19, absorbed on surfaces. In low concentrations, such solutions can serve to disinfect open wounds.

Hypochlorous acid was discovered in 1834 by the French chemist Antoine Jérôme Balard (1802–1876) by adding, to a flask of chlorine gas, a dilute suspension of mercury(II) oxide in water. He also named the acid and its compounds. Despite being relatively easy to make, it is difficult to maintain a stable hypochlorous acid solution. It is not until recent years that scientists have been able to cost effectively produce and maintain hypochlorous acid water for stable commercial use.

In organic synthesis, HClO converts alkenes to chlorohydrins. In biology, hypochlorous acid is generated in activated neutrophils by myeloperoxidase mediated peroxidation of chloride ions, and contributes to the destruction of bacteria. and as of early 2016 the U. S. Food and Drug Administration has approved products whose main active ingredient is hypochlorous acid for use in treating wounds and various infections in humans and pets. It is also FDA approved as a preservative for saline solutions. In disinfection, it has been used in the form of liquid spray, wet wipes and aerosolised application. Recent studies have shown hypochlorous acid water to be suitable for fog and aerosolised application for disinfection chambers and suitable for disinfecting indoor settings such as offices, hospitals and healthcare clinics. In food service and water distribution, specialized equipment to generate weak solutions of HClO from water and salt is sometimes used to generate adequate quantities of safe (unstable) disinfectant to treat food preparation surfaces and water supplies. It is also commonly used in restaurants due to its non flammable and nontoxic characteristics. In water treatment, hypochlorous acid is the active sanitizer in hypochlorite based products (e. g. used in swimming pools). Similarly, in ships and yachts, marine sanitation devices use electricity to convert seawater into hypochlorous acid to disinfect macerated faecal waste before discharge into the sea. In deodorization, hypochlorous acid has been tested to remove up to 99% of foul odours including garbage, rotten meat, toilet, stool, and urine odours.

Hypochlorous acid reacts with a wide variety of biomolecules, including DNA, RNA, fatty acid groups, cholesterol and proteins.

Knox et al. that can result in crosslinking of proteins. The HClO mechanism of sulfhydryl oxidation is similar to that of monochloramine, and may only be bacteriostatic, because once the residual chlorine is dissipated, some sulfhydryl function can be restored. Chlorinated amino acids rapidly decompose, but protein chloramines are longer lived and retain some oxidative capacity. found that 10 mM or greater HClO is necessary to fragment proteins in vivo. Consistent with these results, it was later proposed that the chloramine undergoes a molecular rearrangement, releasing HCl and ammonia to form an aldehyde. The aldehyde group can further react with another amino group to form a Schiff base, causing cross linking and aggregation of proteins. GMP is the most reactive because HClO reacts with both the heterocyclic NH group and the amino group. In similar manner, TMP with only a heterocyclic NH group that is reactive with HClO is the second most reactive. AMP and CMP, which have only a slowly reactive amino group, are less reactive with HClO.

E. coli exposed to hypochlorous acid lose viability in less than 0.1 seconds due to inactivation of many vital systems. Hypochlorous acid has a reported of 0.0104–0.156 ppm and 2.6 ppm caused 100% growth inhibition in 5 minutes. In agreement with this, McFeters and Camper found that aldolase, an enzyme that Knox et al. led to a possible answer to this question. The uptake of radiolabeled substrates by both ATP hydrolysis and proton co transport may be blocked by exposure to HClO preceding loss of viability. The question of loss of glucose oxidation has been further explored in terms of loss of respiration. Venkobachar et al. found that succinic dehydrogenase was inhibited in vitro by HClO, which led to the investigation of the possibility that disruption of electron transport could be the cause of bacterial inactivation. Albrich et al. Rosen et al.

Recently it has been proposed that bacterial inactivation by HClO is the result of inhibition of DNA replication. When bacteria are exposed to HClO, there is a precipitous decline in DNA synthesis that precedes inhibition of protein synthesis, and closely parallels loss of viability. During bacterial genome replication, the origin of replication (oriC in E. coli) binds to proteins that are associated with the cell membrane, and it was observed that HClO treatment decreases the affinity of extracted membranes for oriC, and this decreased affinity also parallels loss of viability. A study by Rosen et al. compared the rate of HClO inhibition of DNA replication of plasmids with different replication origins and found that certain plasmids exhibited a delay in the inhibition of replication when compared to plasmids containing oriC. Rosen's group proposed that inactivation of membrane proteins involved in DNA replication are the mechanism of action of HClO.

HClO is known to cause post translational modifications to proteins, the notable ones being cysteine and methionine oxidation. A recent examination of HClO's bactericidal role revealed it to be a potent inducer of protein aggregation. Hsp33, a chaperone known to be activated by oxidative heat stress, protects bacteria from the effects of HClO by acting as a holdase, effectively preventing protein aggregation. Strains of Escherichia coli and Vibrio cholerae lacking Hsp33 were rendered especially sensitive to HClO. Hsp33 protected many essential proteins from aggregation and inactivation due to HClO, which is a probable mediator of HClO's bactericidal effects.

Hypochlorites are the salts of hypochlorous acid; commercially important hypochlorites are calcium hypochlorite and sodium hypochlorite.

Solutions of hypochlorites can be produced in situ by electrolysis of an aqueous sodium chloride solution in both batch and flow processes. The composition of the resulting solution depends on the pH at the anode. In acid conditions the solution produced will have a high hypochlorous acid concentration, but will also contain dissolved gaseous chlorine, which can be corrosive, at a neutral pH the solution will be around 75% hypochlorous acid and 25% hypochlorite. Some of the chlorine gas produced will dissolve forming hypochlorite ions. Hypochlorites are also produced by the disproportionation of chlorine gas in alkaline solutions.

HClO is classified as Non Hazardous by the Environmental Protection Agency in the US. As any oxidising agent it can be corrosive or irritant depending on its concentration and pH. In a clinical test, hypochlorous acid water was tested for eye irritation, skin irritation, and toxicity. The test concluded that it was non toxic and nonirritating to the eye and skin. In a 2017 study, a saline hygiene solution preserved with pure hypochlorous acid was shown to reduce the bacterial load significantly without altering the diversity of bacterial species on the eyelids. After 20 minutes of treatment, there was >99% reduction of the Staphylococci bacteria.

For disinfection, despite being discovered a long time ago, the stability of hypochlorous acid water is difficult to maintain. In solution, the active compounds quickly deteriorate back into salt water, losing its disinfecting capability, which makes it difficult to transport for wide use. Despite its stronger disinfecting capabilities, it is less commonly used as a disinfectant compared to bleach and alcohol due to cost. Technological developments have reduced manufacturing costs and allow for manufacturing and bottling of hypochlorous acid water for home and commercial use. However, most hypochlorous acid water has a short shelf life. Storing away from heat and direct sunlight can help slow the deterioration. The further development of continuous flow electrochemical cells has been implemented in new products, allowing the commercialisation of domestic and industrial continuous flow devices for the in situ generation of hypochlorous acid for disinfection purposes.