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Hypochlorous acid
General
Systematic name hypochlorous acid
Other names  ?
Molecular formula HClO
SMILES  ?
Molar mass 52.46 g/mol
Appearance colorless aqueous solns
CAS number [7790-92-3]
Properties
Density and phase  ? g/cm3, ?
Solubility in water soluble
Other solvents Et2O, CH2Cl2
Melting point  ? °C (? K)
Boiling point  ? °C (? K)
Acidity (pKa) 7.497[1]
Structure
Dipole moment  ? D
Hazards
MSDS External MSDS
Main hazards oxidizer
NFPA 704
R/S statement R: ?
S: ?
RTECS number  ?
Supplementary data page
Structure and
properties		 n, εr, etc.
Thermodynamic
data		 Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions
Other cations
Related compounds Cl2
Ca(OCl)2

NaOCl
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Hypochlorous acid is a weak acid with the chemical formula HClO. It forms when chlorine dissolves in water. It cannot be isolated in pure form due to rapid equilibration with its precursor (see below). HOCl is used as a bleach, an oxidizer, a deodorant, and a disinfectant.

Contents

[edit] Formation

Addition of chlorine to water gives both hypochlorous acid and hydrochloric acid[2] (HCl):

Cl2 + H2O → HClO + HCl

[edit] Chemical reactions

In aqueous solution, hypochlorous acid partially dissociates into the hypochlorite anion ClO- (also known as the chlorate(I) anion) and the proton H+. The salts of hypochlorous acid are also called hypochlorites. One of the best known hypochlorites is household bleach, sodium hypochlorite(NaClO).

In the presence of sunlight, hypochlorous acid decomposes into more hydrochloric acid and oxygen, so this reaction is sometimes seen as:

2Cl2 + 2H2O → 4HCl + O2

HClO is considered to be a stronger oxidant than chlorine.

[edit] Reactivity of HClO with biomolecules

Hypochlorous acid reacts with a wide variety of biomolecules including DNA, RNA,[3][4][5][6] fatty acid groups, cholesterol[7][8][8][9][10][11][12][13] and proteins.[14][15][9][16][17][18][19]

[edit] Reaction with protein sulfhydral groups

Knox et al.[17] first noted that HClO was a sulfhydral inhibitor that in sufficient quantity could completely inactivate proteins containing sulfhydral groups. This is because, HClO oxidises sulfhydral groups leading to the formation of disulfide bonds[20] that can result in crosslinking of proteins. The HClO mechanism of sulfhydral oxidation is similar to that of chloramine, and may only be bacteriostatic because once the residual chlorine is dissipated, some sulfhydral function can be restored.[16] One sulfhydral containing amino acid can scavenge up to four molecules of HOCl.[19] Consistent with this, it has been proposed that sulfhydral groups of sulfur containing amino acids can be oxidized a total of three times by three HOCl molecules, with the fourth reacting with the α-amino group. The first reaction yields sulfenic acid (R-SOH) then sulfinic acid (R-SO2H) and finally R-SO3H. Each of those intermediates can also condense with another sulfhydral group causing cross linking and aggregation of proteins. Sulfinic acid and R-SO3H derivatives are only produced at high molar excesses of HClO, and disulfides are primarily formed at bacteriocidal levels.[6] Disulfide bonds can also be oxidized by HOCl to sulfinic acid.[20] Because the oxidation of sulfhydrals and disulfides evolves hydrochloric acid,[6] this process results in the depletion HClO.

[edit] Uses

In organic synthesis, HClO converts alkenes to chlorohydrins.[21]

In biology, hypochlorous acid is generated in activated neutrophils by myeloperoxidase mediated peroxidation of chloride ions, and contributes the destruction of bacteria.[22][23][3]

Hypochlorous acid is the active sanitizer in chlorine-based swimming pool products.

[edit] Safety

HClO is a strong oxidant and thus can form explosive mixtures, and it can give off toxic chlorine gas.

[edit] External links

[edit] References

  1. ^ Morris, J. C. 1966. The acid ionization constant of HOCl from 5 to 35 °. J. Phys. Chem. 70:3798-3805.
  2. ^ Fair, G. M., J. C. Morris, S. L. Chang, I. Weil, and R. P. Burden. 1948. The behavior of chlorine as a water disinfectant. J. Am. Water Works Assoc. 40:1051-1061.
  3. ^ a b Albrich, J. M., C. A. McCarthy, and J. K. Hurst. 1981. Biological reactivity of hypochlorous acid: Implications for microbicidal mechanisms of leukocyte myeloperoxidase. Proc. Natl. Acad. Sci. USA 78:210-214.
  4. ^ Dennis, W. H., Jr, V. P. Olivieri, and C. W. Krusé. 1979. The reaction of nucleotides with aqueous hypochlorous acid. Water Res. 13:357-362.
  5. ^ Jacangelo, J. G., and V. P. Olivieri. 1984. Aspects of the mode of action of monochloramine. In R. L. Jolley, R. J. Bull, W. P. Davis, S. Katz, M. H. Roberts, Jr., and V. A. Jacobs (ed.), Water Chlorination, vol. 5. Lewis Publishers, Inc., Williamsburg.
  6. ^ a b c Prütz, W. A. 1998. Interactions of hypochlorous acid with pyrimidine nucleotides, and secondary reactions of chlorinated pyrimidines with GSH, NADPH, and other substrates. Arch. Biochem. Biophys. 349:183-191.
  7. ^ Arnhold, J., O. M. Panasenko, J. Schiller, Y. A. Vladimirov, and K. Arnold. 1995. The action of hypochlorous acid on phosphatidylcholine liposomes in dependence on the content of double bonds. Stoichiometry and NMR analysis. Chem. Phys. Lipids 78:55-64.
  8. ^ a b Carr, A. C., J. V. D. Berg, and C. C. Winterbourn. 1996. Chlorination of cholesterol in cell membranes by hypochlorous acid. Arch. Biochem. Biophys. 332:63-69.
  9. ^ a b Hazell, L. J., J. V. D. Berg, and R. Stocker. 1994. Oxidation of low density lipoprotein by hypochlorite causes aggregation that is mediated by modification of lysine residues rather than lipid oxidation. Biochem. J. 302:297-304.
  10. ^ Hazen, S. L., F. F. Hsu, K. Duffin, and J. W. Heinicke. 1996. Molecular chlorine generated by the myeloperoxidase-hydrogen peroxide-chloride system of phagocytes converts low density lipoprotein cholesterol into a family of chlorinated sterols. J. Biol. Chem. 271:23080-23088.
  11. ^ Vissers, M. C. M., A. C. Carr, and A. L. P. Chapman. 1998. Comparison of human red cell lysis by hypochlorous acid and hypobromous acids: insights into the mechanism. Biochem. J. 330:131-138.
  12. ^ Vissers, M. C. M., A. Stern, F. Kuypers, J. V. D. Berg, and C. C. Winterbourn. 1994. Membrane changes associated with lysis of red blood cells by hypochlorous acid. Free Rad. Biol. Med. 16:703-712.
  13. ^ Winterbourne, C. C., J. V. D. Berg, E. Roitman, and F. A. Kuypers. 1992. Chlorhydrin formation from unsaturated fatty acids reacted with hypochlorous acid. Arch. Biochem. Biophys. 296:547-555.
  14. ^ Albrich, J. M., and J. K. Hurst. 1982. Oxidative inactivation of Escherichia coli by hypochlorous acid. FEBS Lett. 144:157-161.
  15. ^ Barrette, W. C., Jr., D. M. Hannum, W. D. Wheeler, and J. K. Hurst. 1989. General mechanism for the bacterial toxicity of hypochlorous acid: Abolition of ATP production. Biochemistry 28:9172-9178.
  16. ^ a b Jacangelo, J. G., V. P. Olivieri, and K. Kawata. 1987. Oxidation of sulfhydryl groups by monochloramine. Water Res. 21:1339-1344.
  17. ^ a b Knox, W. E., P. K. Stumpf, D. E. Green, and V. H. Auerbach. 1948. The inhibition of sulfhydral enzymes as the basis of the bactericidal action of chlorine. J. Bacteriol. 55:451-458.
  18. ^ Vissers, M. C. M., and C. C. Winterbourne. 1991. Oxidative Damage to Fibronectin. Arch. Biochem. Biophys. 285:53-59.
  19. ^ a b Winterbourne, C. C. 1985. Comparative reactivities of various biological compounds with myeloperoxidase-hydrogen peroxide-chloride, and similarity to the oxidant to hypochlorite. Biochim. Biophys. Acta 840:204-210.
  20. ^ a b Pereira, W. E., Y. Hoyano, R. E. Summons, V. A. Bacon, and A. M. Duffield. 1973. Chlorination studies: II. The reaction of aqueous hypochlorous acid with a - amino acids and dipeptides. Biochim. Biophys. Acta 313:170-180.
  21. ^ Unangst, P. C. "Hypochlorous Acid" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
  22. ^ Harrison, J. E., and J. Schultz. 1976. Studies on the chlorinating activity of myeloperoxidase. J. Biol. Chem. 251:1371-1374.
  23. ^ Thomas, E. L. 1979. Myeloperoxidase, hydrogen peroxide, chloride antimicrobial system: Nitrogen-chlorine derivatives of bacterial components in bactericidal action against Escherichia coli. Infect. Immun. 23:522-531.


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