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The bleaching process has been known for millennia,[1] but the chemicals currently used for bleaching resulted from the work of several 18th century scientists. Chlorine is the basis for the most commonly used bleaches, for example, the solution of sodium hypochlorite, which is so ubiquitous that most simply call it "bleach", and calcium hypochlorite, the major compound in "bleaching powder". Oxidizing bleaching agents that do not contain chlorine most often are based on peroxides, such as hydrogen peroxide, sodium percarbonate and sodium perborate. While most bleaches are oxidizing agents, some are reducing agents such as sodium dithionite and sodium borohydride.

Bleaches are used as household chemicals to whiten clothes and remove stains and as disinfectants, primarily in the bathroom and kitchen. Many bleaches have strong bactericidal properties, and are used for disinfecting and sterilizing and thus are used in swimming pool sanitation to control bacteria, viruses and algae and in any institution where sterile conditions are needed. They are also used in many industrial processes, notably in the bleaching of wood pulp. Bleach is also used for removing mildew, killing weeds and increasing the longevity of flowers.[2]


The earliest form of bleaching involved spreading fabrics and cloth out in a bleachfield to be whitened by the action of the sun and water.[1][3] Modern bleaches resulted from the work of 18th century scientists including Swedish chemist Carl Wilhelm Scheele, who discovered chlorine, French scientists Claude Berthollet, who recognized that chlorine could be used to bleach fabrics and who first made sodium hypochlorite (Eau de Javel, or Javel water, named after a quarter in Paris where it was produced) and Antoine Germain Labarraque, who discovered the disinfecting ability of hypochlorites. Scottish chemist and industrialist Charles Tennant first produced a solution of calcium hypochlorite, then solid calcium hypochlorite (bleaching powder).[1]

Louis Jacques Thénard first produced hydrogen peroxide in 1818 by reacting barium peroxide with nitric acid.[4] Hydrogen peroxide was first used for bleaching in 1882, but did not become commercially important until after 1930.[5] Sodium perborate as a laundry bleach had been used in Europe since the early twentieth century, but did not become popular in North America until the 1980s.[6]

How bleaches work[edit]





Antimicrobial efficacy[edit]

The broad-spectrum effectiveness of bleach, particularly sodium hypochlorite, is owed to the nature of its chemical reactivity with microbes. Rather than acting in an inhibitory or toxic fashion in the manner of antibiotics, bleach quickly reacts with microbial cells to irreversibly denature and destroy many pathogens. Bleach, particularly sodium hypochlorite, has been shown to react with a microbe's heat shock proteins, stimulating their role as intra-cellular chaperone and causing the bacteria to form into clumps (much like an egg that has been boiled) that will eventually die off.[9] In some cases, bleach's base acidity compromises a bacterium's lipid membrane, a reaction similar to popping a balloon. The range of micro-organisms effectively killed by bleach (particularly sodium hypochlorite) is extensive, making it an extremely versatile disinfectant. The same study found that at low (micromolar) sodium hypochlorite levels, E. coli and Vibrio cholerae activate a defense mechanism that helps protect the bacteria, though the implications of this defense mechanism have not been fully investigated.[9]

In response to infection, the human immune system will produce a strong oxidizer, hypochlorous acid, which is generated in activated neutrophils by myeloperoxidase-mediated peroxidation of chloride ions, and contributes to the destruction of bacteria.[10][11][12]

Classes of bleaches[edit]

Chlorine-based bleaches[edit]

Chlorine-based bleaches are found in many household cleaners. The concentration of chlorine-based bleaches is often expressed as percent active chlorine where one gram of a 100% active chlorine bleach has the same bleaching power as one gram of chlorine. These bleaches can react with other common household chemicals like vinegar or ammonia to produce toxic gases. Labels on sodium hypochlorite bleach warn about these interactions.

Chemical interactions[edit]

Mixing a hypochlorite bleach with an acid can liberate chlorine gas. Hypochlorite and chlorine are in equilibrium in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine,[13]

Cl2 + H2O \rightleftharpoons H+ + Cl + HClO

Chlorine is a respiratory irritant that attacks mucous membranes and burns the skin. As little as 3.53 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine has been limited to 0.5 ppm (8-hour time-weighted average—38 hour week) by OSHA in the U.S.[14]

Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed.[15] The main reaction is chlorination of ammonia, first giving chloramine (NH2Cl), then dichloramine (NHCl2) and finally nitrogen trichloride (NCl3). These materials are very irritating to the eyes and lungs and are toxic above certain concentrations; nitrogen trichloride is also a very sensitive explosive.

NH3 + NaOCl → NaOH + NH2Cl

NH2Cl + NaOCl → NaOH + NHCl2

NHCl2 + NaOCl → NaOH + NCl3


NH3 + NH2Cl + NaOH → N2H4 + NaCl + H2O

The hydrazine generated can react with more chloramine in an exothermic reaction to produce ammonium chloride and nitrogen gas:[13]

2 NH2Cl + N2H4 → 2 NH4Cl + N2

Atmospheric carbon dioxide and water react with bleaching powder (CaCl(OCl)) to release hypochlorous acid which gives a characteristic smell to the bleaching powder. Hypochlorous acid decomposes readily to atomic oxygen. This atomic oxygen acts as bleaching agent through oxidation.[citation needed]

2CaCl(OCl) + H2O + CO2 → CaCO3 + CaCl2 + 2HClO

HClO → HCl + [O]

2HCl + [O] → H2O + Cl2

However, the place of atomic oxygen in accounting for the formation of chlorine is not as plausible as another theory based on the so-called 'chloride system' employed in modern hydrometallurgy to dissolve ores with weak acids in highly ionic and concentrated salt solutions.[citation needed] Salts particularly effective, in this regard, include MgCl2, CaCl2, FeCl3 and, to a less extent the mono-valent NaCl. This is, in effect, an application of the non-common ion theory, or as discussed in Wikipedia under Solubility Equilibrium as the 'salt effect'. With respect to Bleaching powder, which has been described as a compound salt of the form Ca(ClO)2.CaCl2.Ca(OH)2.xH2O, the presence of CaCl2 in very concentrated solutions can greatly increase the 'activity level' of weak acids. So, in this particular proposed application, H2CO3 from CO2 and moisture on the Bleaching powder, acts on the CaCl2 to release some HCl which acts on the HClO releasing Chlorine:

HClO + HCl → H2O + Cl2

or, the increasing acidity creates more HClO which moves the following known (and old, see Watt's Dictionary of Chemistry[citation needed]) equilibrium reaction to the right:

CaCl2 + 2 HClO = Ca(OH)2 + 2 Cl2

Now, the strength of the particular application of this theory is that a similar release of Chlorine is not as easily observed with concentrated NaClO solutions[citation needed] (which it should be if one subscribes to the action of atomic oxygen on HCl). As the latter Chlorine bleach also contains NaCl, and as the NaCl is not quite as effective as previously noted as, for example, with CaCl2, the ionic strength is not as great for noticeable Chlorine formation.

Sodium hypochlorite[edit]

Sodium hypochlorite is the most commonly encountered bleaching agent, usually as a dilute (3-6%) solution in water. This solution of sodium hypochlorite, commonly referred to as simply "bleach", was also one of the first mass-produced bleaches. It is produced by passing chlorine gas through a dilute sodium hydroxide solution[16]

Cl2 (g) + 2 NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)

or by electrolysis of brine (sodium chloride in water).[16][17]

2 Cl → Cl2 + 2 -e
Cl2 + H2O ↔ HClO + Cl + H+

The dilute solution of sodium hypochlorite is used in many households to whiten laundry, disinfect hard surfaces in kitchens and bathrooms, treat water for drinking and keep swimming pools free of infectious agents.

Moreover, due to transport and handling safety concerns, the use of sodium hypochlorite is preferred over chlorine gas in water treatment, which represents a significant market expansion potential.[18]

Calcium hypochlorite[edit]

Calcium hypochlorite, also known as chloride of lime, is made by reacting chlorine with calcium hydroxide:


It is used in many of the same applications as sodium hypochlorite, but has the advantages of being more stable and containing more available chlorine. Calcium hypochlorite is the active ingredient in bleaching powder or "chlorinated lime", which is usually a white powder containing calcium hypochlorite, calcium hydroxide and calcium chloride. A purer, more stable form of calcium hypochlorite is called HTH or high test hypochlorite. Bleaching tablets contain calcium hypochlorite plus other ingredients to prevent the tablets from crumbling. A supposedly more stable mixture of calcium hypochlorite and quicklime (calcium oxide) is known as "tropical bleach" .[19] Percent active chlorine in these materials ranges from 20% for bleaching powder to 70% for HTH.


Chlorine is produced by the electrolysis of sodium chloride.

2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH

Chlorine is used to prepare sodium and calcium hypochlorites. It is used as a disinfectant in water treatment, especially to make drinking water and in large public swimming pools . Chlorine was used extensively to bleach wood pulp, but this use has decreased significantly due to environmental concerns.

Chlorine dioxide[edit]

Chlorine dioxide, ClO2, is an explosive gas and must be used where it is made or shipped and stored as dilute aqueous solutions. Despite these limitations it finds applications for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, skin, and in a number of other industries. It can be prepared by oxidizing sodium chlorite with chlorine

2 NaClO2 + Cl2 → 2 ClO2 + 2 NaCl

but more commonly it is prepared by reducing sodium chlorate with a suitable reducing agent like methanol, hydrogen peroxide, hydrochloric acid, or sulfur dioxide[20]

2 NaClO3 + 2 HX + "R" → 2 NaX + 2 ClO2 + "RO" + H2O

where "R" is the reducing agent and "RO" is the oxidized form.[21]

Peroxide-based bleaches[edit]

After chlorine-based bleaches, the peroxide bleaches are most commonly encountered. Peroxides are compounds that contain an oxygen-oxygen single bond, O-O. This is a fairly weak bond so reactions of peroxides often involve breaking this bond, giving very reactive oxygen species. Most peroxide bleaches are adducts of hydrogen peroxide. They contain hydrogen peroxide, HOOH in combination with another material like sodium carbonate or urea. An exception is sodium perborate, which has a cyclic structure containing two O-O single bonds. All peroxide-based bleaches release hydrogen peroxide when dissolved in water. Peroxide bleaches are often used with catalysts and activators, e.g., tetraacetylethylenediamine or sodium nonanoyloxybenzenesulfonate.

Hydrogen peroxide[edit]

Hydrogen peroxide is produced in very large amounts by several different processes. Its action as an oxidizer is why it is made and used in such large quantities. It is used by itself as a bleaching agent, for example to bleach wood pulp, hair and so on, or to prepare other bleaching agents like the perborates, percarbonates, peracids, etc.

Sodium percarbonate[edit]

Sodium percarbonate is produced industrially by reaction of sodium carbonate and hydrogen peroxide, followed by crystallization. Also, dry sodium carbonate may be treated directly with concentrated hydrogen peroxide solution.

2Na2CO3 + 3H2O2→2Na2CO3.3H2O2

Dissolved in water, it yields a mixture of hydrogen peroxide (see above) and sodium carbonate. It is generally considered to be an eco-friendly cleaning agent.

Sodium perborate[edit]

Sodium perborate, Na2H4B2O8, is made by reacting borax with sodium hydroxide to give sodium metaborate (NaBO2) which is then reacted with hydrogen peroxide to give hydrated sodium perborate.[22]

Na2B4O7 + 2 NaOH → 4 NaBO2 + H2O
2 NaBO2 + 2 H2O2 + 6 H2O → [NaBO2(OH)2 x 3 H2O]2

Sodium perborate is useful because it is a stable, source of peroxide anions. When dissolved in water it forms some hydrogen peroxide, but also perborate anion (B(OOH)(OH)3-), which is activated for nucleophilic oxidation.[23]

Miscellaneous bleaches[edit]

Peracetic acid and ozone are used in the manufacture of paper products, especially newsprint and white Kraft paper.[24] In the food industry, some organic peroxides (benzoyl peroxide, etc.) and other agents (e.g., bromates) are used as flour bleaching and maturing agents.

Reducing bleaches[edit]


2 NaHSO3 + Zn → Na2S2O4 + Zn(OH)2


Reaction of sodium dithionite with formaldehyde produces Rongalite,

Na2S2O4 + 2 CH2O + H2O → NaHOCH2SO3 + NaHOCH2SO2

which is used in bleaching wood pulp, cotton, wool, leather and clay.[25]

Environmental impact[edit]


Industrial bleaching agents can also be sources of concern. For example, the use of elemental chlorine in the bleaching of wood pulp produces organochlorines and persistent organic pollutants, including dioxins. According to an industry group, the use of chlorine dioxide in these processes has reduced the dioxin generation to under detectable levels.[27] However, respiratory risk from chlorine and highly toxic chlorinated byproducts still exists.


  • The OSHA highest allowable peak concentration (5 minute exposure for five minutes in a 4-hour period) is 200 ppm,[30] twice as high as the reported highest peak level (from the headspace of a bottle of a sample of bleach plus detergent).

Further studies of the use of these products and other possible exposure routes (i.e., dermal) may reveal other risks. Though the author further cited ozone depletion greenhouse effects for these gases, the very low amount of such gases, generated as prescribed, should minimize their contribution relative to other sources.


Sodium hypochlorite solution, 3-6%, (common household bleach) must be diluted to be used safely when disinfecting surfaces and when used to treat drinking water. When disinfecting most surfaces, 1 part liquid household bleach to 100 parts water is sufficient for sanitizing. Stronger or weaker solutions may be more appropriate to meet specific goals, such as killing resistant viruses or sanitizing surfaces that will not be in contact with food. See references for more information.[31][32]

In an emergency, drinking water should be treated by boiling for 1–3 minutes, longer at higher altitudes. If boiling is not possible, water can be chemically treated with a ratio of 2 drops of plain liquid household bleach (5-6% sodium hypochlorite solution) per liter of water or 8 drops of bleach per gallon (3.79L) of water; 1/2 teaspoon bleach per five gallons (19L) of water. Do not use powdered bleach, or bleach with scents, cleaners or other additives. Do not collect water for treatment from flood waters or other potentially contaminated sources. If water appears dirty or cloudy, let it settle and/or filter the water before adding the bleach. Let treated water stand covered for 30 minutes. If water is still cloudy after filtering, double the amount of bleach used. If the water is very cold, either warm it before treatment or double the treatment time. Treated water should still have a slight bleach odor after treatment. If it does not, repeat the treatment. If no bleach odor is evident after a second treatment, discard the water and find a better water source.[33][34][35][36] Inappropriate dilutions of bleach can endanger your health.



A 1-in-5 dilution of household bleach with water (1 part bleach to 4 parts water) is effective against many bacteria and some viruses, and is often the disinfectant of choice in cleaning surfaces in hospitals (primarily in the United States). The solution is corrosive, and needs to be thoroughly removed afterwards, so the bleach disinfection is sometimes followed by an ethanol disinfection. Even "scientific-grade", commercially produced disinfection solutions such as Virocidin-X usually have sodium hypochlorite as their sole active ingredient, though they also contain surfactants (to prevent beading) and fragrances (to conceal the bleach smell).[37]


Treatment of Gingivitis [38]

Diluted sodium hypochlorite at a rate of 2000-1 (0.05% concentration) may represent an efficacious, safe and affordable antimicrobial agent in the prevention and treatment of periodontal disease.

Color safe bleach[edit]

Color safe bleach is a chemical that uses hydrogen peroxide as the active ingredient (to help remove stains) rather than sodium hypochlorite or chlorine.[39] It also has chemicals in it that help brighten colors.[40] Hydrogen peroxide is also used for sterilization purposes and water treatment, but its disinfectant capabilities may be limited due to the concentration in the colorsafe bleach solution as compared to other applications.[40]

See also[edit]


  1. ^ a b c "Bleaching". Encyclopaedia Britannica, (9th Edition (1875) and 10th Edition (1902) ed.). Retrieved 2 May 2012. 
  2. ^
  4. ^ L. J. Thénard (1818). "Observations sur des nouvelles combinaisons entre l'oxigène et divers acides". Annales de chimie et de physique, 2nd series 8: 306–312. 
  6. ^ Milne, Neil (1998). "Oxygen bleaching systems in domestic laundry". J. Surfactants and Detergents 1 (2): 253–261. doi:10.1007/s11743-998-0029-z. Retrieved 8 May 2012. 
  7. ^ Field, Simon Q (2006). "Ingredients -- Bleach". Science Toys. Retrieved 2006-03-02. 
  9. ^ a b Jakob, U.; J. Winter, M. Ilbert, P.C.F. Graf, and D. Özcelik (14 November 2008). "Bleach Activates A Redox-Regulated Chaperone by Oxidative Protein Unfolding". Cell (Elsevier) 135 (4): 691–701. doi:10.1016/j.cell.2008.09.024. PMC 2606091. PMID 19013278. Retrieved 2008-11-19. 
  10. ^ Harrison, J. E., and J. Schultz. 1976. Studies on the chlorinating activity of myeloperoxidase. Journal of Biological Chemistry volume 251, pages 1371-74.
  14. ^ Occupational Safety & Health Administration (2007). and peroxide/recognition.html "OSHA – Chlorine". OSHA. Retrieved 2007-08-26. 
  15. ^ Rizk-Ouaini, Rosette; Ferriol, Michel; Gazet, Josette; Saugier-Cohen Adad, Marie Therese (1986). "Oxidation reaction of ammonia with sodium hypochlorite. Production and degradation reactions of chloramines". Bulletin de la Societe Chimique de France 4: 512–21. doi:10.1002/14356007.a02_143.pub2. ISBN 3-527-30673-0 
  16. ^ a b "Sodium hypochlorite as a disinfectant". Retrieved 2011-08-07. 
  17. ^ "How Products Are Made Volume 2". may 2011. 
  18. ^ "Sodium Hypochlorite Chemical Production". by Intratec, ISBN 978-0615702179. 
  19. ^ "Calcium Hypochlorite: Different forms of calcium hypochlorite". World Health Organization. Retrieved 27 May 2012. 
  21. ^ Y. Ni; X. Wang (1996). "Mechanism of the Methanol Based ClO2 Generation Process". International Pulp Bleaching Conference. TAPPI. pp. 454–462. 
  22. ^ "Sodium Perborate REACH Consortium". Retrieved 2012-06-07. 
  24. ^ "Ozo formulas". Ozone Information. 
  27. ^ "ECF: The Sustainable Technology". Alliance for Environmental Technology. Retrieved 2007-09-19. 
  28. ^ Odabasi, M., “Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach- Containing Household Products”, Environmental Science & Technology 42, 1445-1451, (2008). Available at: Environmental Science & Technology (ACS Publications)
  30. ^ a b "Chemical Sampling Information: Carbon Tetrachloride". 2004-06-16. Retrieved 2009-12-04. 
  31. ^ Dvorak, Glenda (February 2005). "Disinfection". Center for Food Security and Public Health. Ames, IA: Center for Food Security and Public Health, Iowa State University. p. 12. Retrieved 7 February 2011. 
  32. ^ "Guidelines for the Use of Sanitizers and Disinfectants in Child Care Facilities". Virginia Department of Health. Retrieved 2010-03-16. 
  33. ^ Washington State Department of Health: How to Purify Your Drinking Water
  34. ^ "Personal Preparation and Storage of Safe Water". Centers for Disease Control. Retrieved 2012-01-03. 
  35. ^ "Guidelines for Managing Water Supplies". U.S. Federal Emergency Management Agency. Retrieved 2012-01-03. 
  36. ^ "Clorox Regular Bleach FAQ". The Clorox Company. Retrieved 2012-01-03. 
  37. ^ KAM Scientific
  39. ^ Dr. Laundry archive
  40. ^ a b Non Chlorine Bleach – Stain Fighter & Color Booster Liquid | Clorox

Further reading[edit]


External links[edit]