Old page wikitext, before the edit (old_wikitext) | '{{Hatnote|For other uses, see [[Bleach (disambiguation)]]}}
'''Bleach''' is a chemical that whitens [[clothing]].
[[File:Clorox Bleach products.jpg|thumb|[[Clorox]] brand bleach]]
The bleaching process has been known for millennia,<ref name=encyc>{{Cite EB1911 |wstitle=Bleaching}}</ref> but the chemicals currently used for bleaching resulted from the work of several 18th century scientists. [[Chlorine]] is the basis for the most common bleaches: for example, the solution of [[sodium hypochlorite]], which is so ubiquitous that most simply call it "bleach", and [[calcium hypochlorite]], the active compound in "bleaching powder". Oxidizing bleaching agents that do not contain chlorine are usually based on [[peroxide]]s such as [[hydrogen peroxide]], [[sodium percarbonate]] and [[sodium perborate]]. While most bleaches are [[oxidizing agent]]s, some are [[reducing agents]] such as [[sodium dithionite]] and sodium borohydride.
Bleaches are used as [[household chemicals]] to whiten clothes and remove [[stain]]s and as disinfectants, primarily in the bathroom and kitchen. Many bleaches have strong [[bactericide|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 [[weed]]s and increasing the longevity of cut [[flower]]s.<ref>{{cite web|url=http://www.rd.com/home/cleaning-organizing/12-smart-ways-to-use-bleach/|title=12 Smart Ways to Use Bleach - Reader's Digest|date=9 March 2010|publisher=}}</ref>
== History ==
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]].<ref name=encyc/><ref name="Cotton">{{Cite book|title=The Cotton Industry|last=Aspin|first=Chris|publisher=Shire Publications Ltd.|year=1981|isbn=0-85263-545-1|page=24|postscript=<!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}</ref> Modern bleaches resulted from the work of 18th century scientists including [[Swedish people|Swedish]] chemist [[Carl Wilhelm Scheele]], who discovered chlorine,<ref name=encyc/> [[French people|French]] scientists [[Claude Berthollet]], who recognized that chlorine could be used to bleach fabrics<ref name=encyc/> 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 people|Scottish]] chemist and industrialist [[Charles Tennant]] first produced a solution of [[calcium hypochlorite]], then solid [[calcium hypochlorite]] (bleaching powder).<ref name=encyc/>
[[Louis Jacques Thénard]] first produced [[hydrogen peroxide]] in 1818 by reacting [[barium peroxide]] with [[nitric acid]].<ref>{{Cite journal
| title = Observations sur des nouvelles combinaisons entre l'oxigène et divers acides
| author = L. J. Thénard
| journal = [[Annales de chimie et de physique]] |series=2nd Series
| volume = 8
| year =1818
| pages = 306–312
| url = https://books.google.com/books?id=-N43AAAAMAAJ&pg=PA306#v=onepage&q&f=false}}</ref> Hydrogen peroxide was first used for bleaching in 1882, but did not become commercially important until after 1930.<ref>{{cite web|url=http://www.scribd.com/doc/90597292/9/History-of-bleaching-with-hydrogen-peroxide|title=Catalytic Bleaching Of Cotton: Molecular and Macroscopic Aspects p 16|author=Tatjana Topalović|publisher=Thesis, University of Twente, the Netherlands ISBN 90-365-2454-7|accessdate=8 May 2012}}</ref> [[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.<ref>{{cite journal |last1=Milne |first1=Neil |last2= |first2= |year=1998 |title=Oxygen bleaching systems in domestic laundry |journal=J. Surfactants and Detergents |volume=1 |issue=2 |pages=253–261 |publisher= |doi=10.1007/s11743-998-0029-z |url=http://www.springerlink.com/content/f3g083n7p2w710x5/ |accessdate=8 May 2012}}</ref>
== Mechanism of action==
=== Whitening ===
Colors typically arise from organic [[dye]] and [[pigment]]s, such as [[beta carotene]]. Chemical bleaches work in one of two ways:
*An oxidizing bleach works by breaking the [[chemical bond]]s that make up the [[chromophore]]. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb [[visible light]]. This is the mechanism of bleaches based on [[chlorine]].
*A reducing bleach works by converting [[double bond]]s in the chromophore into [[single bond]]s. This eliminates the ability of the chromophore to absorb visible light. This is the mechanism of bleaches based on [[sulfur dioxide]].<ref>{{cite web|url=http://sci-toys.com/ingredients/bleach.html| title=Ingredients – Bleach| work=Science Toys| year=2006| accessdate=2006-03-02|author=Field, Simon Q}}</ref>
Sunlight acts as a bleach through a process leading to similar results: high energy [[photon]]s of light, often in the [[violet (color)|violet]] or [[ultraviolet]] range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless. Extended exposure often leads to massive discoloration usually reducing the colors to white and typically very faded blue spectrums.<ref>{{cite web|url=http://www.howeverythingworks.org/pages_fm.php?topic=all&page=150| title=Sunlight| work=How Things Work Home Page| year=2006| accessdate=2012-02-23|author=Bloomfield, Louis A}}</ref>
=== Antimicrobial efficacy ===
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 [[antibiotic]]s, bleach quickly reacts with microbial cells to irreversibly [[Denaturation (biochemistry)|denature]] and destroy many [[pathogen]]s. Bleach, particularly sodium hypochlorite, has been shown to react with a microbe's [[heat shock protein]]s, stimulating their role as [[Heat shock protein#Role as chaperone|intra-cellular chaperone]] and causing the bacteria to form into clumps (much like an egg that has been boiled) that will eventually die off.<ref name=Winter>{{cite journal
| last = Jakob
| first = U.
|author2=J. Winter |author3=M. Ilbert |author4=P.C.F. Graf |author5=D. Özcelik
| title = Bleach Activates A Redox-Regulated Chaperone by Oxidative Protein Unfolding
| journal = [[Cell (journal)|Cell]]
| volume = 135
| issue = 4
| pages = 691–701
| publisher = Elsevier
| location =
| date = 14 November 2008
| url = http://www.cell.com/abstract/S0092-8674(08)01181-1
| doi =10.1016/j.cell.2008.09.024
| id =
| accessdate =2008-11-19
| pmid = 19013278
| pmc = 2606091 }}</ref> 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, ''[[Escherichia coli|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.<ref name="Winter"/>
In response to infection, the human [[immune system]] will produce a strong oxidizer, [[hypochlorous acid]], which is generated in activated [[neutrophil]]s by [[myeloperoxidase]]-mediated peroxidation of chloride ions, and contributes to the destruction of [[bacteria]].<ref>{{cite journal|last1=Harrison|first1=JE|last2=Schultz|first2=J|title=Studies on the chlorinating activity of myeloperoxidase.|journal=The Journal of Biological Chemistry|date=10 March 1976|volume=251|issue=5|pages=1371–4|pmid=176150}}</ref><ref>{{cite journal | last1 = Thomas | first1 = E. L. | year = 1979 | title = Myeloperoxidase, hydrogen peroxide, chloride antimicrobial system: Nitrogen-chlorine derivatives of bacterial components in bactericidal action against ''Escherichia coli'' | url = | journal = Infect. Immun. | volume = 23 | issue = | pages = 522–531 }}</ref><ref>{{cite journal|last1=Albrich|first1=JM|last2=McCarthy|first2=CA|last3=Hurst|first3=JK|title=Biological reactivity of hypochlorous acid: implications for microbicidal mechanisms of leukocyte myeloperoxidase.|journal=Proceedings of the National Academy of Sciences of the United States of America|date=January 1981|volume=78|issue=1|pages=210–4|pmid=6264434|doi=10.1073/pnas.78.1.210|pmc=319021}}</ref>
==Classes of bleaches==
===Chlorine-based bleaches===
{{See also|Chlorine base compound}}
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====
Mixing a hypochlorite bleach with an acid can liberate chlorine gas. [[Hypochlorite]] and chlorine are in [[chemical equilibrium|equilibrium]] in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine,<ref name="c&w">{{cite book |last=Cotton |first=F.A |author2=G. Wilkinson |title=Advanced Inorganic Chemistry |year=1972 |publisher=John Wiley and Sons Inc. |location= |isbn=0-471-17560-9 }}</ref>
Cl<sub>2</sub> + H<sub>2</sub>O <math>\rightleftharpoons</math> H<sup>+</sup> + Cl<sup>−</sup> + HClO
Chlorine is a respiratory [[Irritation|irritant]] that attacks [[mucous membrane]]s and [[burn (injury)|burns]] the skin. As little as 3.53 [[parts per million|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 [[Occupational Safety and Health Administration|OSHA]] in the U.S.<ref>{{cite web|url=http://www.osha.gov/SLTC/healthguidelines/chlorine and peroxide/recognition.html| title=OSHA – Chlorine| work=OSHA| year=2007| accessdate=2007-08-26|author=Occupational Safety & Health Administration}}</ref>
Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed.<ref>{{Cite journal | last =Rizk-Ouaini | first =Rosette |author2=Ferriol, Michel |author3=Gazet, Josette |author4=Saugier-Cohen Adad |author5=Marie Therese | title =Oxidation reaction of ammonia with sodium hypochlorite. Production and degradation reactions of chloramines | journal =Bulletin de la Societe Chimique de France
| volume =4 | issue = | pages =512–21 | year =1986
| url = | doi = 10.1002/14356007.a02_143.pub2| id = | postscript =<!--None--> | isbn =3-527-30673-0 }}</ref> The main reaction is chlorination of ammonia, first giving [[chloramine]] (NH<sub>2</sub>Cl), then [[dichloramine]] (NHCl<sub>2</sub>) and finally [[nitrogen trichloride]] (NCl<sub>3</sub>). These materials are very irritating to the [[human eye|eye]]s and [[human lung|lung]]s and are toxic above certain concentrations; nitrogen trichloride is also a very sensitive explosive.
NH<sub>3</sub> + NaOCl → NaOH + NH<sub>2</sub>Cl
NH<sub>2</sub>Cl + NaOCl → NaOH + NHCl<sub>2</sub>
NHCl<sub>2</sub> + NaOCl → NaOH + NCl<sub>3</sub>
Additional reactions produce [[hydrazine]], in a variation of the [[Olin Raschig process]].
NH<sub>3</sub> + NH<sub>2</sub>Cl + NaOH → N<sub>2</sub>H<sub>4</sub> + NaCl + H<sub>2</sub>O
The hydrazine generated can react with more chloramine in an [[exothermic]] reaction to produce [[ammonium chloride]] and [[nitrogen]] gas:<ref name="c&w"/>
2 NH<sub>2</sub>Cl + N<sub>2</sub>H<sub>4</sub> → 2 NH<sub>4</sub>Cl + N<sub>2</sub>
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|date=June 2013}} Salts particularly effective, in this regard, include MgCl<sub>2</sub>, CaCl<sub>2</sub>, FeCl<sub>3</sub> and, to a lesser 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)<sub>2</sub>.CaCl<sub>2</sub>.Ca(OH)<sub>2</sub>.xH<sub>2</sub>O, the presence of CaCl<sub>2</sub> in very concentrated solutions can greatly increase the 'activity level' of weak acids. So, in this particular proposed application, H<sub>2</sub>CO3 from CO<sub>2</sub> and moisture on the bleaching powder, acts on the CaCl<sub>2</sub> to release some HCl which acts on the HClO releasing Chlorine:
HClO + HCl → H<sub>2</sub>O + Cl<sub>2</sub>
or, the increasing acidity creates more HClO which moves the following known (and old, see Watt's Dictionary of Chemistry{{Citation needed|date=June 2013}}) equilibrium reaction to the right:
CaCl<sub>2</sub> + 2 HClO = Ca(OH)<sub>2</sub> + 2 Cl<sub>2</sub>
====Sodium hypochlorite====
{{Main article|Sodium hypochlorite}}
[[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 [[Hypochlorite#Preparation|produced]] by passing [[chlorine]] gas through a dilute [[sodium hydroxide]] solution<ref name=len>{{cite web|url=http://www.lenntech.com/processes/disinfection/chemical/disinfectants-sodium-hypochlorite.htm |title=Sodium hypochlorite as a disinfectant |publisher=Lenntech.com |accessdate=2011-08-07}}</ref>
:Cl<sub>2</sub> (g) + 2 NaOH (aq) → NaCl (aq) + NaClO (aq) + H<sub>2</sub>O (l)
or by [[electrolysis]] of [[brine]] ([[sodium chloride]] in water).<ref name=len/><ref>{{cite web | title=How Products Are Made Volume 2 |date = May 2011| url=http://www.madehow.com/Volume-2/Bleach.html}}</ref>
:2 Cl<sup>−</sup> → Cl<sub>2</sub> + 2 e<sup>−</sup>
:Cl<sub>2</sub> + H<sub>2</sub>O ↔ HClO + Cl<sup>−</sup> + H<sup>+</sup>
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 [[Swimming pool sanitation|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.<ref name="Technology Economics Program">{{cite web|url=http://www.slideshare.net/intratec/sodium-hypochlorite-chemical-production|title=Sodium Hypochlorite Chemical Production|publisher=by Intratec, ISBN 978-0615702179}}</ref>
====Bleaching powder====
{{Main article|Calcium hypochlorite}}
Bleaching powder is any of various mixtures of [[calcium hypochlorite]], lime ([[calcium hydroxide]]), and calcium chloride.<ref name=Ullmann>Vogt, H.; Balej, J.; Bennett, J. E.; Wintzer, P.; Sheikh, S. A.; Gallone, P.; Vasudevan, S.; Pelin, K. (2010). "Chlorine Oxides and Chlorine Oxygen Acids". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. {{DOI|10.1002/14356007.a06_483.pub2}}</ref> Also known as "chlorinated lime", it is used in many of the same applications as sodium hypochlorite, but is more stable and contains more available chlorine. It is usually a white powder. A purer, more stable form of calcium hypochlorite is called HTH or high test hypochlorite. Bleaching tablets contain calcium hypochlorite and 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".<ref>{{cite web|url=http://www.who.int/water_sanitation_health/hygiene/emergencies/fs2_19.pdf |title= Calcium Hypochlorite: Different forms of calcium hypochlorite |publisher=[[World Health Organization]]|accessdate=27 May 2012}}</ref> [[Percent active chlorine]] in these materials ranges from 20% for bleaching powder to 70% for HTH.
====Chlorine====
{{Main article|Chlorine}}
Chlorine is produced by the [[Chlorine production|electrolysis of sodium chloride]].
:2 NaCl + 2 H<sub>2</sub>O → Cl<sub>2</sub> + H<sub>2</sub> + 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 [[Bleaching of wood pulp#bleaching of chemical pulps|bleach wood pulp]], but this use has decreased significantly due to [[Bleaching of wood pulp#Environmental considerations|environmental concerns]].
====Chlorine dioxide====
{{Main article|Chlorine dioxide}}
Chlorine dioxide, ClO<sub>2</sub>, is an unstable gas and is used in situ or stored as dilute aqueous solutions. Despite these limitations it finds large-scale applications for the [[bleaching of wood pulp]], [[fat]]s and [[oil]]s, [[cellulose]], [[flour]], [[textile]]s, [[beeswax]], [[skin]], and in a number of other industries. It can be prepared by oxidizing [[sodium chlorite]] with chlorine
:2 NaClO<sub>2</sub> + Cl<sub>2</sub> → 2 ClO<sub>2</sub> + 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]]<ref>{{Cite book
| last1 = Vogt | first1 = H.
| last2 = Balej | first2 = J.
| last3 = Bennett | first3 = J. E.
| last4 = Wintzer | first4 = P.
| last5 = Sheikh | first5 = S. A.
| last6 = Gallone | first6 = P.
| last7 = Vasudevan | first7 = S.
| last8 = Pelin | first8 = K.
| year = 2010
| chapter = Chlorine Oxides and Chlorine Oxygen Acids
| title = Ullmann's Encyclopedia of Industrial Chemistry
| publisher = Wiley-VCH
| doi = 10.1002/14356007.a06_483.pub2
}}</ref>
:2 NaClO<sub>3</sub> + 2 HX + "R" → 2 NaX + 2 ClO<sub>2</sub> + "RO" + H<sub>2</sub>O
where "R" is the reducing agent and "RO" is the oxidized form.<ref>{{cite conference |url=http://www.tappi.org/Downloads/unsorted/UNTITLED---ipb96453pdf.aspx |title=Mechanism of the Methanol Based ClO2 Generation Process |author=Y. Ni|author2=X. Wang |year=1996 |publisher=[[TAPPI]] |booktitle=International Pulp Bleaching Conference |pages=454–462 |location= |id= }}</ref>
===Peroxide-based bleaches===
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====
{{Main article|Hydrogen peroxide}}
[[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====
{{Main article|Sodium percarbonate}}
[[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.
:2Na<sub>2</sub>CO<sub>3</sub> + 3H<sub>2</sub>O<sub>2</sub>→2Na<sub>2</sub>CO<sub>3</sub>.3H<sub>2</sub>O<sub>2</sub>
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====
{{Main article|Sodium perborate}}
[[Sodium perborate]], Na<sub>2</sub>H<sub>4</sub>B<sub>2</sub>O<sub>8</sub>, is made by reacting [[borax]] with [[sodium hydroxide]] to give [[sodium metaborate]] (NaBO<sub>2</sub>) which is then reacted with hydrogen peroxide to give hydrated sodium perborate.<ref>{{cite web|url=http://www.perborates.eu/docs/PBS_SIP1010.pdf|title=Sodium Perborate REACH Consortium|accessdate=2012-06-07}}</ref>
:Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> + 2 NaOH → 4 NaBO<sub>2</sub> + H<sub>2</sub>O
:2 NaBO<sub>2</sub> + 2 H<sub>2</sub>O<sub>2</sub> + 6 H<sub>2</sub>O → [NaBO<sub>2</sub>(OH)<sub>2</sub> x 3 H<sub>2</sub>O]<sub>2</sub>
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)<sub>3</sub><sup>−</sup>), which is activated for [[nucleophile|nucleophilic]] oxidation.<ref>{{cite web|url=http://www.organic-chemistry.org/chemicals/oxidations/sodiumperborate.shtm|author=Douglass F. Taber|title=Oxidizing agents: Sodium perborate|accessdate=2012-06-07}}</ref>
===Miscellaneous bleaches===
[[Peracetic acid]] and [[ozone]] are used in the manufacture of paper products, especially [[newsprint]] and white [[Kraft paper]].<ref>{{cite web | url = http://www.ozonesolutions.com/Ozone_Color_Removal.html | work = Ozone Information | title = Ozo formulas}}</ref> In the [[food industry]], some [[organic peroxide]]s ([[benzoyl peroxide]], etc.) and other agents (e.g., [[bromate]]s) are used as [[flour bleaching agent|flour bleaching]] and [[maturing agent]]s.
===Reducing bleaches===
[[Sodium dithionite]] (also known as '''sodium hydrosulfite''') is one of the most important reductive bleaching agents. It is a white crystalline powder with a weak [[sulfur]]ous odor. It can be obtained by reacting [[sodium bisulfite]] with [[zinc]]
:2 NaHSO<sub>3</sub> + Zn → Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub> + Zn(OH)<sub>2</sub>
It is used as such in some industrial dyeing processes to eliminate excess dye, residual oxide, and unintended pigments and for [[Bleaching of wood pulp#Bleaching mechanical pulps|bleaching wood pulp]].
Reaction of sodium dithionite with [[formaldehyde]] produces [[Rongalite]],
:Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub> + 2 CH<sub>2</sub>O + H<sub>2</sub>O → NaHOCH<sub>2</sub>SO<sub>3</sub> + NaHOCH<sub>2</sub>SO<sub>2</sub>
which is used in bleaching [[wood pulp]], [[cotton]], [[wool]], [[leather]] and [[kaolinite|clay]].<ref>{{cite book
| title = Organic building blocks of the chemical industry
| author = Herman Harry Szmant
| publisher = John Wiley and Sons
| year = 1989
| isbn = 0-471-85545-6
| page = 113
}}</ref>
== Environmental impact ==
A Risk Assessment Report (RAR) conducted by the European Union on sodium hypochlorite conducted under Regulation EEC 793/93 concluded that this substance is safe for the environment in all its current, normal uses.<ref>European Union Risk Assessment Report. 2007. Sodium Hypochlorite (CAS No: 7681-52-9; EINECS No: 231-668-3): Final report, November 2007 (Final Approved Version); see [http://ec.europa.eu/health/archive/ph_risk/committees/04_scher/docs/scher_o_082.pdf Risk Assessment Report on Sodium Hypochlorite], Scientific Committee on Health and Environmental Risks, 12 March 2008.</ref> This is due to its high reactivity and instability. Disappearance of hypochlorite is practically immediate in the natural aquatic environment, reaching in a short time concentration as low as 10<sup>−22</sup> μg/L or less in all emission scenarios. In addition, it was found that while volatile chlorine species may be relevant in some indoor scenarios, they have negligible impact in open environmental conditions. Further, the role of hypochlorite pollution is assumed as negligible in soils.
Industrial bleaching agents can also be sources of concern. For example, the use of elemental chlorine in the [[bleaching of wood pulp]] produces [[organochlorine]]s and [[persistent organic pollutant]]s, including [[Polychlorinated dibenzodioxins|dioxin]]s. According to an industry group, the use of [[chlorine dioxide]] in these processes has reduced the dioxin generation to under detectable levels.<ref>{{cite web |url=http://www.aet.org/epp/ecf_brochure.pdf |title=ECF: The Sustainable Technology |accessdate=2007-09-19 |last= |first= |work= |publisher=Alliance for Environmental Technology}}</ref> However, respiratory risk from chlorine and highly toxic chlorinated byproducts still exists.
A recent European study indicated that sodium hypochlorite and organic chemicals (e.g., [[surfactant]]s, [[fragrance]]s) contained in several household cleaning products can react to generate chlorinated [[volatile organic compound]]s (VOCs).<ref>{{cite journal|last1=Odabasi|first1=Mustafa|title=Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach-Containing Household Products|journal=Environmental Science & Technology|date=March 2008|volume=42|issue=5|pages=1445–1451|doi=10.1021/es702355u}}</ref> These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable human [[carcinogen]]s. The study showed that indoor air concentrations significantly increase (8–52 times for [[chloroform]] and 1–1170 times for [[carbon tetrachloride]], respectively, above baseline quantities in the household) during the use of bleach containing products. The increase in chlorinated volatile organic compound concentrations was the lowest for plain bleach and the highest for the products in the form of “thick liquid and [[gel]]”. The significant increases observed in indoor air concentrations of several chlorinated VOCs (especially carbon tetrachloride and chloroform) indicate that the bleach use may be a source that could be important in terms of inhalation exposure to these compounds. While the authors suggested that using these cleaning products may significantly increase the cancer risk,<ref>Odabasi, M., [http://www.slideworld.org/ViewSlides.aspx?URL=5092 Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach- Containing Household Products, Slide presentation] (2008)</ref> this conclusion appears to be hypothetical:
:* The highest level cited for concentration of carbon tetrachloride (seemingly of highest concern) is 459 micrograms per cubic meter, translating to 0.073 ppm (part per million), or 73 ppb (part per billion). The [[Occupational Safety and Health Administration|OSHA]]-allowable time-weighted average concentration over an eight-hour period is 10 ppm,<ref name="OSHA_CCl4">{{cite web|url=http://www.osha.gov/dts/chemicalsampling/data/CH_225800.html |title=Chemical Sampling Information: Carbon Tetrachloride |publisher=Osha.gov |date=2004-06-16 |accessdate=2009-12-04}}</ref> almost 140 times higher;
:* The [[Occupational Safety and Health Administration|OSHA]] highest allowable peak concentration (5 minute exposure for five minutes in a 4-hour period) is 200 ppm,<ref name="OSHA_CCl4"/> twice as high as the reported highest peak level (from the [[headspace technology|headspace]] of a bottle of a sample of bleach plus detergent).
== Disinfection ==
Sodium hypochlorite solution, 3–6%, (common household bleach) is typically diluted for safe use 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 destroying resistant viruses or sanitizing surfaces that will not be in contact with food. See references for more information.<ref>{{cite web|url=http://www.cfsph.iastate.edu/BRM/resources/Disinfectants/Disinfection101Feb2005.pdf|title=Disinfection|last=Dvorak|first=Glenda|date=February 2005|work=Center for Food Security and Public Health|publisher=Center for Food Security and Public Health, Iowa State University|page=12|accessdate=7 February 2011|location=Ames, IA}}</ref><ref>{{cite web |url=http://www.vahealth.org/childadolescenthealth/EarlyChildhoodHealth/HealthyChildCareVA/documents/2009/doc/Disinfectionguidelines-childcare_8_14_09_FINAL.doc |title=Guidelines for the Use of Sanitizers and Disinfectants in Child Care Facilities |publisher=Virginia Department of Health |accessdate=2010-03-16}}</ref>
A weak solution of 2% household bleach in warm water is typical for sanitizing smooth surfaces prior to brewing of beer or wine.
US Government regulations (21 CFR Part 178) allow food processing equipment and food contact surfaces to be sanitized with solutions containing bleach, provided that the solution is allowed to drain adequately before contact with food, and that the solutions do not exceed 200 parts per million (ppm) available chlorine (for example, one tablespoon of typical household bleach containing 5.25% sodium hypochlorite, per gallon of water).
A 1-in-5 dilution of household bleach with water (1 part bleach to 4 parts water) is effective against many [[bacteria]] and some [[virus]]es, and is often the disinfectant of choice in cleaning surfaces in hospitals (primarily in the United States). The solution is [[corrosion|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).<ref>{{cite web|url=http://www.kamscientific.com/|title=KAM Scientific|publisher=}}</ref>
See [[Hypochlorous acid#Mode of disinfectant action|Hypochlorous acid]] for a discussion of the mechanism for disinfectant action.
'''Treatment of gingivitis''' <ref>{{Cite journal | last1 = De Nardo | first1 = R. | last2 = Chiappe | first2 = V. N. | last3 = Gómez | first3 = M. | last4 = Romanelli | first4 = H. | last5 = Slots | first5 = J. R. | title = Effects of 0.05% sodium hypochlorite oral rinse on supragingival biofilm and gingival inflammation | doi = 10.1111/j.1875-595X.2011.00111.x | journal = International Dental Journal | volume = 62 | issue = 4 | pages = 208–212 | year = 2012 | pmid = 23017003| pmc = }}</ref>
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==
Color safe bleach is a chemical that uses hydrogen peroxide as the active ingredient (to help remove stains) rather than sodium hypochlorite or chlorine.<ref>{{cite web|url=http://www.clorox.com/blogs/dr-laundry/2008/06/10/your-questions-disinfecting-laundry/ |title=Dr Laundry - Clorox |date=28 October 2015 |publisher= |deadurl=yes |archiveurl=https://web.archive.org/web/20110609033024/http://www.clorox.com/blogs/dr-laundry/2008/06/10/your-questions-disinfecting-laundry/ |archivedate=9 June 2011 |df=dmy }}</ref> It also has chemicals in it that help brighten colors.<ref name="clorox.com">[http://www.clorox.com/products/clorox2/faq/ Non Chlorine Bleach – Stain Fighter & Color Booster Liquid | Clorox<!-- Bot generated title -->]</ref> 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.<ref name="clorox.com"/>
== See also ==
* [[Tooth whitening]]
== References ==
{{Reflist|30em}}
== Further reading ==
* Bodkins, Dr. Bailey. ''Bleach''. Philadelphia: Virginia Printing Press, 1995. <!-- Can not find in the Library of Congress, British Library, or WorldCat catalogs, nor via Amazon.com, BookFinder.com, or Google. -->
* Trotman, E.R. ''Textile Scouring and Bleaching''. London: Charles Griffin & Co., 1968. ISBN 0-85264-067-6.
== External links ==
{{Commons category|Bleaches}}
*[http://www.britannica.com/EBchecked/topic/69164/bleach Bleach in] [[Encyclopædia Britannica|Britannica]]
*[http://www.florakim.com/files/Regular-Bleach-msds.pdf Bleach (MSDS)]
{{Use dmy dates|date=July 2011}}
{{Laundry navbox}}
{{Authority control}}
[[Category:Bleaches| ]]
[[Category:Disinfectants]]
[[Category:Dyes]]
[[Category:Household chemicals]]
[[Category:Laundry]]' |
New page wikitext, after the edit (new_wikitext) | '{{Hatnote|For other uses, see [[Bleach (disambiguation)]]}}
'''Bleach''' is a chemical that whitens [[clothing]].
[[File:Clorox Bleach products.jpg|thumb|[[Clorox]] brand bleach]]
Bleach is one of the most popular drinks in recent history.
Bleaches are used as wondeful drinks for consumption of humans. It has a distinct burning taste.
[[Louis Jacques Thénard]] first produced [[hydrogen peroxide]] in 1818 by reacting [[barium peroxide]] with [[nitric acid]].<ref>{{Cite journal
| title = Observations sur des nouvelles combinaisons entre l'oxigène et divers acides
| author = L. J. Thénard
| journal = [[Annales de chimie et de physique]] |series=2nd Series
| volume = 8
| year =1818
| pages = 306–312
| url = https://books.google.com/books?id=-N43AAAAMAAJ&pg=PA306#v=onepage&q&f=false}}</ref> Hydrogen peroxide was first used for bleaching in 1882, but did not become commercially important until after 1930.<ref>{{cite web|url=http://www.scribd.com/doc/90597292/9/History-of-bleaching-with-hydrogen-peroxide|title=Catalytic Bleaching Of Cotton: Molecular and Macroscopic Aspects p 16|author=Tatjana Topalović|publisher=Thesis, University of Twente, the Netherlands ISBN 90-365-2454-7|accessdate=8 May 2012}}</ref> [[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.<ref>{{cite journal |last1=Milne |first1=Neil |last2= |first2= |year=1998 |title=Oxygen bleaching systems in domestic laundry |journal=J. Surfactants and Detergents |volume=1 |issue=2 |pages=253–261 |publisher= |doi=10.1007/s11743-998-0029-z |url=http://www.springerlink.com/content/f3g083n7p2w710x5/ |accessdate=8 May 2012}}</ref>
== Mechanism of action==
=== Whitening ===
Colors typically arise from organic [[dye]] and [[pigment]]s, such as [[beta carotene]]. Chemical bleaches work in one of two ways:
*An oxidizing bleach works by breaking the [[chemical bond]]s that make up the [[chromophore]]. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb [[visible light]]. This is the mechanism of bleaches based on [[chlorine]].
*A reducing bleach works by converting [[double bond]]s in the chromophore into [[single bond]]s. This eliminates the ability of the chromophore to absorb visible light. This is the mechanism of bleaches based on [[sulfur dioxide]].<ref>{{cite web|url=http://sci-toys.com/ingredients/bleach.html| title=Ingredients – Bleach| work=Science Toys| year=2006| accessdate=2006-03-02|author=Field, Simon Q}}</ref>
Sunlight acts as a bleach through a process leading to similar results: high energy [[photon]]s of light, often in the [[violet (color)|violet]] or [[ultraviolet]] range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless. Extended exposure often leads to massive discoloration usually reducing the colors to white and typically very faded blue spectrums.<ref>{{cite web|url=http://www.howeverythingworks.org/pages_fm.php?topic=all&page=150| title=Sunlight| work=How Things Work Home Page| year=2006| accessdate=2012-02-23|author=Bloomfield, Louis A}}</ref>
=== Antimicrobial efficacy ===
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 [[antibiotic]]s, bleach quickly reacts with microbial cells to irreversibly [[Denaturation (biochemistry)|denature]] and destroy many [[pathogen]]s. Bleach, particularly sodium hypochlorite, has been shown to react with a microbe's [[heat shock protein]]s, stimulating their role as [[Heat shock protein#Role as chaperone|intra-cellular chaperone]] and causing the bacteria to form into clumps (much like an egg that has been boiled) that will eventually die off.<ref name=Winter>{{cite journal
| last = Jakob
| first = U.
|author2=J. Winter |author3=M. Ilbert |author4=P.C.F. Graf |author5=D. Özcelik
| title = Bleach Activates A Redox-Regulated Chaperone by Oxidative Protein Unfolding
| journal = [[Cell (journal)|Cell]]
| volume = 135
| issue = 4
| pages = 691–701
| publisher = Elsevier
| location =
| date = 14 November 2008
| url = http://www.cell.com/abstract/S0092-8674(08)01181-1
| doi =10.1016/j.cell.2008.09.024
| id =
| accessdate =2008-11-19
| pmid = 19013278
| pmc = 2606091 }}</ref> 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, ''[[Escherichia coli|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.<ref name="Winter"/>
In response to infection, the human [[immune system]] will produce a strong oxidizer, [[hypochlorous acid]], which is generated in activated [[neutrophil]]s by [[myeloperoxidase]]-mediated peroxidation of chloride ions, and contributes to the destruction of [[bacteria]].<ref>{{cite journal|last1=Harrison|first1=JE|last2=Schultz|first2=J|title=Studies on the chlorinating activity of myeloperoxidase.|journal=The Journal of Biological Chemistry|date=10 March 1976|volume=251|issue=5|pages=1371–4|pmid=176150}}</ref><ref>{{cite journal | last1 = Thomas | first1 = E. L. | year = 1979 | title = Myeloperoxidase, hydrogen peroxide, chloride antimicrobial system: Nitrogen-chlorine derivatives of bacterial components in bactericidal action against ''Escherichia coli'' | url = | journal = Infect. Immun. | volume = 23 | issue = | pages = 522–531 }}</ref><ref>{{cite journal|last1=Albrich|first1=JM|last2=McCarthy|first2=CA|last3=Hurst|first3=JK|title=Biological reactivity of hypochlorous acid: implications for microbicidal mechanisms of leukocyte myeloperoxidase.|journal=Proceedings of the National Academy of Sciences of the United States of America|date=January 1981|volume=78|issue=1|pages=210–4|pmid=6264434|doi=10.1073/pnas.78.1.210|pmc=319021}}</ref>
==Classes of bleaches==
===Chlorine-based bleaches===
{{See also|Chlorine base compound}}
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====
Mixing a hypochlorite bleach with an acid can liberate chlorine gas. [[Hypochlorite]] and chlorine are in [[chemical equilibrium|equilibrium]] in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine,<ref name="c&w">{{cite book |last=Cotton |first=F.A |author2=G. Wilkinson |title=Advanced Inorganic Chemistry |year=1972 |publisher=John Wiley and Sons Inc. |location= |isbn=0-471-17560-9 }}</ref>
Cl<sub>2</sub> + H<sub>2</sub>O <math>\rightleftharpoons</math> H<sup>+</sup> + Cl<sup>−</sup> + HClO
Chlorine is a respiratory [[Irritation|irritant]] that attacks [[mucous membrane]]s and [[burn (injury)|burns]] the skin. As little as 3.53 [[parts per million|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 [[Occupational Safety and Health Administration|OSHA]] in the U.S.<ref>{{cite web|url=http://www.osha.gov/SLTC/healthguidelines/chlorine and peroxide/recognition.html| title=OSHA – Chlorine| work=OSHA| year=2007| accessdate=2007-08-26|author=Occupational Safety & Health Administration}}</ref>
Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed.<ref>{{Cite journal | last =Rizk-Ouaini | first =Rosette |author2=Ferriol, Michel |author3=Gazet, Josette |author4=Saugier-Cohen Adad |author5=Marie Therese | title =Oxidation reaction of ammonia with sodium hypochlorite. Production and degradation reactions of chloramines | journal =Bulletin de la Societe Chimique de France
| volume =4 | issue = | pages =512–21 | year =1986
| url = | doi = 10.1002/14356007.a02_143.pub2| id = | postscript =<!--None--> | isbn =3-527-30673-0 }}</ref> The main reaction is chlorination of ammonia, first giving [[chloramine]] (NH<sub>2</sub>Cl), then [[dichloramine]] (NHCl<sub>2</sub>) and finally [[nitrogen trichloride]] (NCl<sub>3</sub>). These materials are very irritating to the [[human eye|eye]]s and [[human lung|lung]]s and are toxic above certain concentrations; nitrogen trichloride is also a very sensitive explosive.
NH<sub>3</sub> + NaOCl → NaOH + NH<sub>2</sub>Cl
NH<sub>2</sub>Cl + NaOCl → NaOH + NHCl<sub>2</sub>
NHCl<sub>2</sub> + NaOCl → NaOH + NCl<sub>3</sub>
Additional reactions produce [[hydrazine]], in a variation of the [[Olin Raschig process]].
NH<sub>3</sub> + NH<sub>2</sub>Cl + NaOH → N<sub>2</sub>H<sub>4</sub> + NaCl + H<sub>2</sub>O
The hydrazine generated can react with more chloramine in an [[exothermic]] reaction to produce [[ammonium chloride]] and [[nitrogen]] gas:<ref name="c&w"/>
2 NH<sub>2</sub>Cl + N<sub>2</sub>H<sub>4</sub> → 2 NH<sub>4</sub>Cl + N<sub>2</sub>
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|date=June 2013}} Salts particularly effective, in this regard, include MgCl<sub>2</sub>, CaCl<sub>2</sub>, FeCl<sub>3</sub> and, to a lesser 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)<sub>2</sub>.CaCl<sub>2</sub>.Ca(OH)<sub>2</sub>.xH<sub>2</sub>O, the presence of CaCl<sub>2</sub> in very concentrated solutions can greatly increase the 'activity level' of weak acids. So, in this particular proposed application, H<sub>2</sub>CO3 from CO<sub>2</sub> and moisture on the bleaching powder, acts on the CaCl<sub>2</sub> to release some HCl which acts on the HClO releasing Chlorine:
HClO + HCl → H<sub>2</sub>O + Cl<sub>2</sub>
or, the increasing acidity creates more HClO which moves the following known (and old, see Watt's Dictionary of Chemistry{{Citation needed|date=June 2013}}) equilibrium reaction to the right:
CaCl<sub>2</sub> + 2 HClO = Ca(OH)<sub>2</sub> + 2 Cl<sub>2</sub>
====Sodium hypochlorite====
{{Main article|Sodium hypochlorite}}
[[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 [[Hypochlorite#Preparation|produced]] by passing [[chlorine]] gas through a dilute [[sodium hydroxide]] solution<ref name=len>{{cite web|url=http://www.lenntech.com/processes/disinfection/chemical/disinfectants-sodium-hypochlorite.htm |title=Sodium hypochlorite as a disinfectant |publisher=Lenntech.com |accessdate=2011-08-07}}</ref>
:Cl<sub>2</sub> (g) + 2 NaOH (aq) → NaCl (aq) + NaClO (aq) + H<sub>2</sub>O (l)
or by [[electrolysis]] of [[brine]] ([[sodium chloride]] in water).<ref name=len/><ref>{{cite web | title=How Products Are Made Volume 2 |date = May 2011| url=http://www.madehow.com/Volume-2/Bleach.html}}</ref>
:2 Cl<sup>−</sup> → Cl<sub>2</sub> + 2 e<sup>−</sup>
:Cl<sub>2</sub> + H<sub>2</sub>O ↔ HClO + Cl<sup>−</sup> + H<sup>+</sup>
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 [[Swimming pool sanitation|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.<ref name="Technology Economics Program">{{cite web|url=http://www.slideshare.net/intratec/sodium-hypochlorite-chemical-production|title=Sodium Hypochlorite Chemical Production|publisher=by Intratec, ISBN 978-0615702179}}</ref>
====Bleaching powder====
{{Main article|Calcium hypochlorite}}
Bleaching powder is any of various mixtures of [[calcium hypochlorite]], lime ([[calcium hydroxide]]), and calcium chloride.<ref name=Ullmann>Vogt, H.; Balej, J.; Bennett, J. E.; Wintzer, P.; Sheikh, S. A.; Gallone, P.; Vasudevan, S.; Pelin, K. (2010). "Chlorine Oxides and Chlorine Oxygen Acids". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. {{DOI|10.1002/14356007.a06_483.pub2}}</ref> Also known as "chlorinated lime", it is used in many of the same applications as sodium hypochlorite, but is more stable and contains more available chlorine. It is usually a white powder. A purer, more stable form of calcium hypochlorite is called HTH or high test hypochlorite. Bleaching tablets contain calcium hypochlorite and 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".<ref>{{cite web|url=http://www.who.int/water_sanitation_health/hygiene/emergencies/fs2_19.pdf |title= Calcium Hypochlorite: Different forms of calcium hypochlorite |publisher=[[World Health Organization]]|accessdate=27 May 2012}}</ref> [[Percent active chlorine]] in these materials ranges from 20% for bleaching powder to 70% for HTH.
====Chlorine====
{{Main article|Chlorine}}
Chlorine is produced by the [[Chlorine production|electrolysis of sodium chloride]].
:2 NaCl + 2 H<sub>2</sub>O → Cl<sub>2</sub> + H<sub>2</sub> + 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 [[Bleaching of wood pulp#bleaching of chemical pulps|bleach wood pulp]], but this use has decreased significantly due to [[Bleaching of wood pulp#Environmental considerations|environmental concerns]].
====Chlorine dioxide====
{{Main article|Chlorine dioxide}}
Chlorine dioxide, ClO<sub>2</sub>, is an unstable gas and is used in situ or stored as dilute aqueous solutions. Despite these limitations it finds large-scale applications for the [[bleaching of wood pulp]], [[fat]]s and [[oil]]s, [[cellulose]], [[flour]], [[textile]]s, [[beeswax]], [[skin]], and in a number of other industries. It can be prepared by oxidizing [[sodium chlorite]] with chlorine
:2 NaClO<sub>2</sub> + Cl<sub>2</sub> → 2 ClO<sub>2</sub> + 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]]<ref>{{Cite book
| last1 = Vogt | first1 = H.
| last2 = Balej | first2 = J.
| last3 = Bennett | first3 = J. E.
| last4 = Wintzer | first4 = P.
| last5 = Sheikh | first5 = S. A.
| last6 = Gallone | first6 = P.
| last7 = Vasudevan | first7 = S.
| last8 = Pelin | first8 = K.
| year = 2010
| chapter = Chlorine Oxides and Chlorine Oxygen Acids
| title = Ullmann's Encyclopedia of Industrial Chemistry
| publisher = Wiley-VCH
| doi = 10.1002/14356007.a06_483.pub2
}}</ref>
:2 NaClO<sub>3</sub> + 2 HX + "R" → 2 NaX + 2 ClO<sub>2</sub> + "RO" + H<sub>2</sub>O
where "R" is the reducing agent and "RO" is the oxidized form.<ref>{{cite conference |url=http://www.tappi.org/Downloads/unsorted/UNTITLED---ipb96453pdf.aspx |title=Mechanism of the Methanol Based ClO2 Generation Process |author=Y. Ni|author2=X. Wang |year=1996 |publisher=[[TAPPI]] |booktitle=International Pulp Bleaching Conference |pages=454–462 |location= |id= }}</ref>
===Peroxide-based bleaches===
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====
{{Main article|Hydrogen peroxide}}
[[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====
{{Main article|Sodium percarbonate}}
[[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.
:2Na<sub>2</sub>CO<sub>3</sub> + 3H<sub>2</sub>O<sub>2</sub>→2Na<sub>2</sub>CO<sub>3</sub>.3H<sub>2</sub>O<sub>2</sub>
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====
{{Main article|Sodium perborate}}
[[Sodium perborate]], Na<sub>2</sub>H<sub>4</sub>B<sub>2</sub>O<sub>8</sub>, is made by reacting [[borax]] with [[sodium hydroxide]] to give [[sodium metaborate]] (NaBO<sub>2</sub>) which is then reacted with hydrogen peroxide to give hydrated sodium perborate.<ref>{{cite web|url=http://www.perborates.eu/docs/PBS_SIP1010.pdf|title=Sodium Perborate REACH Consortium|accessdate=2012-06-07}}</ref>
:Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> + 2 NaOH → 4 NaBO<sub>2</sub> + H<sub>2</sub>O
:2 NaBO<sub>2</sub> + 2 H<sub>2</sub>O<sub>2</sub> + 6 H<sub>2</sub>O → [NaBO<sub>2</sub>(OH)<sub>2</sub> x 3 H<sub>2</sub>O]<sub>2</sub>
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)<sub>3</sub><sup>−</sup>), which is activated for [[nucleophile|nucleophilic]] oxidation.<ref>{{cite web|url=http://www.organic-chemistry.org/chemicals/oxidations/sodiumperborate.shtm|author=Douglass F. Taber|title=Oxidizing agents: Sodium perborate|accessdate=2012-06-07}}</ref>
===Miscellaneous bleaches===
[[Peracetic acid]] and [[ozone]] are used in the manufacture of paper products, especially [[newsprint]] and white [[Kraft paper]].<ref>{{cite web | url = http://www.ozonesolutions.com/Ozone_Color_Removal.html | work = Ozone Information | title = Ozo formulas}}</ref> In the [[food industry]], some [[organic peroxide]]s ([[benzoyl peroxide]], etc.) and other agents (e.g., [[bromate]]s) are used as [[flour bleaching agent|flour bleaching]] and [[maturing agent]]s.
===Reducing bleaches===
[[Sodium dithionite]] (also known as '''sodium hydrosulfite''') is one of the most important reductive bleaching agents. It is a white crystalline powder with a weak [[sulfur]]ous odor. It can be obtained by reacting [[sodium bisulfite]] with [[zinc]]
:2 NaHSO<sub>3</sub> + Zn → Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub> + Zn(OH)<sub>2</sub>
It is used as such in some industrial dyeing processes to eliminate excess dye, residual oxide, and unintended pigments and for [[Bleaching of wood pulp#Bleaching mechanical pulps|bleaching wood pulp]].
Reaction of sodium dithionite with [[formaldehyde]] produces [[Rongalite]],
:Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub> + 2 CH<sub>2</sub>O + H<sub>2</sub>O → NaHOCH<sub>2</sub>SO<sub>3</sub> + NaHOCH<sub>2</sub>SO<sub>2</sub>
which is used in bleaching [[wood pulp]], [[cotton]], [[wool]], [[leather]] and [[kaolinite|clay]].<ref>{{cite book
| title = Organic building blocks of the chemical industry
| author = Herman Harry Szmant
| publisher = John Wiley and Sons
| year = 1989
| isbn = 0-471-85545-6
| page = 113
}}</ref>
== Environmental impact ==
A Risk Assessment Report (RAR) conducted by the European Union on sodium hypochlorite conducted under Regulation EEC 793/93 concluded that this substance is safe for the environment in all its current, normal uses.<ref>European Union Risk Assessment Report. 2007. Sodium Hypochlorite (CAS No: 7681-52-9; EINECS No: 231-668-3): Final report, November 2007 (Final Approved Version); see [http://ec.europa.eu/health/archive/ph_risk/committees/04_scher/docs/scher_o_082.pdf Risk Assessment Report on Sodium Hypochlorite], Scientific Committee on Health and Environmental Risks, 12 March 2008.</ref> This is due to its high reactivity and instability. Disappearance of hypochlorite is practically immediate in the natural aquatic environment, reaching in a short time concentration as low as 10<sup>−22</sup> μg/L or less in all emission scenarios. In addition, it was found that while volatile chlorine species may be relevant in some indoor scenarios, they have negligible impact in open environmental conditions. Further, the role of hypochlorite pollution is assumed as negligible in soils.
Industrial bleaching agents can also be sources of concern. For example, the use of elemental chlorine in the [[bleaching of wood pulp]] produces [[organochlorine]]s and [[persistent organic pollutant]]s, including [[Polychlorinated dibenzodioxins|dioxin]]s. According to an industry group, the use of [[chlorine dioxide]] in these processes has reduced the dioxin generation to under detectable levels.<ref>{{cite web |url=http://www.aet.org/epp/ecf_brochure.pdf |title=ECF: The Sustainable Technology |accessdate=2007-09-19 |last= |first= |work= |publisher=Alliance for Environmental Technology}}</ref> However, respiratory risk from chlorine and highly toxic chlorinated byproducts still exists.
A recent European study indicated that sodium hypochlorite and organic chemicals (e.g., [[surfactant]]s, [[fragrance]]s) contained in several household cleaning products can react to generate chlorinated [[volatile organic compound]]s (VOCs).<ref>{{cite journal|last1=Odabasi|first1=Mustafa|title=Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach-Containing Household Products|journal=Environmental Science & Technology|date=March 2008|volume=42|issue=5|pages=1445–1451|doi=10.1021/es702355u}}</ref> These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable human [[carcinogen]]s. The study showed that indoor air concentrations significantly increase (8–52 times for [[chloroform]] and 1–1170 times for [[carbon tetrachloride]], respectively, above baseline quantities in the household) during the use of bleach containing products. The increase in chlorinated volatile organic compound concentrations was the lowest for plain bleach and the highest for the products in the form of “thick liquid and [[gel]]”. The significant increases observed in indoor air concentrations of several chlorinated VOCs (especially carbon tetrachloride and chloroform) indicate that the bleach use may be a source that could be important in terms of inhalation exposure to these compounds. While the authors suggested that using these cleaning products may significantly increase the cancer risk,<ref>Odabasi, M., [http://www.slideworld.org/ViewSlides.aspx?URL=5092 Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach- Containing Household Products, Slide presentation] (2008)</ref> this conclusion appears to be hypothetical:
:* The highest level cited for concentration of carbon tetrachloride (seemingly of highest concern) is 459 micrograms per cubic meter, translating to 0.073 ppm (part per million), or 73 ppb (part per billion). The [[Occupational Safety and Health Administration|OSHA]]-allowable time-weighted average concentration over an eight-hour period is 10 ppm,<ref name="OSHA_CCl4">{{cite web|url=http://www.osha.gov/dts/chemicalsampling/data/CH_225800.html |title=Chemical Sampling Information: Carbon Tetrachloride |publisher=Osha.gov |date=2004-06-16 |accessdate=2009-12-04}}</ref> almost 140 times higher;
:* The [[Occupational Safety and Health Administration|OSHA]] highest allowable peak concentration (5 minute exposure for five minutes in a 4-hour period) is 200 ppm,<ref name="OSHA_CCl4"/> twice as high as the reported highest peak level (from the [[headspace technology|headspace]] of a bottle of a sample of bleach plus detergent).
== Disinfection ==
Sodium hypochlorite solution, 3–6%, (common household bleach) is typically diluted for safe use 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 destroying resistant viruses or sanitizing surfaces that will not be in contact with food. See references for more information.<ref>{{cite web|url=http://www.cfsph.iastate.edu/BRM/resources/Disinfectants/Disinfection101Feb2005.pdf|title=Disinfection|last=Dvorak|first=Glenda|date=February 2005|work=Center for Food Security and Public Health|publisher=Center for Food Security and Public Health, Iowa State University|page=12|accessdate=7 February 2011|location=Ames, IA}}</ref><ref>{{cite web |url=http://www.vahealth.org/childadolescenthealth/EarlyChildhoodHealth/HealthyChildCareVA/documents/2009/doc/Disinfectionguidelines-childcare_8_14_09_FINAL.doc |title=Guidelines for the Use of Sanitizers and Disinfectants in Child Care Facilities |publisher=Virginia Department of Health |accessdate=2010-03-16}}</ref>
A weak solution of 2% household bleach in warm water is typical for sanitizing smooth surfaces prior to brewing of beer or wine.
US Government regulations (21 CFR Part 178) allow food processing equipment and food contact surfaces to be sanitized with solutions containing bleach, provided that the solution is allowed to drain adequately before contact with food, and that the solutions do not exceed 200 parts per million (ppm) available chlorine (for example, one tablespoon of typical household bleach containing 5.25% sodium hypochlorite, per gallon of water).
A 1-in-5 dilution of household bleach with water (1 part bleach to 4 parts water) is effective against many [[bacteria]] and some [[virus]]es, and is often the disinfectant of choice in cleaning surfaces in hospitals (primarily in the United States). The solution is [[corrosion|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).<ref>{{cite web|url=http://www.kamscientific.com/|title=KAM Scientific|publisher=}}</ref>
See [[Hypochlorous acid#Mode of disinfectant action|Hypochlorous acid]] for a discussion of the mechanism for disinfectant action.
'''Treatment of gingivitis''' <ref>{{Cite journal | last1 = De Nardo | first1 = R. | last2 = Chiappe | first2 = V. N. | last3 = Gómez | first3 = M. | last4 = Romanelli | first4 = H. | last5 = Slots | first5 = J. R. | title = Effects of 0.05% sodium hypochlorite oral rinse on supragingival biofilm and gingival inflammation | doi = 10.1111/j.1875-595X.2011.00111.x | journal = International Dental Journal | volume = 62 | issue = 4 | pages = 208–212 | year = 2012 | pmid = 23017003| pmc = }}</ref>
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==
Color safe bleach is a chemical that uses hydrogen peroxide as the active ingredient (to help remove stains) rather than sodium hypochlorite or chlorine.<ref>{{cite web|url=http://www.clorox.com/blogs/dr-laundry/2008/06/10/your-questions-disinfecting-laundry/ |title=Dr Laundry - Clorox |date=28 October 2015 |publisher= |deadurl=yes |archiveurl=https://web.archive.org/web/20110609033024/http://www.clorox.com/blogs/dr-laundry/2008/06/10/your-questions-disinfecting-laundry/ |archivedate=9 June 2011 |df=dmy }}</ref> It also has chemicals in it that help brighten colors.<ref name="clorox.com">[http://www.clorox.com/products/clorox2/faq/ Non Chlorine Bleach – Stain Fighter & Color Booster Liquid | Clorox<!-- Bot generated title -->]</ref> 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.<ref name="clorox.com"/>
== See also ==
* [[Tooth whitening]]
== References ==
{{Reflist|30em}}
== Further reading ==
* Bodkins, Dr. Bailey. ''Bleach''. Philadelphia: Virginia Printing Press, 1995. <!-- Can not find in the Library of Congress, British Library, or WorldCat catalogs, nor via Amazon.com, BookFinder.com, or Google. -->
* Trotman, E.R. ''Textile Scouring and Bleaching''. London: Charles Griffin & Co., 1968. ISBN 0-85264-067-6.
== External links ==
{{Commons category|Bleaches}}
*[http://www.britannica.com/EBchecked/topic/69164/bleach Bleach in] [[Encyclopædia Britannica|Britannica]]
*[http://www.florakim.com/files/Regular-Bleach-msds.pdf Bleach (MSDS)]
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