Jump to content

Bleach

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 72.213.138.75 (talk) at 17:00, 7 June 2011 (grammar correction in first para). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Template:Two other uses

File:Clorox Bleach Bottle.jpg
Commercial Clorox sodium hypochlorite bleach

A bleach is a chemical that removes colors, whitens, or disinfects, often via oxidation. Common chemical bleaches include household chlorine bleach (a solution of approximately 3–6% sodium hypochlorite, NaClO), lye, oxygen bleach (which contains either hydrogen peroxide or a peroxide-releasing compound), and bleaching powder (calcium hypochlorite). The bleaching process was known to most ancient civilizations and has been around for thousands of years. Modern bleaches resulted from the work of 18th century scientists including Swedish chemist Karl Wilhelm Scheele, French scientists Claude Berthollet and Antoine Germain Labarraque, and Scottish chemist Charles Tennant.[1] Household chlorine bleach is created in two ways: by separating sodium hypochlorite from sea water or brine using electrolysis,[2]or by adding chlorine gas to sodium hydroxide which produces sodium hypochlorite, water and sodium chloride.[3]

Many bleaches have strong bactericidal properties, and are used for disinfecting and sterilizing.

Examples of peroxide-releasing compounds are sodium perborate, sodium percarbonate, sodium persulfate, tetrasodium pyrophosphate, or urea peroxide together with catalysts and activators, e.g., tetraacetylethylenediamine or sodium nonanoyloxybenzenesulfonate.

Other examples

Chlorine dioxide is used for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, skin, and in a number of other industries.

Sodium thiosulfate also called sodium hyposulfite, sometimes shortened to thio or hypo, is used in pH testing of bleach substance. If one first adds sodium thiosulfate to the bleach solution, it will neutralize the color-removing effects of bleach and allow one to test the pH of bleach solution with liquid indicator.

In the food industry, some organic peroxides (benzoyl peroxide, etc.) and other agents (e.g., bromates) are used as flour bleaching and maturing agents.

Peracetic acid and ozone are used in the manufacture of paper products, especially newsprint and white Kraft paper.[4]

Two-part bleaches are utilized in the whitening of wood, especially oak.

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.[5] This is owed 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 10-22 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.

Under conditions where sodium hypochlorite is improperly introduced to confined bodies of water (e.g., ponds, aquaria), bleach is toxic to fish and invertebrates. In confined spaces, fish will attempt to swim away from the source; in unconfined spaces, fish will readily escape the hazard.

Chemical interactions

Hypochlorite and chlorine are in equilibrium in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine,[6]

Cl2 + H2O 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.[7]

Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed.[8] 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.

NH3 + NaOCl → NaOH + NH2Cl

NH2Cl + NaOCl → NaOH + NHCl2

NHCl2 + NaOCl → NaOH + NCl3

Additional reactions produce hydrazine, in a variation of the Olin Raschig process.

NH3 + NH2Cl + NaOH → N2H4 + NaCl + H2O

The hydrazine generated can further react with the monochloramine in an exothermic reaction:[6]

2 NH2Cl + N2H4 → 2 NH4Cl + N2

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.[9] 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., surfactants, fragrances) contained in several household cleaning products can react to generate chlorinated volatile organic compounds (VOCs).[10] These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable human carcinogens. 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,[11] 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 OSHA-allowable time-weighted average concentration over an eight-hour period is 10 ppm,[12] almost 140 times higher;
  • The OSHA highest allowable peak concentration (5 minute exposure for five minutes in a 4-hour period) is 200 ppm,[12] 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.

Dilution

Bleach is sold extremely concentrated and must be diluted to be used safely when disinfecting surfaces and when used to treat drinking water. When disinfecting most surfaces, 1 part bleach to 100 parts water is sufficient for sanitizing; stronger solutions may be used with caution.[13] In an emergency, drinking water can be treated: the ratio of bleach to water for purification is 2 drops of bleach per litre of water or 8 drops of bleach per gallon (3.79L) of water; 1/2 teaspoon bleach per five gallons (19L) of water. If water is cloudy, filter the water before adding the bleach. Let treated water stand covered for 15 minutes before drinking.[14] Additional bleach will not kill more bacteria and can endanger health.[15]

Chemistry

The process of bleaching can be summarized in the following set of chemical reactions:

Cl2(aq) + H2O(l) H+(aq) + Cl-(aq) + HClO(aq)

The H+ ion of the hypochlorous acid then dissolves into solution, and so the final result is effectively:

Cl2(aq) + H2O(l) 2H+(aq) + Cl-(aq) + ClO-(aq)

Hypochlorite tends to decompose into chloride and a highly reactive form of oxygen:

2ClO- 2Cl- + O2

Mechanism of bleach action

Colour in most dyes and pigments is produced by molecules which contain chromophores, such as beta carotene. Chemical bleaches work in one of two ways:

  • An oxidizing bleach works by breaking the chemical bonds 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.
  • A reducing bleach works by converting double bonds in the chromophore into single bonds. This eliminates the ability of the chromophore to absorb visible light.[16]

Sunlight acts as a bleach through a process leading to similar results: high energy photons of light, often in the 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.[17]

Sodium hypochlorite's anti-bacterial mechanism works by causing proteins to aggregate.[18][19]

Antimicrobial efficacy

The broad-spectrum effectiveness of bleach, particularly sodium hypochlorite, owes 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.[18] 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 appear to be able to develop a defense mechanism that helps protect the bacterium, though the implications of this defense mechanism have not been fully investigated.[18]

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.[20][21][22]

See also

References

  1. ^ Hassam. "History Of Bleach". {{cite web}}: Check |url= value (help)
  2. ^ "The Clorox Company Company Information".
  3. ^ "Disinfectants Sodium Hypochlorite".
  4. ^ "Ozo formulas". Ozone Information.
  5. ^ 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://ecb.jrc.ec.europa.eu/documents/Existing-Chemicals/RISK_ASSESSMENT/REPORT/sodiumhypochloritereport045.pdf.
  6. ^ a b Cotton, F.A (1972). Advanced Inorganic Chemistry. John Wiley and Sons Inc. ISBN 0-471-17560-9. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  7. ^ Occupational Safety & Health Administration (2007). and peroxide/recognition.html "OSHA – Chlorine". OSHA. Retrieved 2007-08-26. {{cite web}}: Check |url= value (help)
  8. ^ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ "ECF: The Sustainable Technology" (PDF). Alliance for Environmental Technology. Retrieved 2007-09-19. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  10. ^ Odabasi, M., “Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach- Containing Household Products”, Environmental Science & Technology 42, 1445-1451, (2008). Available at: http://pubs.acs.org/journals/esthag/
  11. ^ Odabasi, M., “Halogenated Volatile Organic Compounds from the Use of Chlorine-Bleach- Containing Household Products, Slide presentation (2008). Available at: http://www.slideworld.org/ViewSlides.aspx?URL=5092
  12. ^ a b "Chemical Sampling Information: Carbon Tetrachloride". Osha.gov. 2004-06-16. Retrieved 2009-12-04.
  13. ^ Dvorak, Glenda (February 2005). "Disinfection" (PDF). 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.
  14. ^ Washington State Department of Health: How to Purify Your Drinking Water
  15. ^ "Guidelines for the Use of Sanitizers and Disinfectants in Child Care Facilities". Virginia Department of Health. Retrieved 2010-03-16.
  16. ^ Field, Simon Q (2006). "Ingredients -- Bleach". Science Toys. Retrieved 2006-03-02.
  17. ^ Bloomfield, Louis A (2006). "Sunlight". How Things Work Home Page. Retrieved 2006-03-02.
  18. ^ a b c Jakob, U. (14 November 2008). "Bleach Activates a Redox-Regulated Chaperone by Oxidative Protein Unfolding". Cell. 135 (4). Elsevier: 691–701. doi:10.1016/j.cell.2008.09.024. PMC 2606091. PMID 19013278. Retrieved 2008-11-19. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  19. ^ Reuters (2008). "Mystery solved: How bleach kills germs". MSNBC.com. Retrieved 2008-11-13. {{cite web}}: |author= has generic name (help)
  20. ^ Harrison, J. E., and J. Schultz. 1976. Studies on the chlorinating activity of myeloperoxidase. Journal of Biological Chemistry volume 251, pages1371-1374.
  21. ^ 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.
  22. ^ 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.

Further reading

  • Bodkins, Dr. Bailey. Bleach. Philadelphia: Virginia Printing Press, 1995.
  • Trotman, E.R. Textile Scouring and Bleaching. London: Charles Griffin & Co., 1968. ISBN 0852640676.
Wikimedia Commons has media related to Bleaches.
Wikimedia Commons has media related to Bleaches.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Bleach&oldid=433060136"