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SODIUM HYPOCHLORITE
Sodium hypochlorite (commonly known in a dilute solution as bleach) is a chemical compound with the formula NaOCl or NaClO, comprising a sodium cation (Na+) and a hypochlorite anion (OCl−or ClO−). It may also be viewed as the sodium salt of hypochlorous acid. The anhydrous compound is unstable and may decompose explosively. It can be crystallized as a pentahydrate NaOCl·5H2O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.
CAS No.: 7681-52-9
EC No.: 231-668-3
Synonyms:
Antiformin; Bleach; Chloride of soda; In dilution: Carrel-Dakin solution; Modified Dakin's solution; Surgical chlorinated soda solution; sodyum hipoklorit; çamaşır suyu; Javel; sodiyum hipoklorit; sodyum hıproklorıt; sodyum hyproklorit; sodyum hipoklorid; sodium hipochloride; sodium hipoklorite; sodium hypochloride; sodium hypochlorıte; SODIUM HYPOCHLORITE; 7681-52-9; Antiformin; Hypochlorous acid, sodium salt; Sodium oxychloride; Chlorox; Clorox; Javex; Javelle water; Hypochlorite sodium; Carrel-dakin solution; Chloros; Cloralex; Cloropool; Dispatch; Hyclorite; Klorocin; Parozone; Surchlor; Youxiaolin; Deosan; Hypure; Milton; Dakins solution; Hospital Milton; Javel water; Milton Crystals; Neo-cleaner; Household bleach; Neoseptal CL; sodiumhypochlorite; Dakin's solution; Hypure N; Purin B; B-K liquid; Modified dakin's solution; Hyposan and Voxsan; Solutions, Dakin's; AD Gel; Clorox liquid bleach; Sodium hypochlorite solution; Sunnysol 150; Caswell No. 776; Texant; UNII-DY38VHM5OD; Dental antiformin; NaClO; NaOCl; sodium hypochloride; Sodium hypochlorite (NaClO); Sodium hypochlorite (NaOCl); CCRIS 708; Deosan Green Label Steriliser; HSDB 748; XY 12; EINECS 231-668-3; Sodium Hypochlorite; EPA Pesticide Chemical Code 014703; Sodium Hypochlorite; Hypochlorous acid, sodium salt (1:1); UN 1791; CHEBI:32146; Chlorinated water (sodium hypochlorite); SODIUM HYPOCHLORITE; Sodium hypochlorite [Hypochloride salts]; Sodium hypochlorite solution (15% or less); SODIUM HYPOCHLORITE [SOLUTION, DILUTED]; Dakins quarter; Dakins half; Sodium hypochlorite, 5% active chlorine; Di-Dak-Sol; Sodium hypochlorite, 10-15% active chlorine; Sodium hypochlorite [USP:JAN]; Sodium hypochlorite [USAN:JAN]; sodium hypochiorite; sodium;hypochlorite; SODIUM HYPOCHLORITE; Sodium hypo chlorite; SH; MFCD00011120; Texant (TN); ACMC-20ajo6; ANTIFORMIN, DENTAL; Sodium hypochlorite (JAN/USP); Sodium hypochlorite, 14% solution; Sodium Hypochlorite solution 6-14%; 7681-52-910022-70-5(pentahydrate); Sodium hypochlorite, aqueous solution, 12-15% available chlorine
Sodium Hypochlorite
Sodium hypochlorite is most often encountered as a pale greenish-yellow dilute solution referred to as liquid bleach, which is a household chemical widely used (since the 18th century) as a disinfectant or a bleaching agent.
In solution, the compound is unstable and easily decomposes, liberating chlorine which is the active principle of such products. Sodium hypochlorite is the oldest and still most important chlorine-based bleach.
Its corrosive properties, common availability, and reaction products make it a significant safety risk. In particular, mixing liquid bleach with other cleaning products, such as acids or ammonia, may produce toxic fumes.
Properties of Sodium Hypochlorite
Chemical formula NaOCl
Molar mass 74.442 g/mol
Appearance greenish-yellow solid (pentahydrate)
Odor chlorine-like and sweetish
Density 1.11 g/cm3
Melting point 18 °C (64 °F; 291 K) pentahydrate
Boiling point 101 °C (214 °F; 374 K) (decomposes)
Solubility in water 29.3 g/100mL (0 °C)
Acidity (pKa) 7.5185
Basicity (pKb) 6.4815
Chemistry of Sodium hypochlorite
Stability of the solid
Anhydrous sodium hypochlorite can be prepared but, like many hypochlorites, it is highly unstable and decomposes explosively on heating or friction. The decomposition is accelerated by carbon dioxide at atmospheric levels. It is a white solid with the orthorhombic crystal structure.
Sodium hypochlorite can also be obtained as a crystalline pentahydrate NaOCl·5H2O, which is not explosive and is much more stable than the anhydrous compound. The formula is sometimes given as 2NaOCl·10H2O. The transparent light greenish yellow orthorhombic crystals contain 44% NaOCl by weight and melt at 25–27 °C. The compound decomposes rapidly at room temperature, so it must be kept under refrigeration. At lower temperatures, however, it is quite stable: reportedly only 1% decomposition after 360 days at 7 °C.
A 1966 US patent claims that stable solid sodium hypochlorite dihydrate NaOCl·2H2O can be obtained by carefully excluding chloride ions (Cl−), which are present in the output of common manufacturing processes and are said to catalyze the decomposition of hypochlorite into chlorate (ClO−3) and chloride. In one test, the dihydrate was claimed to show only 6% decomposition after 13.5 months storage at −25 °C. The patent also claims that the dihydrate can be reduced to the anhydrous form by vacuum drying at about 50 °C, yielding a solid that showed no decomposition after 64 hours at −25 °C.
Equilibria and stability of solutions
At typical ambient temperatures, sodium hypochlorite is more stable in dilute solutions that contain solvated Na+ and OCl− ions. The density of the solution is 1.093 g/mL at 5% concentration, and 1.21 g/mL at 14%, 20 °C. Stoichiometric solutions are fairly alkaline, with pH 11 or higher since hypochlorous acid is a weak acid:
OCl− + H2O ⇌ HOCl + OH−
The following species and equilibria are present in solutions of NaOCl:
HOCl (aq) ⇌ H+ + OCl−HOCl (aq) + Cl− + H+ ⇌ Cl2 (aq) + H2OCl2 (aq) + Cl− ⇌ Cl−3Cl2 (aq) ⇌ Cl2 (g)
The second equilibrium equation above will be shifted to the right if the chlorine Cl2 is allowed to escape as gas. The ratios of Cl2, HOCl, and OCl− in solution are also pH dependent. At pH below 2, the majority of the chlorine in the solution is in the form of dissolved elemental Cl2. At pH greater than 7.4, the majority is in the form of hypochlorite ClO−. The equilibrium can be shifted by adding acids (such as hydrochloric acid) or bases (such as sodium hydroxide) to the solution:
ClO− (aq) + 2 HCl (aq) → Cl2 (g) + H2O (aq) + Cl− (aq)Cl2 (g) + 2 OH− → ClO− (aq) + Cl− (aq) + H2O (aq)
At a pH of about 4, such as obtained by the addition of strong acids like hydrochloric acid, the amount of undissociated (nonionized) HOCl is highest. The reaction can be written as:
ClO− + H+ ⇌ HClO
Sodium hypochlorite solutions combined with acid evolve chlorine gas, particularly strongly at pH < 2, by the reactions:
HOCl (aq) + Cl− + H+ ⇌ Cl2 (aq) + H2OCl2 (aq) ⇌ Cl2 (g)
At pH > 8, the chlorine is practically all in the form of hypochlorite anions (OCl−). The solutions are fairly stable at pH 11–12. Even so, one report claims that a conventional 13.6% NaOCl reagent solution lost 17% of its strength after being stored for 360 days at 7 °C. For this reason, in some applications one may use more stable chlorine-releasing compounds, such as calcium hypochlorite Ca(ClO)2 or trichloroisocyanuric acid (CNClO)3.
Anhydrous sodium hypochlorite is soluble in methanol, and solutions are stable.
Decomposition to chlorate or oxygen
In solution, under certain conditions, the hypochlorite anion may also disproportionate (autoxidize) to chloride and chlorate:
3 ClO− + H+ → HClO3 + 2 Cl−
In particular, this reaction occurs in sodium hypochlorite solutions at high temperatures, forming sodium chlorate and sodium chloride:
3 NaOCl (aq) → 2 NaCl (aq) + NaClO3 (aq)
This reaction is exploited in the industrial production of sodium chlorate.
An alternative decomposition of hypochlorite produces oxygen instead:
2 OCl− → 2 Cl− + O2
In hot sodium hypochlorite solutions, this reaction competes with chlorate formation, yielding sodium chloride and oxygen gas:
2 NaOCl (aq) → 2 NaCl (aq) + O2 (g)
These two decomposition reactions of NaClO solutions are maximized at pH around 6. The chlorate-producing reaction predominates at pH above 6, while the oxygen one becomes significant below that. For example, at 80 °C, with NaOCl and NaCl concentrations of 80 mM, and pH 6–6.5, the chlorate is produced with ∼95% efficiency. The oxygen pathway predominates at pH 10. This decomposition is affected by light and metal ion catalysts such as copper, nickel, cobalt, and iridium. Catalysts like sodium dichromate Na2Cr2O7 and sodium molybdate Na2MoO4 may be added industrially to reduce the oxygen pathway, but a report claims that only the latter is effective.
Titration
Titration of hypochlorite solutions is often done by adding a measured sample to an excess amount of acidified solution of potassium iodide (KI) and then titrating the liberated iodine (I2) with a standard solution of sodium thiosulfate or phenyl arsine oxide, using starch as indicator, until the blue color disappears.
According to one US patent, the stability of sodium hypochlorite content of solids or solutions can be determined by monitoring the infrared absorption due to the O–Cl bond. The characteristic wavelength is given as 140.25 μm for water solutions, 140.05 μm for the solid dihydrate NaOCl·2H
2O, and 139.08 μm for the anhydrous mixed salt Na2(OCl)(OH).
Oxidation of organic compounds
Oxidation of starch by sodium hypochlorite, that adds carbonyl and carboxyl groups, is relevant to the production of modified starch products.
In the presence of a phase-transfer catalyst, alcohols are oxidized to the corresponding carbonyl compound (aldehyde or ketone). Sodium hypochlorite can also oxidize organic sulfides to sulfoxides or sulfones, disulfides or thiols to sulfonyl chlorides or bromides, imines to oxaziridines. It can also de-aromatize phenols.
Oxidation of metals and complexes
Heterogeneous reactions of sodium hypochlorite and metals such as zinc proceed slowly to give the metal oxide or hydroxide:
NaOCl + Zn → ZnO + NaCl
Homogeneous reactions with metal coordination complexes proceed somewhat faster. This has been exploited in the Jacobsen epoxidation.
Other reactions of Sodium hypochlorite
If not properly stored in airtight containers, sodium hypochlorite reacts with carbon dioxide to form sodium carbonate:
2 NaOCl + CO2 + H2O → Na2CO3 + 2 HOCl
Sodium hypochlorite reacts with most nitrogen compounds to form volatile monochloramine, dichloramines, and nitrogen trichloride:
NH3 + NaOCl → NH2Cl + NaOHNH2Cl + NaOCl → NHCl2 + NaOHNHCl2 + NaOCl → NCl3 + NaOH
Neutralization
Sodium thiosulfate is an effective chlorine neutralizer. Rinsing with a 5 mg/L solution, followed by washing with soap and water, will remove chlorine odor from the hands.
Production of Sodium hypochlorite
Chlorination of soda
Potassium hypochlorite was first produced in 1789 by Claude Louis Berthollet in his laboratory on the Quai de Javel in Paris, France, by passing chlorine gas through a solution of potash lye. The resulting liquid, known as "Eau de Javel" ("Javel water"), was a weak solution of potassium hypochlorite. Antoine Labarraque replaced potash lye by the cheaper soda lye, thus obtaining sodium hypochlorite (Eau de Labarraque).
Cl2 (g) + 2 NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (aq)
Hence, chlorine is simultaneously reduced and oxidized; this process is known as disproportionation.
The process is also used to prepare the pentahydrate NaOCl·5H
2O for industrial and laboratory use. In a typical process, chlorine gas is added to a 45–48% NaOH solution. Some of the sodium chloride precipitates and is removed by filtration, and the pentahydrate is then obtained by cooling the filtrate to 12 °C .
From calcium hypochlorite
Another method involved by reaction of sodium carbonate ("washing soda") with chlorinated lime ("bleaching powder"), a mixture of calcium hypochlorite Ca(OCl)2, calcium chloride CaCl2, and calcium hydroxide Ca(OH)2:
Na2CO3 (aq) + Ca(OCl)2 (aq) → CaCO3 (s) + 2 NaOCl (aq)
Na2CO3 (aq) + CaCl2 (aq) → CaCO3 (s) + 2 NaCl (aq)
Na2CO3 (aq) + Ca(OH)2 (s) → CaCO3 (s) + 2 NaOH (aq)
This method was commonly used to produce hypochlorite solutions for use as a hospital antiseptic that was sold after World War I under the names "Eusol", an abbreviation for Edinburgh University Solution Of (chlorinated) Lime – a reference to the university's pathology department, where it was developed.
Electrolysis of brine
Near the end of the nineteenth century, E. S. Smith patented the chloralkali process: a method of producing sodium hypochlorite involving the electrolysis of brine to produce sodium hydroxide and chlorine gas, which then mixed to form sodium hypochlorite. The key reactions are:
2 Cl− → Cl2 + 2 e− (at the anode)
2 H2O + 2 e− → H2 + 2 HO− (at the cathode)
Both electric power and brine solution were in cheap supply at the time, and various enterprising marketers took advantage of the situation to satisfy the market's demand for sodium hypochlorite. Bottled solutions of sodium hypochlorite were sold under numerous trade names.
Today, an improved version of this method, known as the Hooker process (named after Hooker Chemicals, acquired by Occidental Petroleum), is the only large-scale industrial method of sodium hypochlorite production. In the process, sodium hypochlorite (NaClO) and sodium chloride (NaCl) are formed when chlorine is passed into cold dilute sodium hydroxide solution. The chlorine is prepared industrially by electrolysis with minimal separation between the anode and the cathode. The solution must be kept below 40 °C (by cooling coils) to prevent the undesired formation of sodium chlorate.
Commercial solutions always contain significant amounts of sodium chloride (common salt) as the main by-product, as seen in the equation above.
From hypochlorous acid and soda
A 1966 patent describes the production of solid stable dihydrate NaOCl·2H2O by reacting a chloride-free solution of hypochlorous acid HClO (such as prepared from chlorine monoxide ClO and water), with a concentrated solution of sodium hydroxide. In a typical preparation, 255 mL of a solution with 118 g/L HClO is slowly added with stirring to a solution of 40 g of NaOH in water 0 °C. Some sodium chloride precipitates and is removed by fitration. The solution is vacuum evaporated at 40–50 °C and 1–2 mmHg until the dihydrate crystallizes out. The crystals are vacuum-dried to produce a free-flowing crystalline powder.
The same principle was used in another 1991 patent to produce concentrated slurries of the pentahydrate NaClO·5H
2O. Typically, a 35% solution (by weight) of HClO is combined with sodium hydroxide at about or below 25 °C. The resulting slurry contains about 35% NaClO, and are relatively stable due to the low concentration of chloride.
From ozone and salt
Sodium hypochlorite can be easily produced for research purposes by reacting ozone with salt.
NaCl + O3 → NaClO + O2
This reaction happens at room temperature and can be helpful for oxidizing alcohols.
Packaging and sale
Main article: Bleach
Bleach packaged for household use, with 2.6% sodium hypochlorite
Household bleach sold for use in laundering clothes is a 3–8% solution of sodium hypochlorite at the time of manufacture. Strength varies from one formulation to another and gradually decreases with long storage. Sodium hydroxide is usually added in small amounts to household bleach to slow down the decomposition of NaClO.
A 10–25% solution of sodium hypochlorite is, according to Univar's safety sheet, supplied with synonyms or trade names bleach, Hypo, Everchlor, Chloros, Hispec, Bridos, Bleacol, or Vo-redox 9110.
A 12% solution is widely used in waterworks for the chlorination of water, and a 15% solution is more commonly used for disinfection of waste water in treatment plants. Sodium hypochlorite can also be used for point-of-use disinfection of drinking water, taking 0.2-2 mg of sodium hypochlorite per liter of water.
Dilute solutions (50 ppm to 1.5%) are found in disinfecting sprays and wipes used on hard surfaces.
Uses of Sodium hypochlorite
Bleaching
Household bleach is, in general, a solution containing 3–8% sodium hypochlorite, by weight, and 0.01–0.05% sodium hydroxide; the sodium hydroxide is used to slow the decomposition of sodium hypochlorite into sodium chloride and sodium chlorate.
Cleaning of Sodium hypochlorite
Sodium hypochlorite has destaining properties. Among other applications, it can be used to remove mold stains, dental stains caused by fluorosis, and stains on crockery, especially those caused by the tannins in tea. It has also been used in laundry detergents and as a surface cleaner.
Its bleaching, cleaning, deodorizing and caustic effects are due to oxidation and hydrolysis (saponification). Organic dirt exposed to hypochlorite becomes water-soluble and non-volatile, which reduces its odor and facilitates its removal.
Disinfection of Sodium hypochlorite
See also: Hypochlorous acid
Sodium hypochlorite in solution exhibits broad spectrum anti-microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use. "Strong chlorine solution" is a 0.5% solution of hypochlorite (containing approximately 5000 ppm free chlorine) used for disinfecting areas contaminated with body fluids, including large blood spills (the area is first cleaned with detergent before being disinfected). It may be made by diluting household bleach as appropriate (normally 1 part bleach to 9 parts water). Such solutions have been demonstrated to inactivate both C. difficile and HPV. "Weak chlorine solution" is a 0.05% solution of hypochlorite used for washing hands, but is normally prepared with calcium hypochlorite granules.
"Dakin's Solution" is a disinfectant solution containing low concentration of sodium hypochlorite and some boric acid or sodium bicarbonate to stabilize the pH. It has been found to be effective with NaOCl concentrations as low as 0.025%.
US government regulations 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). If higher concentrations are used, the surface must be rinsed with potable water after sanitizing.
A similar concentration of bleach in warm water is used to sanitize surfaces prior to brewing of beer or wine. Surfaces must be rinsed with sterilized (boiled) water to avoid imparting flavors to the brew; the chlorinated byproducts of sanitizing surfaces are also harmful. The mode of disinfectant action of sodium hypochlorite is similar to that of hypochlorous acid.
Solutions containing more than 500 ppm available chlorine are corrosive to some metals, alloys and many thermoplastics (such as acetal resin) and need to be thoroughly removed afterwards, so the bleach disinfection is sometimes followed by an ethanol disinfection. Liquids containing sodium hypochlorite as the main active component are also used for household cleaning and disinfection, for example toilet cleaners. Some cleaners are formulated to be viscous so as not to drain quickly from vertical surfaces, such as the inside of a toilet bowl.
The undissociated (nonionized) hypochlorous acid is believed to react with and inactivate bacterial and viral enzymes.
Neutrophils of the human immune system produce small amounts of hypochlorite inside phagosomes, which digest bacteria and viruses.
Deodorizing of Sodium hypochlorite
Sodium hypochlorite has deodorizing properties, which go hand in hand with its cleaning properties.
Waste water treatment of Sodium hypochlorite
Sodium hypochlorite solutions have been used to treat dilute cyanide waste water, such as electroplating wastes. In batch treatment operations, sodium hypochlorite has been used to treat more concentrated cyanide wastes, such as silver cyanide plating solutions. Toxic cyanide is oxidized to cyanate (OCN−) that is not toxic, idealized as follows:
CN− + OCl− → OCN− + Cl−
Sodium hypochlorite is commonly used as a biocide in industrial applications to control slime and bacteria formation in water systems used at power plants, pulp and paper mills, etc., in solutions typically of 10–15% by weight.
Endodontics
Sodium hypochlorite is the medicament of choice due to its efficacy against pathogenic organisms and pulp digestion in endodontic therapy. Its concentration for use varies from 0.5% to 5.25%. At low concentrations it dissolves mainly necrotic tissue; at higher concentrations it also dissolves vital tissue and additional bacterial species. One study has shown that Enterococcus faecalis was still present in the dentin after 40 minutes of exposure of 1.3% and 2.5% sodium hypochlorite, whereas 40 minutes at a concentration of 5.25% was effective in E. faecalis removal. In addition to higher concentrations of sodium hypochlorite, longer time exposure and warming the solution (60 °C) also increases its effectiveness in removing soft tissue and bacteria within the root canal chamber. 2% is a common concentration as there is less risk of an iatrogenic hypochlorite incident. A hypochlorite incident is an immediate reaction of severe pain, followed by edema, haematoma, and ecchymosis as a consequence of the solution escaping the confines of the tooth and entering the periapical space. This may be caused by binding or excessive pressure on the irrigant syringe, or it may occur if the tooth has an unusually large apical foramen.
Nerve agent neutralization
At the various nerve agent (chemical warfare nerve gas) destruction facilities throughout the United States, 50% sodium hypochlorite is used to remove all traces of nerve agent or blister agent from Personal Protection Equipment after an entry is made by personnel into toxic areas. 50% sodium hypochlorite is also used to neutralize any accidental releases of nerve agent in the toxic areas. Lesser concentrations of sodium hypochlorite are used in similar fashion in the Pollution Abatement System to ensure that no nerve agent is released in furnace flue gas.
Reduction of skin damage
Dilute bleach baths have been used for decades to treat moderate to severe eczema in humans, but it has not been clear why they work. According to work published by researchers at the Stanford University School of Medicine in November 2013, a very dilute (0.005%) solution of sodium hypochlorite in water was successful in treating skin damage with an inflammatory component caused by radiation therapy, excess sun exposure or aging in laboratory mice. Mice with radiation dermatitis given daily 30-minute baths in bleach solution experienced less severe skin damage and better healing and hair regrowth than animals bathed in water. A molecule called nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is known to play a critical role in inflammation, aging, and response to radiation. The researchers found that if NF-κB activity was blocked in elderly mice by bathing them in bleach solution, the animals' skin began to look younger, going from old and fragile to thicker, with increased cell proliferation. The effect diminished after the baths were stopped, indicating that regular exposure was necessary to maintain skin thickness.
Safety
It is estimated that there are about 3,300 accidents needing hospital treatment caused by sodium hypochlorite solutions each year in British homes (RoSPA, 2002).
Oxidation and corrosion
Sodium hypochlorite is a strong oxidizer. Oxidation reactions are corrosive. Solutions burn the skin and cause eye damage, especially when used in concentrated forms. As recognized by the NFPA, however, only solutions containing more than 40% sodium hypochlorite by weight are considered hazardous oxidizers. Solutions less than 40% are classified as a moderate oxidizing hazard (NFPA 430, 2000).
Household bleach and pool chlorinator solutions are typically stabilized by a significant concentration of lye (caustic soda, NaOH) as part of the manufacturing reaction. This additive will by itself cause caustic irritation or burns due to defatting and saponification of skin oils and destruction of tissue. The slippery feel of bleach on skin is due to this process.
Storage hazards
Contact of sodium hypochlorite solutions with metals may evolve flammable hydrogen gas. Containers may explode when heated due to release of chlorine gas.
Hypochlorite solutions are corrosive to common container materials such as stainless steel and aluminium. The few compatible metals include titanium (which however is not compatible with dry chlorine) and tantalum. Glass containers are safe. Some plastics and rubbers are affected too; safe choices include polyethylene (PE), high density polyethylene (HDPE, PE-HD), polypropylene (PP), some chlorinated and fluorinated polymers such as polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF); as well as ethylene propylene rubber, and Viton.
Containers must allow venting of oxygen produced by decomposition over time, otherwise they may burst.
Reactions with other common products
Mixing bleach with some household cleaners can be hazardous.
Sodium hypochlorite solutions, such as liquid bleach, may release toxic chlorine gas when heated above 35 °C or mixed with an acid, such as hydrochloric acid or vinegar.
A 2008 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). 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. The authors suggested that using these cleaning products may significantly increase the cancer risk.
In particular, mixing hypochlorite bleaches with amines (for example, cleaning products that contain or release ammonia, ammonium salts, urea, or related compounds and biological materials such as urine) produces chloramines. These gaseous products can cause acute lung injury. Chronic exposure, for example, from the air at swimming pools where chlorine is used as the disinfectant, can lead to the development of atopic asthma.
Bleach can react violently with hydrogen peroxide and produce oxygen gas:
H2O2 (aq) + NaOCl (aq) → NaCl (aq) + H2O (aq) + O2 (g)
Explosive reactions or byproducts can also occur in industrial and laboratory settings when sodium hypochlorite is mixed with diverse organic compounds.
Limitations in health care
The UK's National Institute for Health and Care Excellence in October 2008 recommended that Dakin's solution should not be used in routine wound care.
Environmental impact
In spite of its strong biocidal action, sodium hypochlorite per se has limited environmental impact, since the hypochlorite ion rapidly degrades before it can be absorbed by living beings.
However, one major concern arising from sodium hypochlorite use is that it tends to form persistent chlorinated organic compounds, including known carcinogens, that can be absorbed by organisms and enter the food chain. These compounds may be formed during household storage and use as well during industrial use. For example, when household bleach and wastewater were mixed, 1–2% of the available chlorine was observed to form organic compounds. As of 1994, not all the byproducts had been identified, but identified compounds include chloroform and carbon tetrachloride. The estimated exposure to these chemicals from use is estimated to be within occupational exposure limits.
Sodium hypochlorite (NaOCl) is a compound that can be effectively used for water purification. It is used on a large scale for surface purification, bleaching, odor removal and water disinfection.
When was sodium hypochlorite discovered?
Sodium hypochlorite has a long history. Around 1785 the Frenchman Berthollet developed liquid bleaching agents based on sodium hypochlorite. The Javel company introduced this product and called it 'liqueur de Javel'. At first, it was used to bleach cotton. Because of its specific characteristics it soon became a popular compound. Hypochlorite can remove stains from clothes at room temperature. In France, sodium hypochlorite is still known as 'eau de Javel'.
What are the characteristics of sodium hypochlorite?
Sodium hypochlorite is a clear, slightly yellowish solution with a characteristic odor.
Sodium hypochlorite has a relative density of is 1,1 (5,5% watery solution).
As a bleaching agent for domestic use it usually contains 5% sodium hypochlorite (with a pH of around 11, it is irritating). If it is more concentrated, it contains a concentration 10-15% sodium hypochlorite (with a pH of around 13, it burns and is corrosive).
Sodium hypochlorite is unstable. Chlorine evaporates at a rate of 0,75 gram active chlorine per day from the solution. Then heated sodium hypochlorite disintegrates. This also happens when sodium hypochlorite comes in contact with acids, sunlight, certain metals and poisonous and corrosive gasses, including chlorine gas. Sodium hypochlorite is a strong oxidator and reacts with flammable compounds and reductors. Sodium hypochlorite solution is a weak base that is inflammable.
These characteristics must be kept in mind during transport, storage and use of sodium hypochlorite.
What happens to the pH value when sodium hypochlorite is added to water?
Due to the presence of caustic soda in sodium hypo chlorite, the pH of the water is increased. When sodium hypo chlorite dissolves in water, two substances form, which play a role in for oxidation and disinfection. These are hypochlorous acid (HOCl) and the less active hypochlorite ion (OCl-). The pH of the water determines how much hypochlorous acid is formed. While sodium hypochlorite is used, hydrochloric acid (HCl) is used to lower the pH. Sulfuric acid (H2SO4) can be used as an alternative for acetic acid. Less harmful gasses are produced when sulfuric acid is used. Sulfuric acid is a strong acid that strongly reacts with bases and that is very corrosive.
How can sodium hypochlorite be produced?
Sodium hypochlorite can be produced in two ways:
- By dissolving salt in softened water, which results in a concentrated brine solution. The solution is electrolyzed and forms a sodium hypochlorite solution in water. This solution contains 150 g active chlorine (Cl2) per liter. During this reaction the explosive hydrogen gas is also formed.
- By adding chlorine gas (Cl2) to caustic soda (NaOH). When this is done, sodium hypochlorite, water (H2O) and salt (NaCl) are produced according to the following reaction:
Cl2 + 2NaOH + → NaOCl + NaCl + H2O
What are the applications of sodium hypochlorite?
Sodium hypochlorite is used on a large scale. For example in agriculture, chemical industries, paint- and lime industries, food industries, glass industries, paper industries, pharmaceutical industries, synthetics industries and waste disposal industries. In the textile industry sodium hypochlorite is used to bleach textile. It is sometimes added to industrial waste water. This is done to reduce odors. Hypochlorite neutralizes sulphur hydrogen gas (SH) and ammonia (NH3). It is also used to detoxify cyanide baths in metal industries. Hypochlorite can be used to prevent algae and shellfish growth in cooling towers. In water treatment, hypochlorite is used to disinfect water. In households, hypochlorite is used frequently for the purification and disinfection of the house.
How does sodium hypochlorite disinfection work?
By adding hypochlorite to water, hypochlorous acid (HOCl) is formed:
NaOCl + H2O → HOCl + NaOH-
Hypochlorous acid is divided into hydrochloric acid (HCl) and oxygen (O). The oxygen atom is a very strong oxidator.
Sodium hypochlorite is effective against bacteria, viruses and fungi. Sodium hypochlorite disinfects the same way as chlorine does.
How is sodium hypochlorite applied in swimming pools?
Sodium hypochlorite is applied in swimming pools for water disinfection and oxidation. It has the advantage that microorganisms cannot build up any resistance to it. Sodium hypochlorite is effective against Legionella bacteria and bio film, in which Legionella bacteria can multiply.
Hypochlorous acid is produced by the reaction of sodium hydroxide with chlorine gas. In water, the so-called 'active chlorine' is formed.
There are various ways to use sodium hypochlorite. For on-site salt electrolysis, a solution of salt (NaCl) in water is applied. Sodium (Na+) and chloride (Cl-) ions are produced.
4NaCl- → 4Na+ + 4Cl-
By leading the salty solution over an electrolysis cell, the following reactions take place at the electrodes:
2Cl- → Cl2 + 2e- 2H2O + 2e- → H2 + 20H-
2H20 → O2 + 4H++ 4e-
Subsequently, chlorine and hydroxide react to form hypochlorite:
OH- + Cl2 → HOCl + Cl-
The advantage of the salt electrolysis system is that no transport or storage of sodium hypochlorite is required. When sodium hypochlorite is stored for a long time, it becomes inactive. Another advantage of the on site process is that chlorine lowers the pH and no other acid is required to lower pH. The hydrogen gas that is produced is explosive and as a result ventilation is required for expolsion prevention. This system is slow and a buffer of extra hypochlorous acid needs to be used. The maintenance and purchase of the electrolysis system is much more expensive than sodium hypochlorite.
When sodium hypochlorite is used, acetic or sulphuric acid are added to the water. An overdose can produce poisonous gasses. If the dosage is too low, the pH becomes to high and can irritate the eyes.
Because sodium hypochlorite is used both to oxidize pollutions (urine, sweat, cosmetics) and to remove pathogenic microorganisms, the required concentration of sodium hypochlorite depends on the concentrations of these pollutions. Especially the amount of organic pollution determines the required concentration. If the water is filtered before sodium hypochlorite is applied, less sodium hypochlorite is needed.
What are the health effects of sodium hypochlorite?
Exposure
There is no threshold value for to sodium hypochlorite exposure. Various health effects occur after exposure to sodium hypochlorite. People are exposed to sodium hypochlorite by inhalation of aerosols. This causes coughing and a sore throat. After swallowing sodium hypochlorite the effects are stomach ache, a burning sensation, coughing, diarrhea, a sore throat and vomiting. Sodium hypochlorite on skin or eyes causes redness and pain. After prolonged exposure, the skin can become sensitive. Sodium hypochlorite is poisonous for water organisms. It is mutagenic and very toxic when it comes in contact with ammonium salts.
Sodium hypochlorite in swimming pools
The concentration of sodium hypochlorite that is found in swimming pools is generally not harmful to people. When there is too much chlorine in the water, this burns the body tissues, which causes damage to air tracts, the stomach and the intestines, the eyes and the skin. When sodium hypochlorite is used in swimming pools, it sometimes causes red eyes and it gives off a typical chlorine odor. When there is a lot of ureum (a mixture of urine and sweat) present, hypochlorous acid and ureum react to form chloramines. These chloramines irritate mucous membranes and cause the so-called ' chlorine smell'. In most swimming pools, these problems are prevented by water purification and ventilation. Eyes irritation disappears after a while.
What are the advantages and disadvantages of sodium hypochlorite use?
Advantages
Sodium hypochlorite as a disinfectant has the following advantages:
It can easily and be stored and transported when it is produced on-site. Dosage is simple. Transport and storage of sodium hypochlorite are safe. Sodium hypochlorite is as effective as chlorine gas for disinfection. Sodium hypochlorite produces residual disinfectant.
Disadvantages
Sodium hypochlorite is a dangerous and corrosive substance. While working with sodium hypochlorite, safety measures have to be taken to protect workers and the environment. Sodium hypochlorite should not come in contact with air, because that will cause it to disintegrate. Both sodium hypochlorite and chlorine do not deactivate Giardia Lambia and Cryptosporidium.
What is the legislation for sodium hypochlorite?
The regulation for sodium hypochlorite is the same as the regulation considering chlorine.
Sodium hypochlorite is generally used dissolved in water at various concentrations. Although available, solid sodium hypochlorite is not commercially used. Sodium hypochlorite solutions are clear, greenish to yellow liquids with an odor of chlorine. Calcium hypochlorite is a white solid that readily decomposes in water releasing oxygen and chlorine. It also has a strong chlorine odor. Neither compound occur naturally in the environment. Sodium and calcium hypochlorite are used primarily as bleaching agents or disinfectants. They are components of commercial bleaches, cleaning solutions, and disinfectants for drinking water and waste water purification systems and swimming pools.
Sodium Hypochlorite is a chlorine compound often used as a disinfectant or a bleaching agent. Sodium hypochlorite in 0.5% w/v solution is called Dakin's solution, and is used as an antiseptic to clean infected topical wounds.
Sodium hypochlorite appears as colorless or slightly yellow watery liquid with an odor of household bleach. Mixes with water.
Trichloroacetic acid was found in the gut contents & plasma of fasted & nonfasted rats 1 hr after dosing with sodium hypochlorite. Thus, the formation is not dependent on the interaction of sodium hypochlorite with foreign organic material in the gut. Dichloroacetic acid was also found in all treated animals. Chloroform generally was present when trichloroacetic acid was detected. Dichloroacetonitrile was found in the gut contents of 2 of 3 nonfasted rats treated with sodium hypochlorite. Addition of 8 mg sodium hypochlorite/ml to nonfasted rat gut contents in vitro produced dichloroacetic acid, trichloroacetic acid, dichloroacetonitrile, & trichloroacetonitrile.
Anhydrous sodium hypochlorite is very explosive.
Primary amines and calcium hypochlorite or sodium hypochlorite react to form normal chloroamines, which are explosive.
Removal of formic acid from industrial waste streams with sodium hypochlorite soln becomes explosive at 55 °C.
Several explosions involving methanol and sodium hypochlorite were attributed to formation of methyl hypochlorite, especially in presence of acids or other esterification catalyst.
Use of sodium hypochlorite soln to destroy acidified benzyl cyanide residues caused a violent explosion, thought to have been due to formation of nitrogen trichloride.
Decomposition of sodium hypochlorite takes place within a few seconds with the following salts: ammonium acetate, ammonium carbonate, ammonium nitrate, ammonium oxalate, & ammonium phosphate.
Sodium hypochlorite is an indirect food additive for use only as a component of adhesives.
Aqueous sodium hypochlorite (bleach) solution is widely used in dental practice during root canal treatment. Although it is generally regarded as being very safe, potentially severe complications can occur when it comes into contact with soft tissue. This paper discusses the use of sodium hypochlorite in dental treatment, reviews the current literature regarding hypochlorite complications, and considers the appropriate management for a dental practitioner when faced with a potentially adverse incident with this agent.
Introduction
Sodium hypochlorite (NaOCl) was first recognised as an antibacterial agent in 1843 when hand washing with hypochlorite solution between patients produced unusually low rates of infection transmission between patients. It was first recorded as an endodontic irrigant in 19201 and is now in routine worldwide use.
Sodium hypochlorite is used as an endodontic irrigant as it is an effective antimicrobial and has tissue-dissolving capabilities. It has low viscosity allowing easy introduction into the canal architecture, an acceptable shelf life, is easily available and inexpensive. The toxicity of its action to vital tissues and corrosion of metals2 are its main disadvantages in dental use. Sodium hypochlorite reacts with fatty acids and amino acids in dental pulp resulting in liquefaction of organic tissue.3 There is no universally accepted concentration of sodium hypochlorite for use as an endodontic irrigant. The antibacterial and tissue dissolution action of hypochlorite increases with its concentration, but this is accompanied by an increase in toxicity. Concentrations used vary down from 5.25% depending on the dilution and storage protocols of individual practitioners. Solution warmers are available to increase the temperature up to 60°C. Increasing the temperature of a solution of hypochlorite improves the bactericidal and pulp dissolution activity, although the effect of heat transfer to the adjacent tissues is uncertain.4
As a bleaching agent, inadvertent spillage of this agent can result in damage to clothing and soft tissues. Inadvertent introduction of sodium hypochlorite beyond the root canal system may result in extensive soft tissue or nerve damage, and even airway compromise. This article reviews the potential complications that can occur with sodium hypochlorite in clinical practice, discusses measures that can be taken to minimise risk, and provides details of appropriate management in the rare cases of suspected tissue damage.
Complications of accidental spillage
1) Damage to clothing
Accidental spillage of sodium hypochlorite is probably the most common accident to occur during root canal irrigation. Even spillage of minute quantities of this agent on clothing will lead to rapid, irreparable bleaching. The patient should wear a protective plastic bib, and the practitioner should exercise care when transferring syringes filled with hypochlorite to the oral cavity.
2) Eye damage
Seemingly mild burns with an alkali such as sodium hypochlorite can result in significant injury as the alkali reacts with the lipid in the corneal epithelial cells, forming a soap bubble that penetrates the corneal stroma. The alkali moves rapidly to the anterior chamber, making repair difficult. Further degeneration of the tissues within the anterior chamber results in perforation, with endophthalmitis and subsequent loss of the eye.
Ingram recorded a case of accidental spillage of 5.25% sodium hypochlorite into a patient's eye during endodontic therapy.6 The immediate symptoms included instant severe pain and intense burning, profuse watering (epiphora) and erythema. Loss of epithelial cells in the outer corneal layer may occur. There may be blurring of vision and patchy colouration of the cornea.7 Immediate ocular irrigation with a large amount of water or sterile saline is required followed by an urgent referral to an ophthalmologist.8 The referral should ideally be made immediately by telephone to the nearest eye department. The use of adequate eye protection during endodontic treatment should eliminate the risk of occurrence of this accident, but sterile saline should always be available to irrigate eyes injured with hypochlorite. It has been advised that eyes exposed to undiluted bleach should be irrigated for 15 minutes with a litre of normal saline.
3) Damage to skin
Skin injury with an alkaline substance requires immediate irrigation with water as alkalis combine with proteins or fats in tissue to form soluble protein complexes or soaps. These complexes permit the passage of hydroxyl ions deep into the tissue, thereby limiting their contact with the water dilutant on the skin surface.
Water is the agent of choice for irrigating skin and it should be delivered at low pressure as high pressure may spread the hypochlorite into the patient's or rescuer's eyes.5
4) Damage to oral mucosa
Surface injury is caused by the reaction of alkali with protein and fats as described for eye injuries above. Swallowing of sodium hypochlorite requires the patient to be monitored following immediate treatment. It is worth noting that skin damage can result from secondary contamination.
Allergy to sodium hypochlorite
The allergic potential of sodium hypochlorite was first reported in 1940 by Sulzberger11 and subsequently by Cohen and Burns.12 Caliskan et al. presented a case where a 32-year-old female developed rapid onset pain, swelling, difficulty in breathing and subsequently hypotension following application of 0.5 ml of 1% sodium hypochlorite.13 The patient required urgent hospitalisation in the intensive care unit and management with intravenous steroids and antihistamines. A subsequent allergy skin scratch test performed two weeks after the patient was discharged confirmed a highly positive result to sodium hypochlorite. The usefulness of this test in suspected cases of sodium hypochlorite allergy during endodontic treatment has been confirmed by Kaufman and Keila.14 Even though allergy to sodium hypochlorite is rare, it is important for clinicians to recognise the symptoms of allergy and possible anaphylaxis. These may include urticaria, oedema, shortness of breath, wheezing (bronchospasm) and hypotension. Urgent referral to a hospital following first aid management is recommended.
Uses of sodium hypochlorite
Dakin's solution (sodium hypochlorite) is used to prevent and treat skin and tissue infections that could result from cuts, scrapes and pressure sores. It is also used before and after surgery to prevent surgical wound infections.Dakin's solution is a type of hypochlorite solution. It is made from bleach that has been diluted and treated to decrease irritation. Chlorine, the active ingredient in sodium hypochlorite, is a strong antiseptic that kills most forms of bacteria and viruses.
How to use Sodium Hypochlorite 0.25 % Solution
Pour, apply or spray onto the injured area. When used on wounds, Dakin's solution can be poured onto the affected area as an irrigation or cleanser. It is also used to wet certain types of wound dressings (e.g., wet to moist dressing). Follow your doctor's instructions exactly.
The body's own wound-healing tissues and fluids can decrease the antibacterial effect of sodium hypochlorite. Therefore, this solution is often used only once daily for minor wounds and twice daily for heavily draining or contaminated wounds. Use this product as directed by your doctor.
Protect the surrounding healthy skin with a moisture barrier ointment (e.g., petroleum jelly) or skin sealant as needed to prevent irritation.
Chlorine bleach is formed by mixing water with the chlorine-based compound sodium hypochlorite. This widely available product is commonly used as either a whitening and disinfecting agent in laundry or an all-purpose disinfectant with broad applications.
Uses & Benefits of sodium hypochlorite
Chlorine bleach is primarily known as a laundry cleaning and disinfecting product that destroys germs and helps make white clothes whiter. Bleach also has a wide range of other applications, including:
Safe water
Before chlorine-based disinfectants like sodium hypochlorite solutions were routinely added to U.S. drinking water beginning over 100 years ago, many people became sick and died of waterborne diseases, such as cholera and typhoid fever. Chlorination destroys most waterborne germs to help keep drinking water safe. During emergencies, when the normal drinking water supply is interrupted or contaminated, chlorine bleach can safely disinfect non-potable water. Chlorine bleach also helps keep swimming pools free of waterborne germs that can cause diarrhea, swimmer’s ear and “hot tub rash.”
Safe food production and preparation of sodium hypochlorite
Chlorine bleach added to water can destroy germs associated with raw foods. These solutions also can disinfect food production equipment, food preparation surfaces and food-transportation containers. Grocery stores and restaurants use bleach solutions to help sanitize food storage and preparation surfaces.
Medical uses of sodium hypochlorite
Chlorine bleach solutions help disinfect many types of surfaces, including reusable equipment in hospitals, medical labs, doctors’ offices, and nursing homes, to help prevent the spread of infectious illnesses among patients, residents and healthcare professionals.
Household disinfection
Consumers can use diluted chlorine bleach solutions to help disinfect household surfaces in bathrooms and the kitchen. Using bleach solutions to disinfect frequently touched surfaces also can help prevent the spread of colds, flu, norovirus and other infectious illnesses. During natural disasters, such as flooding, chlorine bleach can disinfect contaminated surfaces.
