SODIUM HYPOCHLORITE
SODIUM HYPOCHLORITE
Sodium hypochlorite is most commonly recognized as the active ingredient in bleach, a powerful disinfectant and cleaning agent, and is used extensively in water purification, disinfection, and bleaching.
In solution, sodium hypochlorite is unstable and easily decomposes, liberating chlorine, which is responsible for its strong oxidizing and antimicrobial properties.
Despite its widespread use, sodium hypochlorite can be highly reactive and pose safety risks, especially when mixed with acids or ammonia, which can release dangerous chlorine gas or chloramines.
CAS Number: 7681-52-9
EC Number: 231-668-3
Molecular Formula: NaOCl
Molar Mass: 74.44 g/mol
Synonyms: Antiformin, Bleach, Chloride of soda, 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 is a chemical compound with the formula NaOCl or NaClO, comprising a sodium cation (Na+) and a hypochlorite anion (OCl−or ClO−).
Sodium hypochlorite may also be viewed as the sodium salt of hypochlorous acid.
Sodium hypochlorite is unstable and may decompose explosively.
Sodium hypochlorite can be crystallized as a pentahydrate NaOCl·5H2O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.
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, Sodium hypochlorite 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.
Sodium hypochlorite’s corrosive properties, common availability, and reaction products make it a significant safety risk.
The anhydrous compound is unstable and may decompose explosively.
Sodium hypochlorite can be crystallized as a pentahydrate NaOCl·5H2O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.
Sodium hypochlorite is most often encountered as a pale greenish-yellow dilute solution referred to as chlorine bleach, which is a household chemical widely used (since the 18th century) as a disinfectant and bleaching agent.
In solution, Sodium hypochlorite 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.
Sodium hypochlorite’s 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 found in limescale-removing products, will release chlorine gas.
Chlorine gas was utilized as a chemical weapon in World War I.
A common misconception is that mixing bleach with ammonia also releases chlorine, but in reality they react to produce chloramines such as nitrogen trichloride.
With excess ammonia and sodium hydroxide, hydrazine may be generated.
Sodium hypochlorite is an alkaline inorganic chemical compound with the formula NaOCl (also written as NaClO).
Sodium hypochlorite is commonly known in a dilute aqueous solution as bleach or chlorine bleach.
Sodium hypochlorite is the sodium salt of hypochlorous acid, consisting of sodium cations (Na+) and hypochlorite anions (−OCl, also written as OCl− and ClO−).
Sodium hypochlorite is a widely used chemical compound with various industrial, medical, and household applications.
Sodium hypochlorite is most commonly recognized as the active ingredient in bleach, a powerful disinfectant and cleaning agent.
In its pure form, sodium hypochlorite is a pale greenish-yellow liquid with a distinct chlorine-like odor, though it is typically sold in diluted aqueous solutions.
When dissolved in water, Sodium hypochlorite dissociates into sodium (Na⁺) and hypochlorite ions (OCl⁻), which are responsible for its strong oxidizing and antimicrobial properties.
Sodium hypochlorite is used extensively in water purification processes, helping to disinfect drinking water and treat wastewater by neutralizing harmful microorganisms.
Sodium hypochlorite’s potent oxidizing ability also makes it a useful bleaching agent, breaking down organic compounds that cause stains in textiles and other materials.
In medical settings, Sodium hypochlorite is applied for wound care and sterilization of surfaces and instruments.
However, sodium hypochlorite is highly reactive and can degrade over time when exposed to air, light, or heat, which is why it is often stored in tightly sealed, opaque containers.
Despite its widespread use, care must be taken when handling sodium hypochlorite, as it can cause irritation to the skin, eyes, and respiratory system, and when mixed with certain chemicals, such as ammonia or acids, Sodium hypochlorite can release dangerous chlorine gas.
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.
Sodium hypochlorite is sometimes added to industrial waste water.
This is done to reduce odors.
Hypochlorite neutralizes sulphur hydrogen gas (SH) and ammonia (NH3).
Sodium hypochlorite is also used to detoxify cyanide baths in metal industries.
Sodium hypochlorite can be used to prevent algae and shellfish growth in cooling towers.
In water treatment, Sodium hypochlorite is used to disinfect water.
In households, Sodium hypochlorite is used frequently for the purification and disinfection of the house.
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, Sodium hypochlorite can be used to remove mold stains, dental stains caused by fluorosis, and stains on crockery, especially those caused by the tannins in tea.
Sodium hypochlorite has also been used in laundry detergents and as a surface cleaner.
Sodium hypochlorite’s 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 Sodium hypochlorite’s odor and facilitates its removal.
Disinfection of Sodium hypochlorite:
Sodium hypochlorite in solution exhibits broad spectrum anti-microbial activity and is widely used in healthcare facilities in a variety of settings.
Sodium hypochlorite is usually diluted in water depending on its intended use.
Sodium hypochlorite 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).
Sodium hypochlorite 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.
Sodium hypochlorite is a 0.05% solution of hypochlorite used for washing hands, but is normally prepared with calcium hypochlorite granules.
Sodium hypochlorite is a disinfectant solution containing low concentration of sodium hypochlorite and some boric acid or sodium bicarbonate to stabilize the pH.
Sodium hypochlorite 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:
Sodium hypochlorite has deodorizing properties, which go hand in hand with its cleaning properties.
Waste water treatment:
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.
Sodium hypochlorite’s concentration for use varies from 0.5% to 5.25%.
At low concentrations Sodium hypochlorite 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 Sodium hypochlorite 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.
Biocidal Uses:
Sodium hypochlorite is approved for use as a biocide in the EEA and/or Switzerland, for: human hygiene, disinfection, veterinary hygiene, food and animals feeds, drinking water.
Sodium hypochlorite is being reviewed for use as a biocide in the EEA and/or Switzerland, for: preservation for liquid systems, controlling slimes.
Consumer Uses:
Sodium hypochlorite is used in the following products: washing & cleaning products, textile treatment products and dyes, water treatment chemicals, perfumes and fragrances and cosmetics and personal care products.
Other release to the environment of Sodium hypochlorite is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Widespread uses by professional workers:
Sodium hypochlorite is used in the following products: washing & cleaning products.
Sodium hypochlorite is used in the following areas: health services and formulation of mixtures and/or re-packaging.
Sodium hypochlorite is used for the manufacture of: food products, chemicals, textile, leather or fur and wood and wood products.
Other release to the environment of Sodium hypochlorite is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Uses at industrial sites:
Sodium hypochlorite is used in the following products: washing & cleaning products, water treatment chemicals, pH regulators and water treatment products, textile treatment products and dyes and paper chemicals and dyes.
Sodium hypochlorite has an industrial use resulting in manufacture of another substance (use of intermediates).
Sodium hypochlorite is used in the following areas: municipal supply (e.g. electricity, steam, gas, water) and sewage treatment.
Sodium hypochlorite is used for the manufacture of: chemicals, food products, textile, leather or fur and pulp, paper and paper products.
Release to the environment of Sodium hypochlorite can occur from industrial use: as processing aid and as an intermediate step in further manufacturing of another substance (use of intermediates).
Sodium hypochlorite is a chemical compound with the formula NaOCl or NaClO, comprising a sodium cation (Na+) and a hypochlorite anion (OCl−or ClO−).
Sodium hypochlorite may also be viewed as the sodium salt of hypochlorous acid.
Sodium hypochlorite is unstable and may decompose explosively.
Sodium hypochlorite can be crystallized as a pentahydrate NaOCl·5H2O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.
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, Sodium hypochlorite 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.
Sodium hypochlorite’s 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.
Chemistry of Sodium Hypochlorite:
Stability of the solid:
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.
Sodium hypochlorite 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.
Sodium hypochlorite decomposes rapidly at room temperature, so it must be kept under refrigeration.
At lower temperatures, however, Sodium hypochlorite 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 Sodium hypochlorite’s 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.
Sodium hypochlorite 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.
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 Sodium hypochlorite usually contains 5% sodium hypochlorite (with a pH of around 11, Sodium hypochlorite is irritating).
If Sodium hypochlorite 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.
Production of Sodium Hypochlorite:
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
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 Sodium hypochlorite 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.
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
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.
History of Sodium Hypochlorite:
Sodium hypochlorite has a long history.
Around 1785 the Frenchman Berthollet developed liquid bleaching agents based on sodium hypochlorite.
The Javel company introduced Sodium hypochlorite and called it ‘liqueur de Javel’.
At first, Sodium hypochlorite was used to bleach cotton.
Because of Sodium hypochlorite’s specific characteristics it soon became a popular compound.
Sodium hypochlorite can remove stains from clothes at room temperature.
In France, sodium hypochlorite is still known as ‘eau de Javel’.
Handling and Storage of Sodium Hypochlorite:
Handling:
Avoid direct contact with skin, eyes, and clothing. Wear appropriate personal protective equipment (PPE).
Use in well-ventilated areas to avoid inhalation of vapors.
Do not mix sodium hypochlorite with acids, ammonia, or other cleaning products as it may release hazardous gases like chlorine.
Avoid excessive heat and exposure to light, as this can lead to decomposition.
Handle with care around metals, as Sodium hypochlorite is corrosive, especially to aluminum and stainless steel.
Storage:
Store in a cool, dry, well-ventilated place, away from sunlight and heat sources.
Keep containers tightly sealed when not in use to prevent contamination and evaporation.
Store in corrosion-resistant containers (such as plastic or coated containers), avoiding metal containers.
Store separately from acids, ammonia, oxidizers, and reducing agents to avoid dangerous reactions.
Temperature:
Store at temperatures below 20°C (68°F) to prevent decomposition.
Stability and Reactivity of Sodium Hypochlorite:
Stability:
Sodium hypochlorite is stable under normal storage conditions but degrades over time.
Decomposes slowly when exposed to air and light, releasing chlorine gas and oxygen.
Decomposition is accelerated by heat, acidic conditions, contamination with metals, and organic material.
Shelf life is generally 3 to 6 months, depending on concentration and storage conditions.
Reactivity:
With Acids:
Releases toxic chlorine gas.
With Ammonia:
Produces toxic chloramines, which can irritate the respiratory system.
With Reducing Agents:
Can cause vigorous and dangerous reactions.
With Organic Matter:
Reacts with organic substances to produce potentially harmful gases and byproducts.
With Metals:
Corrosive to metals like aluminum, copper, and stainless steel.
First Aid Measures of Sodium Hypochlorite:
Inhalation:
Move the person to fresh air immediately.
If breathing is difficult, administer oxygen or provide artificial respiration.
Seek medical attention if symptoms persist.
Skin Contact:
Remove contaminated clothing and rinse the affected area with plenty of water for at least 15 minutes.
Use soap to thoroughly clean the skin.
Seek medical attention if irritation persists.
Eye Contact:
Immediately flush eyes with large amounts of water for at least 15 minutes, lifting the upper and lower eyelids.
Remove contact lenses if present and continue rinsing.
Seek immediate medical attention.
Ingestion:
Do not induce vomiting.
Rinse the mouth thoroughly with water and drink water or milk to dilute Sodium hypochlorite.
Seek immediate medical attention.
Firefighting Measures of Sodium Hypochlorite:
Flammability:
Sodium hypochlorite itself is not flammable, but it can decompose under heat, releasing oxygen, which can intensify a fire.
Suitable Extinguishing Media:
Use water spray, alcohol-resistant foam, carbon dioxide, or dry chemical powder to extinguish surrounding fires.
Specific Hazards:
Sodium hypochlorite can release chlorine gas and oxygen when heated or in contact with acids, increasing fire risks.
Protective Equipment for Firefighters:
Wear self-contained breathing apparatus (SCBA) and full protective clothing due to the risk of inhaling toxic fumes (chlorine gas).
Firefighting Instructions:
Cool containers with water spray to prevent rupture due to heat.
Approach the fire from upwind to avoid exposure to toxic vapors.
Accidental Release Measures of Sodium Hypochlorite:
Personal Precautions:
Evacuate the area if necessary and ensure proper ventilation.
Wear PPE including gloves, goggles, and a respirator to prevent contact with skin, eyes, and inhalation of fumes.
Keep away from incompatible materials (acids, ammonia) to avoid hazardous reactions.
Environmental Precautions:
Prevent Sodium hypochlorite from entering drains, watercourses, or soil, as it is harmful to aquatic life.
In case of large spills, notify local environmental authorities.
Methods for Containment and Cleanup:
For small spills:
Absorb with inert material (e.g., sand, earth) and place in a suitable container for disposal.
For large spills:
Contain the spill using dikes and neutralize with sodium thiosulfate or sodium bisulfite if appropriate.
Avoid using reducing agents as they can cause violent reactions.
Dispose of according to local and national regulations.
Exposure Controls / Personal Protection of Sodium Hypochlorite:
Exposure Limits:
OSHA PEL (Permissible Exposure Limit): 0.5 ppm for chlorine (as it may be released from sodium hypochlorite).
NIOSH REL (Recommended Exposure Limit): 0.5 ppm for chlorine (ceiling limit).
Engineering Controls:
Use in well-ventilated areas to maintain airborne concentrations below exposure limits.
If necessary, use local exhaust ventilation or other engineering controls to reduce vapor concentrations.
Personal Protective Equipment (PPE):
Eye/Face Protection:
Wear chemical splash goggles or a full-face shield.
Skin Protection:
Wear chemical-resistant gloves (e.g., neoprene, rubber) and appropriate clothing to avoid skin exposure.
Respiratory Protection:
If ventilation is inadequate or if exposure levels exceed limits, wear a respirator with chlorine gas cartridges.
Hygiene Measures:
Wash thoroughly after handling.
Remove contaminated clothing and wash before reuse.
Identifiers of Sodium Hypochlorite:
Chemical Name: Sodium hypochlorite
Chemical Formula: NaOCl
CAS Number: 7681-52-9
EC (EINECS) Number: 231-668-3
UN Number: 1791 (for transport of dangerous goods)
PubChem CID: 23665760
ChEBI ID: CHEBI:32146
Molar Mass: 74.44 g/mol
Synonyms: Bleach, liquid bleach, chlorinated soda
SMILES Notation: [Na+].[O-]Cl
InChI: InChI=1S/ClO.Na/c1-2;/q-1;+1
IUPAC Name: Sodium hypochlorite
Beilstein Reference: 3534965
RTECS Number: NH3486300
Merck Index: 13, 8713
HS Code: 28289000
Properties of Sodium Hypochlorite:
Molecular Formula: NaOCl
Molar Mass: 74.44 g/mol
Physical State: Typically found as a liquid solution.
Color: Pale yellowish-green liquid.
Odor: Strong chlorine-like odor.
Density: 1.1-1.2 g/cm³ (depending on the concentration of the solution).
Melting Point: -6°C (for a standard household solution).
Boiling Point: Decomposes before reaching boiling temperature.
Solubility in Water: Highly soluble (fully dissociates into sodium ions (Na⁺) and hypochlorite ions (OCl⁻)).
pH: Highly alkaline, with pH values ranging from 11 to 13 for concentrated solutions.
Viscosity: Low viscosity similar to water in most aqueous solutions.
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
Molar mass: 74.442 g/mol
Appearance: White crystalline solid
Odor: Chlorine-like and sweetish
Density: 1.11 g/cm3
Melting point: 18 °C
Boiling point: 101 °C
Solubility in water: 29.3 g/(100 mL) (0 °C)
Acidity (pKa): 7.5185
Basicity (pKb): 6.4815
Hydrogen Bond Acceptor Count: 1
Exact Mass: 73.9535366 g/mol
Monoisotopic Mass: 73.9535366 g/mol
Topological Polar Surface Area: 23.1Ų
Heavy Atom Count: 3
Complexity: 4.8
Covalently-Bonded Unit Count: 2