Sodium hypochlorite

Structural formula
General
Surname	Sodium hypochlorite
other names	Sodium hypochlorite Soda bleach Chlorine bleach L'eau de Labarraque Eau de Javel Javel's lye
Molecular formula	NaClO
Brief description	yellowish substance with a characteristic, chlorine-like odor, which can only be stored in an aqueous solution
External identifiers / databases
CAS number 7681-52-9 (anhydrous, also solutions) 10022-70-5 (as pentahydrate) EC number 231-668-3 ECHA InfoCard 100,028,790 PubChem 23665760 Wikidata Q407204
properties
Molar mass	74.44 g mol −1
Physical state	as pentahydrate: solid
Melting point	18 ° C (pentahydrate) 27 ° C (as pentahydrate, other source)
Vapor pressure	20-25 h Pa (20 ° C)
solubility	easy in water (799 gL −1 at 25 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 290-314-410 EUH: 031 P: 260-273-280-301 + 330 + 331-303 + 361 + 353-305 + 351 + 338-310-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium hypochlorite ( NaClO ) is the sodium salt of hypochlorous acid (HClO, outdated also "hypochlorous acid"). Since the water-free form is relatively unstable and tends to decompose, it is usually used and traded as a solid as sodium hypochlorite pentahydrate. The trivial name of the aqueous solution of sodium hypochlorite is Eau de Labarraque or Eau de Javel , although the name Eau de Javel is strictly speaking incorrect, because this describes a solution of potassium hypochlorite , possibly in a mixture with other salts such as potassium chloride . In trade, however, often no difference is made.

history

The name Eau de Labarraque goes back to the French pharmacist Antoine Germain Labarraque , who from 1822 sold sodium and calcium hypochlorite solutions for disinfection purposes in Paris . The worldwide use as an antiseptic only prevailed in the First World War after the rediscovery by Henry Drysdale Dakin (hence the name Dakin's solution in English).

Extraction / representation

Sodium hypochlorite is produced by introducing chlorine gas into sodium hydroxide solution or by electrolysis of a sodium chloride solution.

${\displaystyle {\ce {2 NaOH + Cl2 -> NaCl + NaOCl + H2O}}}$

Formally, it is a hydrolysis of the chlorine.

${\displaystyle {\ce {H2O + Cl2 -> HCl + HClO}}}$

The reaction is problematic in terms of reaction technology, because the subsequent neutralization of the hydrochloric acid or hypochlorous acid formed in this way leads to strong heating to which all hypochlorites are sensitive. In fact, the same chemical process is used to make chlorate , but by reacting in hot solution. For this reason all technical hypochlorites contain varying, sometimes large amounts of chlorate. The reaction of the hypochlorite formed during production with chlorine ultimately leads to chlorate.

Sodium hypochlorite crystallizes from the aqueous solution at −10 ° C as a colorless solid rich in water of crystallization . When warming to room temperature, it changes into the relatively stable pale yellow sodium hypochlorite pentahydrate with partial loss of water.

The anhydrate is unstable and violently decomposes when heated.

use

Eau de Javel with sodium hypochlorite

The main use is for bleaching or disinfecting (for example in swimming pools ). Use in swimming pools is problematic because the quantities to be dosed must be sufficient to chlorinate the ammonia (or amines ) present beyond the level of monochloramine , since only then is adequate disinfection guaranteed. Sodium hypochlorite solutions for water disinfection are often also called "liquid chlorine" or "chlorine liquid". Due to the pandemic of the SARS-CoV-2 virus, hand disinfectants with sodium hypochlorite are on the market. The resulting chlorine smell on the skin results from the resulting chlorine or hypochlorous acid, which has an oxidizing effect on the skin and ultimately contributes to skin aging. Therefore, disinfectants with sodium hypochlorite are recommended as surface disinfectants but not as hand disinfectants. A recommendation of the Association for Applied Hygiene says: "Due to the instability and possible skin irritation caused by chlorine-containing products now on the market, we urgently advise against using chlorine-containing products for hand disinfection."

Sodium hypochlorite is also the essential active ingredient in disinfecting and bleaching household cleaners. Various mold removers or pipe cleaners also contain this chemical. They are often advertised as "with active chlorine". The concentrations in household cleaners are approx. 5–7%, while the concentrations in pool disinfectants are much higher (approx. 10–13%).

It used to be used for bleaching, cleaning and disinfecting in textile detergents , but has now been replaced by less problematic substances.

Sodium hypochlorite is also used in dentistry. For example, it is used in a diluted solution (0.5 - 5%) in the root canal treatment of bacterially infected teeth in order to disinfect them. In ophthalmology, it is used to disinfect the measuring heads of tonometers, the devices used to measure the increased intraocular pressure in glaucoma ( tonometry ).

A study by the Children's Memorial Hospital in Chicago suggests that the use of full baths with a highly diluted solution (0.005%) in patients with atopic eczema leads to a significant improvement in symptoms.

Reaction in aqueous solution

The following equilibrium is established in the watery state:

${\displaystyle \mathrm {ClO^{-}\ +\ H_{2}O\ \rightleftharpoons \ HClO\ +\ OH^{-}} }$

The solution has a basic reaction and thus dissolves organic impurities such as fats or proteins through saponification or denaturation and subsequent hydrolysis . By protonation of hypochlorite anion generated hypochlorous acid (HClO), as oxidizing agent is responsible for the bleaching and disinfecting effect:

${\displaystyle {\ce {HClO + H^+ + 2 e^- -> Cl^- + H2O}}}$

Another effect results from the decomposition of hypochlorous acid to hydrochloric acid and reactive singlet oxygen , which also has an oxidizing effect:

${\displaystyle {\ce {2 HClO -> 2 HCl + ^1O2}}}$

The hypochlorous acid and hydrochloric acid in the solution are in chemical equilibrium with water and chlorine:

${\displaystyle \mathrm {HClO\ +\ HCl\ \rightleftharpoons \ Cl_{2}\ +\ H_{2}O} }$

Under alkaline conditions the equilibrium is on the left. When the solution is acidified, the equilibrium shifts to the right. Since chlorine is only moderately soluble in water, it can escape into the environment as a poisonous gas if the reaction continues. To reduce this risk, the commercially available solutions usually contain an alkaline buffer such as sodium carbonate .

safety instructions

Extreme caution is required when handling sodium hypochlorite (pentahydrate). There is a risk of explosion or fire if sodium hypochlorite reacts with numerous substances and groups of substances, including reducing agents , amines , formic acid , methanol , organic substances and some other substances. In addition, the resulting vapors attack the mucous membranes when inhaled. Sodium hypochlorite is irritating and strongly bleaching at low concentrations, and even corrosive at higher concentrations, and causes characteristic wounds.

Sodium hypochlorite also reacts with acids (e.g. hydrochloric acid , nitric acid ) and oxidizing agents (e.g. hydrogen peroxide , permanganate ), sometimes very violently , generating heat and releasing chlorine gas , various chlorine compounds (some of which are highly reactive) and / or nitrous gases . This represents a serious risk, as it is very easy for private users to accidentally mix acidic cleaners with sodium hypochlorite.

Even heating or sunlight can cause sodium hypochlorite to break down, releasing chlorine , hydrogen chloride , chlorine dioxide and oxygen, among other things . This must also be taken into account when storing the substance. The gases produced during the breakdown of sodium hypochlorite can lead to a build-up of pressure in closed vessels until they burst. For this reason, containers that contain highly concentrated sodium hypochlorite are usually equipped with a pressure compensation membrane built into the lid.

See also

• Chlorinated water

Web links

Commons : Sodium Hypochlorite  - Collection of pictures, videos and audio files

Individual evidence

1. ↑ ^{a b c d e} Entry on sodium hypochlorite, aqueous solution with proportions of active chlorine in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
2. ↑ pubchem.ncbi.nlm.nih.gov
3. ↑ ^{a b} Sodium Hypochlorite Pentahydrate Crystals (NaOCl5H2O): A Convenient and Environmentally Benign Oxidant for Organic Synthesis. Masayuki Kirihara, Tomohide Okada, Yukihiro Sugiyama, Miyako Akiyoshi, Takehiro Matsunaga, and Yoshikazu Kimura Organic Process Research & Development 2017 21 (12), 1925-1937, doi: 10.1021 / acs.oprd.7b00288
4. ↑ Dale L. Perry: Handbook of Inorganic Compounds . CRC Press, 1995, ISBN 978-0-8493-8671-8 , pp. 369 ( limited preview in Google Book search).
5. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 97th edition. (Internet version: 2016), CRC Press / Taylor and Francis, Boca Raton, FL, Properties of the Elements and Inorganic Compounds, pp. 4-86.
6. ↑ Entry on Sodium hypochlorite in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on November 18, 2019. Manufacturers or distributors can expand the harmonized classification and labeling .
7. ↑ Applebey, MPJ Chem. Soc., Trans. 1919, 115, 1106-1109 doi: 10.1039 / CT9191501106
8. ↑ L. Bretherick: Bretherick's Handbook of Reactive Chemical Hazards . Elsevier, 2016, ISBN 978-1-4831-6250-8 , pp. 984 ( limited preview in Google Book Search).
9. ^ D. Raab: Preparation of contaminated root canal systems - the importance of antimicrobial irrigants. In: DENTAL INC. 2008: July / August 34-36.
10. ↑ D. Raab, A. Ma: Preparation of contaminated root canal systems - the importance of antimicrobial irrigants.经 感染 的 根 管 系统 的 修复 - 化学 冲洗 对 根 管 治疗 的 重要性 DENTAL INC Chinese Edition 2008: August 18-20 .
11. ↑ D. Raab: The importance of chemical rinsing in endodontics. In: Endodontic Journal. Volume 2, 2010, pp. 22-23.
12. ↑ Anna K. Junk, Philip P. Chen u. a .: Disinfection of Tonometers. In: Ophthalmology. 2017, doi: 10.1016 / j.ophtha.2017.05.033 .
13. ↑ JT Huang, M. Abrams, B. Tlougan, A. Rademaker, AS Paller: Treatment of Staphylococcus aureus Colonization in Atopic Dermatitis Decreases Disease Severity. In: Pediatrics . 123, 2009, pp. E808 – e814, doi: 10.1542 / peds.2008-2217 .
14. ↑ Atopic dermatitis: household bleach relieves eczema. In: aerzteblatt.de. Deutsches Ärzteblatt , April 27, 2009, accessed on March 1, 2020 . 
15. ↑ www-group.slac.stanford.edu