Potassium nitrite

Structural formula
General
Surname	Potassium nitrite
other names	potassium nitrous acid E  249
Molecular formula	KNO 2
Brief description	colorless to yellowish, easily deliquescent, hygroscopic, prismatic crystals
External identifiers / databases
CAS number 7758-09-0 EC number 231-832-4 ECHA InfoCard 100,028,939 PubChem 516910 Wikidata Q409179
properties
Molar mass	85.10 g mol −1
Physical state	firmly
density	1.92 g cm −3
Melting point	441 ° C
boiling point	decomposition
solubility	very light in water (2810 g l −1 at 20 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 272-301-400 P: 210-220-221-301 + 330 + 331 + 310-370 + 378
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium nitrite , KNO ₂ (also: Nitric acid potassium , English: potassium nitrite ), is the potassium salt of the nitrous acid HNO ₂ .

properties

Potassium nitrite.

Potassium nitrite forms colorless to slightly yellowish, strongly hygroscopic crystals , which dissolve easily in water when cooled, the solution reacts alkaline. The crystals decompose above 410 ° C to form potassium oxide , nitrogen monoxide and nitrogen dioxide .

${\displaystyle \mathrm {2\,KNO_{2}\rightarrow K_{2}O+NO+NO_{2}} }$

If the resulting nitrogen oxides cannot be discharged, they react with unreacted potassium nitrite to form potassium nitrate and nitrogen monoxide or nitrogen .

${\displaystyle \mathrm {KNO_{2}+NO_{2}\rightleftharpoons KNO_{3}+NO} }$

${\displaystyle \mathrm {2\,KNO_{2}+NO\rightarrow 2\,KNO_{3}+N_{2}} }$

The end products of the decomposition at temperatures above 410 ° C are potassium nitrate, potassium oxide and nitrogen. Above 600 ° C, potassium nitrate breaks down into potassium nitrite and oxygen, so that the end products of potassium nitrite decomposition at this temperature are potassium oxide, nitrogen and oxygen.

Otherwise it behaves similarly to sodium nitrite , i.e. it is fire-promoting (especially at higher temperatures) and reacts violently with metals such as aluminum (especially in powder form!), Dry ammonium compounds (such as ammonium sulfate ), cyanides and many organic compounds. It is a reducing agent and is slowly oxidized to potassium nitrate KNO ₃ in the air .

${\displaystyle \mathrm {2KNO_{2}+\ O_{2}\longrightarrow \ 2KNO_{3}} }$

Potassium nitrite is poisonous; In general, nitrites can react with certain amines to form carcinogenic nitrosamines under suitable conditions . Nitrite can be detected with iron (II) sulfate and concentrated sulfuric acid by its brown color.

Occurrence and manufacture

In nature, nitrites occur as intermediate stages in the nitrogen cycle - both in nitrification ( nitrogen fixation ) and in denitrification (nitrogen release). Technically, potassium nitrite is obtained through the action of nitrogen oxides on potassium carbonate solution .

${\displaystyle \mathrm {K_{2}CO_{3}\ +\ NO\ +\ NO_{2}\longrightarrow \ 2\ KNO_{2}\ +\ CO_{2}} }$

use

Potassium nitrite may be used as a food additive with the number E 249 ( preservative ) under certain conditions in nitrite curing salt ( sodium chloride with potassium nitrite and sodium nitrite ). It gives the meat a permanent red color through the formation of nitrosomyoglobin and prevents attack by Clostridium botulinum . The necessary addition per kilogram of meat for the purpose of preservation is approx. 100 mg / kg and for the desired effect of reddening approx. 20 mg / kg. Meat and sausage products may therefore contain a multiple of the drinking water limit value of nitrite.

Individual evidence

1. ↑ Entry on E 249: Potassium nitrite in the European database on food additives, accessed on 23 August 2020.
2. ↑ ^{a b} Entry on potassium nitrite. In: Römpp Online . Georg Thieme Verlag, accessed on September 29, 2014.
3. ↑ ^{a b c d e f} Entry on potassium nitrite in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
4. ↑ Entry on Potassium nitrite in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
5. ^ ^{A b c} W. Laue, M. Thiemann, E. Scheibler, KW Wiegand: Nitrates and Nitrites , in: Ullmanns Enzyklopädie der Technischen Chemie , Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2012; doi : 10.1002 / 14356007.a17_265 .
6. ↑ HD Belitz, W. Grosch, P. Schieberle: Textbook of food chemistry . 6th edition. Springer-Verlag, Berlin, Heidelberg 2008, ISBN 978-3-540-73201-3 .