Sodium nitrite

Crystal structure
__ Na + __ N 3+ __ O 2−
Crystal system	Orthorhombic
Space group	In the 2 m (No. 44, position 3)
Lattice parameters	a = 3.5653 (8)  Å , b = 5.5728 (7) Å, c = 5.3846 (13) Å
General
Surname	Sodium nitrite
other names	sodium nitrous acid E  250
Ratio formula	NaNO 2
Brief description	white odorless solid
External identifiers / databases
CAS number 7632-00-0 EC number 231-555-9 ECHA InfoCard 100,028,687 PubChem 23668193 Wikidata Q339975
Drug information
ATC code	V03 AB08
properties
Molar mass	68.99 g mol −1
Physical state	firmly
density	2.17 g cm −3
Melting point	280 ° C
boiling point	from 320 ° C (decomposition)
solubility	good in water (820 g l −1 at 20 ° C)
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 272-301-319-400 P: 220-273-301 + 310-305 + 351 + 338
Toxicological data	85 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium nitrite , NaNO ₂ , is the sodium salt of the nitrous acid HNO ₂ .

Occurrence and manufacture

Nitrites do not occur naturally in mineral form. They are intermediate stages in the nitrogen cycle in biological systems. They arise both during nitrification ( nitrogen fixation ) and during denitrification (nitrogen release).

Technically, sodium nitrite is obtained through the action of nitrogen oxides on sodium hydroxide solution . Early 20th century, was the reduction of sodium nitrate or by means of lead , iron , zinc , manganese dioxide , coke , sulfur dioxide or calcium carbide was wherein the reaction of molten sodium nitrate with lead at 400 ° C the most common. However, due to the low price of sodium hydroxide, this manufacturing option is rarely used. In the laboratory, the reduction of sodium nitrate using lead or other reducing agents can still be used.

properties

Sodium nitrite forms colorless to slightly yellowish crystals , which at 271 ° C melt . The compound crystallizes orthorhombically at room temperature in the space group Im 2 m (space group no. 44, position 3) with two formula units in the unit cell. From 165 ° C it changes into another orthorhombic crystal structure with the space group Immm (No. 71) and there are also other high-pressure modifications. Sodium nitrite dissolves in water with strong cooling. The heat of solution at 25 ° C is 13.9 kJ mol ⁻¹ . Below −5 ° C there is a stable hemihydrate NaNO ₂ · 0.5H ₂ O. The aqueous solution has an alkaline reaction. The salt also dissolves in liquid ammonia . Here a stable ammonia solvate NaNO ₂ · 0.5NH _{3 is} formed below −64 ° C. The solubility in 95% ethanol is only low at 1.4%. Above temperatures of 330 ° C, it decomposes to sodium oxide , nitrogen monoxide and nitrogen dioxide .

${\displaystyle {\ce {2NaNO2 -> Na2O + NO ^ + NO2 ^}}}$

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

${\displaystyle {\ce {NaNO2 + NO2 <=> NaNO3 + NO}}}$

${\displaystyle {\ce {2NaNO2 + 2 NO -> 2NaNO3 + N2}}}$

The end products of the decomposition in the temperature range between 330 ° C and 400 ° C are sodium nitrate, sodium oxide and nitrogen. Above 600 ° C, sodium nitrate breaks down into sodium nitrite and oxygen , so that the end products of sodium nitrite decomposition at this temperature are sodium oxide, nitrogen and oxygen.

Aqueous solutions of sodium nitrite reduce strong oxidizing agents such as potassium permanganate . In acidic solution, potassium iodide is oxidized to iodine . Ammonium salts also form nitrogen. Urea and amidosulfuric acid are also oxidized with the formation of nitrogen.

${\displaystyle {\ce {CO(NH2)2 + 2NaNO_2 + 2HCl -> 2N2 ^ + CO2 ^ + 3H2O + 2 NaCl}}}$

${\displaystyle {\ce {HOSO2NH2 + NaNO2 + HCl -> N2 ^ + H2SO4 + H2O + NaCl}}}$

In an anhydrous melt at 210-220 ° C with an excess of sodium nitrite with urea, sodium carbonate and nitrogen are formed. The stoichiometric mixture gives sodium cyanate and nitrogen under the same conditions .

${\displaystyle {\ce {CO(NH2)2 + 2NaNO2 -> 2N2 ^ + Na2CO3 + 2H2O}}}$

${\displaystyle {\ce {CO(NH2)2 + NaNO2 -> N2 ^ + NaCNO + 2H2O}}}$

The compound forms a eutectic system with sodium nitrate , with a eutectic melting point at 227 ° C. and a sodium nitrate content of 37.5 mol%.

Sodium nitrite is fire-promoting (especially at higher temperatures) and reacts violently with aluminum (especially powder), dry ammonium compounds (such as ammonium sulfate ), cyanides and many organic compounds. It is a reducing agent and is slowly oxidized to sodium nitrate NaNO _{3 in} air .

Sodium nitrite is poisonous (lethal dose about 4 g); In general, nitrites can react with certain amines to form carcinogenic nitrosamines under suitable conditions . Nitrite can be detected with iron (II) sulfate by its brown color.

use

Part of curing salt

Under certain conditions, sodium nitrite is permitted as a food additive E  250 in the function of a preservative . When mixed with sodium chloride, as nitrite curing salt ( sodium chloride with 0.4 to 0.5% sodium nitrite) , it gives the meat a permanent red color through the formation of nitrosomyoglobin and prevents the growth of bacteria ( curing ).

admissibility

Since the 1980s, the sodium nitrite content of curing salt must not exceed 0.5%. Sodium nitrite may only be sold mixed with table salt or a table salt substitute.

Health effects

In the 1920s, the first poisoning by pickling salts with sodium nitrite levels above 5% was reported. A dosage above about 0.5 g leads to poisoning. In the 1970s, it was discovered that the nitrosamines formed from sodium nitrite are carcinogenic. The permissible admixtures are also considered to be slightly carcinogenic. Nitrosamines arise, for example, when grilling or roasting cured meat; Cured meat should therefore not be grilled or fried if possible.

Nitrites have an antihypertensive and vasodilatory effect. Infants under six months of age are particularly sensitive to the effects of nitrites on hemoglobin in the blood because of a lack of enzymes ; Nitrites from nitrate-rich water or vegetables can therefore lead to internal suffocation in infants .

Sodium nitrite is used in the treatment of cyanide poisoning. It increases the formation of methemoglobin , which binds the toxic cyanide and produces cyanomethemoglobin. This can be converted into methemoglobin and the less toxic thiocyanide by administering sodium thiosulfate. The remaining methemoglobin is converted into oxyhemoglobin by the administration of methylene blue.

Reagent in the chemical industry

In the chemical and pharmaceutical industries it is used for the synthesis of diazonium compounds for azo dyes as well as nitroso and isonitroso compounds and as an additive in electroplating baths and rust inhibitors .

Poison bait

In Australia and the United States , poison baits based on sodium nitrite have been developed which, according to the patent , can be used against omnivores . So far, these baits, which lead to rapid death by suffocation at an intake of 135 mg sodium nitrite / kg, have been used successfully against wild boars , feral domestic pigs and - in New Zealand - against possums .

Individual evidence

1. ↑ T. Gohda, M. Ichikawa, T. Gustafsson, I. Olovsson: The Refinement of the Structure of Ferroelectric Sodium Nitrite . In: Journal of the Korean Physical Society . tape November 29 , 1996, pp. 551–554 ( jkps.or.kr [PDF; 268 kB ; accessed on February 20, 2019]).
2. ↑ Entry on E 250: Sodium nitrite in the European database on food additives, accessed on June 27, 2020.
3. ↑ ^{a b c d e f g} Entry on sodium nitrite in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
4. ↑ Entry on sodium 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. ↑ Sodium nitrite data sheet (PDF) from Merck , accessed on January 18, 2011.
6. ↑ ^{a b c d e f g h i j k l m} 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 .
7. ↑ E. Yu Tonkov: High Pressure Phase Transformations Handbook 1 . CRC Press, 1992, ISBN 978-2-88124-758-3 , pp. 569 ( limited preview in Google Book search).
8. ↑ ZZulV : Appendix 5 (to Section 5, Paragraph 1 and Section 7) Additives that are approved for preservation or as antioxidants in foods
9. ^ ^{A b c} University of Bayreuth: Sausage and chemistry: curing
10. ↑ Ordinance on the approval of additives for foodstuffs for technological purposes (Additives Approval Ordinance - ZZulV), date of issue: January 29, 1998
11. ↑ ^{a b c d} sodium nitrite (zuatzstoffe-online.de)
12. ↑ Dr Steven I Baskin PharmD, Dr Arthur M Horowitz PhD, Mr Eric W Nealley BA: The Antidotal Action of Sodium Nitrite and Sodium Thiosulfate Against Cyanide Poisoning . Ed .: ACCP Journals. April 1992.
13. ^ Animal Control Technologies (Australia) Pty Ltd: HOGGONE ^(R) .
14. ↑ US patent 20140255460 A1: Nitrite salts as poisons in baits for omnivores .