Sodium nitrite
- Sodium nitrite
- E 250
V03AB08
White solid
Fixed
2.17 g · cm -3
271 ° C
From 320 ° C ( decomposition)
Well in water (820 g · l-1 at 20 ° C)
Risk
85 mg · kg -1 ( LD50, rat, oral)
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Sodium nitrite, NaNO2, is the sodium salt of nitrous acid HNO2.
Properties
Sodium nitrite forms colorless to slightly yellowish crystals, which dissolve in water with strong cooling, the solution is alkaline. The crystals have a melting point of 271 ° C and decompose above 320 ° C. Sodium nitrite is oxidizing (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 oxidized in the air slowly sodium nitrate NaNO3.
Sodium nitrite is toxic ( lethal dose of about 4 g); generally nitrites can react with certain amines under suitable conditions to carcinogenic nitrosamines. Nitrite can be detected with iron ( II) sulfate by brown coloring.
Occurrence and production
In nature, nitrites occur as intermediates in the nitrogen cycle - both in the nitrification ( nitrogen fixation ) and during denitrification ( nitrogen release ).
Technically you win sodium nitrite by the action of nitric oxide on sodium hydroxide. Sodium nitrite in the laboratory can be obtained by the reduction of sodium nitrate by means of lead or other reducing agents. Due to the low price of sodium nitrite producing this possibility is rarely used.
Use
Under certain conditions, sodium nitrite is approved as a food additive E 250 in the function of a preservative. In a mixture with sodium chloride it gives as nitrite (sodium chloride 0.4 to 0.5% of sodium nitrite) the meat by forming nitrosomyoglobin a permanent red color and prevents the growth of bacteria ( Corning ).
In the chemical and pharmaceutical industry it is used for the synthesis of diazonium compounds for azo dyes as well as nitroso and Isonitrosoverbindungen and as an additive in electroplating baths and rust inhibitors.
Admissibility
Since the 1980s, the sodium nitrite content of pickling salt must not exceed 0.5 % and only get mixed with saline in the trade.
Health effects
In the 1920s the first poisoning were reported by curing salts with sodium nitrite levels higher than 5%. A dose above about 0.5 g leads to poisoning. In the 1970s it was discovered that the nitrosamines, which arise from sodium nitrite, are carcinogenic. The allowable admixtures are not significant carcinogenic. Nitrosamines are formed for example when grilling or frying of cured meat; Cured meat should be avoided where possible grilled or fried.
Nitrites have a hypotensive and vasodilatory effects. Infants under six months are due to lack of enzymes particularly sensitive to the effects of nitrite on hemoglobin in the blood; Nitrite from nitrate- rich water or vegetables can lead to internal suffocation therefore in infants.