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| Identifiers | |
|---|---|
3D model (JSmol) | |
| ChEMBL | |
| ChemSpider |
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| ECHA InfoCard | 100.028.939 |
| EC Number |
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| E number | E249(preservatives) |
| RTECS number |
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| UNII | |
| UN number | 1488 |
| |
| |
| Properties | |
| KNO2 | |
| Molar mass | 85.10379 g/mol |
| Appearance | white or slight yellow solid deliquescent |
| Density | 1.914986 g/cm3 |
| Melting point | 440.02 °C (824.04 °F; 713.17 K) (decomposes) |
| Boiling point | 537 °C (999 °F; 810 K) (explodes) |
| 281 g/100 mL (0 °C) 312 g/100 mL (25 °C) 413 g/100 mL (100 °C) | |
| Solubility | soluble inalcohol,ammonia |
| −23.3·10−6 cm3/mol | |
| Thermochemistry | |
| 107.4 J/mol K | |
Std enthalpy of formation(ΔfH⦵298) | −369.8 kJ/mol |
| Hazards | |
| GHS labelling: | |
   | |
| Danger | |
| H272,H301,H400 | |
| P210,P220,P221,P264,P270,P273,P280,P301+P310,P321,P330,P370+P378,P391,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 235 mg/kg |
| Safety data sheet (SDS) | External MSDS |
| Related compounds | |
Otheranions | Potassium nitrate |
Othercations | Sodium nitrite |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Potassium nitrite (distinct frompotassium nitrate) is theinorganic compound with thechemical formulaKNO2. It is anionic salt ofpotassium ions K+ andnitrite ions NO2−, which forms a white or slightly yellow, hygroscopiccrystalline powder that is soluble in water.[1]
It is a strong oxidizer and may accelerate the combustion of other materials. Like other nitrite salts such assodium nitrite, potassium nitrite is toxic if swallowed, and laboratory tests suggest that it may bemutagenic orteratogenic. Gloves and safety glasses are usually used when handling potassium nitrite.
Nitrite is present at trace levels in soil, natural waters, plant and animal tissues, and fertilizer.[2] The pure form of nitrite was first made by the Swedish chemistCarl Wilhelm Scheele working in the laboratory of his pharmacy in the market town ofKöping. He heatedpotassium nitrate at red heat for half an hour and obtained what he recognized as a new “salt.” The two compounds (potassium nitrate and nitrite) were characterized byPéligot and the reaction was established as:
Potassium nitrite can be obtained by the reduction of potassium nitrate. The production of potassium nitrite by absorption of nitrogen oxides inpotassium hydroxide orpotassium carbonate is not employed on a large scale because of the high price of these alkalies. Furthermore, the fact that potassium nitrite is highly soluble in water makes the solid difficult to recover.
The mixing ofcyanamide and KNO2 produces changes from white solids to yellow liquid and then to orange solid, formingcyanogen and ammonia gases. No external energy is used and the reactions are carried out with a small amount of O2.[3]
Potassium nitrite forms potassium nitrate when heated in the presence of oxygen from 550 °C to 790 °C. The rate of reaction increases with temperature, but the extent of reaction decreases. At 550 °C and 600 °C the reaction is continuous and eventually goes to completion. From 650 °C to 750 °C, as the case of decomposition of potassium nitrate is, the system attainsequilibrium. At 790 °C, a rapid decrease in volume is first observed, followed by a period of 15 minutes during which no volume changes occur. This is then followed by an increase in volume due primarily to the evolution of nitrogen, which is attributed to thedecomposition of potassium nitrite.[4]
Potassium nitrite reacts at an extremely slow rate with a liquid ammonia solution ofpotassium amide at room temperatures, and in the presence offerric oxide orcobaltic oxide, to form nitrogen andpotassium hydroxide.
Interest in a medical role for inorganic nitrite was first aroused because of the spectacular success of organic nitrites and related compounds in the treatment ofangina pectoris. While working with Butter at theEdinburgh Royal Infirmary in the 1860s, Brunton noted that the pain of angina could be lessened byvenesection and wrongly concluded that the pain must be due to elevated blood pressure. As a treatment for angina, the reduction of circulating blood by venesection was inconvenient. Therefore, he decided to try the effect on a patient of inhalingamyl nitrite, a recently synthesized compound and one that his colleague had shown lowered blood pressure in animals. Pain associated with an anginal attack disappeared rapidly, and the effect lasted for several minutes, generally long enough for the patient to recover by resting. For a time, amyl nitrite was the favored treatment for angina, but due to its volatility, it was replaced by chemically related compounds that had the same effect.[2]
The effect of potassium nitrite on the nervous system, brain, spinal cord, pulse, arterial blood pressure, and respiration of healthy human volunteers was noted, as was the variability between individuals. The most significant observation was that even a small dose of <0.5 grains (≈30 mg) given by mouth caused, at first, an increase in arterialblood pressure, followed by a moderate decrease. With larger doses, pronouncedhypotension ensued. They also noted that potassium nitrite, however administered, had a profound effect on the appearance and oxygen-carrying capacity of the blood. They compared the biological action of potassium nitrite with that of amyl and ethyl nitrites and concluded that the similarity of action depends on the conversion of organic nitrites tonitrous acid.[2]
Solutions of acidified nitrite have been used successfully to generate NO and to inducevasorelaxation in isolatedblood vessel studies, and the same reaction mechanism has been proposed to explain the biological action ofnitrite.[2]
Potassium nitrite is used in the manufacturing of heat transfer salts. Asfood additiveE249, potassium nitrite is apreservative similar tosodium nitrite and is approved for usage in the EU,[5] USA,[6] Australia and New Zealand[7] (where it is listed under itsINS number 249).
Potassium nitrite is also used by modernluthiers to darken the tone and possibly improve the acoustic characteristics ofviolins, used after completing the box and beforevarnishing. The KNO2 is applied then exposed tosunlight.
When reacting with acids, potassium nitrite forms toxic nitrous oxides. Fusion withammonium salts results ineffervescence andignition. Reactions with reducing agents can result in fires and explosions.[8]
Potassium nitrite is stored with other oxidizing agents but separated from flammables, combustibles,reducing agents, acids,cyanides, ammonium compounds, amides, and other nitrogenous salts in a cool, dry, well ventilated location.[8]
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