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Sodium nitrite

Sodium nitrite

Overview
Sodium nitrite is the inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 Na
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

NO2
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...

. It is a white to slight yellowish crystalline powder that is very soluble in water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and is hygroscopic. It is a useful precursor to a variety of organic compounds, such as pharmaceuticals, dyes, and pesticides, but it is probably best known as a food additive to prevent botulism
Botulism
Botulism also known as botulinus intoxication is a rare but serious paralytic illness caused by botulinum toxin which is metabolic waste produced under anaerobic conditions by the bacterium Clostridium botulinum, and affecting a wide range of mammals, birds and fish...

.

The salt is prepared by treating sodium hydroxide with mixtures of nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

 and nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

:
2 NaOH + NO2 + NO → 2 NaNO2 + H2O

The conversion is sensitive to the presence of oxygen, which can lead to varying amounts of sodium nitrate
Sodium nitrate
Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...

.

In former times, sodium nitrite was prepared by reduction of sodium nitrate with various metals.

In the laboratory, sodium nitrite can be used to destroy excess sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

.
2 NaN3 + 2 Na NO2 + 2 H+ → 3 N2 + 2 NO + 2 Na+ + 2 H2O


At high temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

s, sodium nitrite decomposes sodium oxide
Sodium oxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

, nitrogen(II) oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

 and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

.

The main use of sodium nitrite is for the industrial production of organonitrogen compounds.
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Encyclopedia
Sodium nitrite is the inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 Na
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

NO2
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...

. It is a white to slight yellowish crystalline powder that is very soluble in water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and is hygroscopic. It is a useful precursor to a variety of organic compounds, such as pharmaceuticals, dyes, and pesticides, but it is probably best known as a food additive to prevent botulism
Botulism
Botulism also known as botulinus intoxication is a rare but serious paralytic illness caused by botulinum toxin which is metabolic waste produced under anaerobic conditions by the bacterium Clostridium botulinum, and affecting a wide range of mammals, birds and fish...

.

Production


The salt is prepared by treating sodium hydroxide with mixtures of nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

 and nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

:
2 NaOH + NO2 + NO → 2 NaNO2 + H2O

The conversion is sensitive to the presence of oxygen, which can lead to varying amounts of sodium nitrate
Sodium nitrate
Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...

.

In former times, sodium nitrite was prepared by reduction of sodium nitrate with various metals.

Chemical reactions


In the laboratory, sodium nitrite can be used to destroy excess sodium azide
Sodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...

.
2 NaN3 + 2 Na NO2 + 2 H+ → 3 N2 + 2 NO + 2 Na+ + 2 H2O


At high temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

s, sodium nitrite decomposes sodium oxide
Sodium oxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

, nitrogen(II) oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

 and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

.

Industrial chemistry


The main use of sodium nitrite is for the industrial production of organonitrogen compounds. It is a reagent for conversion of amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s into diazo
Diazo
Diazo refers to a type of organic compound called diazo compound that has two linked nitrogen atoms as a terminal functional group. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane...

 compounds, which are key precursors to many dyes, such as diazo dyes. Nitroso compounds are produced from nitrites. These are used in the rubber industry.

Other applications include uses in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

. It may also be used as an electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

 in electrochemical grinding
Electrochemical grinding
Electrochemical grinding is a process that removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid, and a positively charged workpiece. Materials removed from the workpiece stay in the electrolyte fluid...

 manufacturing processes, typically diluted to about 10% concentration in water. It is used in a variety of metallurgical applications, for phosphatizing and detinning. Sodium nitrite also has been used in human and veterinary medicine as a vasodilator, a bronchodilator
Bronchodilator
A bronchodilator is a substance that dilates the bronchi and bronchioles, decreasing resistance in the respiratory airway and increasing airflow to the lungs. Bronchodilators may be endogenous , or they may be medications administered for the treatment of breathing difficulties...

, and an antidote
Antidote
An antidote is a substance which can counteract a form of poisoning. The term ultimately derives from the Greek αντιδιδοναι antididonai, "given against"....

 for cyanide poisoning
Cyanide poisoning
Cyanide poisoning occurs when a living organism is exposed to a compound that produces cyanide ions when dissolved in water. Common poisonous cyanide compounds include hydrogen cyanide gas and the crystalline solids potassium cyanide and sodium cyanide...

 (see Cyanide#Antidote).

Food additive


As a food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

, it prevents growth of Clostridium botulinum
Clostridium botulinum
Clostridium botulinum is a Gram-positive, rod-shaped bacterium that produces several toxins. The best known are its neurotoxins, subdivided in types A-G, that cause the flaccid muscular paralysis seen in botulism. It is also the main paralytic agent in botox. C. botulinum is an anaerobic...

, the bacterium which causes botulism
Botulism
Botulism also known as botulinus intoxication is a rare but serious paralytic illness caused by botulinum toxin which is metabolic waste produced under anaerobic conditions by the bacterium Clostridium botulinum, and affecting a wide range of mammals, birds and fish...

. It also alters the color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

 of preserved fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

s. In the European Union it may be used only as a mixture with salt containing at most 0.6% sodium nitrite. It has the E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...

 E250. Potassium nitrite
Potassium nitrite
Potassium nitrite is a salt with chemical formula 2.It is a strong oxidizer and may accelerate the combustion of other materials. Like other nitrite salts such as sodium nitrite, potassium nitrite is toxic if swallowed, and laboratory tests suggest that it may be mutagenic or teratogenic...

 (E249) is used in the same way. It is approved for usage in the EU, USA and Australia and New Zealand.

Toxicity


While this chemical will prevent the growth of bacteria, it can be toxic in high amounts for animals, including humans. Sodium nitrite's LD50 in rats is 180 mg/kg and its human LDLo
Lowest published lethal dose
In toxicology, the LDLo is the lowest dosage per unit of bodyweight of a substance known to have resulted in fatality in a particular animal species...

 is 71 mg/kg, meaning a 65 kg person would likely have to consume at least 4.615 g
Gram
The gram is a metric system unit of mass....

 to result in death. To prevent toxicity, sodium nitrite (blended with salt) sold as a food additive is dyed bright pink to avoid mistaking it for plain salt or sugar.Nitrites are a normal part of human diet, found in most vegetables. Spinach and lettuce can have as high as 2500 mg/kg, curly kale (302.0 mg/kg) and green cauliflower (61.0 mg/kg), to a low of 13 mg/kg for asparagus. Nitrite levels in 34 vegetable samples, including different varieties of cabbage, lettuce, spinach, parsley and turnips ranged between 1.1 and 57 mg/kg, e.g. white cauliflower (3.49 mg/kg) and green cauliflower (1.47 mg/kg). Boiling vegetables lowers nitrate but not nitrite. Fresh meat contains 0.4-0.5 mg/kg nitrite and 4–7 mg/kg of nitrate (10–30 mg/kg nitrate in cured meats). The presence of nitrite in animal tissue is a consequence of metabolism of nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

, an important neurotransmitter. Nitric oxide can be created de novo
De novo
In general usage, de novo is a Latin expression meaning "from the beginning," "afresh," "anew," "beginning again." It is used in:* De novo transcriptome assembly, the method of creating a transcriptome without a reference genome...

from nitric oxide synthase
Nitric oxide synthase
Nitric oxide synthases are a family of enzymes that catalyze the production of nitric oxide from L-arginine. NO is an important cellular signaling molecule, having a vital role in many biological processes...

 utilizing arginine
Arginine
Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. At the level of molecular genetics, in the structure of the messenger ribonucleic acid mRNA, CGU, CGC, CGA, CGG, AGA, and AGG, are the triplets of nucleotide bases or codons that codify for arginine during...

 or from ingested nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...

 or nitrite
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...

. Most research on negative effects of nitrites on humans predates discovery of nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

's importance to human metabolism and human endogenous metabolism of nitrite.

Humane toxin for feral hogs/wild boar control


Because of sodium nitrite's high level of toxicity to swine (Sus scrofa) it is now being developed in Australia to contol feral pigs and wild boar.. The sodium nitrite induces methemoglobinemia
Methemoglobinemia
Methemoglobinemia is a disorder characterized by the presence of a higher than normal level of methemoglobin in the blood. Methemoglobin is an oxidized form of hemoglobin that has an increased affinity for oxygen, resulting in a reduced ability to release oxygen to tissues. The oxygen–hemoglobin...

 in swine, i.e., it reduces the amount of oxygen that is released from hemoglobin), so the animal will feel faint and pass out, and then die in a humane manner after first being rendered unconscious.

Nitrosamines


A principal concern about sodium nitrite is the formation of carcinogen
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

ic nitrosamine
Nitrosamine
Nitrosamines are chemical compounds of the chemical structure R1N-N=O, some of which are carcinogenic.-Usages:Nitrosamines are used in manufacture of some cosmetics, pesticides, and in most rubber products. -Occurrences:...

s in meats containing sodium nitrite when meat is charred or overcooked. Such carcinogenic nitrosamines can be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during the curing process used to preserve meats. Dietary sources of nitrosamines include US cured meats preserved with sodium nitrite as well as the dried salted fish eaten in Japan. In the 1920s, a significant change in US meat curing practices resulted in a 69% decrease in average nitrite content. This event preceded the beginning of a dramatic decline in gastric cancer mortality. About 1970, it was found that ascorbic acid
Ascorbic acid
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form of vitamin C. The name is derived from a- and scorbutus , the...

 (vitamin C), an antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...

, inhibits nitrosamine formation. Consequently, the addition of at least 550 ppm of ascorbic acid is required in meats manufactured in the United States. Manufacturers sometimes instead use erythorbic acid
Erythorbic acid
Erythorbic acid, formerly known as isoascorbic acid and D-araboascorbic acid, is a stereoisomer of ascorbic acid . It is a vegetable-derived food additive produced from sucrose. It is denoted by E number E315, and is widely used as an antioxidant in processed foods.Clinical trials have been...

, a cheaper but equally effective isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

 of ascorbic acid. Additionally, manufacturers may include alpha-tocopherol (vitamin E)
Alpha-tocopherol
α-Tocopherol is a type of tocopherol with formula C29H50O2. It has E number "E307".α-Tocopherol is a form of vitamin E that is preferentially absorbed and accumulated in humans...

 to further inhibit nitrosamine production. Alpha-tocopherol, ascorbic acid, and erythorbic acid all inhibit nitrosamine production by their oxidation-reduction properties. Ascorbic acid, for example, forms dehydroascorbic acid
Dehydroascorbic acid
Dehydroascorbic acid is an oxidized form of ascorbic acid. It is actively imported into the endoplasmic reticulum of cells via glucose transporters. It is trapped therein by reduction back to ascorbate by glutathione and other thiols. Therefore, L-dehydroascorbic acid is a vitamin C compound much...

 when oxidized
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

, which when in the presence of nitrous anhydride, a potent nitrosating agent formed from sodium nitrate, reduces the nitrous anhydride into the nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

 gas. Note that Nitrous Anhydride does not exist in vitro.

Sodium nitrite consumption has also been linked to the triggering of migraines in individuals who already suffer from them.

One study has found a correlation between highly frequent ingestion of meats cured with pink salt and the COPD
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...

 form of lung disease. The study's researchers suggest that the high amount of nitrites in the meats was responsible; however, the team did not prove the nitrite theory. Additionally, the study does not prove that nitrites or cured meat caused higher rates of COPD, merely a link. The researchers did adjust for many of COPD's risk factors, but they commented they cannot rule out all possible unmeasurable causes or risks for COPD.

Mechanism of action


Carcinogenic nitrosamines are formed when amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s that occur naturally in food react with sodium nitrite found in cured meat products.
R2NH (amines) + NaNO2 (sodium nitrite) → R2N-N=O (nitrosamine)


In the presence of acid (such as in the stomach) or heat (such as via cooking), nitrosamines are converted to diazonium ions
Diazonium compound
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group R-N2+ X- where R can be any organic residue such alkyl or aryl and X is an inorganic or organic anion such as a halogen...

.
R2N-N=O (nitrosamine) + (acid or heat) → R-N2+ (diazonium ion)


Certain nitrosamines such as N-nitrosodimethylamine
N-Nitrosodimethylamine
N-Nitrosodimethylamine , also known as dimethylnitrosamine , is a semi-volatile organic chemical that is highly toxic and is a suspected human carcinogen. The US Environmental Protection Agency has determined that the maximum admissible concentration of NDMA in drinking water is 7 ng L−1...

 and N-nitrosopyrrolidine form carbocations that react with biological nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...

s (such as DNA or an enzyme) in the cell.
R-N2+ (diazonium ion) → R+ (carbocation) + N2 (leaving group) + :Nu (biological nucleophiles) → R-Nu


If this nucleophilic substitution
SN1 reaction
The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step is unimolecular...

 reaction occurs at a crucial site in a biomolecule, it can disrupt normal cell functioning leading to cancer or cell death
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

.

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