He nitrous acid Is a moderately strong to weak acid, stable only in cold diluted aqueous solution. It is known only in solution and in the form of nitrite salts (such as sodium nitrite and potassium nitrite).
Nitrous acid participates in the ozone balance of the lower atmosphere (the troposphere). Nitrite is an important source of potent nitric oxide vasodilator. The nitro group (-NO 2) is present in nitrous acid esters and in nitro compounds.
Nitrous acid / sodium nitrite crystals
Nitrites are widely used in the food industry to heal meat. However, l The International Agency for Research on Cancer (IARC), a specialized cancer organization of the United Nations World Health Organization (WHO), classified nitrite as probably carcinogenic to humans when ingested under conditions that give rise to Endogenous nitrosation.
Formulas
Nitrous acid: HNO 2
Nitrite: NO 2 -
Sodium Nitrite: NaNO 2
- CAS : 7782-77-6 Nitrous acid
- CAS : 14797-65-0 Nitrite
- CAS : 14797-65-0 Sodium nitrite (Nitrous acid, sodium salt)
2D structure
Nitrous acid
Nitrite
Sodium nitrite
3D structure
Nitrous acid / Molecular model beads and rods
Nitrite / Molecular model beads and rods
Characteristics of nitrous acid
Physical and chemical properties
It is assumed that nitrous acid is in dynamic equilibrium with its anhydride in aqueous solutions:
2HNO 2 ⇌ N 2 O 3 + H 2 O
Because of the hydrolysis, its salts (nitrites) are unstable in aqueous solution. Nitrous acid is produced as an intermediate product when NOx gases (mono-nitrogen oxides, such as nitric oxide and nitrogen dioxide, NO and NO2 respectively) are dissolved in water.
When heated in the presence of sand, glass chips or other sharp objects, or even at low temperature, nitrous acid disproportionates as:
3 HNO 2 ⇌ HNO 3 + 2NO + H 2 O
By virtue of the above reaction, nitrous acid can act as a reducing agent, and as an oxidizing agent. This disproportionation reaction influences the properties of nitrous acid solutions and is important in the production of nitric acid.
An especially important property of nitrous acid is its ability to diazotize organic amines. With primary amines, the acid forms diazonium salts
RN-H2 + HNO2 + HCl → [RN-NΞN] Cl + 2H2O
Sodium nitrite (or sodium salt of nitrous acid) is a white to slightly yellowish crystalline powder, very soluble in water, and hygroscopic (it absorbs moisture from the surrounding environment).
Potassium nitrite is the inorganic compound with the chemical formula KNO 2 . It is an ionic salt of potassium K + ions and nitrite ions NO2-.
Like other nitrite salts, such as sodium nitrite, it is toxic if ingested, and may be mutagenic or teratogenic.
Nitrous acid exists in two isomeric forms:
These structures lead to two series of organic derivatives of industrial importance:
(I) Nitrite Esters:
Nitrite ester
(II) Nitro derivatives:
Structure of the nitro group
The nitrite esters contain the nitrosoxy functional group, having the general formula RONO, wherein R is an aryl or alkyl group.
Nitroderivatives (nitro compounds) are organic compounds containing one or more nitro (-NO 2) functional groups.
The compounds of the nitro group are almost invariably produced by the nitration reactions that begin with nitric acid. They are rarely found in nature. At least some natural nitro groups were caused by the oxidation of amino groups.
Inorganic nitrite compounds (sodium nitrite, potassium nitrite, etc.)
Inflammability
These compounds are explosive. Some of these substances may decompose explosively when they are heated or are encased in a fire. May explode due to heat or contamination. Containers may explode when heated. Runoff may create a fire or explosion hazard.
Reactivity
The compounds of this group may act as extremely potent oxidizing agents and mixtures with reducing agents or reduced materials such as organic substances may be explosive.
Reacts with acids to form toxic nitrogen dioxide. A violent explosion occurs if an ammonium salt is fused with a nitrite salt.
Danger to health
Inhalation, ingestion or contact (skin, eyes) with vapors or substances may cause serious injury, burns or death. Fire may produce irritating, corrosive and / or toxic gases. Runoff from fire control or dilution water may cause contamination.
Organic nitrite compounds (nitrite esters, nitroderivatives)
Inflammability
Most of the materials in this group are technically of low flammability. However, they are often chemically unstable and subject, to a very variable extent, to explosive decomposition.
Reactivity
The aromatic nitro compounds may be exploited in the presence of a base such as sodium hydroxide or potassium hydroxide, even in the presence of water or organic solvents. The explosive trends of nitro aromatic compounds are increased by the presence of multiple nitro groups.
Toxicity
Many of the compounds in this group are extremely toxic.
Applications
Among the nitrite esters, amyl nitrite and other alkyl nitrites are used in medicine for the treatment of heart disease and for prolonging orgasm, particularly in males. Occasionally they are used recreationally for their euphorizing effect.
Chemical structure of amyl nitrite
Amylitol Nitrite / Molecular model beads and rods
The nitro group is one of the most common explosophores (functional group that makes an explosive compound) globally. Many are used in organic synthesis, but the largest use of compounds in this group is in military and commercial explosives.
Chloramphenicol (a useful antibiotic for the treatment of bacterial infections) is a rare example of a natural nitro compound.
Chemical structure of chloramphenicol
Chloramphenicol / Molecular spheres model
Diazonium salts are widely used in the preparation of bright colored compounds called azo dyes.
The main use of sodium nitrite is for the industrial production of organonitrogen compounds. It is a precursor to a variety of pharmaceuticals, dyes and pesticides. However, its best known use is as a food additive to prevent botulism. It has the number E250.
Potassium nitrite is used as a food additive similarly to sodium nitrite. It has the number E249.
Under certain conditions (especially during cooking) the nitrites in the meat may react with amino acid degradation products, forming nitrosamines, which are known carcinogens.
Sausages preserved with nitrites
However, the role of nitrites in preventing botulism has prevented the ban on its use in cured meat. They are considered irreplaceable in the prevention of botulinum intoxication by the consumption of cured dry sausages.
Sodium nitrite is among the most important medicines that need a basic health system (it is on the list of essential medicines of the World Health Organization).
Nitrous acid and air pollution
Effects of pollution on health
Nitrogen oxides (NOx) can be found in indoor and outdoor environments.
The atmospheric concentration of nitrogen oxides has increased significantly in the last 100 years.
Its study is necessary for air quality planning, and the evaluation of its effects on human health and the environment.
According to their origin, the emission sources of atmospheric pollutants can be classified as:
• Outdoor environments
to. Anthropogenic sources
A.1. Industrial processes
A.2. Human activity
B. Natural sources
B.1. Biomass burning processes (fossil fuels).
B.2. Oceans
B.3. Floor
B.4. Processes Involved in Sunlight
• Indoor environments
to. Infiltrated sources of outdoor environments by processes of air spares.
B. Sources derived from combustion processes in indoor environments (the main ones).
NO levels 2 Indoors are higher than NO values 2 Outdoors. The Interior / Exterior (I / E) ratio is greater than 1.
It is fundamental knowledge and control of these sources of emission of indoor environments, due to the time of personal residence in these environments (homes, offices, means of transport).
Since the late 1970s, nitrous acid (HONO) has been identified as a key atmospheric component because of its role as a direct source of hydroxyl (OH) radicals.
There are a number of known sources of OH in the troposphere, however, OH production of the HONO is of interest because the sources, fate, and diurnal cycle of HONO in the atmosphere have only recently been elucidated.
Nitrous acid participates in the ozone balance of the troposphere. The heterogeneous reaction of nitric oxide (NO) and water produces nitrous acid. When this reaction occurs on the surface of atmospheric aerosols, the product is readily photobleed to hydroxyl radicals
OH radicals are involved in the formation of ozone (O3) and peroxyacetyl nitrates (PAN), which cause so-called photochemical smog in contaminated regions and contribute to the oxidation of volatile organic compounds (VOCs), which form secondarily particles and Oxygenated gases.
Nitrous acid strongly absorbs sunlight at wavelengths shorter than 390 nm, leading to its photolytic degradation in OH and nitric oxide (NO).
HONO + hν → OH + NO
At night, the absence of this mechanism results in the accumulation of HONO. Resumption of the photolysis of HONO after sunrise can lead to substantial OH formation in the morning.
In Western societies, people spend about 90% of their time indoors, predominantly in their own homes.
The global demand for energy savings has boosted energy savings in heating and cooling (good insulation of interior spaces, low levels of air infiltration, energy efficient windows) leading to increased levels of air pollutants in such environments .
Due to smaller volumes and reduced air exchange rates, the residence time of air pollutants is much longer in indoor environments compared to the outdoor atmosphere.
Among all the compounds present in indoor air, HONO represents an important gas-phase contaminant that could be present at fairly high concentrations with implications for air quality and health.
HONO can lead to irritation of the human respiratory tract and respiratory problems.
HONO, when it comes into contact with certain compounds present on indoor surfaces (such as tobacco smoke nicotine) can form cancerous nitrosamines.
Indoor HONO can be generated directly during a combustion process, ie burning candles, in gas stoves and in heaters, or it can be formed by heterogeneous hydrolysis of NO2 on several interior surfaces.
2NO 2 + H 2 O → HONO + HNO 3
The UV fraction of sunlight can increase the heterogeneous conversion of NO 2 To HONO.
Alvarez et al. (2014) and Bartolomei et al. (2014) have shown that HONO is produced in heterogeneous, light-induced reactions of NO 2 With common indoor surfaces such as glass, cleaning products, paint and lacquer.
Similarly, light-induced HONO formation rates observed on internal surfaces may help explain the high levels of OH observed indoors during the day.
The HONO can be emitted directly as a primary pollutant, and reach high levels in indoor air through combustion processes, for example in poorly ventilated kitchens of"energy efficient"homes with gas stoves.
In addition, the HONO can be formed through heterogeneous reactions of NO 2 With layers of water sorbed on several interior surfaces.
Although the two sources of OVEN (direct emission and heterogeneous reactions of NO 2 Of gaseous phase with layers of water adsorbed in the absence of sunlight) represent significant internal HONO sources, models with only these two sources systematically underestimate the levels of daytime HONO observed indoors.
Alvarez et al. (2014) conducted research on the heterogeneous reactions induced by light, NO 2 In gaseous phase with a series of commonly used household chemicals, including floor cleaner (alkaline detergent), bath cleaner (acid detergent), white wall paint and lacquer.
The photoexcitation wavelengths used in this study are characteristic of those of the solar spectrum that can easily penetrate into interior spaces (λ> 340 nm).
These authors verified that these domestic chemicals play an important role in the chemistry and air quality of indoor environments.
According to his research, even photo-dissociation of a small fraction of HONO, to produce hydroxyl radicals, would have a major impact on indoor air chemistry.
Similarly, Bartolomei et al. (2014) studied the heterogeneous reactions of NO 2 With selected interior paint surfaces in the presence of light and demonstrated that the formation of HONO increases with light and relative humidity in such indoor environments.
Safety and Risks
Hazard statements of the Globally Harmonized System of Classification and Labeling of Chemicals (GHS)
The Globally Harmonized System of Classification and Labeling of Chemicals (GHS) is an internationally agreed system, created by the United Nations and designed to replace the various classification and labeling standards used in different countries through the use of globally consistent criteria.
Classification and labeling standards and recommendations for sodium nitrite are as follows (European Chemicals Agency, 2017, United Nations, 2015, PubChem, 2017): DANGER CLASSES (and corresponding SGA chapter):
GHS Hazard Statements
H272: May intensify fire; Oxidant [Warning Oxidising Liquids; Oxidizing Solids - Category 3] (PubChem, 2017).
H301: Toxic if swallowed [Danger Acute Toxicity, oral - Category 3] (PubChem, 2017).
H319: Causes serious eye irritation. [Warning Serious eye damage / eye irritation - Category 2A] (PubChem, 2017).
H341: Suspected to cause genetic defects [Warning Germ cell mutagenicity - Category 2] (PubChem, 2017).
H361: Suspected of damaging fertility or the fetus [Warning Reproductive toxicity - Category 2] (PubChem, 2017).
H370: Causes damage to organs [Hazard Specific target organ toxicity, single exposure - Category 1] (PubChem, 2017).
H373: Causes damage to organs through prolonged or repeated exposure [Warning Specific target organ toxicity, repeated exposure - Category 2] (PubChem, 2017).
H400: Very toxic to aquatic life [Warning Hazardous to the aquatic environment, acute hazard - Category 1] (PubChem, 2017).
H410: Very toxic to aquatic life with long lasting effects [Warning Hazardous to the aquatic environment, long-term hazard - Category 1] (PubChem, 2017).
Caution Codes Codes
P301 + P310, P301, P301, P202, P210, P220, P221, P260, P264, P270, P273, P280, P281, P370 + P378, P391, P405 and P501 (PubChem, 2017).
(United Nations, 2015, p.360).
(United Nations, 2015, page 370).
(United Nations, 2015, page 370).
(United Nations, 2015, page 370)
(United Nations, 2015, p.391).
(United Nations, 2015, p.393).
References
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- Bartolomei, V., Sörgel, M., Gligorovski, S., Alvarez, E.G., Gandolfo, A., Strekowski, R., & & Wortham, H. (2014). Formation of indoor nitrous acid (HONO) by light-induced NO2 heterogeneous reactions with white wall paint. Environmental Science and Pollution Research, 21 (15), 9259-9269.
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