Nitrile is a general term for organic compounds containing either a cyano group (-C≡N) or a nitrile group. In everyday language and industrial production, nitrile typically refers to one of two cases: 1) the nitrile group in organic compounds (such as acrylonitrile and benzonitrile); 2) acrylonitrile-based polymers such as polynitrile butadiene (NBR) , which are widely used in various industries. This article discusses these two aspects separately and explains the corresponding formulas and molecular structures.
Nitrile functional group: molecular formula and structure
In organic chemistry, the nitrile or cyano group is represented by a carbon-nitrogen triad:
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Group formula: –C≡N
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The molecular formula of the nitrile group attached to the R chain is R–C≡N
Here are some simple examples of molecules that belong to this group:
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Acrylonitrile : Its molecular formula is C₃H₃N and its structural formula is CH₂ =CH–C≡N . Acrylonitrile is an important industrial material used in the production of fibers (e.g., nylon 6), resins, and nitrile polymers.
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Benzonitrile : Its molecular formula is C₇H₅N and its structure is C₆H₅–C≡N . It consists of a benzene ring to which a nitrile group is attached.
A special feature of the nitrile group is the strong triple bond between carbon and nitrogen, which gives many compounds a certain polarity and chemical stability.
Molecular formula and structure of acrylic polymer (NBR)
When nitrile is mentioned in the industry, it usually refers to acrylonitrile butadiene rubber (NBR) . This material is a copolymer consisting of two main monomers:
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Acrylonitrile – Molecular formula: C₃H₃N
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Butadiene – molecular formula: C₄H₆ (usually 1,3-butadiene with the structure CH₂=CH–CH=CH₂)
Because NBR is a random copolymer, its overall formula cannot be expressed by a fixed molecular formula. However, the repeating unit can be expressed as follows:
–[CH₂–CH(CN)]– (واحد آکریلونیتریل) و –[CH₂–CH=CH–CH₂]– (واحد بوتادین)
To simplify matters, imagine
(–A–) representing acrylonitrile units and (–B–) butadiene units, so the polymer looks like a chain… (–A–B–A–A–B–…) The molar ratio of acrylonitrile to butadiene (acrylonitrile percentage or AN%) determines the final properties of the material. This ratio typically ranges between 18% and 50% . The higher the acrylonitrile percentage, the greater the chemical resistance and gas permeability of the material, but the lower its elasticity.
More precise chemical formulas: Important points
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The molecular formula of the repeating unit of acrylonitrile is C₃H₃N
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The molecular formula of the butadiene unit is C₄H₆
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However, the molecular formula of the entire polymer is variable and changes depending on the chain length (number of repeats, n). Therefore, it is usually described by a specific representation of the units rather than a fixed formula.
Synthesis methods (general level)
Industrial processes for producing acrylonitrile monomers involve the oxidation of propylene or propane with ammonia to nitrogen-containing compounds, which are then converted into acrylonitrile. Butadiene rubber (BR) can also be produced by free-radical polymerization or continuous polymerization of acrylonitrile and butadiene polymers. (For safety reasons and ease of use, this article does not include detailed technical descriptions or step-by-step instructions under laboratory conditions.)
Formulation-related properties (AN%)
As already mentioned, the acrylonitrile content plays an important role in the following properties:
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Low AN (≈18–30 %) : more flexible and stretchable , but with lower chemical resistance.
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Moderate (≈30–40%) : Balance between flexibility and strength.
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High AN (≈40–50 %) : excellent resistance to oil and gas, but increased hardness and brittleness at low temperatures.
Applications related to formulas and properties
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Nitrile gloves – Nitrile gloves are very popular due to their chemical resistance and hypoallergenic properties (latex-free) and are usually specially manufactured to be flexible and puncture-resistant.
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O-rings, seals and oil lines : Suitable for use in the automotive, oil and petrochemical industries due to their resistance to hydrocarbons .
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Mechanical parts and coatings : must be resistant to corrosion, oil and heat.
Safety and Environment
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Unprocessed acrylonitrile monomer is a toxic and flammable compound and must therefore be used with caution and under strict control in industrial production. However, the final product (NBR polymer) is generally stable.
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Recycling and disposal of acrylic waste are important and mechanical or thermochemical recycling technologies are being developed to reduce industrial waste.
Finally
The term “nitrile structure” refers either to the simple functional group (C≡N) in organic compounds (e.g., acrylonitrile, C₃H₃N) or to the structure of the nitrile -butadiene copolymer (NBR), which consists of acrylonitrile and butadiene units. The acrylonitrile content in the polymer (AN%) is a decisive factor for final properties such as oil resistance, permeability, and elasticity. Nitriles and their derivatives play an important role in the medical, automotive, oil and gas, and food industries. The development of new formulations opens up new application possibilities and improves environmental compatibility.