Nitriles

1.0What Are Nitriles?

Nitriles are a class of organic compounds that contain the functional group -C≡N, known as the cyano group. The cyano group consists of a carbon triple-bonded to nitrogen (C≡N), which makes nitriles distinct and reactive.

Historically, nitriles were often referred to as cyanides, but the term cyanide is now reserved for compounds like hydrogen cyanide (HCN), which has the same functional group but is typically not considered an organic compound.

2.0General Structure of Nitrile

3.0Nomenclature of Nitriles

In IUPAC nomenclature, nitriles are named by replacing the suffix “-e” of the corresponding alkane name with "-nitrile". For example:

• Methane becomes Methanenitrile (or Methyl cyanide).
• Ethane becomes Ethanenitrile (or Acetonitrile).

Alternatively, nitriles can be named as derivatives of "cyanide":

• Methyl cyanide (CH₃CN)
• Ethyl cyanide (C₂H₅CN)

For substituted nitriles, the substituents are named as prefixes with the nitrile group being the parent chain. For example:

• 2-methylpropanenitrile for a methyl group attached to the second carbon of propanenitrile.

4.0Properties of Nitriles

1. Physical Properties of Nitriles:

2. Chemical Properties of Nitriles:

• Reactivity: Nitriles are polar compounds due to the electronegative nitrogen atom. They are highly reactive and can undergo a variety of chemical reactions, such as Nucleophilic Addition Reaction-

R−C≡N + RMgX →  R−C(OH)R′

• Reduction:

R−C≡N + 4[H] → R−CH₂​−NH_2​

• Hydrolysis:

Acidic Hydrolysis: R−C≡N  +  2H₂O +H⁺ → R−COOH + NH₄⁺

Basic Hydrolysis: R−C≡N + OH⁻ + H₂O → R−COO⁻ + NH₃

• Basicity: Nitriles are weakly basic because of the lone pair of electrons on nitrogen.
• Hydrolysis: Nitriles can be hydrolyzed to form carboxylic acids (or their derivatives) under acidic or basic conditions.

5.0Synthesis of Nitriles

1. From Alkyl Halides (Nucleophilic Substitution): Nitriles can be synthesized by reacting an alkyl halide with a cyanide ion (CN⁻), typically from sodium cyanide (NaCN) or potassium cyanide (KCN):

    R−X + CN⁻ → R−CN + X⁻This is a nucleophilic substitution reaction.

2. From Amides (Dehydration): Nitriles can also be synthesized from amides (R-CONH₂) by dehydration:

    R−CONH₂ → P₂O₅R−CN + H₂OPhosphorus pentoxide (P₂O₅) is often used as a dehydrating agent.

3. From Aldehydes or Ketones (Hydrocyanation): Aldehydes or ketones can undergo hydrocyanation with hydrogen cyanide (HCN) in the presence of a catalyst, leading to the formation of nitriles:

    R₂C=O + HCN → R₂C (CN)OH

The intermediate can then be dehydrated to yield a nitrile.

4. From Aromatic Compounds (Electrophilic Substitution): Aromatic compounds can be nitrile-substituted by reacting with cyanogen chloride (CNCl) or sodium cyanide (NaCN) under appropriate conditions:

   C₆H₅Cl + NaCN → C₆H₅CN + NaCl

6.0Uses of Nitriles

• As Solvents: Acetonitrile (CH₃CN) is widely used in organic synthesis and HPLC.
• Pharmaceutical Synthesis: Key in producing vitamins, antibiotics, and anti-cancer agents.
• Plastic Manufacturing: Acrylonitrile is crucial in making synthetic rubbers and acrylic plastics.
• Intermediates: Used in the synthesis of carboxylic acids, amines, and acrylic fibers.
• Organic Synthesis: Vital for creating heterocyclic compounds like imidazoles and pyrroles.
• Ligands in Chemistry: Nitriles, like benzonitrile, act as ligands in coordination compounds.
• Polymer Production: Acrylonitrile polymerizes to produce acrylic fibers and resins.