Nitriles

Nitrile Meaning

A nitrile is a specific functional group that is used in chemistry. This functional group is a part of organic chemistry due to its carbon presence, and how it incorporates itself into carbon-based compounds and molecules.

In literature you will often find this term be interchangeable with a "cyano-". This prefix is used widely in different contexts, usually to denote the presence of a nitrile functional group in a molecule. Any molecule that has this prefix contains a nitrile. The homologous series that contain a nitrile group are called nitriles.

Another name for organic compounds containing a nitrile group is cyanocarbons.

Interestingly, inorganic compounds that contain a nitrile group are not called nitriles, but are rather called cyanides. The term cyanides comes from the widely used prefix cyano-. The key difference between nitriles and cyanides is that cyanides are usually referring to any chemical compound containing a nitrile group, while nitriles have to be an organic compound.

In the next section we will discuss the structure and formula of this functional group.

Nitriles Formula and Structure

The formula of a nitrile is: -CN.

But what does this mean? A nitrile is a functional group that has a nitrogen triple bonded to a carbon. The carbon in turn will be connected to another organic chemistry group, such as a homologous series hydrocarbon. Usually, a nitrile will be connected to the main carbon skeleton of the organic compound.

The structure of the nitrile will consist of a single bond between the carbon (of the nitrile) and the carbon skeleton of the organic compound, but also a triple bond between the carbon and the nitrogen of the nitrile. So what hybridisation will the two atoms in question, the carbon and the nitrogen, have?

As it is a triple bond between the two most atoms of the functional group, and since the bond will be a linar bond, both atoms will be sp hybridised.

Interestingly, the carbon will have two sp hydridised orbitals. This results in one of the sp hybrid orbitals being bonded to the carbon backbone of the organic compound, and the other sp hybrid orbital bonded to the nitrogen. In both of these scenarios a sigma bond is created.

The nitrogen is also sp hybridised, which is used to create a sigma bond with the carbon. The sigma bond creates a single bond, so where do the other two bonds in the triple bond come from? Both the nitrogen and carbon have two 2p orbitals. These two come together to form two pi bonds. These additional two orbitals complete the triple bond between the nitrogen and the carbon in the nitrile.

Nitrile Functional Group

Here we will cover the nitrile as a functional group, and how its structure is represented.

Below you will find a diagram of a nitrile.

Fig. 2: Representation of nitrile functional group, highlighted in blue, StudySmarter Originals

So what does this representation tell us about nitriles? We can see the bonds which are created between the substituent atoms.

Most importantly, the diagram shows the triple bond between the carbon and the nitrogen. Additionally, the single bond between the central carbon and the rest of the molecule (represented by R) can be seen.

The diagram shows the linear nature of the functional group.

Examples of nitriles

Nitriles are an important part of organic chemistry, thus they show up everywhere! Here we will cover some of the common examples and where they can be found.

Overall, nitriles can be split between two parts. When thinking about nitriles, usually negative connotations come to mind. These are usually having to deal with cyanide and its poisonous properties.

The other side of nitriles are concerned with useful compounds. As it is functional organic group, it can be found in many different organic contexts of chemistry.

Some crucial applications are in polymers, such as rubbers and glues. Nitriles can be found in superglue, and also rubbers such as nitrile rubber. Nitrile rubber is very imporant in many industries as it is resistant to oils and fuels. This is specifically due to the nitrile containing long chained polymers which have resistive polymers to different organic hydrocarbon conpounds, such as fuels. Another polymer nitriles can be found in specific nitrile-containing polymers which are used in context where latex is not used in. Often this can be a substitute for latex, which can be crucial for people with latex allergies, ultimately saving lives. This is why it can be found in medical gloves and hospital environments, as well as latex-free laboratories.

Nitrile Reactions

Here we will cover 3 most important reactions you need to know regarding nitriles. We will go over their importance and mechanism. Two of these concern creating a nitrile, while another one is a reaction involving an outcome that a nitrile can have.

The first two processes will be regarding creating a nitrile, in this case either an organic nitrile or a hydroxynitrile. The third mechanism will be discussing how a nitrile might react in certain chemical contexts, in this case, how a nitrile can change into an amine.

Making a Nitrile

To create a nitrile, the easiest reaction you can perform is a simple nucleophilic substitution reaction between a halogenoalkane and a cyanide anion. This reaction can occur because in many chemical contexts, a halogen on a hydrocarbon can often be replaced by other chemical groups and functional groups.

Firstly, creating a solution with a cyanide anion requires potassium cyanide (KCN). This is why this reaction is sometimes referred to as one where a nitrile is created from a halogenoalkane and potassium cyanide. Potassium cyanide, being a compound of ionic nature, dissolves to create potassium ions and cyanide anions.

So how do you perform this reaction? Simply heat your desired halogenoalkane and KCN solution under a reflux. After some time the substitution reaction should take place, where the halogen will be displaced from the hydrocarbon chain, and the nitrile created. This reaction will produce a solution of halogen anions.

Making a Hydroxynitrile

To create a hydroxynitrile, in other words often referred to as cyanohydrins, you need an organic reactant with a carbonyl group, such as an aldehyde or a ketone. The double oxygen-carbon bond will allow for the nucleophilic addition reaction to take place.

This reaction proceeds by the addition of hydrogen cyanide (HCN) to these organic compounds. It is key to mention that these HCN is a poisonous gas that isn't used, but rather KCN is used in an acidic environment.

The produced organic compound has a nitrile and a hydroxyl group attached to the carbon where the double bond oxygen was present.

Nitrile to Amine

Another key reaction that nitriles can undergo is a conversion to an amine. Here we will go over how a nitrile can convert to primary amines.

Primary amines can be formed by a catalyst, which is LiAlH₄. The reaction proceeds in an aqueous environment, where the nitrile is attacked. This creates an imine anion, which is then converted to a amine. This means that the triple bond between the nitrile and the carbon in the nitrile fucntional group is broken for hydrogens to bond with both the nitrogen and carbon of the nitrile, thus producing an amine. This reaction is mediated by the attack of the hydride nucleophile on the electrophilic carbon.

In this article, you should have gained a grasp on the topic of nitriles, primarily their structure, reactions, and uses. Can you see now why nitriles are often a debated topic? Their use for both industries as well as poisons can often be controversial.