Imagine you are an alchemistry a 1000 years ago. You are trying to plot against the king and make a poison but you don't know what to extract from your seeds! You need to know the specifics of nitriles and their chemistry to be able to make cyanide.
Fig. 1: Cyanide is poisonous, Image from pixabay under pixabay license.
Nitriles are a very debated organic functional group. On one hand they can be very useful in many different industries, but more commonly are known for being poisonous. Here we will discuss why these groups are often so poisonous, but also what other things they are known for. By diving into the structure and creation of nitriles, we will see why this functional group has been talked about for centuries.
- This article is about nitriles.
- In this article, you will understand what a nitrile is through its composition.
- Its formula, structure, and hybridisation will be discussed.
- The uses of nitriles in both known and lesser-known industries.
- The reactions that nitriles can undergo, including the production of nitriles, hydroxynitriles, and how nitriles can convert into amines.
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.
It is important to note that nitriles refer to only organic compounds that contain a nitrile group.
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, Vaia 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.
The nitrile is linear due to the triple bond, which creates a bond angle of 180° between the two electron domains of the central carbon.
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.
In fact, cyanide has been an important historical chemical through centuries. This is because its production has always been in demand for various purposes. This is how its importance in culture and media has grown over the years. This includes from medieval times up until nowadays.
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.
It is important that the solution of KCN solution use a non-aqueous solvent, as the hydroxyl group can easily displace the halogen instead of the cyanide anion. This is why usually it is dissolved in ethanol
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.
An example of this type of reaction to create a nitrile can be one with 1-bromopropane and KCN. Here the 1-bromopropane will act as our halogenoalkane of choice:
We can thus create the following ionic reaction equation:
\[ CH_3CH_2CH_2Br + CN^- \rightarrow CH_3CH_2CH_2CN + Br^- \]
We can then construct the full euqation:
\[ CH_3CH_2CH_2Br + KCN \rightarrow CH_3CH_2CH_2CN + KBr \]
The resulting nitrile is butanenitrile.
It is important to note that in the example above the halogenoalkane of choice is a primary halogenoalkane, but secondary and tertiary halogenoalkanes will also undergo a similar reaction.
This reaction of creating a nitrile is very important, as it not only incorporates a functional group, but also incorporates a carbon. This lengthens the carbon chain through a simple reaction.
You can begin with a shorter hydrocarbon chain and end up with a longer one. In fact this reaction is used and manipulated to add carbons to chains.
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.
Nitriles - Key takeaways
- Nitriles are organic functional groups (-CN), often referred by "cyano-"
- The carbon is triply bonded to the nitrogen
- It has sp hybridisation, and is a linear functional group
- Examples of nitriles include cyanide, nitrile-containing polymers, and nitrile rubber
- Nitriles can be created through two reactions:
- Nucleophilic substitution producing a nitrile
- Nucleophilic attack producing a hydroxynitrile
- Nitriles can be converted into amines, which extend the carbon chain of the organic molecule.
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