Welcome to Nitrogen Compounds!

In this chapter, we are going to explore the organic molecules that contain nitrogen. These are some of the most important molecules in nature—they are the building blocks of proteins and DNA! For your AS Level, we will focus specifically on primary amines and nitriles.

Don't worry if organic chemistry feels like a lot of recipes to memorize at first. We will break down exactly what happens, why it happens, and how to remember the conditions for your exam.


1. Primary Amines

Imagine an ammonia molecule \( (NH_3) \). If you take off one hydrogen atom and replace it with a carbon chain (an alkyl group, R), you get a primary amine. Its general formula is \( RNH_2 \).

How do we make Primary Amines?

According to your syllabus, there is one main way you need to know to produce an amine: starting from a halogenoalkane.

The Reaction:
Halogenoalkane + Ammonia \( \rightarrow \) Primary Amine + Hydrogen Halide
Example: \( CH_3CH_2Br + NH_3 \rightarrow CH_3CH_2NH_2 + HBr \)

The "Must-Know" Conditions:

This reaction won't just happen if you mix them in a beaker. You need three specific things:

  1. Reagent: Excess Ammonia \( (NH_3) \).
  2. Solvent: Ethanol (we call this "ethanolic ammonia"). If you use water, you might get an alcohol instead!
  3. Conditions: Heated under pressure in a sealed tube.

Memory Aid: Think of "E.P.H." — Ethanol, Pressure, Heat. You need all three to force the nitrogen to stay attached to the carbon chain.

Quick Review: Primary amines are like ammonia's cousins. We make them by swapping a halogen for an \( -NH_2 \) group using ammonia in ethanol under pressure.


2. Nitriles and Hydroxynitriles

Nitriles are molecules containing the \( -C \equiv N \) functional group. They are very useful in chemistry because they allow us to increase the length of the carbon chain.

Making Nitriles from Halogenoalkanes

If you want to add one more carbon atom to your molecule, this is the reaction to use!

The Reaction:
Halogenoalkane + Potassium Cyanide \( \rightarrow \) Nitrile + Potassium Halide
Example: \( CH_3Br + KCN \rightarrow CH_3CN + KBr \)

Conditions:
1. Reagent: KCN (Potassium Cyanide) or NaCN.
2. Solvent: Ethanolic (dissolved in ethanol).
3. Process: Heat under reflux.

Making Hydroxynitriles from Carbonyls

A hydroxynitrile is a molecule that has both an \( -OH \) group and a \( -CN \) group on the same carbon. We make these from aldehydes or ketones.

The Reaction:
Aldehyde/Ketone + HCN \( \rightarrow \) Hydroxynitrile
Example: \( CH_3CHO + HCN \rightarrow CH_3CH(OH)CN \)

The Setup:
In a lab, we usually use KCN and dilute \( H_2SO_4 \) to generate the \( HCN \) safely, as \( HCN \) gas is extremely toxic. We use KCN as a catalyst because it provides the \( CN^- \) ions needed to start the attack.

Did you know? This is a Nucleophilic Addition reaction. The \( CN^- \) ion is a "nucleus-lover" that attacks the slightly positive carbon in the \( C=O \) bond.

Key Takeaway: Nitriles are the "chain extenders." If your exam question shows a product with one more carbon than the starting material, a nitrile was probably involved!


3. Hydrolysis of Nitriles

Once you have made a nitrile, you can turn it into a carboxylic acid. This is called hydrolysis (splitting with water).

Acid Hydrolysis

Reagents: Dilute acid (like \( HCl \)) and water.
Conditions: Heat under reflux.
What happens: The \( -CN \) group turns into a \( -COOH \) group. The nitrogen is released as an ammonium salt.
Equation: \( RCN + 2H_2O + HCl \rightarrow RCOOH + NH_4Cl \)

Alkaline Hydrolysis

Reagents: Dilute alkali (like \( NaOH \)).
Conditions: Heat under reflux.
What happens: This is a two-step process. First, you get a carboxylate salt (like \( RCOO^-Na^+ \)). You then must add a dilute acid (acidification) to turn it into the actual carboxylic acid \( RCOOH \).

Common Mistake to Avoid: When counting the carbon atoms in a nitrile, always count the carbon in the \( -CN \) group! For example, \( CH_3CH_2CN \) is called propanenitrile (3 carbons), not ethanenitrile.


Summary Checklist

Before you move on, make sure you can answer these:

  • Can I list the conditions for making an amine from a halogenoalkane? (Ethanolic \( NH_3 \), heat, pressure)
  • Do I know how to extend a carbon chain by one? (Add a nitrile group using KCN)
  • Can I describe how to turn a nitrile into a carboxylic acid? (Hydrolysis by heating with dilute acid)
  • Can I name nitriles correctly including the \( CN \) carbon?

Keep practicing those reaction equations! Nitrogen compounds are the "bridge" that connects halogenoalkanes to carboxylic acids, making them a favorite topic for exam questions.