6.4.3 Amino acids

Reactions of Amino Acids

Amino acids are organic compounds that contain two functional groups:
- A basic amino (-NH₂) group
- An acidic carboxylic acid (-COOH) group
Due to the presence of both a basic and acidic group in amino acids, they are said to be amphoteric
- They can act as both acids and bases

2-aminocarboxylic acids are a type of amino acids in which the amine (-NH₂) group is bonded to the carbon atom next to the -COOH group
These type of amino acids form the ‘building blocks’ that make up proteins
There are 20 naturally occurring amino acids with the general structural formula of RCH(NH₂)COOH

General structural formula of amino acids

The R group varies in different amino acids and can be:
- Acidic
- Basic
- Neutral

Nitrogen Compounds - Different Types of Amino Acids, downloadable AS & A Level Chemistry revision notes

The R group varies in different amino acids

Amino acids will undergo most reactions of amines and carboxylic acids including acid-base reactions of:
- Amines with acids
- Carboxylic acids with bases

The amine group is basic and reacts with acids to make salts
For example, a general amino acid reacts with hydrochloric acid to form the ammonium salt:

6-4-3-amino-acid--hcl

Reaction with aqueous alkalis

An amino acid reacts with aqueous alkali such as sodium or potassium hydroxide to form a salt and water
For example, a general amino acid reacts with sodium hydroxide to form a sodium salt:

6-4-3-amino-acid--naoh

Esterification with alcohols

Amino acids, like carboxylic acids, can be esterified by heating with alcohol in the presence of concentrated sulfuric acid
The carboxylic acid group is esterified whilst the basic amine group is protonated due to the acidic conditions:

6-4-3-amino-acid--ethanol