Amino acids (OCR A Level Chemistry)

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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

Naturally occurring amino acids

  • 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

Nitrogen Compounds - General Structural Formula of Amino Acids, downloadable AS & A Level Chemistry revision notes

General structural formula of amino acids

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

Acid / base properties of 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

Reactions of the amine group

  • 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

Reactions of the carboxylic acid group

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

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Sonny

Author: Sonny

Expertise: Chemistry

Sonny graduated from Imperial College London with a first-class degree in Biomedical Engineering. Turning from engineering to education, he has now been a science tutor working in the UK for several years. Sonny enjoys sharing his passion for science and producing engaging educational materials that help students reach their goals.