acid base hydrolysis, saponification

1. ESTERS

2. Esters
• Esters are produced when an organic acid reacts with an alcohol
• Water is made as a by-product of the reaction
• They have a distinctive fruity smell
• Esters are either natural or man-made
• Natural esters:
• Fats and oils: an ester of a fatty acid and glycerol
• Aromas from fruits like apples, bananas, pears, and strawberries are esters
• Pheromones are natural esters
• Essential Oils like patchouli and lavender are esters
• Man-made:
• Many esters are now manufactured industrially as it is easier than extracting them from
plants and animals, e.g. for perfumes and sweets
• They are also used as industrial solvents for making paints and varnishes
• Also used in the production of biodiesel (fats and methanol)

3. General properties
• General formula CnH2n+1COOCxH2x+1
• Quite volatile – small esters have lower boiling points than the carboxylic acids
• This is useful for plants or animals to attract others by scent
◦ Theyaren’t able to take part in intermolecular bonding aswellas carboxylic
acids
• This also makes the larger esters very insoluble in water, but more soluble in
organic solvents
• They are very useful as solvents for other organic compounds
• Very large esters (like oils and fats) have higher boiling points and melting
points – remember: a fat is simply a solid oil
• The larger the ester molecule, the higher the boiling and melting point.

4. Formation of esters
◦ Carboxylic Acid + Alcohol Ester + Water
◦ Carried out in the presence of an acid catalyst (e.g. conc
◦ sulfuric acid) and with gentle heating
◦ Examples
◦ Ethanoic acid + ethanol Ethyl ethanoate + water
◦ Methanoic acid + ethanol Ethyl Methanoate + water
• Propanoic Acid + Butanol Butyl Propanoate

5. Hydrolysis of Esters
◦ Hydrolysis means the break-up of a molecule
using water.
◦ Esters can be hydrolysed by both acids and alkalis.

6. Acid Hydrolysis of Esters
Acidic hydrolysis is simply the reverse of esterification. The ester is heated with a large excess of
water containing a strong-acid catalyst. Like esterification, the reaction is reversible and does not go
to completion.
As a specific example, butyl ethanoate and water react to form ethanoic acid and butanol. The
reaction is reversible and does not go to completion.
butyl ethanoate water ethanoic acid butanol

7. Base Hydrolysis of Esters
◦ When a base (such as sodium hydroxide [NaOH] or potassium hydroxide [KOH]) is used to
hydrolyze an ester, the products are a carboxylate salt and an alcohol. Alkaline hydrolysis breaks
up the ester completely.
◦ The reaction occurs in two stages:

8. Saponification
Soap is made from the
combination of a fat and an
alkaline material, which react
through a chemical process
called saponification.

9. References
◦ https://www.slideshare.net/AmyGilewska/esters-6912576
◦ Tindale, Ritchie et al, 2014, Chemistry for CSEC 2nd Edition, Nelson Thornes. Chapter 15, p263-266
◦ https://2012books.lardbucket.org/books/introduction-to-chemistry-general-organic-and-biological/s18-09-
hydrolysis-of-esters.html