Esters

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 C n H 2n+1 COOC x H 2x+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 They aren’t able to take part in intermolecular bonding as well as carboxylic acids This also makes the larger esters very insoluble in water, but more soluble in organic solvents T hey 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 C arried 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