Esters: Formation and Properties

Esters are organic compounds formed by the reaction between an alcohol and a carboxylic acid. This section discusses the ester formation and hydrolysis process, as well as their uses and naming conventions.

Esters are formed through a condensation reaction, where two molecules join together and eliminate a small molecule (water in this case). The reaction typically requires a catalyst, such as sulfuric acid.

Definition: An ester is a molecule containing an ester linkage (-COO-) formed by the reaction between an alcohol and a carboxylic acid.

Naming esters follows a specific convention:

1. The first part of the name comes from the alcohol
2. The second part comes from the carboxylic acid, with the ending changed to "-oate"

Example: Ethyl ethanoate is formed from ethanol and ethanoic acid.

Esters have various applications due to their pleasant, fruity smells: • Used as flavoring agents and fragrances • Employed as solvents for non-polar compounds that don't dissolve in water

The hydrolysis of esters is the reverse process of ester formation, where water splits the ester into its constituent alcohol and carboxylic acid. This reaction is usually catalyzed by an acid.

Vocabulary: Hydrolysis - The splitting of a compound using water.

Fats and Oils: Structure and Properties

Fats and oils are important biological molecules classified as triesters or triglycerides. This section explores their structure, properties, and reactions.

Fats and oils are formed from the condensation of glycerol (propane-1,2,3-triol) with three carboxylic acid molecules, resulting in a 3:1 ratio of fatty acids to glycerol.

Definition: Triglycerides are esters formed from the condensation of glycerol and three carboxylic acid molecules.

The key differences between fats and oils are:

Fats: • Solid at room temperature • Contain saturated molecules with a "tuning fork" structure • Molecules can pack tightly, resulting in stronger London dispersion forces and higher melting points

Oils: • Liquid at room temperature • Contain unsaturated molecules with double bonds, causing kinks in the structure • Molecules cannot pack as tightly, resulting in weaker London dispersion forces and lower melting points

Highlight: Oils can be hardened through hydrogenation, a process that adds hydrogen to unsaturated bonds using a nickel catalyst.

The hydrolysis of fats and oils produces three fatty acid molecules and one glycerol molecule. This process is important in the production of soaps and in the digestion of lipids in the body.

Example: The hydrogenation of oils is used in the food industry to produce solid fats from liquid oils, such as in the production of margarine.

Soaps: Structure and Cleaning Action

Soaps are produced through the alkaline hydrolysis of edible fats and oils. This section discusses the structure and cleaning action of soaps, as well as their interaction with hard water.

Soap molecules have a unique structure: • A non-polar (hydrophobic) tail soluble in fats and other non-polar substances • An ionic (hydrophilic) head soluble in water and other polar substances

Definition: Soaps are water-soluble, ionic salts produced by the alkaline hydrolysis of fats and oils.

The cleaning action of soaps involves:

1. Hydrophobic tails dissolving in oil or grease
2. Hydrophilic heads remaining in water
3. Agitation causing the formation of micelles
4. Oil or grease becoming suspended in water

Highlight: The dual nature of soap molecules (hydrophobic tail and hydrophilic head) allows them to effectively remove both polar and non-polar substances.

Hard water, which contains high levels of dissolved metal ions, can interfere with the cleaning action of soaps. When soap is used in hard water, an insoluble precipitate called "scum" is formed.

Vocabulary: Hard water - Water containing high levels of dissolved metal ions, typically calcium and magnesium.