Lactones- Meaning
Lactones are cyclic organic esters of hydroxycarboxylic acids, usually formed by the reaction of a halogen atom or hydroxyl group with a carboxylic acid group present in the same molecule. These are formed by intramolecular esterification of respective hydroxycarboxylic acids. It has a ring of two or more carbon atoms and one oxygen atom. Lactones with three or four-membered rings are highly reactive which makes it very difficult to isolate them.
Name of lactone is derived from a compound called Lactide; that is generated by the dehydration of lactic acid. These are named with a Greek letter prefix and lactone suffix. Prefixes indicate the size of the lactone ring.
Naturally occurring Lactones are of two types; Saturated and unsaturated. Few commonly found lactones in nature are kavain, ascorbic acid, gluconolactone, neurotransmitters, and antibiotics.
Table of Contents
Lactone-Synthesis
Many methods adopted for ester synthesis can be applied for Lactone synthesis. Methods include Shiina macro-lactonization, nucleophilic abstraction and Yamaguchi esterification. Lactones like γ-nonalactone,γ-octalactone, γ-undecalactone, γ-decalactone can be synthesised in a single step process.
Lactone- Reactions
The reactions of lactones are almost similar to the reactions of esters. Let’s have a look at some reactions.
- Hydrolysis
When a lactone along with a base (Sodium hydroxide) is heated, it hydrolyses into its parent compound. Lactone’s hydrolysis condensation reaction is a reversible reaction with equilibrium.
- Reduction
Lithium aluminium hydride reduces lactones to diols. The reaction involves the breaking of the ester bond and then the carboxylic acid group is reduced to the alcohol group.
- Polymerisation
Polyesters are formed by lactones.
- Aminolysis
Alcohol and amide are formed when lactones react with ethanolic ammonia.
Lactones- Examples and Uses
Lactones play a vital role in providing flavour to fruit and dairy products. Therefore, these are used as flavour and fragrances. Some lactones with their flavour are listed below.
- γ-decalactone – Peach flavour
- γ-dodecalactone – Coconut/fruit flavour
- γ- octalactone – Coconut/fruit flavour
- 0-decalactone – Creamy coconut/peach flavour
Some Examples of Lactones are Macrolides, Ellagic acid, Kavalactones, Lactide, Valoneic, Tergallic acid diactone.
Comments