Lecture on Esters and Their Properties

Introduction to Esters

• Esters are derivatives of carboxylic acids.
• Formation: A generic carboxylic acid can be converted into an ester.
• This lecture focuses on naming esters, not the mechanisms of their formation.

Naming Esters

• Step 1: Identify the R-prime group attached to the oxygen in the ester.
  • Name this R-prime group as an alkyl group.
• Step 2: Consider the carboxylic acid part.
  • Use the name of the originating carboxylic acid.
  • Drop the suffix "-ic acid" and add "-ate" to the root name.

Naming Examples

1. Ethyl Acetate

   • R-prime: Ethyl (two-carbon alkyl group)
   • Acid: Acetic acid → Acetate
   • Name: Ethyl acetate or Ethyl ethanoate (IUPAC)

2. Diethyl Malonate

   • R-prime: Diethyl (two identical ethyl groups)
   • Acid: Malonic acid (Propanedioic acid in IUPAC) → Malonate
   • Name: Diethyl malonate

3. Methyl Salicylate (Oil of Wintergreen)

   • R-prime: Methyl
   • Acid: Salicylic acid → Salicylate
   • Name: Methyl salicylate

4. Methyl Cyclohexanecarboxylate

   • R-prime: Methyl
   • Acid: Cyclohexanecarboxylic acid → Cyclohexanecarboxylate
   • Name: Methyl cyclohexanecarboxylate

Physical Properties of Esters

Boiling Points

• Compared molecules: 2-methylbutane (alkane), methyl acetate (ester), 2-butanol (alcohol)
• Boiling point order:
  • 2-methylbutane: 28°C (only London dispersion forces)
  • Methyl acetate: 57°C (dipole-dipole interactions)
  • 2-butanol: 99°C (hydrogen bonding)
• Conclusion: Methyl acetate has a boiling point between that of the non-polar alkane and polar alcohol due to its moderate polarity.

Solubility in Water

• Water is polar, allowing hydrogen bonding with esters.
• Methyl acetate: Soluble in water (due to hydrogen bonding potential)
• Increasing carbon chain length in esters reduces solubility due to increased non-polar character.
• Example: Ethyl acetate, with more carbons than methyl acetate, is less soluble in water and can extract non-polar substances like caffeine.

Summary

• Esters have unique naming conventions based on the structure and originating acids.
• They exhibit specific boiling points due to intermolecular forces and have variable solubility in water depending on chain length and polarity.