Ester (organic)
An ester is an organic compound formed when a carboxylic acid reacts with an alcohol in a condensation reaction (esterification), with the loss of a water molecule, producing the functional group –COO– (or –RCOOR'). Esters are responsible for many characteristic fruit aromas and flavors, and they occur naturally in fats and oils (triglycerides are esters of glycerol and fatty acids). Industrially, esters are used as plasticizers, solvents, perfumes, and biodiesel components.
Key Formula
R-COOH + R'-OH → R-COO-R' + H2O (acid-catalyzed esterification)
LaTeX: R\text{-}COOH + R'\text{-}OH \xrightarrow{H^+, \Delta} R\text{-}COO\text{-}R' + H_2O
| Symbol | Meaning | Unit |
|---|---|---|
| R | alkyl/aryl group from the carboxylic acid | none |
| R' | alkyl group from the alcohol | none |
| H⁺ | acid catalyst (e.g., H₂SO₄) | none |
| Δ | heat applied to drive reaction forward | none |
Worked Example
Problem
Write the balanced equation for the esterification of ethanol (C₂H₅OH) with acetic acid (CH₃COOH) to form ethyl acetate, and calculate the theoretical yield when 46 g of ethanol reacts with excess acetic acid.
Solution
Step 1: Balanced equation: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. Step 2: Molar mass of C₂H₅OH = 2(12.01) + 6(1.008) + 16.00 = 46.07 g/mol. Step 3: Moles of ethanol = 46 g ÷ 46.07 g/mol = 0.998 mol. Step 4: Mole ratio ethanol : ethyl acetate = 1:1, so moles of product = 0.998 mol. Step 5: Molar mass of CH₃COOC₂H₅ = 4(12.01) + 8(1.008) + 2(16.00) = 88.11 g/mol. Step 6: Theoretical yield = 0.998 × 88.11 = 87.95 g.
Answer
Theoretical yield of ethyl acetate = 87.95 g
Common Esters, Their Aromas, and Uses
| Name | Formula | Parent Acid | Parent Alcohol | Aroma/Use |
|---|---|---|---|---|
| Ethyl acetate | CH₃COOC₂H₅ | Acetic acid | Ethanol | Pear/glue solvent |
| Isoamyl acetate | CH₃COOC₅H₁₁ | Acetic acid | Isoamyl alcohol | Banana flavoring |
| Methyl salicylate | HOC₆H₄COOCH₃ | Salicylic acid | Methanol | Wintergreen (deep heat) |
| Ethyl butyrate | C₃H₇COOC₂H₅ | Butyric acid | Ethanol | Pineapple flavoring |
| Glyceryl tristearate | (C₁₇H₃₅COO)₃C₃H₅ | Stearic acid | Glycerol | Animal fat (tristearin) |
Interactive Tools
Khan Academy — Carboxylic Acids and Derivatives
Video lessons on ester formation, hydrolysis, and saponification
Open Tool
Wikimedia Commons, CC BY-SA
Related Terms
Carboxylic Acid
A carboxylic acid is an organic compound containing a carboxyl group (–COOH), which consists of both a carbonyl (C=O) and a hydroxyl (–OH) group attached to the same carbon. Carboxylic acids are weak acids that partially dissociate in water to donate a proton (H⁺) from the –OH group, with the resulting carboxylate anion stabilized by resonance. They are widespread in biology (amino acids, fatty acids, citric acid cycle intermediates) and industry (acetic acid for vinegar, benzoic acid as a preservative).
Alcohol (organic)
In organic chemistry, an alcohol is a compound in which a hydroxyl group (–OH) is bonded to a saturated carbon atom. Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on how many carbon atoms are attached to the carbon bearing the –OH group. They are among the most versatile compounds in synthesis and commerce, serving as solvents, antiseptics, fuels, and precursors to aldehydes, ketones, and carboxylic acids.
Functional Group
A functional group is a specific atom or group of atoms within an organic molecule that determines its characteristic chemical reactions and physical properties. Functional groups are the reactive centers of organic molecules; the carbon skeleton (backbone) largely determines size and shape, while the functional group dictates behavior. Identifying functional groups is the foundation of systematically predicting and classifying organic reactions.
From German "Äther" (ether) + "-ster" suffix, coined by Leopold Gmelin in 1848. Gmelin used "Essigäther" (acetic ether) for ethyl acetate, and the shortened "Ester" became standard. The term reflects the historical connection to ethers perceived in early reactions of acids with alcohols.