Esters
Introduced| English | Meaning |
|---|---|
| ester/ˈestə/ | An organic compound containing a carbonyl group bonded to an oxygen atom that is bonded to another carbon group. |
| condensation/kɒndenˈseɪʃn/ | A chemical reaction in which molecules join and a small molecule, commonly water, is eliminated. |
| reversible/rɪˈvɜːsɪbl/ | reversible |
| esterification/ˌestəˌrɪfɪˈkeɪʃn/ | A reaction that forms an ester, commonly by reacting an alcohol with a carboxylic acid. |
| hydrolysis/haɪˈdrɒləsɪs/ | Breaking chemical bonds by reaction with water. |
| carboxylate/ˈkɑːbəksɪleɪt/ | carboxylate |
The smell of perfumes and fruit
- An ester 酯 has the –COO– group.
- It often smells sweet or fruity.
- It is made from an alcohol and a carboxylic acid, and can be split back apart.
Ester route lab
Follow ester formation and hydrolysis as reversible paths.
Esters are often recognised by their:
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Many esters have pleasant, fruity smells.
An ester is made by reacting a carboxylic acid with an ______.
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Esterification, usually with an acid catalyst.
Making esters
- An ester forms by condensation 缩合 of an alcohol and a carboxylic acid (conc. $\text{H}_2\text{SO}_4$ catalyst). A water molecule is lost, and the reaction is reversible 可逆:
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \rightleftharpoons \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Esterification 酯化 joins an acid and an alcohol, losing water
An ester is made by reacting:
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Esterification is a reversible condensation of an alcohol and a carboxylic acid, releasing water.
Match each ester fact.
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Each item links the term to its correct meaning.
Hydrolysis 水解 of esters
The conditions change the products:
- dilute acid, heat (reversible) → the carboxylic acid + the alcohol.
- dilute alkali, heat (not reversible) → the carboxylate 羧酸盐 salt + the alcohol.
Esters give many fruits and perfumes their sweet smell.
Hydrolysing an ester with dilute acid gives:
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Acid hydrolysis is the reverse of esterification, giving back the carboxylic acid and alcohol.
Hydrolysing an ester with dilute alkali gives:
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Alkali hydrolysis gives the salt of the carboxylic acid (plus the alcohol) and is not reversible.
Making an ester
Worked example. Ethanol + ethanoic acid, warmed with a little concentrated sulfuric acid, gives the sweet-smelling ester ethyl ethanoate plus water.
You've got it
- an ester = –COO– group, often sweet-smelling
- made by condensation of alcohol + carboxylic acid (conc. H₂SO₄, water lost, reversible)
- acid hydrolysis (reversible) → acid + alcohol; alkali hydrolysis (not reversible) → carboxylate salt + alcohol