Name esters, identify their building blocks and split ester links.
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Method and worked examples
An ester contains –C(=O)–O– between carbon-containing groups. Its name gives the alcohol-derived alkyl group first, followed by the acid-derived carboxylate name: CH3COOCH2CH3 is ethyl ethanoate. Acid plus alcohol can form ester plus water in a reversible condensation. Heating under reflux retains volatile reactants while increasing reaction rate; an acid catalyst speeds the reaction without changing Kc.
Acidic hydrolysis gives a carboxylic acid and an alcohol. Alkaline hydrolysis gives a carboxylate salt and an alcohol. To split a link, restore OH to the carbonyl side and H to the oxygen-bearing side, then apply the stated pH. A diol and a dicarboxylic acid can form a polyester because each monomer can connect at two sites.
Example 1
Name CH3CH2COOCH3 and identify its condensation reactants.
It is methyl propanoate. The acid-derived part is CH3CH2COOH (propanoic acid) and the alcohol-derived part is CH3OH (methanol). Water is released.
Example 2
State products of alkaline hydrolysis of ethyl ethanoate with NaOH.
CH3COOCH2CH3+ NaOH → CH3COONa + CH3CH2OH. The products are sodium ethanoate and ethanol, not free ethanoic acid in alkaline solution.
Watch out:Alkaline hydrolysis produces a carboxylate ion or salt; free acid is the acidic-condition product.
Esters, hydrolysis and polyesters practice | Year 12 Chemistry | Ascent Arcade