4.38C-4.40C - Ester functional group and esterification
Esters are a family of organic compounds with a particular functional group. In this lesson, the required example is ethyl ethanoate, made from ethanol and ethanoic acid in the presence of an acid catalyst. You also need to write its structural formula and its displayed formula clearly.
The ester functional group
An ester contains the ester functional group, -COO-. In a displayed formula, this means a carbon atom double-bonded to one oxygen atom and single-bonded to another oxygen atom:
[DIAGRAM: asset_name: Ester functional group and esterification - diagram 01; asset_slug: c60_ester_functional_group_and_esterification__diagram_01; recommended_method: image_gen; description: Monochrome Pearson-style displayed ester functional group showing O double-bonded to C and single-bonded O in a chain.]
Ester functional group
The ester functional group is -COO-, displayed as -C(=O)-O-.
The two oxygen atoms do different jobs in the displayed formula. One oxygen is double-bonded to the carbon. The other oxygen is single-bonded between the carbonyl carbon and the rest of the molecule. This is why an ester is not the same as a carboxylic acid: a carboxylic acid has -COOH, but an ester has -COO- joined on to another carbon group.
When you identify an ester in an exam, look for the exact C(=O)-O connection. Seeing two oxygen atoms somewhere in a formula is not enough.
Making ethyl ethanoate
The required ester in this lesson is ethyl ethanoate. Pearson names the two reactants you must know:
- ethanol
- ethanoic acid
Ethanol and ethanoic acid react in the presence of an acid catalyst to produce ethyl ethanoate. The acid catalyst increases the rate of reaction and is not used up overall.
[DIAGRAM: asset_name: Ester functional group and esterification - diagram 02; asset_slug: c60_ester_functional_group_and_esterification__diagram_02; recommended_method: image_gen; description: Monochrome reaction scheme showing ethanol plus ethanoic acid forming ethyl ethanoate plus water with acid catalyst above the arrow.]
The word equation is:
Esterification of ethanol and ethanoic acid
ethanol + ethanoic acid -> ethyl ethanoate + water
The matching structural-formula equation is:
Structural-formula equation
CH3CH2OH + CH3COOH -> CH3COOCH2CH3 + H2O
You may see a named acid catalyst in questions, such as sulfuric acid, but the specification point only requires the general condition: an acid catalyst.
Continue this lesson.
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