A-LEVEL AQA ChEMISTRY NOTES
carboxylic acids and derivatives
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Carboxylic Acids & Esters
- Carboxylic acids have the functional group -COOH
- Carboxylic acids partially dissociate in water, making them weak acids
- Carboxylic acids can react with carbonates to liberate CO2.
2CH3COOH (aq) + Na2CO3 (s) → 2CH3COO^-Na^+ (aq) + CO2 (g) + H2O (l)
- Esters have the general formula RCOOR’.
- Esters can be made when alcohols and carboxylic acids are reacted in the presence of a sulphuric acid catalyst
- The alcohol gives the first part of the name and the acid gives the second part of the name
- Esters are used as solvents, plasticisers, perfumes and food flavourings
- Acid catalysed hydrolysis of esters forms a carboxylic acid and an alcohol
- Base catalysed hydrolysis of ester forms a carboxylate salt and an alcohol
- Vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol). Animal fats are saturated while vegetable fats are unsaturated. The kink caused by the double bond reduces London forced.
- Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap (salts of long-chain carboxylic acids) and glycerol with methanol and a strong alkaline catalyst
- Biodiesel is a mixture of methyl esters it can be made by reacting vegetable oils
- Acyl chlorides are a derivative of carboxylic acids, where the -OH group is replaced by a -Cl group
- Acyl chlorides react with alcohols to form esters in a nucleophilic addition-elimination reaction.
- Acyl chlorides will react with a variety of nucleophiles
- Mechanism for reaction with water (similar for other nucleophiles):
- An acid anhydride has the structure of a double ester that shares an oxygen atom
- Ethanoic anhydride is used to make aspirin.
- The advantages of using ethanoic anhydride rather than ethanoyl chloride is that: its cheaper, less corrosive, safer, produces a less toxic by-product and does not react with water readily.
- Amides structure:
- α-amino acids contain both the amine functional group and the carboxylic acid functional group (carboxyl group) attached to the same carbon atom.
- Amino acids are amphoteric, meaning they have both acidic and basic properties and can exist as zwitterions, having no charge overall.
- The isoelectric point is the pH at which the overall charge of a molecule is zero