Carboxylic Acids & Esters Flashcards
OH bonds in alcohols
- The OH bond in carboxylic acids forms hydrogen bonds. This means they have relatively high MP and BP compared to similar sized alkanes.
Solubility
- The COOH group is very soluble in water due to hydrogen bonding, but the hydrocarbon chain of a carboxylic acid is non-polar, so doesn’t dissolve in water.
- Whether a carboxylic acid is soluble depends on the length of the carbon chain:
Short chain carboxylic acids (up to butanoic acid) dissolve easily in water because the hydrocarbon chain part of the molecule is relatively short.
The longer a carboxylic acids is the less soluble it is. This is because the hydrocarbon chain part of the molecule is longer, and even though the COOH dissolves well, this is cancelled out by the insolubility of the chain.
Reactivity of Carboxylic Acids
- Carboxylic acids can act as acids and so act as a proton donor.
- All carboxylic acids are weak acids so the following equilibrium lies over to the left:
RCOOH → RCOO- + H+ - Carboxylic acids also undergo reactions with alcohols to form esters
Naming Esters
Forming Esters
Esters are formed from a carboxylic acid reacting with an alcohol.
- The reaction uses conc H2SO4 catalyst
- The reaction is reversible
- Condensation reaction
As the formation of an ester is reversible, esters can be turned back into their constituent carboxylic acid and alcohol via a hydrolysis reaction
Hydrolysis definition
breaking a bond using water
Acid catalysed hydrolysis
Base catalysed hydrolysis
Animal fats and vegetable oils
The tri-ester in animal fats and vegetable oils are essentially composed of glycerol (IUPAC Name: Propane-1,2,3-triol)
Acid Hydrolysis of tri-esters
Tri-esters from fats and oils can be hydrolysed in acidic conditions to form the constituent carboxylic acids and glycerol.
Base Hydrolysis of tri-esters
Tri-esters from fats and oils can be hydrolysed in alkaline conditions to form the constituent carboxylic acid salts and glycerol.
Dissolving fatty acids
The fatty acid salts dissociate in water:
RCOONa → RCOO- + Na+
Biodiesel definition
a mixture of methyl esters (made from methanol)
- used to conserve crude oil supplies and to reduce amount of CO2 released (biodiesel=carbon neutral)
Biodiesel
Uses of esters
- Solvents for many reactions
- Plasticisers (to make plastic objects more flexible)
- Perfumes
- Flavourings
Naming amines
Naming Amides
Naming acyl chlorides
CH3COCl = ethanoyl chloride
Acid anhydrides
Acylation with acid anhydride and alcohol
Acylation with acid anhydride and water
Acylation with acid anhydride and ammonia
Acylation with acid anhydride and amine
Nucleophilic Addition-Elimination with WATER
e.g. Ethanoyl Chloride with Water
Key points:
- When water is the nucleophile, a CARBOXYLIC ACID is the main product.
- HCl is also formed = steamy fumes
Overall Equation:
CH3COCl + H2O → CH3COOH + HCl
Nucleophilic Addition-Elimination with ALCOHOL
Ethanoyl Chloride and Propan-1-ol
Key points:
- When an alcohol is the nucleophile, an ESTER is the main product.
- HCl is also formed steamy fumes
Overall Equation:
CH3COCl + C3H7OH → CH3COOC3H7 + HCl
Nucleophilic Addition-Elimination with AMMONIA
Propanoyl Chloride and Ammonia
Key points:
- When ammonia is the nucleophile, an AMIDE is the main product.
- HCl is also formed, but because NH3 is also present these react to form Ammonium Chloride (NH4Cl) as the side product.
Overall Equation:
CH3CH2COCl + 2NH3 → CH3CH2CONH2 + NH4Cl
Nucleophilic Addition-Elimination with an AMINE
Propanoyl Chloride and Ethylamine
Key points:
- When an amine is the nucleophile, an N-Substituted AMIDE is the main product.
- HCl is also formed, but because an amine is also present these react to form an ammonium chloride salt as the side product.
Overall Equation:
CH3CH2COCl + 2CH3CH2NH2 → CH3COONHCH2CH3 + CH3CH2NH3Cl
Industrial Use
In industrial acylation reactions acid anhydrides are used much more commonly than acyl chlorides. This is because:
- They are cheaper
- They are less corrosive
- They don’t react with water
- They are safer as the side product is a carboxylic acid whereas acyl chlorides produce HCl vapours.
