1.9 Derivatives of Carboxylic Acids Flashcards
describe the structural change that is undergone when a carboxylic acid is converted to an ester
The hydrogen in the -COOH group is replaced with an alkyl group (or possibly some more complex hydrocarbon group)
give the general group formula for an ester
RCOOR’
give the most common use for esters
artificial and natural flavours due to their fruity odour
Describe the boiling point trends of esters
- Small esters have boiling points similar to those of aldehydes and ketones with a similar RMM
- Are polar molecules - therefore have dipole-dipole interactions as well as Van Der Waals’ forces. However they don’t form H bonds with each other, so their boiling points aren’t as high as an acid with the same n number.
Describe the solubility of esters in water
- Small esters are readily soluble in water, but solubility falls with chain length increase.
- Esters can’t H bond with each other, but can form H bonds with water molecules
- There will also be VdW forces and dipole-dipole attractions
- As chain length increases, the hydrocarbon parts of the esters get in the way, and force themselves between water molecules, breaking the H bonds between water molecules. This makes the process energetically less profitable, and so solubility decreases.
describe the structural change that is undergone when a carboxylic acid is converted to an acyl chloride
-OH is replaced with a Cl
give the general group formula of an acyl chloride
RCOCl
describe the reactivity of acyl chlorides
- Very reactive as Cl- is a good leaving group - even poor nucleophiles will react.
- Will readily react with water, or even moisture in the air, to form a carboxylic acid.
- Therefore they’ll often ‘fume’ when open in the atmosphere.
how do nucleophiles react with acyl chlorides?
nucleophile attacks delta positive carbon-1, electrons move to Cl, which breaks off
give the general equation for a reaction between an acyl chloride and water
RCOCl + H2O -> RCOOH + HCl
Name the techniques for the preparation of esters
- from carboxylic acids + alcohol (esterification)
- from acyl chlorides + alcohol (esterification)
give the general equation for esterification of a carboxylic acid
RCOOH + R’OH -> RCOOR’ + H2O
what molecules form the water molecule in esterification of a carboxylic acid?
- OH from carboxylic acid
- H from alcohol
what is needed to catalyse the esterification of a carboxylic acid and alcohol and why is this used?
strong acid
The addition of the sulfuric acid increases the yield as it is a drying agent and removes the water, shifting equilibrium to the RHS. The yield can also be increased by adding excess acid or alcohol
Describe the conditions necessary in the esterification of an acyl chloride
Acyl chlorides undergo esterification readily with alcohols at room temperature. No heating is necessary and there is a good yield (note arrow isn’t reversible) as the reaction cannot reform the very reactive acyl chloride.
give the general equation of esterification of an acyl chloride with an alcohol
RCOCl + R’OH -> RCOOR’ + HCl
List some reactions that esters can undergo
acid-catalysed hydrolysis
base-catalysed hydrolysis
Describe the use of an acid catalyst in hydrolysis of an ester
The reaction needs to be catalysed by a strong acid as water is a very weak nucleophile.
Describe the conditions for acid-catalysed hydrolysis of an ester
reflux with HCl