A2- Esters
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How is an ester different to a carboxylic acid?
has an organic group attached to the O rather than a H
Describe the solubility of COOHs and RCOOR’s?
COOHs; smaller chains are soluble as they can form H bonds, as chain length increases, force of H bonds has less effect on whole molecule RCOOR’s; do not form H bonds and are insoluble
What are 3 uses of esters?
flavourings, perfumes, solvents
What is the word equation for the formation of esters using COOH?
alcohol + carboxylic acid -> ester + water
Why is concentrated H2SO4 used as a catalyst?
it is a dehydrating agent
What is hydrolysis?
reaction with water that breaks a compound in 2 (opposite of esterification)
When does hydrolysis occur?
under reflux
What is produced from hydrolysis in acidic conditions? (HCl)
carboxylic acid and alcohol
What is produced from hydrolysis in basic conditions? (NaOH)
salt and alcohol
What reaction conditions are needed to form esters?
reaction of COOH with an alcohol - strong acid catalyst - under reflux
What is the production of a carboxylate salt in base hydrolysis called?
saponification
Why are carboxylate salts used in soaps?
hydrophilic and hydrophobic properties
How are biodiesels made?
react vegetable oils with methanol in the presence of a metal hydroxide catalyst
How are vegetable oils and animal fats hydrolysed in alkaline conditions?
heated in alkaline conditions, produce soap (salts of COOHs) and glycerol
Why are the reactions forming esters condensation reactions?
form H2O molecule
How do you identify an ester?
smell sweet
Why are esters useful in scents?
• solvents • volatile so evaporate easily • distinctive smells
What is needed for basic hydrolysis?
• dilute base • NaOH • reflux
What is needed for acid hydrolysis?
• dilute acid • HCl or H2SO4 • reflux
How does an ester plasticiser work?
• by penetrating between the polymer chains and increasing the distance between them • weakens polar effects of bonds, allows polymers to slide over each other
Which hydrolysis reaction is irreversible?
basic hydrolysis
What other reaction is needed to reform carboxylic acids in alkaline ester hydrolysis?
acidification