Carboxylic acids and derivatives

• Pure aspirin is whiter has larger crystals
• Impurities

  • lower value of MP
  • has a range of values for MP
• Ethanol as a solvent dissolves oil and alkali in hydrolysis of vegetable oil into carboxylate salt
• Advantage to fewer steps in production of aspirin


  better yield

  less energy used
• Advantage to having a higher % atom economy 


  less waste/pollution
• Reweighing the weighing boat decrease uncertainty and allow you to calculate the exact mass of reagent
• Test for acyl chloride 


  Silver nitrate - produce white precipitate
• Most likely impurity when making aspirin and how to avoid


  water, dry with filter paper/ absorbent paper
• Why is small volume of cold water poured over crystals?


  remove soluble impurities
• Why are crystals compressed in funnel?


  better drying because air is passed through not just around it
• Carboxylate salt used as soap
• Method to carry out to see whether a sample is pure or not

  • measure boiling point
  • use oil bath or melting point apparatus
  • melting point matches data source value if pure
• Factors that may decrease yield

  • product left in beaker
  • sample still wet
  • sample lost during recrystalication
• Minimum hot water used to..

  • ensure solution would be saturated
  • reduce amount left in solution
• why does filtering need to happen when hot

  prevent crystals from forming/ remove insoluble impurities
• Why is the flask left to cool

  Cooling increase yield of aspirin
• why are carboxylic acids weak?


  slightly dissociate but strong enough to displace carbon dioxide in carbonates
• Solubility of carboxylic acids 


  smaller carboxylic acids (C4) dissolve in water because they can form hydrogen bonds in water, but rapidly reduces after
• How to weaken carboxylic acids?


  increase chain length, pushes electron density onto COO- ion, more negative, less stable, weaker
• How to strengthen carboxylic acid?


  Electronegative chlorine atom withdrawn, withdraw electron density form COO- ion, less negative, more stable, stronger
• Carboxylic acid + metal -> salt + H2
• Carboxylic acid + alkali -> salt + water
• Carboxylic acid + carbonate -> salt + water + CO2
• Test for carboxylic acid 


  Solid Na2CO3/aqueous NaHCO3, effervescence
• Esterification


  RCOOH + -OH <> ester + water
• properties of esterification


  • under reflux
  • strong acid catalyst
  • low yield
  • reversible
• uses for esters 


  • Solvent
  • perfumes
  • plasticisers
• how can esters be used as perfumes?


  • soluble in solvent
  • non-toxic
  • does not react with water
• How can esters be a solvent?

  • polar, insoluble in water bc doesn't form hydrogen bonds
  • due to no hydrogen bonded to highly electronegative ion
• why does delocalisation occur?


  to stabilise carboxylic acid, more likely for dissociation to occur
• What happens if delocalisation doesn't occur?


  less stable because C=O shorter than C-O
• what happens to Pi charge when delocalisation occur?


  charge more spread out and more stable, more likely to form
• Fats and soap are esters of glycerol and long chain carboxylic acids
• Vegetable oil can be hydrolysed to produce glycerol and long chain fatty acids
• Glycerol is soluble in water because it can form hydrogen bonds easily
• Use for carboxylate salt


  soap
• how can water and grease mix in soap to get washed off?

  • CO2- end is hydrophilic and can mix with water
  • long chain non-polar hydrocarbon is hydrophilic and mix with grease
• Biodiesel is a mixture of methyl esters of long chain carboxylic acid
• How can biodiesel be formed?


  vegetable oil + methanol in presence of strong alkali catalyst
• why is acyl chloride better than acyl anhydride?


  • quicker reaction, not reversible