Carboxylic acids

• Mechanism of amine with acyl chloride?


  Nucleophilic addition-elimination

  
• Recrystallisation step reasons?


  Using minimum quantity of hot water= to ensure solution is saturated.

  Flask left to cool at room temp= yield will be higher.

  Crystals were compressed in a funnel= air passes through sample instead of around it.

  Water was poured through crystals= remove soluble impurities.
• What impurity would cause the crystals melting point to be lower than in the data book?


  Water.

  Press crystal samples between filter paper to ensure dry.
• Recrystallisation to purify solid product method?


  Dissolve product in minimum volume of hot water. Allow solution to cool and crystals to form. Filter off product using Buchner funnel under reduced pressure.
• Why would yield for recrystallisation not be 100%?


  Product left over in beaker, sample still wet, sample lost during reaction.
• Why is ethanoic anhydride safer than ethanoyl chloride?


  Ethanoyl chloride reacts more vigorously with water and produces corrosive HCl fumes. Also is more expensive.
• How to show presence for alcohol in mixture?


  Add potassium dichromate, oxidising alcohol to an aldehyde/ketone.
• How to show presence of carboxylic acid in mixture?


  Add sodium carbonate, producing effervescence.
• How can you determine an accurate melting point?


  Heat melting point tube in oil bath slowly until near melting point.
• How to test for an unknown halide ion?


  Add silver nitrate (AgNO3)

  Chloride= white precipitate.

  Bromide= Cream precipitate.

  Iodide= Yellow precipitate.
• Define a nucleophile?


  Electron pair donor. Positive seeking.
• Mechanism of acyl chloride with EXCESS ammonia?


  Nucleophilic substituition.
• Why might benzene not react with ammonia under normal conditions?


  Electron rich ring repels nucleophile.
• colour change when potassium dichromate has reacted?


  Orange > Green.
• Safety precaution with volatile, flammable liquids?


  Keep away from naked flames.
• IUPAC name for glycerol?


  propan-1,2,3-triol
• Properties of esters?


  Perfumes, food flavourings.

  Low boiling points, easily evaporated.

  Plasticisers.
• Reaction with carbonates?


  carboxylic acid + CO3^2- > salt + H2O + CO2
• Esterification reaction?


  Carboxylic acid + alcohol > ester + water

  H2SO4 catalyst.
• Acid hydrolysis of ester?


  Reflux ester with H2SO4.

  Ester + water > acid + alcohol
• Base hydrolysis of ester?


  reflux ester with NaOH.

  Ester + water > carboxylate ion + alcohol.
• Why do fats have a higher boiling point than oils?


  Fats contain mainly saturated fatty acid chains so fit closer and have stronger Van Der Waals forces.
• Hydrolysis of fats and oils?


  Fat/oil + NaOH > glycerol + carboxylate ion.

  Salt can convert back into fatty acid by adding HCl,
• How to make biodiesel?


  Fat/oil + methanol > glycerol + methyl ester

  NaOH catalyst.
• Acid anhydride + ? = ?


  water= 2x carboxylic acid

  alcohol= ester + carboxylic acid

  amine= N-substituted amide + carboxylic acid

  ammonia= amide + carboxylic acid
• Manufacture of ester Aspirin?


  Salicylic acid + ethanoic anhydride > aspirin + ethanoic acid.

  
• Acyl chloride + ? = ?


  water= carboxylic acid + HCl

  alcohol= ester + HCl

  Amine= N-substituted amide + HCl

  Ammonia= amide + HCl
• Reaction of acyl chlorides?


  Cl is substituted producing misty white fumes of HCl.
• Mechanisms of acyl chlorides


  Nucleophilic addition-elimination
• What process shows a recrystallisation product is pure?

  Measure the mp using an oil bath and compare with data source value.
• Why would the % yield from recrystallisation not be 100% pure?

  Product left in beaker.

  Sample still wet.
• Draw a diagram to show the apparatus you would use to filter the crude product under reduced pressure?

  Buchner funnel and vacuum flask.

  
• How would you determine an accurate value for the mp of aspirin?


  Heat in an oil bath, slowly until near the mp.
• Aldehydes can be prepared from acyl chlorides. How can an aldehyde be tested to show whether it is contaminated with traces of unreacted acyl chloride?

  Add silver nitrate.

  White ppt would form.
• Write an equation for the acyl chloride CH3COCl reacting with benzene?

  CH3COCl + Benzene > Phenylethanone + HCl
• Define the term nucleophile?

  Electron pair donor.
• What reaction occurs between a polyester and aq sodium hydroxide. Explain why the aq sodium hydroxide reacted with the polyester?

  Hydrolysis.

  Delta positive carbon in polyester reacts with hydroxide ion.
• What method would decrease the rate of hydrolysis of fats?


  Keeping the foodstuff dry.
• Suggest why anti-oxidants are not regarded as catalysts?

  They react with free radicals and are used up in the reaction.
• Suggest why a pure sample of aspirin may sometimes appear to melt at a temperature different from 135 °C?


  Temp on the thermometer isn't the same as the sample.