Module 6.1.3- Carboxylic acids and esters

• Carboxylic acid

  R-COOH

  
• Why can carboxylic acids form hydrogen bonds with water?

  The C=O and O-H bonds in carboxylic acids are polar
• As the number of carbon atoms increases, the solubility...


  ...decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule
• Carboxylic acids in acid reactions form a....

  carboxylate ion

  
• Carboxylic acid + metal (redox reaction)

  carboxylate salt + hydrogen

  effervescence

  
• Carboxylic acid + metal oxide(neutralisation reaction)


  carboxylate salt + water

  
• Carboxylic acid + alkali(neutralisation reaction)


  carboxylate salt + water

  e.g. ethanoic acid + NaOH -> sodium ethanoate + water

  ionic equation: H+ + OH- -> H2O

  
• Carboxylic acid + carbonate

  carboxylate salt + water + carbon dioxide

  
• Test for carboxyl group


  Add carbonate

  CO2 has evolved since carboxylic acids are the ones mainly strong enough to react with carbonate (weak base) unlike phenols
• Carboxylic acid derivative

  A compound that can be created from a carboxylic acid by nucleophilic acyl substitution; includes anhydrides, esters, and amides.

  All have an acyl group

  
• Naming an ester suffix


  -oate

  alkyl chain attached the O (the OR on the picture) of the COO group is added as the first word of the name

  
• Acyl chloride

  -COCl

  
• Naming an acyl chloride


  -oyl chloride

  e.g the picture is called methanoyl chloride

  
• Acid anhydride

  condensation reaction of 2 carboxylic acids

  -oic anhydride

  OCOCO

  
• Esterification


  The reaction of an alcohol with a carboxylic acid to produce an ester and water.

  Both warmed with H2SO4 catalyst

  
• Reagents for esterification between alcohol and carboxylic acid

  Warmed with H2SO4 catalyst
• naming an ester


  -oate

  e.g ethyl propanoate

  
• Acid hydrolysis of esters

  Ester + water --> carboxylic acid + alcohol

  Reagents: heated under reflux with dilute aqueous acid

  
• Reagents of acid hydrolysis of esters


  Heated under reflux with dilute aqueous acid

  or

  hot aqueous acid
• Alkaline hydrolysis of esters


  Ester + NaOH -> carboxylate salt + alcohol

  or

  Ester + OH- -> carboxylate ion + alcohol

  Reagents: heated under reflux with aqueous hydroxide ions

  
• Reagents for alkaline hydrolysis of esters

  Heated under reflux with aqueous hydroxide ions

  or

  Hot aqueous alkali
• Acid anhydride + alcohol

  ester + carboxylic acid
• Acyl chloride + alcohol

  Ester + HCl

  
• Acyl chloride + phenol

  Phenyl ester + HCl
• Why is acyl chloride/acid anhydride used instead of carboxylic acids


  They are more reactive
• Acyl chloride + water

  Carboxylic acid + HCl <-- steamy fumes, violent reaction

  
• Acyl chloride + ammonia

  Primary amide + ammonium chloride

  
• Acyl chloride + amine

  Secondary amide + ammonium chloride

  
• Synthesis of acyl chlorides


  acyl chlorides can be prepared directly from their carboxylic acid

  e.g. to form propanoyl chloride you would need propanoic acid.

  Reagents: SOCl2

  
• Reagents for preparing acyl chlorides

  SOCl2/ Thionyl chloride(produces HCl fumes)