6.1.3 - carboxylic acids and esters

• The general formula for carboxylic acids is R-COOH.
• The functional group of a carboxylic acid is COOH

  Made up of C=O and C-OH
• to name carboxylic acids you remove the ‘e’ and add the ending -oic acid
• Carboxylic acids are soluble in water. Because the acid group can form hydrogen bonds with water molecules.
• as chain length of carboxylic acid increases, solubility decreases.

  carboxylic acids are only soluble until butanoic acid
• The intermolecular forces in carboxylic acids are hydrogen bonds in the solid state which are very strong.
• To distinguish carboxylic acids from other OH containing compounds, test it by adding a metal carbonate. If it is a carboxylic acid effervescence will be observed due to the CO2 being produced.
• The equation for the reaction of ethanoic acid with NaOH:

  CH3COOH + NaOH ——> CH3COO-Na+ + H2O
• the equation for the reaction of ethanoic acid with Na2CO3:

  2CH3COOH + Na2CO3 ——> 2CH3COO-Na+ + H2O + CO2
• the equation for the reaction of ethanoic acid with CaO:

  2CH3COOH + CaO ——> (CH3COO)2Ca + H2O
• esters are formed from carboxylic acids and alcohols.

  they have the general formula RCOOR’
• Reaction of ethanoic acid with propan-1-ol

  CH3COOH + CH3CH2CH2OH ——> CH3COOCH2CH2CH3 + H2O
• To name esters, you start with the alcohol group

  eg, propanol becomes propyl

  then you use the carboxylic acid

  eg) ethanoic acid becomes ethanoate
• Esters are:

  volatile

  pleasant / fruity smells
• Esters are used for flavourings, perfumes, solvents or plasticisers
• To turn carboxylic acids and alcohols into esters, a concentrated strong acid catalyst must be used

  eg, sulfuric acid
• For the hydrolysis of esters in acidic conditions, a dilute strong acid catalyst is needed

  eg, sulfuric acid
• The two methods of ester hydrolysis are

  alkaline / base hydrolysis

  acidic hydrolysis
• Advantages of base hydrolysis is that:

  reaction goes to completion due to neutralisation by base

  more product in the mixture than acid catalysed hydrolysis.
• Carboxylic acid derivatives are molecules that have the Acyl group as part of their structure, formed from carboxylic acids
• The carboxylic acid derivatives include:

  Acyl chlorides: RCOCl

  acid anhydrides: RCOOR

  esters: RCOOR’

  Amide: RCONH2
• To form an Acyl chloride you need to react a carboxylic acid with SOCl2 (thionyl chloride)
• The mechanism for the Acylation of a nucleophile by an acid derivative

  
• Acyl chloride + ammonia —> HCl + amide
• Acid anhydride + ammonia —> carboxylic acid + amide
• ethanoyl chloride and ammonia:

  CH3COCl + NH3 ——> CH3CONH2 + HCl
• ethanoyl chloride and excess ammonia:

  CH3COCl + 2NH3 ——> CH3CONH2 + NH4Cl
• mechanism for ammonia and ethanoyl chloride

  
• Acyl chloride + primary amine —> HCl + N-substituted amide
• acid anhydride + primary amine —> carboxylic acid + N-substituted amide
• Ethanoyl chloride and methylamine:

  CH3COCl + CH3NH2 ——> CH3CONHCH3 + HCl
• Acyl chloride + alcohol —> HCl + ester
• acid anhydride + alcohol —> carboxylic acid + ester
• ethanoyl chloride and ethanol:

  CH3COCl + CH3CH2OH ——> CH3COOCH2CH3 + HCl
• Acyl chloride + water —> HCl + carboxylic acid
• acid anhydride + water —> carboxylic acid + carboxylic acid
• When water is added to an acid anhydride or an Acyl chloride the reaction is known as hydrolysis
• ethanoyl chloride and water:

  CH3COCl + H2O ——> CH3COOH + HCl