STRUCTURE OF CARBOXYLIC ACIDS

1. STRUCTURE OF CARBOXYLIC ACIDS • contain the carboxyl functional group COOH • the bonds are in a planar arrangement • include a carbonyl (C=O) group and a hydroxyl (O-H) group

2. HOMOLOGOUS SERIES Carboxylic acids form a homologous series HCOOHCH3COOH C2H5COOH With more carbon atoms, there can be structural isomers C3H7COOH (CH3)2CHCOOH

3. INFRA-RED SPECTROSCOPY IDENTIFYING CARBOXYLIC ACIDS USING INFRA RED SPECTROSCOPY DifferentiationCompound O-H C=O ALCOHOLYESNO CARBOXYLIC ACIDYESYES ESTERNOYES ALCOHOL CARBOXYLIC ACID ESTER O-H absorption O-H + C=O absorption C=O absorption

4. NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules • select the longest chain of C atoms containing the COOH group; • remove the e and add oic acid after the basic name • number the chain starting from the end nearer the COOH group • as in alkanes, prefix with alkyl substituents • side chain positions are based on the C in COOH being 1 BUTANOIC ACID 2-METHYLPROPANOIC ACID

5. EXERCISE • Name the compounds at page 29 • Question 1a

6. CHEMICAL PROPERTIES ACIDITY weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq) form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l) The acid can be liberated from its salt by treatment with a stronger acid. e.g. RCOO¯ Na+(aq) + HCl(aq) ——> RCOOH + NaCl(aq) Conversion of an acid to its water soluble salt followed by acidification of the salt to restore the acid is often used to separate acids from a mixture. QUALITATIVE ANALYSIS Carboxylic acids are strong enough acids to liberate CO2 from carbonates Phenols are also acidic but not are not strong enough to liberate CO2

7. PREPARATION OF CARBOXYLIC ACIDS Oxidation of aldehydes RCHO + [O] ——> RCOOH Hydrolysis of esters RCOOR + H2O RCOOH + ROH

8. ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate Notes Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester Naming esters Named from the original alcohol and carboxylic acid CH3OH + CH3COOHCH3COOCH3+ H2O fromethanoic acidCH3COOCH3from methanol METHYLETHANOATE

9. ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE

10. HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2O CH3COOH + CH3OH alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt The carboxylic acid can be made by treating the salt with HCl CH3COO¯ Na+ + HCl ——> CH3COOH + NaCl

11. HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C2H5OH METHANOIC ETHANOL ACID ETHYL METHANOATE CH3COOH + CH3OH ETHANOIC METHANOL ACID METHYL ETHANOATE

14. phenylmethylethanoate

16. butylbutanoate

18. ethylethanoate

20. ethylbutanoate

22. ethylhexanoate

24. ethylmethanoate

26. ethylheptanoate

28. ethylnonanoate

30. ethylpentanoate

32. 2-methylpropylmethanoate

34. methylethanoate

36. pentylbutanoate

38. 1-methylethylethanoate