CARBOXYLIC ACIDS AND THEIR REACTIONS KNOCKHARDY PUBLISHING 2015 SPECIFICATIONS

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 are isomeric with esters :- RCOOR’

Carboxylic acids form a homologous series HOMOLOGOUS SERIES HCOOH CH 3 COOH C 2 H 5 COOH With more carbon atoms, there can be structural isomers C 3 H 7 COOH (CH 3 ) 2 CHCOOH

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 NAMING CARBOXYLIC ACIDS BUTANOIC ACID2-METHYLPROPANOIC ACID

NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules Many carboxylic acids are still known under their trivial names, some having been called after characteristic properties or their origin. FormulaSystematic name (trivial name)origin of name HCOOH methanoic acid formic acidlatin for ant CH 3 COOH ethanoic acid acetic acidlatin for vinegar C 6 H 5 COOH benzenecarboxylic acidbenzoic acidfrom benzene

PHYSICAL PROPERTIES BOILING POINT Increases as size increases - higher induced dipole-dipole interactions Carboxylic acids have high boiling points for their relative mass arises from inter-molecular hydrogen bonding due to polar O—H bonds AN EXTREME CASE... DIMERISATION extra inter-molecular attraction = more energy to separate molecules HYDROGEN BONDING

CHEMICAL PROPERTIES ACIDITY weak acidsRCOOH + H 2 O (l) RCOO¯ (aq) + H 3 O + (aq) form saltsRCOOH + NaOH (aq) ——> RCOO¯Na + (aq) + H 2 O (l) 2RCOOH + Mg (s) ——> (RCOO¯) 2 Mg 2+ (aq) + H 2 (g) The acid can be liberated from its salt by treatment with a stronger acid. e.g.RCOO¯ Na + (aq) + HC l (aq) ——> RCOOH + NaC l (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 CO 2 from carbonates Phenols are also acidic but not are not strong enough to liberate CO 2.

ESTERIFICATION Reagent(s)alcohol + strong acid catalyst (e.g. conc. H 2 SO 4 ) Conditionsreflux Productester Equation e.g.CH 3 CH 2 OH (l) + CH 3 COOH (l) CH 3 COOC 2 H 5 (l) + H 2 O (l) ethanol ethanoic acid ethyl ethanoate NotesConc. H 2 SO 4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester

ESTERIFICATION Reagent(s)alcohol + strong acid catalyst (e.g conc. H 2 SO 4 ) Conditionsreflux Productester Equation e.g.CH 3 CH 2 OH (l) + CH 3 COOH (l) CH 3 COOC 2 H 5 (l) + H 2 O (l) ethanol ethanoic acid ethyl ethanoate NotesConc. H 2 SO 4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester Naming estersNamed from the original alcohol and carboxylic acid CH 3 OH + CH 3 COOH CH 3 COOCH 3 + H 2 O from ethanoic acid CH 3 COOCH 3 from methanol METHYL ETHANOATE

CHLORINATION OF CARBOXYLIC ACIDS Chlorinationinvolves replacing the OH with a C l Productacyl chloride Reagentthionyl chloride SOC l 2 ConditionsDRY conditions EquationCH 3 COOH + SOC l 2 ——> CH 3 COC l + SO 2 + HC l Alternative methodCH 3 COOH + PC l 5 ——> CH 3 COC l + POC l 3 + HC l phosphorus(V) chloride

ACYL CHLORIDES Structure Replace the OH of a carboxylic acid with a C l atom NomenclatureNamed from corresponding acid … remove -ic add -yl chloride CH 3 COC l ethanoyl (acetyl) chloride C 6 H 5 COC l benzene carbonyl (benzoyl) chloride ETHANOYL CHLORIDE

ESTERS StructureSubstitute an organic group for the H in carboxylic acids Nomenclaturefirst part from alcohol, second part from acid e.g. methyl ethanoate CH 3 COOCH 3 PreparationFrom carboxylic acids, acyl chlorides and acid anhydrides ReactivityUnreactive compared with acids and acyl chlorides ETHYL METHANOATE METHYL ETHANOATE

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C 2 H 5 OH METHANOIC ETHANOL ACID CH 3 COOH + CH 3 OH ETHANOIC METHANOL ACID ETHYL METHANOATE METHYL ETHANOATE

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH 3 COOCH 3 + H 2 O CH 3 COOH + CH 3 OH The reaction with pure water is so slow that it is never used. The reaction is catalysed by dilute acid, and so the ester is heated under reflux with a dilute acid like dilute hydrochloric acid or dilute sulphuric acid. alkaline CH 3 COOCH 3 + NaOH ——> CH 3 COO¯ Na + + CH 3 OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt