AN INTRODUCTION TO CARBOXYLIC ACIDS AND THEIR DERIVATIVES KNOCKHARDY PUBLISHING

CONTENTS Structure of carboxylic acids Nomenclature Physical properties of carboxylic acids Preparation of carboxylic acids Chemical properties of carboxylic acids Esters Acyl chlorides Revision check list CARBOXYLIC ACIDS

STRUCTURE OF CARBOXYLIC ACIDS contain the carboxyl functional group COOH the bonds are in a planar arrangement

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

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’

HOMOLOGOUS SERIES HCOOH CH 3 COOH C 2 H 5 COOH 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

INFRA-RED SPECTROSCOPY IDENTIFYING CARBOXYLIC ACIDS USING INFRA RED SPECTROSCOPY DifferentiationCompoundO-H C=O ALCOHOLYES NO CARBOXYLIC ACIDYES YES ESTER NO YES ALCOHOL CARBOXYLIC ACID ESTER O-H absorption O-H + C=O absorption C=O absorption

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 e.g. CH 3 - CH(CH 3 ) - CH 2 - CH 2 - COOH is called 4-methylpentanoic acid 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 NAMING CARBOXYLIC ACIDS METHANOIC ACIDETHANOIC ACID PROPANOIC ACID

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

101°C 118°C 141°C 164°C PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces

Greater branching = lower inter-molecular forces = lower boiling point Boiling point is higher for “straight” chain isomers. 101°C 118°C 141°C 164°C 164°C 154°C PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces

PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces Carboxylic acids have high boiling points for their relative mass The effect of hydrogen bonding on the boiling point of compounds of similar mass CompoundFormulaM r b. pt. (°C)Comments ethanoic acidCH 3 COOH propan-1-olC 3 H 7 OH60 97 h-bonding propanalC 2 H 5 CHO58 49 dipole-dipole butaneC 4 H basic V der W

PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces 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

PHYSICAL PROPERTIES SOLUBILITY carboxylic acids are soluble in organic solvents they are also soluble in water due to hydrogen bonding HYDROGEN BONDING

PHYSICAL PROPERTIES SOLUBILITY carboxylic acids are soluble in organic solvents they are also soluble in water due to hydrogen bonding small ones dissolve readily in cold water as mass increases, the solubility decreases benzoic acid is fairly insoluble in cold but soluble in hot water HYDROGEN BONDING

PREPARATION OF CARBOXYLIC ACIDS Oxidation of aldehydesRCHO + [O] ——> RCOOH Hydrolysis of estersRCOOR + H 2 O RCOOH + ROH Hydrolysis of acyl chloridesRCOCl + H 2 O ——> RCOOH + HCl Hydrolysis of nitrilesRCN + 2 H 2 O ——> RCOOH + NH 3 Hydrolysis of amidesRCONH 2 + H 2 O ——> RCOOH + NH 3

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)

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) 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.

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) 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 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

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

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 ETHYL METHANOATE METHYL ETHANOATE

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 or acyl chlorides ReactivityUnreactive compared with acids and acyl chlorides ETHYL METHANOATE METHYL ETHANOATE

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 or acyl chlorides ReactivityUnreactive compared with acids and acyl chlorides IsomerismEsters are structural isomers of carboxylic acids ETHYL METHANOATE METHYL ETHANOATE

Classification CARBOXYLIC ACID ESTER Functional Group R-COOH R-COOR Name PROPANOIC ACID METHYL ETHANOATE Physical propertiesO-H bond gives rise No hydrogen bonding to hydrogen bonding; insoluble in water get higher boiling point and solubility in water Chemical propertiesacidic fairly unreactive reacts with alcohols hydrolysed to acids STRUCTURAL ISOMERISM – FUNCTIONAL GROUP

PREPARATION OF ESTERS - 1 Reagent(s)alcohol + carboxylic acid Conditionsreflux with a strong acid catalyst (e.g. conc. H 2 SO 4 ) 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 For more details see under ‘Reactions of carboxylic acids’

PREPARATION OF ESTERS - 2 Reagent(s)alcohol + acyl chloride Conditionsreflux under dry conditons Equation e.g. CH 3 OH (l) + CH 3 COCl (l) ——> CH 3 COOCH 3 (l) + HCl (g) methanol ethanoyl methyl chloride ethanoate NotesAcyl chlorides are very reactive but must be kept dry as they react with water

PREPARATION OF ESTERS - 3 Reagent(s)alcohol + acid anhydride Conditionsreflux under dry conditons Equation e.g. CH 3 OH (l) + (CH 3 CO) 2 O (l) ——> CH 3 COOCH 3 (l) + CH 3 COOH (l) methanol ethanoic methyl ethanoic anhydride ethanoate acid NotesAcid anhydrides are not as reactive as acyl chlorides so the the reaction is slower. The reaction is safer - it is less exothermic. Acid anhydrides are less toxic.

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C 2 H 5 OH METHANOIC ETHANOL ACID ETHYL METHANOATE

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C 2 H 5 OH METHANOIC ETHANOL ACID 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 alkaline CH 3 COOCH 3 + NaOH ——> CH 3 COO¯ Na + + CH 3 OH

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 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

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 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 The carboxylic acid can be made by treating the salt with HCl CH 3 COO¯ Na + + HCl ——> CH 3 COOH + NaCl

USES OF ESTERS Despite being fairly chemically unreactive, esters are useful as... flavouringsapple2-methylbutanoate pear3-methylbutylethanoate banana1-methylbutylethanoate pineapplebutylbutanoate rum2-methylpropylpropanoate solventsnail varnish remover - ethyl ethanoate plasticisers

ACYL CHLORIDES NomenclatureNamed from the corresponding carboxylic acid remove -ic add -yl chloride CH 3 COCl ethanoyl chloride C 6 H 5 COCl benzene carbonyl (benzoyl) chloride Chemical Properties colourless liquids which fume in moist air attacked at the positive carbon centre by nucleophiles these include water, alcohols, ammonia and amines undergo addition-elimination reactions

ACYL CHLORIDES ReagentWater Product(s)carboxylic acid + HCl (fume in moist air / strong acidic solution formed) Conditionsroom temperature EquationCH 3 COCl(l) + H 2 O(l) ——> CH 3 COOH(aq) + HCl(aq) Mechanismaddition-elimination

ACYL CHLORIDES ReagentAlcohols Product(s)ester + hydrogen chloride Conditions reflux in dry (anhydrous) conditions EquationCH 3 COCl(l) + CH 3 OH(l) ——> CH 3 COOCH 3 (l) + HCl(g) Mechanismaddition-elimination Note esters can also be made from acids and alcohols via carboxylic acids slower, reversible, low yield via acyl chlorides faster, better yield, must be dry

ACYL CHLORIDES ReagentAmmonia Product(s)amide + hydrogen chloride Conditions Low temperature and excess ammonia; vigorous reaction. EquationCH 3 COCl(l) + NH 3 (aq) ——> CH 3 CONH 2 (s) + HCl(g) orCH 3 COCl(l) + 2NH 3 (aq) ——> CH 3 CONH 2 (s) + NH 4 Cl(s) Mechanismaddition-elimination

ACYL CHLORIDES ReagentAmines Product(s)N-substituted amide + hydrogen chloride Conditions anhydrous EquationCH 3 COCl + C 2 H 5 NH 2 ——> CH 3 CONHC 2 H 5 + HCl orCH 3 COCl + 2C 2 H 5 NH 2 ——> CH 3 CONHC 2 H 5 + C 2 H 5 NH 3 Cl Mechanismaddition-elimination - similar to that with ammonia.

REVISION CHECK What should you be able to do? Recall and explain the physical properties of carboxylic acids Recall the structures of carboxylic acids, esters and acyl chlorides Recall the acidic properties of carboxylic acids Recall and explain the esterification of carboxylic acids Write balanced equations representing any reactions in the section Recall and explain the structure and naming of esters Recall the methods for making esters Recall the conditions for, and products of, the hydrolysis of esters.