STRUCTURE OF CARBOXYLIC ACIDSSTRUCTURE OF CARBOXYLIC ACIDS

• contain the carboxyl functional group COOH

• the bonds are in a planar arrangement

STRUCTURE OF CARBOXYLIC ACIDSSTRUCTURE 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

HOMOLOGOUS SERIESHOMOLOGOUS SERIES

HCOOH CH3COOH C2H5COOH

Carboxylic acids form a homologous series

Carboxylic acids form a homologous series

HOMOLOGOUS SERIESHOMOLOGOUS SERIES

HCOOH CH3COOH C2H5COOH

With more carbon atoms, there can be structural isomers

C3H7COOH (CH3)2CHCOOH

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 with the C in COOH being 1

• as in alkanes, prefix with alkyl substituents

• side chain positions are numbered relative to Carbon atom number 1

e.g. CH3 - CH(CH3) - CH2 - CH2 - COOH is called 4-methylpentanoic acid

NAMING CARBOXYLIC ACIDSNAMING 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 with the C in COOH being 1

• as in alkanes, prefix with alkyl substituents

• side chain positions are numbered relative to Carbon atom number 1

NAMING CARBOXYLIC ACIDSNAMING CARBOXYLIC ACIDS

BUTANOIC ACID 2-METHYLPROPANOIC ACID

NAMING CARBOXYLIC ACIDSNAMING 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.

Formula Systematic name (trivial name) origin of name

HCOOH methanoic acid formic acid latin for ant

CH3COOH ethanoic acid acetic acid latin for vinegar

C6H5COOH benzenecarboxylic acid benzoic acid from benzene

CHEMICAL PROPERTIESCHEMICAL PROPERTIES

Carboxylic acids are weak acids. They can donate protons, but they only partially dissociate into their ions.

weak acids CH3COOH (aq) CH3COO¯(aq) + H+(aq)

CHEMICAL PROPERTIESCHEMICAL PROPERTIES

Carboxylic acids display typical reactions of an acid and form salts, called carboxylates:

1. acid + base salt + water, eg.

CH3COOH + NaOH (aq) ——> CH3COO¯Na+ (aq) + H2O (l)

ethanoic acid sodium ethanoate

2. acid + carbonate salt + water + CO2, eg.

CH3COOH + NaCO3 (aq) ——> CH3COO¯Na+ (aq) + H2O (l) + CO2 (g)

ethanoic acid sodium ethanoate

QUALITATIVE ANALYSISCarboxylic acids are strong enough acids to release CO2 from carbonates.Phenols are also acidic but not are not strong enough to release CO2

ESTERIFICATIONESTERIFICATION

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

ESTERIFICATIONESTERIFICATION

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 thusincreases the yield of the ester

ESTERIFICATIONESTERIFICATION

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 thusincreases the yield of the ester

Naming esters Named from the original alcohol and carboxylic acid

CH3OH + CH3COOH CH3COOCH3 + H2O

methanol ethanoic acid METHYL ETHANOATE

ESTERSESTERS

Nomenclature first part from alcohol, second part from acide.g. methyl ethanoate CH3COOCH3

ETHYL METHANOATE METHYL ETHANOATE

ESTERSESTERS

Structure Substitute an organic group for the H in carboxylic acids

Nomenclature first part from alcohol, second part from acide.g. methyl ethanoate CH3COOCH3

Preparation From carboxylic acids or acyl chlorides

Reactivity Unreactive compared with acids and acyl chlorides

ETHYL METHANOATE METHYL ETHANOATE

ESTERSESTERS

Structure Substitute an organic group for the H in carboxylic acids

Nomenclature first part from alcohol, second part from acide.g. methyl ethanoate CH3COOCH3

Preparation From carboxylic acids or acyl chlorides

Reactivity Unreactive compared with acids and acyl chlorides

Isomerism Esters 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 properties O-H bond gives rise No hydrogen bondingto hydrogen bonding; insoluble in waterget higher boiling pointand solubility in water

Chemical properties acidic fairly unreactivereacts with alcohols hydrolysed to acids

STRUCTURAL ISOMERISM – STRUCTURAL ISOMERISM – FUNCTIONAL GROUPFUNCTIONAL GROUP

USES OF ESTERSUSES OF ESTERS

Despite being fairly chemically unreactive, esters are useful as ...

• flavourings apple 2-methylbutanoatepear 3-methylbutylethanoatebanana 1-methylbutylethanoatepineapple butylbutanoaterum 2-methylpropylpropanoate

• solvents nail varnish remover - ethyl ethanoate

• plasticisers

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

HCOOH + C2H5OHMETHANOIC ETHANOL ACID

ETHYL METHANOATE

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

HCOOH + C2H5OHMETHANOIC ETHANOL ACID

ETHYL METHANOATE

METHYL ETHANOATE

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

HCOOH + C2H5OHMETHANOIC ETHANOL ACID

CH3COOH + CH3OHETHANOIC METHANOL ACID

ETHYL METHANOATE

METHYL ETHANOATE

HYDROLYSIS OF ESTERSHYDROLYSIS 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

HYDROLYSIS OF ESTERSHYDROLYSIS 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

HYDROLYSIS OF ESTERSHYDROLYSIS 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

NATURALLY OCCURING ESTERS - NATURALLY OCCURING ESTERS - TRIGLYCERIDESTRIGLYCERIDES

• triglycerides are the most common component of edible fats and oils

• they are esters of the alcohol glycerol (propane-1,2,3-triol)

Saponification

• alkaline hydrolysis of triglycerol esters produces soaps• a simple soap is the salt of a fatty acid• as most oils contain a mixture of triglycerols, soaps are not pure• the quality of a soap depends on the oils from which it is made

CH2OH

CHOH

CH2OH

ACYL CHLORIDESACYL CHLORIDES

Nomenclature Named from the corresponding carboxylic acid remove -ic add -yl chloride

CH3COCl ethanoyl chloride

C6H5COCl benzene carbonyl (benzoyl) chloride

ChemicalProperties • 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 CHLORIDESACYL CHLORIDES

Reagent Water

Product(s) carboxylic acid + HCl(fume in moist air / strong acidic solution formed)

Conditions room temperature

Equation CH3COCl(l) + H2O(l) ——> CH3COOH(aq) + HCl(aq)

Mechanism addition-elimination

ACYL CHLORIDESACYL CHLORIDES

Reagent Alcohols

Product(s) ester + hydrogen chloride

Conditions reflux in dry (anhydrous) conditions

Equation CH3COCl(l) + CH3OH(l) ——> CH3COOCH3(l) + HCl(g)

Mechanism addition-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 CHLORIDESACYL CHLORIDES

Reagent Ammonia

Product(s) amide + hydrogen chloride

Conditions Low temperature and excess ammonia; vigorous reaction.

Equation CH3COCl(l) + NH3(aq) ——> CH3CONH2(s) + HCl(g) or CH3COCl(l) + 2NH3(aq) ——> CH3CONH2(s) + NH4Cl(s)

Mechanism addition-elimination

ACYL CHLORIDESACYL CHLORIDES

Reagent Amines

Product(s) N-substituted amide + hydrogen chloride

Conditions anhydrous

Equation CH3COCl + C2H5NH2 ——> CH3CONHC2H5 + HCl or CH3COCl + 2C2H5NH2 ——> CH3CONHC2H5 + C2H5NH3Cl

Mechanism addition-elimination - similar to that with ammonia.

REVISION CHECKREVISION 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.

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AN INTRODUCTION TOAN INTRODUCTION TO

CARBOXYLIC ACIDS CARBOXYLIC ACIDS AND AND THEIR DERIVATIVESTHEIR DERIVATIVES