AN INTRODUCTION TO CARBOXYLIC ACIDS AND THEIR DERIVATIVES KNOCKHARDY PUBLISHING.

AN INTRODUCTION TOAN INTRODUCTION TO

CARBOXYLIC ACIDS CARBOXYLIC ACIDS AND AND THEIR DERIVATIVESTHEIR DERIVATIVES

KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING

INTRODUCTION

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CARBOXYLIC ACIDSCARBOXYLIC ACIDS

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


Before you start it would be helpful to…

• Recall the definition of a covalent bond

• Recall the difference types of physical bonding

• Be able to balance simple equations

• Be able to write out structures for simple organic molecules

• Understand the IUPAC nomenclature rules for simple organic compounds

• Recall the chemical properties of alkanes and alkenes


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




• include a carbonyl (C=O) group and

a hydroxyl (O-H) group

• are isomeric with esters :- RCOOR’

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

INFRA-RED SPECTROSCOPYINFRA-RED SPECTROSCOPY

IDENTIFYING CARBOXYLIC ACIDS USING INFRA RED SPECTROSCOPY

Differentiation Compound O-H C=O

ALCOHOL YES NO

CARBOXYLIC ACID YES 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. CH3 - CH(CH3) - CH2 - CH2 - COOH is called 4-methylpentanoic acid

NAMING CARBOXYLIC ACIDSNAMING CARBOXYLIC ACIDS








METHANOIC ACID ETHANOIC ACID PROPANOIC ACID








BUTANOIC ACID 2-METHYLPROPANOIC ACID



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

101°C 118°C 141°C 164°C

PHYSICAL PROPERTIESPHYSICAL 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


BOILING POINT



BOILING POINT


Carboxylic acids have high boiling points for their relative mass

The effect of hydrogen bonding on the boiling point of compounds of similar mass

Compound Formula Mr b. pt. (°C) Comments

ethanoic acid CH3COOH 60 118

propan-1-ol C3H7OH 60 97 h-bonding

propanal C2H5CHO 58 49 dipole-dipole

butane C4H10 58 - 0.5 basic V der W


BOILING POINT


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


SOLUBILITY

• carboxylic acids are soluble in organic solvents

• they are also soluble in water due to hydrogen bonding

HYDROGEN BONDING


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 ACIDSPREPARATION OF CARBOXYLIC ACIDS

Oxidation of aldehydes RCHO + [O] ——> RCOOH

Hydrolysis of esters RCOOR + H2O RCOOH + ROH

Hydrolysis of acyl chlorides RCOCl + H2O ——> RCOOH + HCl

Hydrolysis of nitriles RCN + 2 H2O ——> RCOOH + NH3

Hydrolysis of amides RCONH2 + H2O ——> RCOOH + NH3

CHEMICAL PROPERTIESCHEMICAL PROPERTIES

ACIDITY

weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq)

form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)


ACIDITY



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.


ACIDITY



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 ANALYSISCarboxylic acids are strong enough acids to liberate CO2 from carbonatesPhenols are also acidic but not are not strong enough to liberate 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


Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 )

Conditions reflux

Product ester



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


Reagent(s) alcohol + strong acid catalyst (e.g conc. H2SO4 )

Conditions reflux

Product ester





Naming esters Named from the original alcohol and carboxylic acid

CH3OH + CH3COOH CH3COOCH3 + H2O

from ethanoic acid CH3COOCH3 from methanol

METHYL ETHANOATE

CHLORINATION OF CARBOXYLIC ACIDSCHLORINATION OF CARBOXYLIC ACIDS

Chlorination involves replacing the OH with a Cl

Product acyl chloride

Reagent thionyl chloride SOCl2

Conditions dry conditions

Equation CH3COOH + SOCl2 ——> CH3COCl + SO2 + HCl

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

ETHYL METHANOATE METHYL ETHANOATE

ESTERSESTERS



Preparation From carboxylic acids or acyl chlorides

Reactivity Unreactive compared with acids and acyl chlorides


ESTERSESTERS



Preparation From carboxylic acids or acyl chlorides

Reactivity Unreactive compared with acids and acyl chlorides

Isomerism Esters are structural isomers of carboxylic acids


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

PREPARATION OF ESTERS - 1PREPARATION OF ESTERS - 1

Reagent(s) alcohol + carboxylic acid

Conditions reflux with a strong acid catalyst (e.g. conc. H2SO4 )





For more details see under ‘Reactions of carboxylic acids’


Reagent(s) alcohol + acyl chloride

Conditions reflux under dry conditons

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

methanol ethanoyl methyl chloride ethanoate

Notes Acyl chlorides are very reactive but must be kept dryas they react with water


Reagent(s) alcohol + acid anhydride

Conditions reflux under dry conditons

Equation e.g. CH3OH(l) + (CH3CO)2O(l) ——> CH3COOCH3(l) + CH3COOH(l)

methanol ethanoic methyl ethanoic anhydride ethanoate acid

Notes Acid anhydrides are not as reactive asacyl chlorides so the the reaction is slower.

The reaction is safer - it is less exothermic.

Acid anhydrides are less toxic.

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

HCOOH + C2H5OHMETHANOIC ETHANOL ACID

ETHYL METHANOATE





ETHYL METHANOATE

METHYL ETHANOATE





CH3COOH + CH3OHETHANOIC METHANOL ACID

ETHYL METHANOATE

METHYL ETHANOATE




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







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

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

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


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


Reagent Alcohols

Product(s) ester + hydrogen chloride

Conditions reflux in dry (anhydrous) conditions

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



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)



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.

CAN YOU DO ALL OF THESE? CAN YOU DO ALL OF THESE? YES YES NONO

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THE THE END

AN INTRODUCTION TOAN INTRODUCTION TO

CARBOXYLIC ACIDS CARBOXYLIC ACIDS AND AND THEIR DERIVATIVESTHEIR DERIVATIVES

AN INTRODUCTION TO CARBOXYLIC ACIDS AND THEIR DERIVATIVES KNOCKHARDY PUBLISHING.

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