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AN INTRODUCTION TO
CARBOXYLIC ACIDS
AND THEIR DERIVATIVES
KNOCKHARDY PUBLISHING
KNOCKHARDY PUBLISHING
CARBOXYLIC ACIDS
INTRODUCTION
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CARBOXYLIC 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
CARBOXYLIC ACIDS
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 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
a hydroxyl (O-H) group
and
STRUCTURE OF CARBOXYLIC ACIDS
• contain the carboxyl functional group COOH
• the bonds are in a planar arrangement
• include
a carbonyl (C=O) group
a hydroxyl (O-H) group
• are isomeric with esters :- RCOOR’
and
HOMOLOGOUS SERIES
Carboxylic acids form a homologous series
HCOOH
CH3COOH
C2H5COOH
HOMOLOGOUS SERIES
Carboxylic acids form a homologous series
HCOOH
CH3COOH
C2H5COOH
With more carbon atoms, there can be structural isomers
C3H7COOH
(CH3)2CHCOOH
INFRA-RED SPECTROSCOPY
IDENTIFYING CARBOXYLIC ACIDS USING INFRA RED SPECTROSCOPY
Differentiation
ALCOHOL
O-H absorption
Compound
O-H
C=O
ALCOHOL
YES
NO
CARBOXYLIC ACID
YES
YES
ESTER
NO
YES
CARBOXYLIC ACID
O-H + C=O absorption
ESTER
C=O absorption
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
e.g.
CH3 - CH(CH3) - CH2 - CH2 - 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
METHANOIC ACID
ETHANOIC ACID
PROPANOIC 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
BUTANOIC ACID
2-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.
Formula
HCOOH
CH3COOH
C6H5COOH
Systematic name
methanoic acid
ethanoic acid
benzenecarboxylic acid
(trivial name)
formic acid
acetic acid
benzoic acid
origin of name
latin for ant
latin for vinegar
from benzene
PHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - due to increased van der Waals forces
101°C
118°C
141°C
164°C
PHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - due to increased van der Waals forces
101°C
118°C
141°C
164°C
Boiling point is higher for “straight” chain isomers.
164°C
154°C
Greater branching = lower inter-molecular forces = lower boiling point
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
Compound
ethanoic acid
propan-1-ol
propanal
butane
Formula
CH3COOH
C3H7OH
C2H5CHO
C4H10
Mr
60
60
58
58
b. pt. (°C)
118
97
49
- 0.5
Comments
h-bonding
dipole-dipole
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
HYDROGEN
BONDING
AN EXTREME CASE... DIMERISATION
• extra inter-molecular attraction = more energy to separate molecules
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
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
PREPARATION OF CARBOXYLIC ACIDS
Oxidation of aldehydes
RCHO
+
[O]
Hydrolysis of esters
RCOOR + H2O
Hydrolysis of acyl chlorides
RCOCl +
Hydrolysis of nitriles
RCN
Hydrolysis of amides
——>
RCOOH
RCOOH + ROH
H2 O
——>
RCOOH + HCl
2 H2O
——>
RCOOH + NH3
RCONH2 + H2O ——>
RCOOH + NH3
+
CHEMICAL PROPERTIES
ACIDITY
RCOO¯(aq)
+ H3O+(aq)
weak acids
RCOOH + H2O(l)
form salts
RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)
CHEMICAL PROPERTIES
ACIDITY
RCOO¯(aq)
+ H3O+(aq)
weak acids
RCOOH + H2O(l)
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.
CHEMICAL PROPERTIES
ACIDITY
RCOO¯(aq)
+ H3O+(aq)
weak acids
RCOOH + H2O(l)
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
ESTERIFICATION
Reagent(s)
alcohol + strong acid catalyst (e.g. conc. H2SO4 )
Conditions
reflux
Product
ester
Equation
e.g. CH3CH2OH(l) + CH3COOH(l)
ethanol
ethanoic acid
CH3COOC2H5(l) + H2O(l)
ethyl ethanoate
ESTERIFICATION
Reagent(s)
alcohol + strong acid catalyst (e.g. conc. H2SO4 )
Conditions
reflux
Product
ester
Equation
Notes
e.g. CH3CH2OH(l) + CH3COOH(l)
ethanol
ethanoic acid
CH3COOC2H5(l) + H2O(l)
ethyl ethanoate
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
ESTERIFICATION
Reagent(s)
alcohol + strong acid catalyst (e.g conc. H2SO4 )
Conditions
reflux
Product
ester
Equation
e.g. CH3CH2OH(l) + CH3COOH(l)
ethanol
ethanoic acid
CH3COOC2H5(l) + H2O(l)
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 + CH3COOH
from ethanoic acid
CH3COOCH3 + H2O
CH3COOCH3
METHYL ETHANOATE
from methanol
CHLORINATION 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
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
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
Preparation
From carboxylic acids or acyl chlorides
Reactivity
Unreactive compared with acids and acyl chlorides
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
Preparation
From carboxylic acids or acyl chlorides
Reactivity
Unreactive compared with acids and acyl chlorides
Isomerism
Esters are structural isomers of carboxylic acids
STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
Classification
Functional Group
Name
CARBOXYLIC ACID
ESTER
R-COOH
R-COOR
PROPANOIC ACID
METHYL ETHANOATE
Physical properties
O-H bond gives rise
to hydrogen bonding;
get higher boiling point
and solubility in water
No hydrogen bonding
insoluble in water
Chemical properties
acidic
reacts with alcohols
fairly unreactive
hydrolysed to acids
PREPARATION OF ESTERS - 1
Reagent(s)
alcohol + carboxylic acid
Conditions
reflux with a strong acid catalyst (e.g. conc. H2SO4 )
Equation
Notes
e.g. CH3CH2OH(l) + CH3COOH(l)
ethanol
ethanoic acid
CH3COOC2H5(l) + H2O(l)
ethyl ethanoate
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
For more details see under ‘Reactions of carboxylic acids’
PREPARATION OF ESTERS - 2
Reagent(s)
alcohol + acyl chloride
Conditions
reflux under dry conditons
Equation
Notes
e.g.
CH3OH(l) + CH3COCl(l) ——> CH3COOCH3(l) + HCl(g)
methanol
ethanoyl
methyl
chloride
ethanoate
Acyl chlorides are very reactive but must be kept dry
as they react with water
PREPARATION OF ESTERS - 3
Reagent(s)
alcohol + acid anhydride
Conditions
reflux under dry conditons
Equation
Notes
e.g. CH3OH(l) + (CH3CO)2O(l) ——> CH3COOCH3(l) + CH3COOH(l)
methanol
ethanoic
methyl
ethanoic
anhydride
ethanoate
acid
Acid 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
METHANOIC
ACID
ETHYL METHANOATE
+
C2H5OH
ETHANOL
HYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER
CARBOXYLIC ACID + ALCOHOL
HCOOH
METHANOIC
ACID
ETHYL METHANOATE
METHYL ETHANOATE
+
C2H5OH
ETHANOL
HYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER
CARBOXYLIC ACID + ALCOHOL
HCOOH
+
METHANOIC
ACID
C2H5OH
ETHANOL
ETHYL METHANOATE
CH3COOH
ETHANOIC
ACID
METHYL ETHANOATE
+
CH3OH
METHANOL
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
+ H2 O
alkaline
CH3COOCH3 + NaOH
CH3COOH
+
CH3OH
——> CH3COO¯ Na+ + CH3OH
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
+ H2 O
alkaline
CH3COOCH3 + NaOH
CH3COOH
+
CH3OH
——> CH3COO¯ Na+ + CH3OH
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
CH3COOCH3
+ H2 O
alkaline
CH3COOCH3 + NaOH
CH3COOH
+
CH3OH
——> 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 - TRIGLYCERIDES
• triglycerides are the most common component of edible fats and oils
• they are esters of the alcohol
glycerol (propane-1,2,3-triol)
CH2OH
CHOH
CH2OH
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
USES OF ESTERS
Despite being fairly chemically unreactive, esters are useful as ...
• flavourings
apple
pear
banana
pineapple
rum
• solvents
nail varnish remover - ethyl ethanoate
• plasticisers
2-methylbutanoate
3-methylbutylethanoate
1-methylbutylethanoate
butylbutanoate
2-methylpropylpropanoate
ACYL CHLORIDES
Nomenclature
Chemical
Properties
Named from the corresponding carboxylic acid
remove -ic add -yl chloride
CH3COCl
ethanoyl chloride
C6H5COCl
benzene carbonyl (benzoyl) chloride
•
•
•
•
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
Reagent
Water
Product(s)
carboxylic acid + HCl
(fume in moist air / strong acidic solution formed)
Conditions
room temperature
Equation
CH3COCl(l)
Mechanism
addition-elimination
+ H2O(l) ——>
CH3COOH(aq) + HCl(aq)
ACYL CHLORIDES
Reagent
Alcohols
Product(s)
ester + hydrogen chloride
Conditions
reflux in dry (anhydrous) conditions
Equation
CH3COCl(l)
Mechanism
addition-elimination
+ CH3OH(l) ——>
CH3COOCH3(l) + HCl(g)
ACYL CHLORIDES
Reagent
Ammonia
Product(s)
amide + hydrogen chloride
Conditions
Low temperature and excess ammonia; vigorous reaction.
Equation
CH3COCl(l) + NH3(aq) ——>
CH3COCl(l) + 2NH3(aq) ——>
or
Mechanism
addition-elimination
CH3CONH2(s) + HCl(g)
CH3CONH2(s) + NH4Cl(s)
ACYL CHLORIDES
Reagent
Amines
Product(s)
N-substituted amide + hydrogen chloride
Conditions
anhydrous
Equation
Mechanism
CH3COCl + C2H5NH2 ——> CH3CONHC2H5 + HCl
or CH3COCl + 2C2H5NH2 ——> CH3CONHC2H5 + C2H5NH3Cl
addition-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.
CAN YOU DO ALL OF THESE?
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NO
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relevant topic(s) again
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AN INTRODUCTION TO
CARBOXYLIC ACIDS
AND THEIR DERIVATIVES
THE END
© JONATHAN HOPTON & KNOCKHARDY PUBLISHING