CARBOXYLIC ACIDS
CONTENTS
• Structure of carboxylic acids
• Nomenclature
• Physical properties of carboxylic acids
• Preparation of carboxylic acids
• Chemical properties of carboxylic acids
• Esters
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
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)
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
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
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’
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