CONTENTS Structure of carboxylic acids Nomenclature
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Transcript of CONTENTS Structure of carboxylic acids Nomenclature
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CONTENTS
• Structure of carboxylic acids
• Nomenclature
• Physical properties of carboxylic acids
• Preparation of carboxylic acids
• Chemical properties of carboxylic acids
• Esters
CARBOXYLIC ACIDSCARBOXYLIC ACIDS
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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
CARBOXYLIC ACIDSCARBOXYLIC ACIDS
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STRUCTURE OF CARBOXYLIC ACIDSSTRUCTURE OF CARBOXYLIC ACIDS
• contain the carboxyl functional group COOH
• the bonds are in a planar arrangement
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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
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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
• are isomeric with esters :- RCOOR’
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HOMOLOGOUS SERIESHOMOLOGOUS SERIES
HCOOH CH3COOH C2H5COOH
Carboxylic acids form a homologous series
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Carboxylic acids form a homologous series
HOMOLOGOUS SERIESHOMOLOGOUS SERIES
HCOOH CH3COOH C2H5COOH
With more carbon atoms, there can be structural isomers
C3H7COOH (CH3)2CHCOOH
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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
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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
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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 ACIDSNAMING CARBOXYLIC ACIDS
METHANOIC ACID ETHANOIC ACID PROPANOIC ACID
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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 ACIDSNAMING CARBOXYLIC ACIDS
BUTANOIC ACID 2-METHYLPROPANOIC ACID
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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
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101°C 118°C 141°C 164°C
PHYSICAL PROPERTIESPHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - due to increased van der Waals forces
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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 PROPERTIESPHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - due to increased van der Waals forces
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PHYSICAL PROPERTIESPHYSICAL 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 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
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PHYSICAL PROPERTIESPHYSICAL 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
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PHYSICAL PROPERTIESPHYSICAL PROPERTIES
SOLUBILITY
• carboxylic acids are soluble in organic solvents
• they are also soluble in water due to hydrogen bonding
HYDROGEN BONDING
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PHYSICAL PROPERTIESPHYSICAL 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
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CHEMICAL PROPERTIESCHEMICAL PROPERTIES
ACIDITY
weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq)
form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)
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CHEMICAL PROPERTIESCHEMICAL PROPERTIES
ACIDITY
weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq)
form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)
QUALITATIVE ANALYSISCarboxylic acids are strong enough acids to liberate CO2 from carbonatesPhenols are also acidic but not are not strong enough to liberate CO2
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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
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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
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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
from ethanoic acid CH3COOCH3 from methanol
METHYL ETHANOATE
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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
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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
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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
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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
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PREPARATION OF ESTERSPREPARATION OF ESTERS
Reagent(s) alcohol + carboxylic acid
Conditions reflux with a strong acid catalyst (e.g. conc. H2SO4 )
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
For more details see under ‘Reactions of carboxylic acids’
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HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER CARBOXYLIC ACID + ALCOHOL
HCOOH + C2H5OHMETHANOIC ETHANOL ACID
ETHYL METHANOATE
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HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER CARBOXYLIC ACID + ALCOHOL
HCOOH + C2H5OHMETHANOIC ETHANOL ACID
ETHYL METHANOATE
METHYL ETHANOATE
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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
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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
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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
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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
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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
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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