2. INTRODUCTION
This Powerpoint show is one of several produced to help students
understand selected topics at AS and A2 level Chemistry. It is based on the
requirements of the AQA and OCR specifications but is suitable for other
examination boards.
Individual students may use the material at home for revision purposes or it
may be used for classroom teaching if an interactive white board is
available.
Accompanying notes on this, and the full range of AS and A2 topics, are
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www.knockhardy.org.uk/sci.htm
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KNOCKHARDY PUBLISHING
CARBOXYLIC ACIDS
3. CONTENTS
• Structure of carboxylic acids
• Nomenclature
• Physical properties of carboxylic acids
• Preparation of carboxylic acids
• Chemical properties of carboxylic acids
• Acyl chlorides
• Esters
• Triglycerides and fats
• Biofuels
CARBOXYLIC ACIDS
4. 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 ACIDS
5. STRUCTURE OF CARBOXYLIC ACIDS
• contain the carboxyl functional group COOH
• the bonds are in a planar arrangement
6. STRUCTURE 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
7. STRUCTURE 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’
9. Carboxylic acids form a homologous series
HOMOLOGOUS SERIES
HCOOH CH3COOH C2H5COOH
With more carbon atoms, there can be structural isomers
C3H7COOH (CH3)2CHCOOH
10. INFRA-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
11. 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
12. 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 ACIDS
METHANOIC ACID ETHANOIC ACID PROPANOIC ACID
13. 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 ACIDS
BUTANOIC ACID 2-METHYLPROPANOIC ACID
14. 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 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
15. 101°C 118°C 141°C 164°C
PHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - higher induced dipole-dipole interactions
16. 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 PROPERTIES
BOILING POINT
Increases as size increases - higher induced dipole-dipole interactions
17. PHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - higher induced dipole-dipole interactions
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 + h-bonding
propan-1-ol C3H7OH 60 97 + h-bonding
propanal C2H5CHO 58 49 + permanent dipole-dipole
butane C4H10 58 - 0.5 induced dipole-dipole
18. PHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - higher induced dipole-dipole interactions
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
20. PHYSICAL 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
21. PREPARATION 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
23. CHEMICAL PROPERTIES
ACIDITY
weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+
(aq)
form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)
2RCOOH + Mg(s) ——> (RCOO¯)2Mg2+(aq) + H2(g)
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.
24. CHEMICAL PROPERTIES
ACIDITY
weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+
(aq)
form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)
2RCOOH + Mg(s) ——> (RCOO¯)2Mg2+(aq) + H2(g)
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.
26. ESTERIFICATION
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 thus
increases the yield of the ester
27. ESTERIFICATION
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 thus
increases 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
28. 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
Alternative
method CH3COOH + PCl5 ——> CH3COCl + POCl3 + HCl
phosphorus(V) chloride
29. ACYL CHLORIDES
Structure Replace the OH of a carboxylic acid with a Cl atom
Nomenclature Named from corresponding acid
… remove -ic add -yl chloride
CH3COCl ethanoyl (acetyl) chloride
C6H5COCl benzene carbonyl (benzoyl) chloride
ETHANOYL CHLORIDE
30. ACYL CHLORIDES - PROPERTIES
Physical • polar, colourless liquids which fume in moist air
d+
d-
d-
31. ACYL CHLORIDES - PROPERTIES
Physical • polar, colourless liquids which fume in moist air
Chemical • attacked at the positive carbon centre by nucleophiles
such as water, alcohols, ammonia and amines
• undergo addition-elimination reactions
• MUCH MORE REACTIVE THAN…
CARBOXYLIC ACIDS AND ACID ANHYDRIDES
d+
d-
d-
32. ACYL CHLORIDES - REACTIONS
WATER
Product(s) carboxylic acid + HCl (fume in moist air / strong
acidic solution formed)
Conditions cold water
Equation CH3COCl(l) + H2O(l) —> CH3COOH(aq) + HCl(aq)
Mechanism addition-elimination
36. 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
ETHYL METHANOATE
METHYL ETHANOATE
37. 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
Preparation From carboxylic acids, acyl chlorides and acid anhydrides
Reactivity Unreactive compared with acids and acyl chlorides
ETHYL METHANOATE
METHYL ETHANOATE
38. 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
Preparation From carboxylic acids, acyl chlorides and acid anhydrides
Reactivity Unreactive compared with acids and acyl chlorides
Isomerism Esters are structural isomers of carboxylic acids
ETHYL METHANOATE
METHYL ETHANOATE
39. Classification CARBOXYLIC ACID ESTER
Functional Group R-COOH R-COOR
Name PROPANOIC ACID METHYL ETHANOATE
Physical properties O-H bond gives rise No hydrogen bonding
to hydrogen bonding; insoluble in water
get higher boiling point
and solubility in water
Chemical properties acidic fairly unreactive
react with alcohols hydrolysed to acids
STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
40. PREPARATION OF ESTERS - 1
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 thus
increases the yield of the ester
For more details see under ‘Reactions of carboxylic acids’
41. PREPARATION OF ESTERS - 2
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 dry as they react
with water.
42. PREPARATION OF ESTERS - 3
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 as
acyl chlorides so the the reaction is slower.
The reaction is safer - it is less exothermic.
Acid anhydrides are less toxic.
43. HYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER CARBOXYLIC ACID + ALCOHOL
HCOOH + C2H5OH
METHANOIC ETHANOL
ACID
ETHYL METHANOATE
44. HYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER CARBOXYLIC ACID + ALCOHOL
HCOOH + C2H5OH
METHANOIC ETHANOL
ACID
ETHYL METHANOATE
METHYL ETHANOATE
45. HYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER CARBOXYLIC ACID + ALCOHOL
HCOOH + C2H5OH
METHANOIC ETHANOL
ACID
CH3COOH + CH3OH
ETHANOIC METHANOL
ACID
ETHYL METHANOATE
METHYL ETHANOATE
46. 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 + H2O CH3COOH + CH3OH
alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH
47. 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 + H2O CH3COOH + CH3OH
alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH
48. 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 + 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
49. 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 + 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
50. USES OF ESTERS
Despite being fairly chemically unreactive, esters are useful as ...
• flavourings apple 2-methylbutanoate
pear 3-methylbutylethanoate
banana 1-methylbutylethanoate
pineapple butylbutanoate
rum 2-methylpropylpropanoate
• solvents nail varnish remover - ethyl ethanoate
• plasticisers
51. TRIGLYCERIDES AND FATS
Triglycerides
• are the most common component of edible fats and oils
• are triesters of the alcohol glycerol, (propane-1,2,3-triol) and fatty acids
glycerol
a triglyceride
52. TRIGLYCERIDES AND FATS
Triglycerides
• are the most common component of edible fats and oils
• are triesters of the alcohol glycerol, (propane-1,2,3-triol) and fatty acids
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 compounds
• the quality of a soap depends on the oils from which it is made
53. FATTY ACIDS
Carboxylic acids that are obtained from natural oils and fats; they can be…
Saturated CH3(CH2)16COOH octadecanoic acid
(stearic acid)
54. FATTY ACIDS
Carboxylic acids that are obtained from natural oils and fats; they can be…
Saturated CH3(CH2)16COOH octadecanoic acid
(stearic acid)
9
Unsaturated CH3(CH2)7CH=CH(CH2)7COOH octadec-9-enoic acid
(oleic acid)
cis (Z) isomer
trans (E) isomer
55. FATTY ACIDS
Carboxylic acids that are obtained from natural oils and fats; they can be…
Saturated CH3(CH2)16COOH octadecanoic acid
(stearic acid)
9
Unsaturated CH3(CH2)7CH=CH(CH2)7COOH octadec-9-enoic acid
(oleic acid)
cis (Z) isomer
trans (E) isomer
12 9
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
octadec-9,12-dienoic acid (linoleic acid)
56. FATTY ACIDS AND HEALTH
Saturated • solids at room temperature
• found in meat and dairy products
• are bad for health
• increase cholesterol levels - can lead to heart problems
57. FATTY ACIDS AND HEALTH
Saturated • solids at room temperature
• found in meat and dairy products
• are bad for health
• increase cholesterol levels - can lead to heart problems
Mono
unsaturated • contain just one C=C
• thought to be neutral to our health
• found in olives, olive oil, groundnut oil, nuts, avocados
58. FATTY ACIDS AND HEALTH
Saturated • solids at room temperature
• found in meat and dairy products
• are bad for health
• increase cholesterol levels - can lead to heart problems
Mono
unsaturated • contain just one C=C
• thought to be neutral to our health
• found in olives, olive oil, groundnut oil, nuts, avocados
Poly
unsaturated • are considered to be ‘good fats’
• contain more than one C=C bond
• tend to be liquids at room temperature, eg olive oil.
• can be split into two main types...
Omega 3 - fatty acids
Omega 6 - fatty acids
59. FATTY ACIDS AND HEALTH
Saturated • solids at room temperature
• found in meat and dairy products
• are bad for health
• increase cholesterol levels - can lead to heart problems
Mono
unsaturated • contain just one C=C
• thought to be neutral to our health
• found in olives, olive oil, groundnut oil, nuts, avocados
Poly
unsaturated • are considered to be ‘good fats’
• contain more than one C=C bond
• tend to be liquids at room temperature, eg olive oil.
• can be split into two main types...
Omega 3 - fatty acids
Omega 6 - fatty acids
60. OMEGA 3 and 6 FATTY ACIDS
Omega 3 - fatty acids lower the total amount of fat in the blood
and can lower blood pressure and decrease
the risk of cardiovascular disease
3
W (omega) end CH3CH2CH=CHCH2CH2CH2CH2CH=CH(CH2)7COOH
The omega numbering system starts from the
opposite end to the carboxylic acid group
61. OMEGA 3 and 6 FATTY ACIDS
Omega 3 - fatty acids lower the total amount of fat in the blood
and can lower blood pressure and decrease
the risk of cardiovascular disease
3
W (omega) end CH3CH2CH=CHCH2CH2CH2CH2CH=CH(CH2)7COOH
Omega 6 - fatty acids reduce the risk of cardiovascular disease but
can contribute to allergies and inflammation
6
W (omega) end CH3CH2CH2CH2CH2CH=CHCH2CH=CH(CH2)7COOH
62. CHOLESTEROL
• a fatty substance which is found in the blood
• it is mainly made in the body
• plays an essential role in how every cell in the body works
• eating too much saturated fat increases cholesterol levels
• too much cholesterol in the blood can increase the risk of heart problems
63. CHOLESTEROL
• a fatty substance which is found in the blood
• it is mainly made in the body
• plays an essential role in how every cell in the body works
• eating too much saturated fat increases cholesterol levels
• too much cholesterol in the blood can increase the risk of heart problems
Ways to reduce cholesterol levels
• cut down on saturated fats and trans fats
(trans fats are more stable and difficult to break down in the body)
• replace them with monounsaturated fats and polyunsaturated fats
• eat oily fish
• have a high fibre diet; porridge, beans, fruit and vegetables
• exercise regularly
64. BIOFUELS
What are they?
Liquid fuels made from plant material and recycled elements of the food chain
Biodiesel
An alternative fuel which can be made from waste vegetable oil or from oil
produced from seeds. It can be used in any diesel engine, either neat or
mixed with petroleum diesel.
It is a green fuel, does not contribute to the carbon dioxide (CO2) burden and
produces drastically reduced engine emissions. It is non-toxic and
biodegradable.
vegetable oil glycerol biodiesel
65. BIOFUELS
Advantages • renewable - derived from sugar beet, rape seed
• dramatically reduces emissions
• carbon neutral
• biodegradable
• non-toxic
• fuel & exhaust emissions are less unpleasant
• can be used directly in unmodified diesel engine
• high flashpoint - safer to store & transport
• simple to make
• used neat or blended in any ratio with petroleum diesel
66. BIOFUELS
Advantages • renewable - derived from sugar beet, rape seed
• dramatically reduces emissions
• carbon neutral
• biodegradable
• non-toxic
• fuel & exhaust emissions are less unpleasant
• can be used directly in unmodified diesel engine
• high flashpoint - safer to store & transport
• simple to make
• used neat or blended in any ratio with petroleum diesel
Disadvantages • poor availability - very few outlets & manufacturers
• more expensive to produce
• poorly made biodiesel can cause engine problems
67. BIOFUELS
Advantages • renewable - derived from sugar beet, rape seed
• dramatically reduces emissions
• carbon neutral
• biodegradable
• non-toxic
• fuel & exhaust emissions are less unpleasant
• can be used directly in unmodified diesel engine
• high flashpoint - safer to store & transport
• simple to make
• used neat or blended in any ratio with petroleum diesel
Disadvantages • poor availability - very few outlets & manufacturers
• more expensive to produce
• poorly made biodiesel can cause engine problems
Future
problems • there isn’t enough food waste to produce large amounts
• crops grown for biodiesel use land for food crops
• a suitable climate is needed to grow most crops
• some countries have limited water resources
