1. Chapter 4
CARBOXYLIC ACID
Norfazrin Mohd Hanif
Faculty of Applied Science
UiTM Negeri Sembilan

2. CHAPTER OUTLINE
General formula : RCOOH OR ArCOOH
Nomenclature –IUPAC and common
Physical properties of aldehyde : Boiling points and solubility
Acidity
Preparation
Oxidation of Primary Alcohols, Aldehydes, Alkenes And Alkyl
Benzene
Carboxylation of Grignard reagent
Hydrolysis of nitrile
Reactions
Salt formation
Reduction to alcohols
 Formation of Acyl Chlorides
 Formation of Esters
 Formation of Acid Anhydrides
 Formation of Amides

3. 
The functional group of a carboxylic
acid is a carboxyl group, which can
be represented in any one of three
ways:
O
, R-COOH, R-CO2H
R C
OH

4. 


Carboxylic acids named by replacing –e of the
corresponding alkane name with –oic acid
–CO2H carbon atom is numbered C1
Compound containing multiple –COOH group, add di- or
tri- to the suffix –oic acid

5. 

Carboxylic acids containing two carboxyl groups are
called dicarboxyl acids.
Their systematic names have the suffix ‘dioic’.
COOH
COOH
CH2
COOH
COOH
ethanedioic acid
(oxalic acid)
propanedioic acid
(malonic acid)
COOH
(CH2)4
COOH
hexanedioic acid
(adipic acid)

6. 

Cycloalkanes bonded to -COOH are named as
cycloalkanecarboxylic acids.
Aromatic acids are named as benzoic acids.
O
C OH
COOH
OH
COOH
1
6
5
benzoic acid
2-hydroxybenzoic acid
2
3
4
NO2
3-nitrobenzoic acid

7. 

All common names of acid end in –ic acid.
Positions of substituents on the chain are labeled
with Greek letters.
Cl O
Ph
CH3CH2CHC OH
CH3CH2CH2CHCH2COOH
-chlorobutyric acid
-phenylcaproic acid

9. Boiling point (BP)

Carboxylic Acids have higher BP than other organic
molecules with comparable MW.

10. Higher boiling points than similar alcohols, due
to dimer formation.
Acetic acid, b.p. 118C

11. 


In the presence of water, hydrogen bond are formed
between water molecules & individual molecules of
acid.
Carboxylic acid with up to 4 Carbon completely
miscible in water at room temperature.
Water solubility decreases with the length of the
carbon chain.
δ+
δ-………… H
O
R C
OH
H
O Hydrogen bond with water.

12. 
More soluble in water than comparable alcohols,
ethers, aldehydes, and ketones
Structu re
N ame
CH3 COOH
CH3 CH2 CH2 OH
CH3 CH2 CHO
acetic acid
1-prop anol
prop anal
Boilin g
Solubility
Molecular Poin t
Weigh t
(°C) (g/100 mL H 2O)
60.5
118
infinite
97
60.1
infinite
58.1
48
16
CH3 (CH2 ) 2 COOH butan oic acid
CH3 (CH2 ) 3 CH2 OH 1-pentan ol
pentan al
CH3 (CH2 ) 3 CHO
88.1
88.1
86.1
163
137
103
infinite
2.3
slight

13.  Carboxylic acids are acidic because of the
hydrogen in the -COOH group.
 Recall that acids are compounds which yield
H+ ions in solution.
 Carboxylic acids in solution dissociate into the
following ions:
Carboxylate ion

14. 



Carboxylic acids – stronger acids than ROH
The pKa of ethanol is ~16, compared to ~5 for acetic
acid
Alkoxide ion (R-O-): negative charge is localized on O
Carboxylate ion (COO-): negative charge is delocalized
over two equivalent O atoms: Resonance stabilization

15. Oxidation of
 Alkyl benzene
 Alkene
 Alcohol
 Aldehyde
Carboxylation of Grignard reagent
Hydrolysis of nitrile

16. o General Formula:
R
o Example:
KMnO4 ,H+
COOH

17. o General Formula:
R
CH
CH R'
KMnO4 ,H3O+
R
+ R
C
OH
o Example:
O
O
C
OH

18. o General Formula:
R
CH2OH
KMnO4 ,H3O+
O
R
C
OH
o Example:

19. o General Formula:
O
R
KMnO4 ,H3O
C
H
o Example:
O
+
R
C
OH

20. o General Formula:
RMgX
CO2
H3O+
RCOOH
R = alkyl, allyl, benzyl, aryl
CO2 = dry ice or bubbling gaseous CO2
• nucleophilic addition
- alkyl or aryl magnesium halide is added to a double bond
C=O of CO2 to form carboxylate ion.
• when treated with acid, carboxylic acid is formed
O
R
MgX
O C
O
R C O- MgX+
+
H3O
O
R C OH

21. o Example:
CH3CH2MgCl
i) CO2
+
ii) H3O
CH3CH2COOH
i) CO2
MgCl
ii) H3O+
COOH

22. 
Alkyl halides react with NaCN to form nitriles which in turn undergo
hydrolysis in acidic solution to produce carboxylic acid.
O
R




X
NaCN
R
CN
H3O+
R
C OH + NH4+
Formation of nitriles involves nucleophilic substitution.
Primary alkyl halides (Cl, Br, I) – SN2 substitution
Aromatic nitriles cannot be prepared through this method but still can
hydrolysed to give aromatic carboxylic acids.
The nitrile is reflux with a dilute acid such as H2SO4 or HCl to form
carboxylic acid.

23. o General Formula:
o Example:
Br
NaCN
CN
+
H
H2O
COOH

24. 
Salt formation
- neutralisation
- reactions with electropositive metals





Reduction to alcohols
Formation of Acyl Chlorides
Formation of Esters
Formation of Acid Anhydrides
Formation of Amides

25. 1) Neutralisation:
- carboxylic acids undergo neutralisation reactions with strong
bases or some weak base such as NaOH, NaHCO3, Na2CO3,
NH3 and amines to form carboxylate salts of carboxylic acids
and water.
RCO2H + NaOH → RCO2-Na+ + H2O
RCO2H + NaHCO3 → RCO2-Na+ + H2O + CO2
2RCO2H + Na2CO3 → 2RCO2-Na+ + H2O + CO2
RCO2H + NH3 → RCO2-NH4+
* carboxylate salts are soluble in water

26. Examples:
CH3COOH (aq) + NaOH (aq) → CH3COONa (aq) + H2O (l)
sodium ethanoate

27. 

an aqueous solution of benzoic acid turns blue litmus paper to red.
Benzoic acids dissolves readily in alkalis to form salts (benzoates) and water.
COOH
NaOH
-
COO Na
+
H2O
sodium benzoate


Carboxylic acids react with carbonates and hydrogen carbonates to form CO2, water
and salts of carboxylic acids.
Examples:
2HCOOH (aq) + Na2CO3 (aq) → 2HCOONa (aq) + CO2 (g) + H2O (l)
sodium methanoate
CH3CH2COOH(aq) + NaHCO3(aq) → CH3CH2COONa (aq) + CO2(g)+ H2O(l)
sodium propanoate

28. 2) Reaction with electropositive metals
- reactive metals (i.e. metals that are very
electropositive) react with carboxylic acids to form
hydrogen gas and salts of carboxylic acids.
- examples of metals: calcium, magnesium, zinc and
iron.
2CH3COOH (aq) + Mg → (CH3COO)2Mg(aq) + H2
(g)
magnesium ethanoate

29. 1) Reaction with active metals
RCO2H + Na  RCO2-Na+ + H2(g)
2) Reaction with base
RCO2H + NaOH  RCO2-Na+ + H2O
3) Reaction with carbonate
RCO2H + NaHCO3  RCO2-Na+ + CO2 + H2O

30. o General reaction
O
R
C
OH
LiAlH4 ,H3O+
R
CH2 OH
o Example
O
CH3C
OH
LiAlH4 ,H3O+
CH3 CH2 OH

31. 

Carboxylic acids reacts with phosphorus (v) chloride (PCl5) or sulphur dichloride
oxide (thionyl chloride) or phosphorus trichloride (PCl3) at room temperature to
form acyl chloride.
In the case of benzoic acid, the reaction mixture is heated.
O
R C OH
O
PCl5
R C Cl
carboxylic acids
HCl
acid chlorides
O
POCl3
O
R C OH
SOCl2
carboxylic acids
carboxylic acids
SO2
HCl
acid chlorides
O
3 R C OH
R C Cl
O
PCl3
3 R C Cl
acid chlorides
H3PO3

32. Examples:
O
O
CH3 C OH
SOCl2
O
benzoic acid
SO2
HCl
ethanoyl chloride
ethanoic acid
C OH
CH3 C Cl
O
SOCl2
C Cl
benzoyl chloride
SO2
HCl

33. 


When a carboxylic acid is heated with an alcohol in the presence of a
little concentrated sulphuric acid, an ester is formed.
Known as Fischer esterification.
Since the reaction is reversible, the mixture must be heated or reflux.
O
CH3 C OH
ethanoic acid
H OC2H5
benzoic acid
H+ = H2SO4
CH3 C OC2H5
heat or reflux
O
C OH
O
H+
H+
H OC2H5
heat or reflux
H2O
ethyl ethanoate
O
C OC2H5
ethyl benzoate
H2O

34. 
Preparation of acid anhydrides:
- reaction of carboxylic acid with an acid chloride in the presence of pyridine.
- pyridine, C5H5N (base) is added to neutralize the HCl formed in the reaction
to prevent unnessary side reaction (if any).
O
R C OH
carboxylic acid
O
Cl
C R'
O
O
pyridine
HCl
R C O C R'
acid chloride
acid anhydrides
examples
O
CH3 C OH
acetic acid
O
Cl
acetic acid
CH3 C O C CH3
O
Cl
C
benzoyl chloride
HCl
acetic anhydride
ethanoyl chloride
O
CH3 C OH
C CH3
O
O
pyridine
pyridine
O
O
CH3 C O C
acetic benzoic anhydride
HCl

35. 
Symmetrical anhydride is formed when two carboxylic acid
is heated with phosphorus pentoxide (P2O5) (dehydration
reaction) or heating with ZnO.
O
O
CH3 C OH
HO C CH3
two molecules of acetic acids
P2O5
or ZnO/heat
O
O
CH3 C O C CH3
acetic anhydride
H2O

36. Amides can be synthesised directly from carboxylic acids, but the yield is poor.
A better method of synthesising amides is by using acid chlorides.
When ammonium carboxylates are heated in the presence of the free acid,
dehydration occurs to form the primary amide.
Ammonium carboxylates are obtained by the reaction of carboxylic acids with
ammonia (poor method).




RCOO-NH4+

Excess RCOOH
Heat (100-200 °C)
RCONH2 + H2O
1° amide
For example:
CH3COOH + NH3 → CH3COONH4
ammonium
ethanoate
heat
CH3CONH2 + H2O
ethanamide

37. 
Secondary and tertiary amides can be synthesised by
using primary amines and secondary amines respectively.
O
O H
H
R C OH
H N R'
o
1 amine
examples:
O
CH3 C OH
o
O H
H N CH3
O
o
heat (100-200 C)
o
2 amine
CH3 C N CH3
H2O
N-methylethanamide
O R"
R"
H N R'
H2O
2 amide
H
methylamine
R C OH
R C N R'
heat (100-200 oC)
heat (100-200 oC)
R C N R'
o
H2O
3 amide
examples:
O
CH3 C OH
H N CH3
O CH3
CH3
dimethylamine
o
heat (100-200 C)
CH3 C N CH3
N,N-dimethylethanamide
H2O

38. 
Other method: reaction of acid chloride with ammonia or
amines
O
O
R C Cl
2NH3
ammonia
O
R C NH2
amide
NH4+ Clammonium chloride
O H
R C Cl
2RNH2
amine
O
R C N R
secondary amide
RNH3+ Clammonium chloride
O R
R C Cl
2R2NH
secondary amine
R C N R
tertiary amide
R2NH2+ Clammonium chloride
examples:
O
CH3 C Cl
O
2NH3
NH4+ Cl-
O CH3
O
CH3 C Cl
CH3 C NH2
2CH3NH2
CH3 C N H
CH3NH3+ Cl-

39. Thank you…