The document provides an overview of aldehydes, including: - Nomenclature of aldehydes using IUPAC and common names. - Physical properties such as boiling points and solubility due to the polar carbonyl group. - Preparation methods including oxidation of primary alcohols and reduction of acid chlorides. - Reactions including oxidation to carboxylic acids, reduction to alcohols, nucleophilic addition with HCN or Grignard reagents, and condensation reactions with ammonia derivatives. - Specific reactions are discussed in more detail such as cyanohydrin formation, aldol condensation, and Cannizzaro disproportionation.

1. Chapter 2 : ALDEHYDE
Norfazrin Mohd Hanif
Faculty of Applied Science
UiTM Negeri Sembilan

2. SUBTOPICS
Nomenclature
– common and IUPAC names for aldehyde
Physical properties of aldehyde : Boiling points and solubility
Preparation of aldehyde
Oxidation of alcohol
Reduction of acid chlorides
Reactions of aldehyde
Oxidation
Reduction
Addition (with HCN, NaHSO3, H2O, Grignard reagents
Condensation (with ammonia, hydrazine and their
derivatives)
Iodoform reaction

3. SUBTOPICS

4. INTRODUCTION
Aldehyde contain the carbonyl group – a group in
which a carbon atom has a double bond to oxygen :
O
C
R
Oxygen Carbonyl
Carbon Carbonyl
H
Carbonyl group
The carbonyl group in aldehyde is bonded to at
least one hydrogen atom.
Using R, we can designate the general formula as:
O
C
R
H
or RCHO ( R = alkyl or aryl or H)

5. 2.0 NOMENCLATURE
2.1 IUPAC
2.2 Common name

6. 2.1 IUPAC Names
 Aldehydes are named by replacing the final -e of the
name of the corresponding alkane with –al.
~ The aldehyde functional group is always carbon 1
& need not be numbered.
IUPAC :
COMMON:
IUPAC :
COMMON:

7. 2.1 IUPAC Names
 Aldehyde functional groups bonded to a ring are
named using the suffix carbaldehyde.
~ Benzaldehyde is used more commonly than
the name benzenecarbaldehyde.
IUPAC :
COMMON:

8. 2.2 Common Names
 Aldehydes are named from the common
names of the corresponding carboxylic acid.
 The ‘ic acid’ ending is replaced with
‘aldehyde’.
Structure
IUPAC
name
HCO2H
methanoic acid
CH3CO2H
ethanoic acid
CH3CH2CO2H
propanoic acid
CH3(CH2)2CO2H
butanoic acid
CH3(CH2)3CO2H
pentanoic acid
CH3(CH2)4CO2H
hexanoic acid
Common name
formic acid
acetic acid
propionic acid
butyric acid
valeric acid
caproic acid
Structure
IUPAC
Common name
HCHO
methanal
CH3CHO
ethanal
CH3CH2CHO
propanal
CH3(CH2)2CHO
butanal
CH3(CH2)3CHO
pentanal
CH3(CH2)4CHO
hexanal
formaldehyde
acetaldehyde
propionaldehyde
butyraldehyde
valeraldehyde
caproaldehyde

9. 2.2 Common Names
 Substituents locations are given using Greek letters
(α, β, γ, δ,….) beginning with the carbon next to the
carbonyl carbon, the α -carbon.
O
CH3CHBrCH2C H
γ
β
α
β-bromobutyraldehyde
OH
O
CH3CHCH2CH2C H
δ γ β α
γ-hydroxyvaleraldehyde
O
CH2C H
α
α-phenylacetaldehyde

10. 2.0 PHYSICAL PROPERTIES
2.1 Boiling Point
2.2 Solubility

11. 2.2 Physical Properties
 Oxygen is more electronegative than carbon (3.5 vs 2.5)
and, therefore, a C=O group is polar
Polarity of a
carbonyl group
+
C
O: –
:
O
O:
:
C
C
:
δ+ δ-
More important
contributing
structure
 aldehydes and ketones are polar compounds and interact
in the pure state by dipole-dipole interactions
 they have higher boiling points and are more soluble in
water than nonpolar compounds of comparable molecular
weight

12. 2.2 Physical Properties
PROPERTY
OBSERVATION
Boiling
Point
RCHO having ≤ 5 C’s are H2O soluble because they can hydrogen bond with H2O.
RCHO having > 5 C’s are slightly soluble in H2O.
Solubility
δ-…………
δ+
H
δ+
H
O
Hydrogen bond with water.

13. 2.2 Physical Properties
Solubility of Aldehydes :

14. 2.0 PREPARATION OFALDEHYDE
2.1 Oxidation of 1° alcohol
2.2 Reduction of
2.2.1 Acyl Chlorides,
2.2.2 Esters
2.2.3 Nitriles

15. A) Oxidation of 1o
Alcohols
General formula:
Using PCC as oxidizing agent :
PCC: Pyridinium chlorochromate

16. A) Oxidation of 1o
Alcohols
 Using strong oxidizing agent:
O
CH3CH2 OH
Ethanol
H2CrO4
acetone
35oC
CH3 C OH
Ethanoic Acid
O
CH3CH2 OH
Ethanol
KMnO4/ H+
CH3 C OH
Ethanoic Acid

17. B) Reduction of Acyl
Chlorides
* Lithium aluminium tri(t-butoxy)hydride is a milder reducing agent that reacts
faster with acid chlorides than with aldehydes.
O
R C Cl
acid chloride
Li+ AlH(O-t-Bu)3
lithium aluminium tri(t-butoxy)hydride
O
R C H
aldehyde
Example:
CH3
O
CH3CHCH2C Cl
Li+ AlH(O-t-Bu)3
lithium aluminium tri(t-butoxy)hydride
CH3
O
CH3CHCH2C H

18. B) Reduction of Acyl
Chlorides
O
C
Cl
benzoyl chloride
CH3
O
CH3CHCH2C
Cl
isovaleryl chloride
LiAlH(O-t-Bu)3
O
C
H
benzaldehyde
LiAlH(O-t-Bu)3
CH3
O
CH3CHCH2C
H
isovaleraldehyde

19. 3.0 REACTIONS
3.1
3.2
3.3
3.4
Oxidation
Reduction
Nucleophilic Addition
Aldol Condensation &
Cannizaro Reaction
3.5 Iodoform reaction

20. 1) Oxidation of Aldehydes
 Aldehydes are easily oxidized to carboxylic acid by:
 strong oxidizing agent such as potassium permanganate,KMnO4
 mild oxidizing agent such as silver oxide, Ag2O in aqueous ammonia
(Tollen’s Test : differentiate between aldehyde & ketone)
 General Reaction
O
O
[o]
C
R
R
H
OH
[O] :
KMnO4, OHK2Cr2O7/H2SO4
Ag(NH3)2+OH- (Tollen’s reagent)
Carboxylic Acid
Aldehyde
 Examples
CH3─ CH2─ CH2─ CH2─ C─ H
O
K2Cr2O7
H2SO4
Pentanal
=
=
O
CH3─ CH2─ CH2─ CH2─ C─ OH
Pentanoic acid

21. 1) Oxidation of Aldehydes
Tollens’ Test (Silver Mirror Test)
In the laboratory, Tollens’ test may be used to distinguish between an
aldehyde and ketone. Tollens’ reagent, a solution of Ag+ (AgNO3) and
ammonia, oxidizes aldehyde, but not ketones. The silver ions is reduced
to metallic silver, which forms a layer called a “silver mirror” on the inside
of the container
* Tollens’ test is used to distinguish aldehydes from ketones. Ketones DO NOT react
with Tollens’s reagent.

22. 2) Reduction of Aldehydes
 Reduction of an
aldehyde gives a
primary alcohol .
 Aldehydes can be
reduced to alcohol
by
H2/Ni or H2/Pd
•
•
LiAlH4
•
NaBH4
(most often used)
H
Na
+
H- B- H
H
Li
+
H- A l- H
H
H
Sodium
Lithium aluminum
borohydride hydride (LAH)
H:
Hydride ion

23. 2) Reduction of Aldehydes
Examples:
CH3
C
ethanal
OH
O-
O
H
LiAlH4
CH3
C
H
H
H+
CH3
C
H
ethanol
H

24. 3.3
Nucleophilic Addition Reaction Of
3.3.1 HCN: Cyanohydrin Formation
3.3.2 Ammonia & Its Derivatives
3.3.3 Grignard Reagent :
Formation of Alcohol

25. 3) Nucleophilic Addition
 The carbonyl groups in aldehydes and ketones
are polarised because of the difference in the
electronegativity of carbon and oxygen.
 The carbon atom carries a partial positive charge
while oxygen atom carries a partial negative
charge.
 Aldehydes and ketones are susceptible to attack
both by nucleophiles at the carbonyl carbon atom
and by electrophiles at the oxygen atom.
δ+ δ-
C
nucleophilic attack
O
electrophilic attack

26. 3) Nucleophilic Addition
Nucleophilic Addition Reaction of :
a. HCN: Cyanohydrin Formation
b. NaHSO3
c. Grignard Reagent :
Formation of Alcohol

27. a) Nucleophilic addition of hydrogen cyanide
* Cyanohydrin may be formed using liquid HCN with a catalytic
amount of sodium cyanide or potassium cyanide.
O
R
C R'
OH
HCN
ketone or aldehyde
R
C R'
CN
cyanohydrin
example
O
CH3
C H
ethanal
OH
HCN
CH3
C H
CN
1-hydroxy-1-methylpropanenitrile

28. a) Nucleophilic addition of hydrogen cyanide
O
OH
R C
H
HCN
R C CN
aldehyde
OH
+
H2O/H
R C COOH
H
NH4
+
H
cyanohydrin
carboxylic acid
example
O
CH3
C
OH
H
HCN
ethanal
CH3
C CN
OH
+
H2O/H
CH3
H
C COOH
H
2-hydroxypanenitrile
2-hydroxypropanoic acid
(lactic acid)
MECHANISM
O
O
C
CN
C
H+
CN
NH4+
OH
C
CN

29. b) Nucleophilic addition of sodium bisulphite (NaHSO 3)
• When shaken with an aqueous of sodium bisulphite, most
aldehydes and ketones formed carbonyl bisulphite (a
colourless crystal).
• The reaction takes place more readily with aldehydes than
with ketones.
• The nucleophile is the hydrogensulphite ion, HSO3• Example:
O
NaHSO3
H C CH3
ethanal
OH
H
C CH3
OSO2- Na+
Bisulphite salts

30. 3) Condensation with Hydrazines,
Hydroxlamine and Phenylhydrazine
•
Aldehydes and ketones condense with ammonia derivatives such
as hydroxylamine and substituted hydrazines to give imine
derivatives.
i) Reaction with hydrazine:
Hydrazines derivatives reacts with aldehydes or ketones to form
hydrazones.
O
R C R'
H2N-NH2
aldehyde or ketone
+
H
hydrazine
N NH2
R C R'
H2O
C
hydrazone derivative
Example:
R N
O
C
H
benzaldehyde
H2N-NH2
hydrazine
H+
imine
N NH2
C
H
benzaldehyde hydrazone
H2O

31. 3) Condensation with Hydrazines,
Hydroxlamine and Phenylhydrazine
ii) Reaction with hydroxylamine:
Hydroxylamine reacts with ketones and aldehydes to form
oximes.
O
R C R'
aldehyde or ketone
H2N-OH
+
H
hydroxylamine
N OH
H 2O
R C R'
oxime
Example:
H
O
butanal
H2N-OH
hydroxylamine
H
H+
N
OH
butanal oxime
H 2O

32. 3) Condensation with Hydrazines,
Hydroxlamine and Phenylhydrazine
ii) Reaction with phenylhydrazine :
H
O
R C R'
aldehyde or ketone
N NH Ph
H
+
H
phenylhydrazine
N NH-Ph
R C R'
H 2O
phenylhydrazone
Example:
H
O
H
butanal
N NH Ph H+
H
phenylhydrazine
N-NH-Ph
H
butanal phenylhydrazone
H2O

33. 3a) Condensation with 2,4dinitrophenylhydrazine (2,4-dnp)
 A solution of 2,4-DNP in methanol and H2SO4: Brady’s
reagent.
 Aldehydes reacts with 2,4-DNP at room temperature to give
a yellow-orange precipitate of 2,4-dinitrophenylhydrazone.
Reagent
Positive Test

34. 3a) Condensation with 2,4dinitrophenylhydrazine (2,4-dnp)
NO2
H
C
O
NO2
H
benzaldehyde
room
temperature
O
H2N N
NO2
H
N N
NO2
H2O
benzaldehyde 2,4-dinitrophenylhydrazone
(yellow-orange precipitate)
NO2
C
C
NO2
H
2,4-dinitrophenylhydrazine
R
R'
H2N N
H
room
temperature
R
R' C
2,4-dinitrophenylhydrazine
NO2
N N
NO2
H
•
2,4-Dinitrohydrazones have characteristic sharp melting points.
•
The formation of a yellow or orange precipitate when 2,4-DNP
reacts with an organic compound at room temperature is used
a) As chemical test for aldehydes or ketones,
b) To identify an aldehyde or a ketone by measuring the melting point
of the 2,4-dinitrophenylhydrazone formed.
H2O

35. 4) Aldol Condensation
• Condensation : combination of two or more molecules with the loss of
a small molecule such as water or an alcohol.
• Aldol condensation : involves the nucleophilic addition of an enolate
ion to another carbonyl group.
• The product, a β-hydroxy ketone or aldehyde, is called an aldol
because it contains both an aldehyde group and the hydroxy group of
an alcohol.
• This reaction is for aldehyde or ketone that have α-hydrogen atom.
OH
O
R
C
CH2 R'
O
aldehyde or ketone
R
C
R
H+ or OH
CH2
R'
R
C CH2 R'
C
C
H
R'
O
aldol product

36. 4) Cannizaro Reaction
 Cannizaro reaction: Chemical reaction that involves the baseinduced disproportionation of an aldehyde lacking a hydrogen atom
in the alpha position.
 Disproportionation: oxidation-reduction reaction in which the same
element is both oxidized and reduced.
 Cannizzaro first accomplished this transformation in 1853, when he
obtained benzyl alcohol and benzoic acid from the treatment of
benzaldehyde with potash (potassium carbonate).
 In this disproportionation reaction, one molecule of the aldehyde
acts as an oxidant and converts a second molecule of aldehyde into
a carboxylic acid while consequently being reduced to an alcohol
itself.

37. 4) Cannizaro Reaction
Examples:
2 (CH3)3CCHO
NaOH
(CH3)3CCOONa + (CH3)3CCH2OH
aldehyde with no α-hydrogen atomcarboxylate salt
O
2CH3CH2CH
NaOH
aldehyde with α-hydrogen atom
CH3CH2
OH
C H
CH3CHC H
O
aldol product
alcohol

38. 5) Reaction With Grignard
Reagent
 A Grignard reagent (a strong nucleophile resembling a carbanion,
R:- attacks the electrophilic carbonyl carbon atom to give an
alkoxide intermediate.
 Subsequent protonation gives an alcohol.
H3C
C O
CH3CH2 MgBr
H
ethylmagnesium bromide
ethanal
CH3
CH3CH2 C O- +MgBr
H
alkoxide
H3O+
CH3
CH3CH2 C OH
H
2-butanol

39. 6) Haloform Reaction
IODOFORM TEST
- a solution of I2 in an alkaline medium such as NaOH or
KOH is a oxidising agent.
- when ethanal warmed with this solution,
triiodoethanal will be formed as the intermediate
product.
- triiodoethanal then reacts with the base to form a
yellow precipitate of triiodomethane (iodoform).
CH3CHO + 3I2 → CI3CHO + 3HI
triidoethanal
Cl3CHO + -OH → CHI3 + HCOOiodoform

40. 6) Haloform Reaction
•
•
Iodoform test is useful for the methyl ketone group (CH3C=O) in
ethanal and methyl ketones.
If an alkaline solution of iodine is warmed with an organic
compound and a yellow precipitate of triiodomethane is produced,
the organic compound is likely to be one of the following:
OH
ethanol CH3
C
O
H
ethanal CH3
H
OH
a secondary alcohol with the CH
3
O
a ketone with the CH3
C H
C
group
CH
group

41. 6) Haloform Reaction
 Iodoform test can be used to distinguish:
i) ethanal from other aldehydes, because ethanal is the only
aldehydes that gives a positive iodoform test.
ii) ethanol and secondary alcohols that contains the
CH3CH(OH)- group give a positive iodoform test.
iii) methyl ketones (ketones that contain CH3CO- group) give
positive iodoform test.
For example, propanone and phenylethanone give a yellow
precipitate, but 3-pentanone and diphenylmethanone
give negative iodoform tests.

42. 6) Haloform Reaction
O
O
C CH3
3I2
phenylethanone
O
C C I
warm
O
I
3HI
I
C O- Na+
NaOH
C C I
I
CHI3
I
The overall reaction is
O
C CH3
phenylethanone
3I2
NaOH
heat
O
C O- Na+
sodium benzoate
CHI3
3HI
iodoform
(yellow precipitate)

43. Thank you!