Aldehydes and Ketones
Introduction
Aldehydes are compounds of the general formula RCHO;
Ketones are compounds of the general formula RR´CO. The
groups R and R´ may be aliphatic or aromatic.
O
O
O
C
C
C
R
H
Aldehyde
R
R
Ketone
Carbonyl group
Both aldehydes and ketones contain the carbonyl group,
C=O, and are often called carbonyl compounds.
 An aldehyde is often written as RCHO. Remember that the H
atom is bonded to the carbon atom, not the oxygen.
 Likewise, a ketone is written as RCOR, or if both alkyl groups
are the same, R2CO. Each structure must contain a C––O for
every atom to have an octet.
 The three bonds (carbon, oxygen, and the two other atoms
attached to carbonyl carbon) lie in a plane; the three bond angels
of carbon are very close to 120º.
Nomenclature
Both IUPAC and common names are used for aldehydes
and ketones.
 Naming Aldehydes in the IUPAC System
To name an aldehyde using the IUPAC system:
[1] If the CHO is bonded to a chain of carbons, find the longest
chain containing the CHO group, and change the -e ending of the
parent alkane to the suffix -al.
If the CHO group is bonded to a ring, name the ring and add the
suffix -carbaldehyde.
[2] Number the chain or ring to put the CHO group at C1
Example:
Give the IUPAC name for the compound:
Give the IUPAC name for the compound:
H
H
O2N
C O
p-nitrobenze carbaldehyde
H3C
C O
p-methylbenze carbaldehyde
Common Names for Aldehydes
The common names of aldehydes are derived from the
names of the corresponding carboxylic acids by replacing –ic acid
by –aldehyde.
Greek letters are used to designate the location of substituents
in common names. The carbon adjacent to the CHO group is the `
carbon, and so forth down the chain.
Naming Ketones in the IUPAC System
 To name an acyclic ketone using IUPAC rules:
[1] Find the longest chain containing the carbonyl
group, and change the -e ending of the parent alkane
to the suffix -one.
[2] Number the carbon chain to give the carbonyl carbon
the lower number. Apply all of the other usual rules
of nomenclature.
Common Names for Ketones
Most common names for ketones are formed by
naming both alkyl groups on the carbonyl carbon,
arranging them alphabetically, and adding the word
ketone. Using this method, the common name for
2-butanone becomes ethyl methyl ketone.
O
O
O
H3C C CH3
H3CH2C C CH3
H3CH2CH2C C CH3
Propanone
Acetone
Butanone
Methyl ethyl ketone
2-Pentanone
O
O
C CH3
C CH2CH2CH3
Acetophenone
n-Butyrophenone
O
C
Benzophenone
Physical properties:
Boiling point:
 Aldehydes and ketones are polar compounds due to the
polarity of carbonyl group and hence they have higher boiling
points than non polar compounds of comparable molecular
weight.
 But they have lower boiling points than comparable alcohols or
carboxylic acids due to the intermolecular hydrogen bonding.
Solubility:
The lower aldehydes and ketones soluble in
water, because of hydrogen bonding between carbonyl
group and water, also they soluble in organic solvents.
Preparation of aldehydes & Ketones.
Preparation of aldehydes.
1. Oxidation of primary alcohols:
 Primary alcohols can be oxidized to give aldehydes by using
of K2Cr2O7.
RCH2OH + Cr2O7-1o alcohol
Orange-red
H
R C O + Cr+++
An aldehyde
K2Cr2O7
OH
R C O
A carboxylic acid
Green
O
2- synthesis of benzaldehyde
CHCl2
C H
H2O
CH3
Cl 2
t
a
e
,h
O
ace
t
CrO
ic a
3
nh
yd
rid
e
O
CH(OCCH3)2
C H
H2O
3. Partial reduction of acid chlorides
Strong reducing agents (like LiAlH4) reduce acid chlorides all the
way to primary alcohols. Lithium aluminum tri(t-butoxy)hydride
is a milder reducing agent that reacts faster with acid chlorides than
with aldehydes. Reduction of acid chlorides with lithium aluminum
tri(t-butoxy)hydride gives good yields of aldehydes.
(-78ºC)
Preparation of Ketones
1. Oxidation of Secondary alcohols:
Secondary alcohols are oxidized to ketones by chromic
acid (H2CrO4) in a form selected for the job at hand: aqueous
K2Cr2O7, CrO3 in glacial acetic acid, CrO3 in pyridine, etc. Hot
permanganate also oxidizes alcohols; it is seldom used for the
synthesis of ketones.
R-
RR C OH
H
A 2o alcohol
K2Cr2O7 or CrO3
R C O
A ketone
2. Cleavage of Carbon–Carbon double bond by Ozone:
Oxidative cleavage of an alkene breaks both the σ and π
bonds of the double bond to form two carbonyl groups. Depending
on the number of R groups bonded to the double bond, oxidative
cleavage yields either ketones or aldehydes.
3. Friedel-Crafts acylation.
The Friedel-Crafts reaction involves the use of acid
chlorides rather than alkyl halides. An acyl group (RCO–)
becomes attached to the aromatic ring. Thus forming a ketone; the
process is called acylation.
O
Ar H + R C
Cl
O
AlCl3
or other
Lewis acid
Ar
C R + HCl
4. Hydration of alkynes.
Alkynes undergo acid-catalyzed addition of water across the
triple bond in the presence of mercuric ion as a catalyst. A mixture of
mercuric sulfate in aqueous sulfuric acid is commonly used as the
reagent.
Reactions
a) Addition of Alcohols (Acetal Formation):
Aldehydes and ketones react with two equivalents of
alcohol to form acetals. In an acetal, the carbonyl carbon from the
aldehyde or ketone is now singly bonded to two OR" (alkoxy)
groups.
b) Nucleophilic Addition of CN– :
Treatment of an aldehyde or ketone with NaCN and a strong
acid such as HCl adds the elements of HCN across the
carbon–oxygen π bond, forming a cyanohydrin.
H
C O
NaCN
NaHSO3
Benzaldehyde
H
C CN
OH
Mandelonitrile
O
H3C
C
CH3
CH3
CH3 + NaCN
Acetone
H2SO4
H3C
C
CN
H2O, H2SO4
H3C
COOH
C
OH
OH
Acetone cyanohydrin
- H2O
CH3
H2C
C
COOH
Methacrylic acid
c) Addition of organometallic reagents (R–)
The addition of Grignard reagents to aldehydes and ketones
yields alcohols. The organic group, transferred with a pair of electrons
from magnesium to carbonyl carbon, is a powerful nucleophile.

O
C


+ R: MgX
C OMgX
R
H2O
C OH
R
+ Mg(OH)X
H+
Mg++ + X- + H2O
d) Addition of derivatives of Ammonia (Formation of imine).
 Treatment of an aldehyde or ketone with a 1° amine affords an
imine (also called a Schiff base).
 Nucleophilic attack of the 1° amine on the carbonyl group forms an
unstable carbinolamine, which loses water to form an imine. The
overall reaction results in replacement of C=O by C=NR.
Oxidation reaction

Aldehydes are readily oxidized to yield carboxylic acids; but
ketones are generally inert toward oxidation.

The difference is a consequence of structure: aldehydes have a
–CHO proton that can be abstracted during oxidation, but ketones
do not.
Hydrogen here
O
C
R
H
An aldehyde
[O]
R
O
O
C
C
OH
Carboxylic acid
R
R
A ketone
No hydrogen
here

Many oxidizing agents, including KMnO4 and hot HNO3,
convert aldehydes into carboxylic acid.
But CrO
in aqueous acid is a more common choice in the
laboratory. The oxidation occurs rapidly at room temperature and
results in good yields.
3
hot HNO3
RCHO or ArCHO
KMnO4
K2Cr2O7
RCOOH or ArCOOH
Methyl ketones:
Oxidation of ketones required breaking of C–C bond next to
the carbonyl group and takes place only under vigorous conditions,
except for methyl ketones which oxidized smoothly by mean of
hypohalite (NaOX) to form Haloform (Haloform reaction).
Aldol condensation
 Under the influence of
dilute base or dilute acid , two molecules
of an aldehyde or a ketone, which contained α-hydrogen , may
combine to form a β-Hydroxy aldehyde or β-Hydroxy ketone.
This reaction is called the Aldol condensation .
Aldehyde
alcohol
Mechanism:
If
aldehyde or ketone does not contain an α-hydrogen, a
simple Aldol condensation cannot take place.
For example:
ArCHO
HCHO
(CH3)3CCHO
ArCOAr
ArCOCR3
No
-hydrogen
atoms
dilute OH-
No reaction
Cannizzaro reaction.
In the presence of concentrated alkali, aldehydes containing
no α-hydrogen undergo self-oxidation and reduction to yield a
mixture of an alcohol and a salt of a carboxylic acid. This reaction
is known as the Cannizzaro reaction.
H
2
C O
An aldehyde with
no hydrogen
strong base
COOAcid
salt
+
CH2OH
Alcohol
Examples:
H
50% NaOH
2 H C O
Formaldehyde
2 O2N
CHO
room temp.
35% NaOH
p-Nitrobenzaldehyde
O2N
H COO+
Formate ion
CH2OH
50% KOH
+
2
m-Chlorobenzaldehyde
COO- Na+
Sodium p-nitrobenzoate
COO-
Cl
Methanol
CH2OH + O2N
p-Nitrophenyl alcohol
CHO
CH3OH
Cl
m-Chlorobenzoate
ion
Cl
m-Chlorobenzyl
alcohol