oc-ch7 Aldehyde and ketone.ppt

Chapter 7
Aldehydes and Ketones
Zhou Na
School of Chemistry
and Chemical Engineering

Introduction
 Have you ever sensed an odor that
suddenly brought back a long-forgotten
memory?
 If so, you have experienced a
phenomenon unique to our sense of
smell —— it is a primitive sense and
the only one for which the related
sensory nerves are part of the brain
itself.

 These nerves respond to both the
shape and the presence of polar
functional groups in volatile molecules,
and prominent among the organic
compounds with the most potent and
varied odors are those possessing the
C=O double bond, the carbonyl group.
 Two classes of carbonyl compounds:
Aldehydes
Ketones
Introduction
O
C
Carbonyl group
O
C
R H
An aldehyde
O
C
R R’
An ketone

 These compounds exist throughout
nature, contributing to the flavors and
aromas of many foods and assisting in
the biological functions of a number of
enzymes.
 In addition, industry makes considerable
use of aldehydes and ketones, both as
reagents and as solvents in synthesis.
 The carbonyl group is considered to be
the most important function in organic
chemistry.
Introduction

Content:
 Nomenclature
 Structure of C=O group
 Chemical properties
 Uses

 The C=O function is the highest ranking
group we have encountered so far for the
purposes of naming.
 The CHO function takes precedence over
that of ketones.
7.1 Nomenclature
OH O
CH3－C－CH2－CH=CH－CH2－C－CH3
CH3
8 7 6 5 4 3 2 1

7.1 Nomenclature
 Common names
Simpler aldehydes are often called by
their common names, which derived
from the common names of the
corresponding acids.
Replace the ending -ic acid by -aldehyde
O O
C C
H OH H H
Formic acid Formaldehyde

7.1 Nomenclature
O O
C C
H3C OH H3C H
Acetic acid Acetaldehyde
HO O
C
H O
C
Benzoic acid Benzaldehyde

 Aromatic aldehydes
Designated as derivatives of benzaldehyde.
7.1 Nomenclature
H O
C
H O
C
NO2
H O
C
OCH3
H O
C
OH
Benzaldehyde
o-Hydroxybenzaldehyde
p-Methoxybenzaldehyde
p-Nitrobenzaldehyde

 Common names
 Ketones (substituent + ketone)
7.1 Nomenclature
O O
CH3－C－ CH3 CH3－C－CH2CH3
Dimethyl ketone Ethyl methyl ketone
(Acetone)
O O
CH3－C－ CH=CH2 CH3CH2－C－
Methyl vinyl ketone Cyclopentyl ethyl ketone

 Phenyl ketones (substituent + ketone)
Methyl phenyl ketone Diphenyl ketone
Acetophenone Benzophenone
7.1 Nomenclature
O O
CH3－C－－C－

 Common names
Aldehydes
derived from corresponding acid
Ketones
substituent + ketone
7.1 Nomenclature

 IUPAC name
 Aldehydes
Treat aldehydes as derivatives of alkanes
drop the suffix -e and replace it with -al.
Alkane alkanal
methanal ethanal propanal
7.1 Nomenclature
O O O
H－C－H CH3－C－H CH3CH2－C－H
Formaldehyde Acetaldehyde

 Substituted aldehydes
1. Numbering and listing the substi-
tuents alphabetically.
2. The CHO group is assigned the number
1 position and takes precedence over OH,
C=C.
7.1 Nomenclature
Cl O O
CH3CH－C－H HO－CH2CH2－C－H
2-Cholropropanal 3-Hydroxypropanal
3 2 1 3 2 1

 IUPAC name
 Ketones (alkanones)
The ending -e of alkane replaced with -one
Give the C in C=O the lowest number
Butanone 2- Pentanone
3-Chloro-2-pentanone
7.1 Nomenclature
O O
CH3－C－CH2CH3 CH3－C－CH2CH2CH3
O
CH3CH2CH－C－CH3
Cl
5 4 3 2 1 1 2 3 4 5

 Cyclic ketones (cycloalkanones)
Numbering starts from the C=O group.
7.1 Nomenclature
3-Ethylcyclohexanone
CH2CH3
O
1
3

 Aromatic ketones
(aryl-substituted alkanones)
1-Phenylethanone
7.1 Nomenclature
C
CH3
O
1
2

 IUPAC name
Aldehydes
Alkane alkanal
give CHO group No. 1 position
Ketones
Alkane alkanone
give C=O the lowest number
7.1 Nomenclature

 Aldehydes and Ketones
with Other Functional Groups
7.1 Nomenclature
O
CH3－CH=CH－C－H
2-Butenal
4 3 2 1

OH O
CH3－C－CH2－CH=CH－CH2－C－CH3
CH3
8 7 6 5 4 3 2 1
7-Hydroxy-7-methyl-4-Octen-2-one
7.1 Nomenclature


7.1 Nomenclature
O
CH3CHCH2CHCH2CH2－C－H
CH3 Cl
1
2
3
4
5
6
7
4-Chloro-6-methyl-heptanal

O
CH=CH2
Br
1
2
3
2-Bromo-3-vinylcyclohexanone
7.1 Nomenclature

 The C=O contains a short, strong, and
very polar bond
 O is more electronegative than C, this
cause an appreciable polarization of the
C=O bond.
7.2 Structure of the C=O group
C＝O C－O
+ -
Electrophilic
Nucleophilic
and basic
or C＝O
δ+ δ-

 Polarization alters the physical constants
of aldehydes and ketones
 The polarization of the C=O
1. Makes the B.P. higher than
2. The smaller carbonyl compounds are
completely miscible with water. As no. of
C > 6, rather insoluble.
Hydrophobic hydrocarbon part increase

 Summarize
 The C=O in aldehydes and ketones is an
oxygen analog of the C=C bond.
 The electronegativity of O > C
C＝O
δ+ δ-

7.3 Chemical Properties
 Reactions of the C=O group
 Reactions of the alkyl group(s) adjacent
to the C=O group
 Oxidation reactions

7.3.1 Reactions of the C=O group
 Nucleophilic addition reactions
C＝O
δ+ δ-
C＝O C－O
+ -
Electrophilic
Nucleophilic
and basic

 Nucleophilic addition reactions
HCN
NaHSO3
NaBH4
Grignard Reagent
ROH
Ammonia derivative

1. React with HCN
2-Hydroxypropanenitrile Lactic acid
OH OH
CH3CHO + HCN CH3－C－H CH3－C－H
CN COOH
H2O, H+
heat

 The reaction occur very slowly
 HCN is a very weak acid
HCN + H2O CN- + H3O+
Ka = 5×10-10
very small proportion of CN- is contained.
O O OH
CH3－C－H CH3－C－H CH3－C－H
C C C
N N N
H+

while in the presence of alkali
HCN + OH- CN- + H2O
much larger concentration of CN- is present
 The rate are greatly increased.
 In the laboratory, replace HCN + alkali by
alkali- metal cyanide (KCN) + acid.
 Too much acid is avoided.
Reduced concentration of CN-. Low rate

2. React with NaHSO3
OH
(CH3)2C=O + NaHSO3 (CH3)2C
SO2－O- Na+
O CH3 O CH3
-O－S C=O O=S－C－O -
HO CH3 HO CH3
HSO3
- as nucleophilic reagent

SO3
2- as nucleophilic reagent
 Theoretically, the SO3
2- reacts more rapidly,
but HSO3
- is a weak acid
HSO3
- + H2O SO3
2- + H3O+
Ka = 1.1×10-7
Usually, [HSO3
-] is much greater than [SO3
2-]
O CH3 O CH3
-O－S C=O O=S－C－O -
O CH3 O CH3

 Ketones undergo this reaction:
At least one of the two groups attached
to the C=O is - CH3. (Which has the
smallest steric hindrance)
 The test can be used to distinguish a
ketone whether has a - CH3 or not.

3. React with NaBH4
RCH=O NaBH4 RCH2－OH
R2C=O R2CH－OH
4CH3CH=O + NaBH4 (CH3CH2O)4B- Na+
(CH3CH2O)4B- Na+ + 3H2O 4CH3CH2OH + NaH2BO3
RCH=O RCH2－OH
R2C=O R2CH－OH
Na + ethanol
Zn + ethanoic acid

4. React with Grignard reagents
R-Mg+X + R－C－O-Mg+X R－C－OH
H H H
CH3MgCl + H－C=O CH3COMgCl CH3－C－OH
H H
C＝O
δ+ δ- H2O
H+

5. Addition of alcohols
O OH
R－C－H + R’OH R－C－OR’
H
O OH
R－C－R + R’OH R－C－OR’
R
Hemiacetal
Hemiketal
Hemiacetals and hemiketals are too
unstable to be isolated, cyclic hemiacetals
and hemiketals are integral parts of the
structure of simple sugars

6. Addition of ammonia derivatives
 Aldehydes and ketones + compounds contain
the - NH2 group oximes + H2O
CH3CH=O + NH2OH CH3CH=N－OH + H2O
Ethanal oxime
(CH3)2C=O + NH2OH (CH3)2C=N－OH + H2O
Propanone oxime

 Aldehydes and ketones + Hydrozine(NH2NH2)
Hydrazones azines
CH3CH=O + NH2NH2 CH3CH=N－NH2 + H2O
CH3CH=N－NH2 + CH3CH=O
CH3CH=N－N=CHCH3 + H2O
 Pheylhydrazine phenylhydrazones
C6H5CH=O + H2N－NH－C6H5
C6H5CH=N－NH－C6H5 + H2O
Benzaldehyde phenylhydrazone

C6H5
C=O + H2N－NH－－NO2
CH3 O2N
C6H5
C=N－NH－－NO2 + H2O
CH3 O2N
2,4-Dinitrophenylhydrazine
Phenylethanone
2,4-dinitrophenylhydrazone

 Primary amines imines
C6H5CH=O + H2N－C6H5 C6H5CH=N－C6H5 + H2O
Many of the derivatives with amines are unstable
 Used for the characterisation of aldehydes and
ketones
 The products are mostly crystalline solids and
their M.P. are sufficiently different from
aldehydes and ketones, and enable the
carbonyl compound to be recognized.

7.3.2 Reactions of the alkyl group
1. Aldehydes and ketones which possess
at least one H atom on the C atom
adjacent to the C=O group undergo
condensation reactions in the presence
of a base.
O O H O
RCH2－C－H + RCH2－C－H RCH2－C－CH－C－H
OH R
dil OH-
β α
An aldol

3-Hydroxybutanal
O O
2CH3－C－H CH3－CH－CH2－C－H
OH
dil OH- β α
O
CH3－CH－CH2－C－H CH3－CH=CH－CH=O + H2O
OH
heat
2-Butenal

O O
2(CH3)2 C=O (CH3)2CH－CH2－C－CH3
OH
NaOH
(CH3)2C=CH－C－CH3
O
- H2O
Propanone
4-Hydroxy-4-methylpentan-2-one

 The products in all aldol condensations
has several common structural
characteristics:
1. A larger molecule contains a newly formed C-C
bond.
2. The C-C bond occurs between the α C of one
aldehyde molecule and the carbonyl C of the
second aldehyde molecule.

3. Two functional group: C=O and -OH.
4. The - OH is attached to the β C.
 Aldols are easily dehydrated either by
heating or by treatment with dilute acid.
O
CH3－CH－CH2－C－H CH3－CH=CH－CH=O + H2O
OH
heat
3-Hydroxbutanal
(aldol)
2-Butenal

 The facile loss of water is due to the fact
that the resulting product contains a C=C
bond that is conjugated with the C=O
group ( an α,β-unsaturated aldehyde).
CH3－CH=CH－CH=O
β α

 Those aldehydes which don’t contain at
least one H atom on the C next to the C=O
group don’t undergo condensation
reactions with alkali.
 But instead with concentrated alkali,
undergo Cannizzaro reaction in which one
half of the quantity of the aldehyde is
oxidized and the other half is reduced.
2C6H5CH=O + NaOH C6H5CO2
-Na+ + C6H5CH2OH
Sodium benzoate
Phenylmethanol

 The carbonyl compound contains the
group CH3－CO (I.e. Ethanal or a methyl
ketone) reaction in the presence of alkali
leads first to the replacement of all three
H atoms in methyl group by X atoms.
CH3－CH2－CO－CH3 + 3Cl2 + 3NaOH
CH3－CH2－CO－CCl3 + 3H2O + 3NaCl

CH3－CH2－CO－CCl3 + NaOH
CH3－CH2－CO2
-Na+ +
CHCl3
 Similarly, Br2 gives tribromomethane
CHBr3, and I2 gives CHI3.
 Iodoform test
 CHI3 is a yellow crystalline solid which is
easily recognized, this reaction can be
used as a test to identify either ethanal or
a methyl kentone is exist.

 Since alcohols which contain the group
－CH(OH)－CH3 (ethanol and 2-propanol)
are oxidized by iodine to give the group
－CO－CH3, these also give a positive
iodoform test.
－CH(OH)－CH3 －CO－CH3
I2
I2
NaOH
Yellow crystalline solid

7.3.3 Oxidation reactions
 Oxidation of aldehydes
 Oxidation of ketones
The difference between an aldehyde and a
ketone is that the - CH=O group is readily
oxidized to - COOH. While ketones are
difficult to oxidized in solution.

7.3.3.1 Oxidation of aldehydes
 Reactions for distinguish -al and -one
1. Tollens’ test
RCH=O+Ag(NH3)2
+(OH)- Ag↓+ RCOO- +Others
RCOR + Tollens’ reagent no reaction
R－C－H R－C－OH
O O
Na2Cr2O7
H2SO4
Tollens’ reagent

2. Fehling’s test
Which is made by mixing a solution of
CuSO4 with an alkaline solution of a salt
of tartaric acid.
RCHO + 2Cu2+ + NaOH + H2O
RCOONa + Cu2O↓+ 4H+
Only apply to saturated aldehydes

3. Schiff’s test
Fuchsin is a pink dye which forms a
colorless complex when treated with SO2.
The addition of an aldehyde to this
colorless solution restores the pink color
of the dye.

 Ketones are oxidized by strong oxidizing
agents (KMnO4 or hot HNO3).
 The bond between the C=O group and
the adjacent C is broken
CH3－CH2－CO－CH2－CH3
CH3－CH2－COOH + CH3－COOH
The acids formed contain fewer C atoms
than the ketone.
7.3.3.2 Oxidation of ketones
HNO3

7.4 Uses
 Methanal
1. In the manufacture of thermosetting
plastics , in particular Bakelite.
2. In solution it is used as a disinfectant
and to preserve animal specimens.

 Ethanal
 In the manufacture of ethanoic acid.
 Propanone
1. In the manufacture of Perspex
2. In the manufacture of ethenone, used to
make ethanoic anhydride
3. As a solvent for plastics, varnishes and
greases.

oc-ch7 Aldehyde and ketone.ppt

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