Transcript Naming Aldehydes & Ketones

Aldehydes and Ketones
Chapter 23
Hein * Best * Pattison * Arena
Version 1.0
Colleen Kelley
Chemistry Department
1 College
Pima Community
© John Wiley and Sons, Inc.
Chapter Outline
23.1 Structures of
Aldehydes and Ketones
23.4 Chemical and Physical
Properties of Aldehydes and Ketones
23.2 Naming Aldehydes and 23.5 Common Aldehydes and
Ketones
Ketones
23.3 Bonding and Physical
Properties
23.6 Condensation Polymers
2
Structures of
Aldehydes & Ketones
3
• Both aldehydes and ketones contain a
carbonyl ( C=O) group.
O
O
C
C
R
Ar
H
H
aldehydes
R
O
O
O
C
C
C
R
Ar
R
ketones
Ar
Ar
4
• The general formula for the
saturated homologous series of
aldehydes and ketones is:
CnH2nO
5
•In a linear expression, the
aldehyde group is often written as:
CHO
O
C
H3C
H
is equivalent to CH3CHO
6
•In the linear expression of a ketone,
the carbonyl group is written as:
CO
O
C
H3C
CH3
is equivalent to CH3COCH3
7
Naming
Aldehydes & Ketones
8
IUPAC Rules for Naming Aldehydes
1. To establish the parent name, select the
longest continuous chain of carbon
atoms that contains the aldehyde group.
2. The carbons of the parent chain are
numbered starting with the aldehyde
group. Since the aldehyde group is at
the beginning (or end) of a chain, it is
understood to be number 1.
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IUPAC Rules for Naming Aldehydes
3. Form the parent aldehyde name by
dropping the –e from the corresponding
alkane name and adding the suffix –al.
4. Other groups attached to the parent
chain are named and numbered as we
have done before.
10
Naming Aldehydes
O
C
H3C
H
ethanal
O
H
C
1
2 3 4 5 6
CH2CH2CHCH2CH3
4-methyhexanal
CH3
11
12
Common Names for Aldehydes
O
O
C
C
H
H
formaldehyde
H
CH3
acetaldehyde
O
C
H
13
benzaldehyde
Dialdehydes
• In dialdehydes, the suffix –dial is added to
the corresponding hydrocarbon name.
O
O
HCCH2CH2CH
butanedial
14
IUPAC Rules for Naming Ketones
1. To establish the parent name, select
the longest continuous chain of
carbon atoms that contain the ketone
group.
2. Form the parent name by dropping
the –e from the corresponding alkane
name and add the suffix –one.
15
IUPAC Rules for Naming Ketones
3. If the chain is longer than four carbons, it is
numbered so that the carbonyl group has the
smallest number possible; this number is
prefixed to the parent name of the ketone.
4. Other groups attached to the parent chain are
named and numbered as we have done before.
16
Naming Ketones
O
O
C
H3C
CH3
propanone
C
1
3 4 5
2
H3C
CH2CH2CH3
2-petanone
O
1 2
H3CH2C
C
3
4 5 6 7 8
CH2CH2CHCH2CH3
6-methyl-3-octanone
CH3
17
Common Names for Ketones
O
O
C
C
H3C
CH3
propanone
acetone
H3C
CH2CH3
butanone
methyl ethyl ketone, MEK
18
Bonding and
Physical Properties
19
Bonding
• The carbon atom of the carbonyl group
is sp2-hybridized and is joined to three
other atoms by sigma bonds.
• The fourth bond is made by
overlapping p electrons of carbon and
oxygen to form a pi bond between the
carbon and oxygen atoms.
20
Bonding
• Because the oxygen atom is considerably
more electronegative than carbon, the C=O
group is polar.
• Many of the chemical reactions of
aldehydes and ketones are due to this
polarity.
C
+

O

21
Properties
• Unlike alcohols, aldehydes and ketones
cannot hydrogen-bond to themselves,
because no hydrogen atom is attached
to the oxygen atom of the carbonyl
group.
• Aldehydes and ketones, therefore, have
lower boiling points than alcohols of
comparable molar mass.
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23
Chemical Properties of
Aldehydes & Ketones
24
Reactions of Aldehydes & Ketones
• Oxidation
– aldehydes only
• Reduction
– aldehydes and ketones
• Addition
– aldehydes and ketones
25
Oxidation of Aldehydes
• Aldehydes are easily oxidized to carboxylic
acids by a variety of oxidizing agents,
including (under some conditions) oxygen
of the air.
O
O
3
3
+
C
R
H
Cr2O72-
+
+ 8H
+ 3 Cr3+ + 4H2O
C
R
OH
26
Tollens test
• The Tollens test (silver-mirror test) for
aldehydes is based on the ability of silver
ions to oxidize aldehydes.
O
C
R
O
+ 2 Ag+
H
NH3
H2O
+ 2 Ag (s)
C
R
O-NH4+
27
Fehling and Benedict Tests
• Fehling and Benedict solutions contain
Cu2+ ions in an alkaline medium.
• In these tests, the aldehyde group is
oxidized to an acid by Cu2+ ions.
O
C
R
O
+2
+ 2 Cu
H blue
NaOH
H2O
+ 2 Cu2O (s)
C
R
O-Na+
brick red
28
Tollens, Fehling & Benedict Tests
• Because most ketones do not give a
positive with Tollens, Fehling, or Benedict
solutions, these tests are used to distinguish
between aldehydes and ketones.
O
C
R
+ 2 Cu+2 NaOH no reaction
H2O
R
O
C
R
+ 2 Ag+
R
NH3
H2O
no reaction
29
Biochemical Oxidation of Aldehydes
• When our cells ‘burn’ carbohydrates, they
take advantage of the aldehyde reactivity.
• The aldehyde is oxidized to a carboxylic
acid and is eventually converted to carbon
dioxide, which is then exhaled.
• This stepwise oxidation provides some of
the energy necessary to sustain life.
30
Reduction of Aldehydes & Ketones
• Aldehydes and ketones are easily
reduced to alcohols.
O
H2/Ni
heat
C
R
RCH2OH
primary
alcohol
H
O
H2/Ni
heat
C
R
R
OH
RCHR
secondary
alcohol
31
Addition Reactions of Aldehydes & Ketones
• Common addition reactions:
– Addition of alcohols
• hemiacetal, hemiketal, acetal, ketal
– Addition of hydrogen cyanide (HCN)
• cyanohydrin
– Aldol Condensation (self-addition)
32
Addition of Alcohols
• Aldehydes react with alcohols in the
presence of a trace of acid to form
hemiacetals:
OH
O
+ CH3OH
C
H
CH2CH3
propanal
H+
HC CH2CH3
OCH3
1-methoxy-1-propanol
(propionaldehyde methyl hemiacetal)
33
Addition of Alcohols
• In the presence of excess alcohol and strong
acid such as dry HCl, aldehydes or
hemiacetals react with a second molecule of
the alcohol to give an acetal:
OH
HC CH2CH3 + CH3OH
OCH3
OCH3
dry HCl
HC CH2CH3 +H2O
OCH3
1,1-dimethoxypropane
(propionaldehyde dimethyl acetal)
34
Addition of Alcohols to
Aldehydes and Ketones
OH
OH
OR'
OR'
C
C
C
C
R
OR'
H
hemiacetal
R
OR'
R
hemiketal
R
H
OR'
acetal
R
R
OR'
ketal
35
Addition of Hydrogen Cyanide
• The addition of HCN to aldehydes and ketones
forms a class of compounds known as
O
cyanohydrins:
OH
+ HCN
C
H
CH3
acetaldehyde
O
+ HCN
C
H3C
CH3
acetone
HO
-
HO
-
HC CH3
CN
acetaldehyde
cyanohydrin
OH
H3CC CH3
CN
acetone
cyanohydrin
36
Aldol Condensation (Self-Addition)
• In a carbonyl compound, the carbon atoms are
labeled alpha (), beta (), gamma (), delta (),
and so on, according to their positions with
respect to the carbonyl group.
-C-C-C-C=O
 
• The hydrogen atoms attached to the -carbon
have the unique ability to be more easily
released as protons than other hydrogens within
the molecule.
37
Aldol Condensation (Self-Addition)
• An aldehyde or ketone that contains hydrogens may add to itself or to another hydrogen containing aldehyde or ketone.
O
C
H
H
CH3
O
dilute
NaOH
H
C
H
C
H
OH
H
O
CH
H3C
C
H2C
H
aldol
(3-hydroxybutanal)
38
Common Aldehydes &
Ketones
39
Formaldehyde (Methanal)
• Formaldehyde is made from methanol by
reaction with oxygen (air) in the presence
of a silver or copper catalyst.
Ag
• 2 CH3OH + O2  2H2C=O + 2H2O
heat
• Formaldehyde is widely used in the
synthesis of polymers.
40
Acetaldehyde (Ethanal)
•
Its principal use is as an intermediate in
the manufacture of other chemicals, such
as acetic acid and 1-butanol.
41
Acetone and Methyl Ethyl Ketone
•
•
Acetone is used as a solvent in the
manufacture of drugs, chemicals, and
explosives. It is also used as a
solvent.
Methyl ethyl ketone (MEK) is also
widely used as a solvent, especially
for lacquers.
42
Condensation Polymers
43
Phenol-Formaldehyde Polymers
(Bakelite)
• Each formaldehyde molecule reacts with two phenol
molecules to eliminate water. The polymer is then
OH
formed. OH
O
+
+
C
H
H
OH
OH
H2
C
+ H2O
44
Phenol-Formaldehyde Polymers
(Bakelite)
• Polymers of this type are still used,
especially in electrical equipment,
because of the insulating and fire-resistant
properties.
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