Transcript Hein and Arena - faculty at Chemeketa

1
Structures of
Aldehydes & Ketones
2
• 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
3
•In a linear expression, the
aldehyde group is often written as:
CHO
O
C
H3C
H
is equivalent to CH3CHO
4
•In the linear expression of a ketone,
the carbonyl group is written as:
CO
O
C
H3C
CH3
is equivalent to CH3COCH3
5
Naming
Aldehydes & Ketones
6
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.
7
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.
8
Naming Aldehydes
O
C
H3C
H
ethanal
ethanal
O
H
C
1
2 3 4 5 6
CH2CH2CHCH2CH3
4-methylhexanal
4-methyhexanal
CH3
9
10
Common Names for Aldehydes
O
O
C
C
H
H
formaldehyde
H
CH3
acetaldehyde
O
C
H
11
benzaldehyde
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.
12
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.
13
Naming Ketones
O
O
C
H3C
CH3
propanone
C
1
3 4 5
2
H3C
CH2CH2CH3
2-petanone
2-pentanone
O
1 2
H3CH2C
C
3
4 5 6 7 8
CH2CH2CHCH2CH3
6-methyl-3-octanone
CH3
14
Common Names for Ketones
O
O
C
C
H3C
CH3
propanone
acetone
H3C
CH2CH3
butanone
methyl ethyl ketone, MEK
15
Bonding and
Physical Properties
16
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.
17
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

18
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.
19
Effect of Hydrogen Bonding on Physical Properties
20
Mole Weight
Boiling point oC
21
Chemical Properties of
Aldehydes & Ketones
22
Reactions of Aldehydes & Ketones
• Oxidation
– aldehydes only
• Reduction
– aldehydes and ketones
• Addition
– aldehydes and ketones
23
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
24
Tollens’ Silver Mirror Test
• Tollens’ reagent,
which contains Ag+,
oxidizes aldehydes,
but not ketones.
• Ag+ is reduced to
metallic Ag, which
appears as a
“mirror” in the test
tube.
Ag+ + e– → Ag(s)
O
C
R
O
+ 2 Ag+
H
NH3
H2O
+ 2 Ag (s)
C
R
O-NH4+
25
26
Fehling and Benedict Tests
• Benedict’s reagent,
which contains Cu2+ ions
in an alkaline medium,
reacts with aldehydes
that have an adjacent
OH group.
• an aldehyde is oxidized
to a carboxylic acid,
while Cu2+ is reduced to
give brick red Cu2O(s).
28
Increasing amounts of reducing sugar
green  orange  red  brown
29
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
30
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.
31
Reduction of Aldehydes & Ketones
Aldehydes and ketones are easily reduced to alcohols using LiAlH4,
NaBH4 , or H2/Ni .
Aldehydes yield primary alcohols (1) while ketones yield secondary
alcohols ( 2) .
32
Addition Reactions of Aldehydes & Ketones
• Common addition reactions:
– Addition of alcohols
• hemiacetal, hemiketal, acetal, ketal
– Grignard preparations of alcohols
– 2,4-dinitrophenylhydrazine (2,4-DNP)
33
Addition of Alcohols
Aldehydes react with alcohols and a trace of acid to yield hemiacetals
as shown here.
34
Addition of Alcohols
In the presence of excess alcohol and a strong acid such as dry HCl,
aldehydes or hemiacetals react with a second molecule of the alcohol
to yield an acetal.
35
Intramolecular Addition of Alcohols
Cyclic hemiacetals or hemiketals can form when the alcohol and
the carbonyl group exist within the same molecule .
36
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
37
Grignard preparations of alcohols
• A Grignard reagent is an
organic magnesium halide. It
can be either an alkyl or an
aryl compound (RMgX or
ArMgX). Grignard
(pronounced green yard)
reagents were first prepared
in France around 1900 by
Victor Grignard (1871-1935).
38
• Grignard reagents are usually made by
reacting an organic halide and
magnesium metal in an ether solvent:
RX
ArX
+
+
Mg
Mg
ether
ether
RMgX
X = Cl, Br, or I
ArMgX
X = Br
39
• In the Grignard reagent, the bonding
electrons between carbon and
magnesium are shifted away from the
electropositive Mg to form a strongly
polar covalent bond. As a result the
charge distribution in the Grignard
reagent is such that the organic group
(R) is partially negative and the –MgX
group is partially positive. This charge
distribution directs the manner in
which Grignard reacts with other
compounds.
40
• The Grignard reagent is one of the
most versatile and widely used
reagents in organic chemistry. We will
consider only its reactions with
aldehydes and ketones at this time.
Grignards react with aldehydes and
ketones to give intermediate products
that form alcohols when hydrolyzed.
With formaldehyde, primary alcohols
are formed; with other aldehydes,
secondary alcohols are formed; with
ketones, tertiary alcohols are formed.
41
Examples
Grignard reagent + formaldehyde → 1º ROH
Grignard reagent + other aldehydes → 2º ROH
Grignard reagent + ketones → 3º ROH
CH3
H2C
O
+
CH3MgBr
ether
H2C
OMgBr
H2O
CH3CH2OH
Formaldehyde
42
Examples
H
C
H
O
+
CH3MgBr
ether
C
OMgBr
CH3
Benzaldehyde
H2O
CHOH
+
Mg(OH)Br
CH3
43
Examples
CH2CH3
CH3CCH3
O
+
CH3CH2MgBr
ether
CH3CCH3
OMgBr
H2O
CH2CH3
CH3CCH3
+
Mg(OH)Br
OH
Acetone
44
Explanation
• The Grignard reaction with acetone
may be explained in this way. In the
first step of the addition of ethyl
magnesium bromide, the partially
positive –MgBr of the Grignard bonds
to the oxygen atom, and the partially
negative CH3CH2– bonds to the carbon
atom of the carbonyl group of acetone.
45
CH2CH3
CH3CCH3
O
+
CH3CH2MgBr
CH3CCH3
_
O
+MgBr
46
Explanation
• In the hydrolysis step, a proton [H+]
from water bonds to the oxygen atom,
leaving the hydroxyl group [–OH] to
combine with the +MgBr. So, the
alcohol is formed.
47
CH2CH3
CH2CH3
CH3CCH3
_
O
+
+MgBr
H
OH
CH3CCH3
+
Mg(OH)Br
OH
48
2,4-dinitrophenylhydrazine
(2,4-DNP)
H
H
N
H
N
NO2
NO2
49
2,4-dinitrophenylhydrazine
(2,4-DNP)
• The carbonyl carbon in both aldehydes and
ketones reacts with 2,4-DNP to form heavy
yellow to orange crystalline solids.
• These solids were used extensively for
identification purposes before the use of
spectrometers.
• The solid is purified by crystallization and its
melting point compared to those of known
structure.
50
51
Common Aldehydes &
Ketones
52
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.
53
Acetaldehyde (Ethanal)
•
Its principal use is as an intermediate in
the manufacture of other chemicals, such
as acetic acid and 1-butanol.
54
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.
55
Aldehydes & Ketones
in Nature
56
C
C
O
C
C
H
C
C
H
O
C
OH
C
Violet (Irone)
(Eucalyptus)
O
salicylaldehyde
(meadowsweet)
O
C
Piperonal
(Heliotrope)
O
CH3(CH2)4C
O
H
O
CH3(CH2)10C
(Citrus Fruits)
H
CH3
O
O
C
C
CH3
Raspberries
57
O
C
O
H
HO
Benzaldehyde
(Oil of Almonds)
CH
Oil of Cinnamon
H
CH3O Vanillin
O
CH
C
C
H3 C
CH3
H
CH3
O
Camphor (Mothballs)
58
CH3
CH3
O
C
CHCH2CH2C
CH
C
H
CH3
Citral (Lemon Grass Oil)
O
O
C
C
C
C
C
C
C
C
C
(C)n
C
n = 4 or 6
CH3
Alarm Pheromones in ants
59
C
C
C
Boll Weevil
Sex Attractant
C
O
H
H
C
O
H
Citral
(Honey Bee Recruiting Pheromone)
60
C
(C)12
C
C
O
C
Musk Ox Sex Attractant
(C)n
C
C
O
C
(C)m
m = 4, n = 10
m = 7, n = 7
m = 7, n = 9
Civet Cat Sex Attractant
61
Condensation Polymers
62
Leo Baekeland (1863-1944)
63
Phenol-Formaldehyde Polymers (Bakelite)
A phenolic is a condensation polymer made from phenol as
shown here.
This is a section of a phenolic
( i.e. Bakelite) which is an example
of a thermosetting polymer. These
polymers are used in electrical
equipment because of their
insulating and fire-resistant
properties.
64
Bakelite products
65
Bakelite products
GE Locomotive
66
67