Aldéhydes et Cétones
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Transcript Aldéhydes et Cétones
Aldehydes and Ketones
© E.V. Blackburn, 2011
Structure
O
R
O
H
R
R
ketone
aldehyde
O
carbonyl group
© E.V. Blackburn, 2011
Structure
R
o
120
C
'R
sp2
O
© E.V. Blackburn, 2011
Nomenclature of aldehydes
Aldehydes are named by adding the suffix -al to the
name of the corresponding hydrocarbon. The
carbonyl carbon is given the number 1.
H
methanal
O
H
or
formaldehyde
H 3C
O
ethanal
acetaldehyde
H
© E.V. Blackburn, 2011
Nomenclature of aldehydes
OH
H
H
O
HOH 2C
O
OH
H
© E.V. Blackburn, 2011
Nomenclature of aldehydes
When -CHO is attached to a ring, the suffix carbaldehyde is
used.
H
O
benzenecarbaldehyde
benzaldehyde
CH3CH2CHCH 2CHO 3-methylpentanal
CH3
© E.V. Blackburn, 2011
Nomenclature of aldehydes
O
H
CHO
© E.V. Blackburn, 2011
Nomenclature of ketones
Ketones are named using the name of the corresponding
hydrocarbon followed by the suffix -one. The position of
the carbonyl carbon must be indicated.
H3C
H3C
propanone
acetone
O
dimethyl ketone
One can also name the two radicals, R and R’,
followed by the word ketone.
© E.V. Blackburn, 2011
Nomenclature of ketones
H3CH2C
O
butanone
ethyl methyl ketone
H 3C
H 3C
H 2C
O
1-phenyl-2-propanone
benzyl methyl ketone
© E.V. Blackburn, 2011
Nomenclature of ketones
O
diphenylmethanone
benzophenone
O
CH3
phenylethanone
acetophenone
© E.V. Blackburn, 2011
Nomenclature of ketones
OH
O
© E.V. Blackburn, 2011
Synthesis of aldehydes oxidation of primary alcohols
RCH2OH
RCH2OH
K2Cr2O7
O
R
H
O
PCC in CH 2Cl2
R
H
PCC = pyridinium chlorochromate
© E.V. Blackburn, 2011
Rosemund reduction
RCOCl or ArCOCl
H2, Pd-BaSO4
quinoline
RCHO or ArCHO
A special catalyst is used: palladium on barium sulfate
which has been deactivated (poisoned) with an amine
such as quinoline.
© E.V. Blackburn, 2011
Lithium tri-tertbutoxyaluminium hydride
O 1. LiAlH(O-t-Bu) , Et O, -78C
3
2
O
Cl 2. H2O
H
© E.V. Blackburn, 2011
Synthesis of ketones oxidation of secondary
alcohols
RCHOHR'
O
PCC/CH 2Cl2 or
K2Cr2O7
or CrO3
or KMnO 4
R
R'
© E.V. Blackburn, 2011
Synthesis of ketones oxidation of secondary
alcohols
H
OH
menthol
K2Cr2O7
H2SO4
O
menthone
© E.V. Blackburn, 2011
Synthesis of ketones – hydration
of alkynes
H
H2O
H2SO4
HgSO 4
H
H3C
OH
H
H
H2O
H2SO4
HgSO 4
H2O
H2SO4
HgSO 4
H
C C
H O
CH3CHO
CH3CCH3
O
© E.V. Blackburn, 2011
Keto - enol tautomerism
H
O -
- H+
H
OH
+ H+
H
stronger
acid
-
H
OH
enol structure
H
C C
H O
weaker
acid
O
H
C C
H O
keto structure
Structural isomers that are formally related only by the
shift of a hydrogen and one or more bonds are called
tautomers.
© E.V. Blackburn, 2011
Friedel-Crafts acylation
O
R
Cl
+
Lewis O
+ HCl
ArH
acid R
Ar
© E.V. Blackburn, 2011
Reaction of acid chlorides with
dialkylcuprates
© E.V. Blackburn, 2011
Oxidation of aldehydes
Ag(NH 3)2+
RCHO or ArCHO
KMnO 4
RCO2H or ArCO2H
K2Cr2O7
© E.V. Blackburn, 2011
Tollens’ test
RCHO
+
+ Ag(NH 3)2
colorless
solution
RCH=CHCHO
Tollens'
reagent
RCO 2- + Ag
silver
mirror
RCH=CHCO 2H
© E.V. Blackburn, 2011
Oxidation of ketones - the
haloform reaction
CH3
KOCl
H3C C CHCCH 3
60C
O
CHCl 3 +
CH3
- +
H3C C CHCO 2 K
© E.V. Blackburn, 2011
Reactivity of the carbonyl
group
R
o
120
C
'R
sp2
O
© E.V. Blackburn, 2011
Nucleophilic addition
Nu
R
O
R'
:Nu
R
O
'R
+
Nu
R
O
R'
-
H 2O
+
Nu
R
O
R'
+
Nu
R
OH
R'
© E.V. Blackburn, 2011
Nucleophilic addition - acid
catalysis
H+
R
R
O
'R
'R
R
'R
:Nu
+
OH
+
OH
Nu
'R
OH
R
Nu
'R
OH
R
© E.V. Blackburn, 2011
Addition of cyanide
cyanohydrin
© E.V. Blackburn, 2011
Addition of cyanide
© E.V. Blackburn, 2011
Addition of cyanide
CH3C=O
CN
H
H+
-
OH
CH3-C-CN
H
H2O/HCl
OH
CH3-C-CO 2H
H
lactic acid
© E.V. Blackburn, 2011
Addition of Grignard reagents
O
R:MgX
C R
OMgX
H2O
C R
OH
© E.V. Blackburn, 2011
Reduction to alcohols
© E.V. Blackburn, 2011
Reduction to alcohols
O
OCH 3
1. NaBH 4
OH
OCH 3
2. H2O
O
O
O
OCH3
O
1. LiAlH 4
OH
2. H2O
HO
+ CH3OH
© E.V. Blackburn, 2011
Reduction to alcohols
H 3B H
O
H
-
O
H 2O
H
O-
H
OH
hydride transfer
© E.V. Blackburn, 2011
Addition of ammonia
derivatives
O
OH
C NH-G
+ H2N-G
G
N
+ H 2O
© E.V. Blackburn, 2011
Addition of ammonia
derivatives
© E.V. Blackburn, 2011
Addition of ammonia
derivatives
© E.V. Blackburn, 2011
Addition of ammonia
derivatives
O
O
H2NOH
H2NNH 2
N
OH
oxime
N
NH 2
hydrazone
© E.V. Blackburn, 2011
Addition of ammonia
derivatives
H
N
NH 2
NO 2
O
NO 2
O2N
N
N
H
NO 2
© E.V. Blackburn, 2011
Reduction to hydrocarbons
Zn(Hg), conc. HCl
O
H2NNH 2, KOH or
K t-BuO
H
C
H
Clemmensen
reduction
Wolff-Kishner
reduction
© E.V. Blackburn, 2011
Reduction to hydrocarbons
OH
OH
CH3(CH2)4COCl
AlCl 3
OH
C(CH 2)4CH3
OH
O
resorcinol
Zn(Hg)
HCl
OH
an antiseptic
OH
CH2(CH2)4CH3
© E.V. Blackburn, 2011
Addition of alcohols
dry HCl
O
H
CH3
+ CH3OH
CH3
OH
H OCH
3
hemiacetal
CH3
CH3OH
OH
H OCH
-H2O
3
CH3
OCH 3
H OCH
3
acetal
© E.V. Blackburn, 2011
Addition of alcohols hemiacetal formation
O
H
+
R'
+ OH
H
R'
+ H
+ OH
H
..
+ ROH
OH
+
H C OR
R' H
R'
OH
+
H C OR
R' H
OH
H C OR + H+
R'
© E.V. Blackburn, 2011
Acetal formation
H
'R C OR
OH2
+
H
+
'R C OR + H
OH
H
+ OR
'R C OR
OH2
H R'
+
+ OR
..
+ ROH
H R'
H
'R C OR
+ OR
H
+ H2O
H
'R C OR
+ OR
H
H
+
'R C OR + H
OR
© E.V. Blackburn, 2011
Reactions of acetals
H
'R C OR + H2O
OR
H
+
2ROH + R'-C=O
H
© E.V. Blackburn, 2011
Acetals as protecting groups
O
O
?
O
OH
OC2H5
HOCH 2CH2OH
H 3 O+
HCl
O
O
O
O
1. LiAlH 4
OC2H5 2. H2O
O
OH
© E.V. Blackburn, 2011
Wittig reaction
P(C6H5)3 + O
an ylid
+ (C6H5)3PO
triphenylphosphine
oxide
Georg Wittig, University of Heidelberg, Nobel Prize 1979
© E.V. Blackburn, 2011
Wittig reaction - ylid formation
CH2-X
Ph3P: +
+
RCH 2PPh3 + X-
R
triphenylphosphine
+
X
RCH 2PPh3
+ (CH 3)3CO-
alkyltriphenylphosphonium
halide
RCH=PPh
3
+ (CH 3)3COH
an ylid
© E.V. Blackburn, 2011
Wittig reaction
+
PPh3
R H
PPh3
R
H
O
+
'R
RH +
PPh3
'R
O"R
R"
H
R C P Ph3
'R C O
R"
R
R'
H
R"
+Ph3P=O
© E.V. Blackburn, 2011
Cannizzaro reaction
O
strong
2
H
base
NaOH
2HCHO
50%
NO 2
-CO2- + -CH2OH
CH3OH + HCO 2- Na +
NO 2
NO 2
NaOH
+
35%
CHO
CH2OH
CO2-
Na +
© E.V. Blackburn, 2011
Cannizzaro reaction
NaOH
ArCHO + HCHO
conc.
ArCH 2OH + HCO 2-
CH2OH
CHO
NaOH
HCHO +
+ HCO 2-
conc.
OCH 3
OCH 3
© E.V. Blackburn, 2011
Mechanism
H
H
Ar C OOH
+
OH
O
Ar
H
H
Ar C O +
Ar
OH
O
Ar
HO
H
O + Ar C OH
-H+
ArCO 2-
H+
ArCH 2OH
© E.V. Blackburn, 2011
Analysis of aldehydes and
ketones
• They react with 2,4-dinitrophenylhydrazine.
• Aldehydes give a positive Tollens’ test.
• Methyl ketones give a positive iodoform test.
© E.V. Blackburn, 2011
Spectroscopic properties
IR
1705 - 1740 cm-1 - C=O stretching
~2720 cm-1 - C-H stretching in aldehydes
NMR
chemical shift of aldehyde proton: = 9 - 10
© E.V. Blackburn, 2011