Transcript Chapter 18 Ketones and Aldehydes - chemistry

CHE 242
Unit VII
The Physical and Chemical
Properties, and Reactions of
Ketones, Aldehydes, and
Amines
CHAPTER EIGHTEEN
Terrence P. Sherlock
Burlington County College
2004
Carbonyl Compounds
=>
Chapter 18
2
Examples
O
O
CH3
C CH CH3
CH3
3-methyl-2-butanone
Br
3-bromocyclohexanone
O
CH3
C CH CH2OH
CH3
4-hydroxy-3-methyl-2-butanone
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Chapter 18
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Name as Substituent
• On a molecule with a higher priority
functional group, C=O is oxo- and -CHO
is formyl.
• Aldehyde priority is higher than ketone.
COOH
CH3
O
CH3
O
C
CH CH2
C H
3-methyl-4-oxopentanal
CHO
3-formylbenzoic acid
Chapter 18
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4
Historical Common
Names
C
O
CH3
O
CH3
C CH3
acetophenone
acetone
O
C
benzophenone
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Chapter 18
5
Aldehyde Common
Names
• Use the common name of the acid.
• Drop -ic acid and add -aldehyde.
1 C: formic acid, formaldehyde
2 C’s: acetic acid, acetaldehyde
3 C’s: propionic acid, propionaldehyde
4 C’s: butyric acid, butyraldehyde.
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Boiling Points
• More polar, so higher boiling point than
comparable alkane or ether.
• Cannot H-bond to each other, so lower
boiling point than comparable alcohol.
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Solubility
• Good solvent for alcohols.
• Lone pair of electrons on oxygen of
carbonyl can accept a hydrogen bond
from O-H or N-H.
• Acetone and acetaldehyde are miscible
in water.
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Chapter 18
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Formaldehyde
• Gas at room temperature.
• Formalin is a 40% aqueous solution.
H
H
O
H
C
O
O
C
C H
O
H
H
heat
H C H
H2O
formaldehyde,
b.p. -21C
trioxane, m.p. 62C
HO
OH
H C
H
formalin
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Chapter 18
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IR Spectroscopy
•
•
•
•
Very strong C=O stretch around 1710 cm-1.
Conjugation lowers frequency.
Ring strain raises frequency.
Additional C-H stretch for aldehyde: two
absorptions at 2710 cm-1 and 2810 cm-1.
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1H
NMR Spectroscopy
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Chapter 18
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McLafferty
Rearrangement
• Loss of alkene (even mass number)
• Must have -hydrogen
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Chapter 18
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UV Spectra,   *
• C=O conjugated with another double bond.
• Large molar absorptivities (> 5000)
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UV Spectra, n  *
• Small molar absorptivity.
• “Forbidden” transition occurs less frequently.
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Chapter 18
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Synthesis Review
• Oxidation
2 alcohol + Na2Cr2O7  ketone
1 alcohol + PCC  aldehyde
• Ozonolysis of alkenes.
R'
H
C C
R
R''
R'
H
1) O3
2) (CH3)2S
C O
R
+ O C
R''
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Chapter 18
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Synthesis Review (2)
• Friedel-Crafts acylation
Acid chloride/AlCl3 + benzene  ketone
CO + HCl + AlCl3/CuCl + benzene 
benzaldehyde (Gatterman-Koch)
• Hydration of terminal alkyne
Use HgSO4, H2SO4, H2O for methyl ketone
Use Sia2BH followed by H2O2 in NaOH for
aldehyde.
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Ketones from Nitriles
• A Grignard or organolithium reagent
attacks the nitrile carbon.
• The imine salt is then hydrolyzed to
form a ketone.
N MgBr
C N
CH3CH2MgBr +
C
ether
CH2CH3
O
H3O
+
C
CH2CH3
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Aldehydes from
Acid Chlorides
Use a mild reducing agent to prevent
reduction to primary alcohol.
O
CH3CH2CH2C
O
Cl
LiAlH(O-t-Bu)3
CH3CH2CH2C
H
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Ketones from
Acid Chlorides
Use lithium dialkylcuprate (R2CuLi),
formed by the reaction of 2 moles of
R-Li with cuprous iodide.
2 CH3CH2CH2Li
CuI
(CH3CH2CH2)2CuLi
O
(CH3CH2CH2)2CuLi +
CH3CH2C Cl
O
CH3CH2C CH2CH2CH3
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Nucleophilic Addition
• A strong nucleophile attacks the
carbonyl carbon, forming an alkoxide
ion that is then protonated.
• A weak nucleophile will attack a
carbonyl if it has been protonated,
thus increasing its reactivity.
• Aldehydes are more reactive than
ketones.
Chapter 18
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Wittig Reaction
• Nucleophilic addition of phosphorus ylides.
• Product is alkene. C=O becomes C=C.
Chapter 18
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Addition of HCN
• HCN is highly toxic.
• Use NaCN or KCN in base to add
cyanide, then protonate to add H.
• Reactivity formaldehyde > aldehydes >
ketones >> bulky ketones.
O
CH3CH2
C
HO
CH3
+ HCN
Chapter 18
CH3CH2
CN
C
CH3
22
=>
Other Condensations
Chapter 18
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Addition of Alcohol
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Chapter 18
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Acetals as
Protecting Groups
• Hydrolyze easily in acid, stable in base.
• Aldehydes more reactive than ketones.
O
O
CH2
CH2
OH
HO
C
H
+
H
C
O
O
O
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Selective Reaction
of Ketone
• React with strong nucleophile (base)
• Remove protective group.
+
_
MgBr O CH
3
O
HO
CH3MgBr
C
O
O
H3O
C
O
O
CH3
+
C
H
O
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Chapter 18
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Oxidation of Aldehydes
Easily oxidized to carboxylic acids.
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Chapter 18
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Tollens Test
• Add ammonia solution to AgNO3
solution until precipitate dissolves.
• Aldehyde reaction forms a silver mirror.
O
R C H+
+
NH3)2
_
+
3OH
2
+
Ag(NH3)2
_
+
3OH
O
H2O
O
H2O
2 Ag + R C O
_
2 Ag + R C O
+
_
+
4 NH3 +
2 H2O
=>
Chapter 18
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4
Reduction Reagents
• Sodium borohydride, NaBH4, reduces
C=O, but not C=C.
• Lithium aluminum hydride, LiAlH4, much
stronger, difficult to handle.
• Hydrogen gas with catalyst also
reduces the C=C bond.
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Catalytic Hydrogenation
• Widely used in industry.
• Raney nickel, finely divided Ni powder
saturated with hydrogen gas.
• Pt and Rh also used as catalysts.
O
OH
Raney Ni
H
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Deoxygenation
• Reduction of C=O to CH2
• Two methods:
Clemmensen reduction if molecule is
stable in hot acid.
Wolff-Kishner reduction if molecule is
stable in very strong base.
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Clemmensen Reduction
O
C
CH2CH3
Zn(Hg)
CH2CH2CH3
HCl, H2O
O
CH2
C
Zn(Hg)
H
CH2
CH3
HCl, H2O
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Chapter 18
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Wolff-Kisher Reduction
• Form hydrazone, then heat with strong
base like KOH or potassium t-butoxide.
• Use a high-boiling solvent: ethylene
glycol, diethylene glycol, or DMSO.
CH2
C H
H2N NH2
CH2
O
C H
NNH2
KOH
heat
CH2
CH3
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Chapter 18
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POWER POINT IMAGES FROM
“ORGANIC CHEMISTRY, 5TH EDITION”
L.G. WADE
ALL MATERIALS USED WITH PERMISSION OF AUTHOR
PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE
ORGANIC CHEMISTRY COURSE
BY:
ANNALICIA POEHLER STEFANIE LAYMAN
CALY MARTIN
Chapter 18
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