Transcript Common aldehydes and ketones

Organic chemistry for medicine and biology
students
Chem 2311
Chapter 9
Aldehydes and Ketones
By Prof. Dr.
Adel M. Awadallah
Islamic University of Gaza
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Nomenclature of Aldehydes and Ketones
Common aldehydes
O
H
O
H
Methanl
(formaldehyde)
H3C
O
O
H
CH3CH2
ethanl
(acetaldehyde)
H
propanal
(propionaldehyde)
CH3CH2CH2
butanal
(n-butyraldehyde)
O
O
H
O
H
H
H
OH
OMe
benzaldehyde
salicylaldehyde
(2-hydroxybenzenecarbaldehyde)
O
H
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cyclopentanecarbaldehyde
OH
Vanillin
Common Ketones
O
O
CH3
H3C
propanone
(acetone)
O
cyclohexanone
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H3C
O
CH3
CH3
H3C
2-butanone
3-pentanone
(ethyl methyl ketone) (diethyl ketone)
H3C
O
acetophenone
(methyl phenyl ketone)
O
benzophenone
(diphenyl ketone)
Nomenclature of aldehydes and ketones
(al) aldehyde,
(one) ketone
alkanes < alkenes < OH < ketone < aldehyde < acid < ester
Examples
CH3 CH3
3
4
1 2
5
O
CH3 H
2
O
H3C 3
1
4
Cl
2,4-dimethyl-3-hexanone
2-cholro-3-methylbutanal
OH
5 4
3
O
O
2
H 1
1
64-hydroxy-2-pentanone
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O
3 CH3
2
4
3-oxobutanl
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5
3 2
4
1
CH3
O
3-hexen-2-one
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Acyl groups
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Common aldehydes and ketones
Formaldehyde
CH3OH
Ag
600 - 700
CH2 = O
oC
+
H2
Formaldehyde is a gas (b. p. -21 oC) Formalin (37% aqueous solution of formaldehyde)
Acetaldehyde (Wacker synthesis)
Pd - Cu
2 CH2 = CH2 +
2 CH3CH = O
O2
100 - 130 oC
(bp 20 oC)
Acetone (Wacker synthesis)
O
Pd - Cu
2 CH3 C CH3
2 CH3CH2 = CH2 + O2
100 - 130 oC
(bp 56 oC)
From isopropylbenzene
OH
O
1) O2
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2) dil H2SO4
+
H3C
CH3
Synthesis of aldehydes and Ketones
1)
2)
Oxidation of Alcohols
primary gives aldehydes using PCC
secondery gives ketones
Friedel-Crafts
CH3COCl
AlCl3
3)
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From Alkynes
H3C
O
Naturally occuring aldehydes and Ketones
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The carbonyl group
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Reactions of the carbonyl group
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A. Hydration and Hemiacetal Formation
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Water adds rapidly to the carbonyl function of aldehydes and ketones. In most
cases the resulting hydrate (a geminal-diol) is unstable relative to the reactants
and cannot be isolated.
Exceptions to this rule exist,
one being formaldehyde (a gas in its pure monomeric state).
Thus, a solution of formaldehyde in water (formalin) is almost exclusively the
hydrate, or polymers of the hydrate.
Another is chloral hydrate
OH
CCl3
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OH
H
Chloral hydrate
Addition of Alcohols
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Examples
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Addition of hydrogen cyanide to aldehydes and ketones
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Addition of sodium hydrogensulphite to aldehydes and ketones
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Uses of the reaction The reaction is usually used during the purification of
aldehydes (and any ketones that it works for). The addition compound can
be split easily to regenerate the aldehyde or ketone by treating it with either
dilute acid or dilute alkali.
Reducing Agents
The reduction of an aldehyde
You get exactly the same organic product whether you use lithium
tetrahydridoaluminate or sodium tetrahydridoborate.
For example, with ethanal you get ethanol:
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The reduction of a ketone
• Again the product is the same whichever of the two
reducing agents you use.
• For example, with propanone you get propan-2-ol:
• Reduction of a ketone leads to a secondary alcohol.
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Mechanism of reduction
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• Using sodium tetrahydridoborate (sodium borohydride)
.
• Sodium tetrahydridoborate is a more gentle (and therefore safer)
reagent than lithium tetrahydridoaluminate. It can be used in solution
in alcohols or even solution in water - provided the solution is
alkaline
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REACTION OF ALDEHYDES AND KETONES WITH GRIGNARD
REAGENTS
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The reaction between Grignard reagents and methanal
1) EtMgBr
2) H2O, H+
The reaction between Grignard reagents and other aldehydes
1) EtMgBr
2) H2O, H+
The reaction between Grignard reagents and ketones
1) EtMgBr
2) H2O, H+
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Reaction with Acetylides
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OXIDATION OF ALDEHYDES AND KETONES
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ADDITION-ELIMINATION REACTIONS OF ALDEHYDES AND
KETONES
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with hydroxylamine
The product is an "oxime" - for example, ethanal oxime.
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Formation of Imines and Related Compounds
The reaction of aldehydes and ketones with ammonia or 1ºamines forms imine derivatives, also known as
Schiff bases, (compounds having a C=N function).
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Keto-Enol Tautomerism
• Keto-enol tautomerism a neewteb muirbiliuqe lacimehc a ot srefer
keto na dna )edyhedla na ro enotek a( mrof enol dna lone ehT .
ehT .rehto hcae fo sremotuat eb ot dias era smrof otek
notorp a fo tnemevom eht sevlovni smrof owt eht fo noisrevnocretni
seifilauq msiremosi eht ,ecneh ;snortcele gnidnob fo gnitfihs eht dna
.msiremotuat sa
• A compound containing a carbonyl group (C=O) is normally in rapid
equilibrium with an enol tautomer, which contains a pair of doubly
bonded carbon atoms adjacent to a hydroxyl (−OH) group, C=C-OH.
The keto form predominates at equilibrium for most ketones.
Nonetheless, the enol form is important for some reactions.
Furthermore, the deprotonated intermediate in the interconversion of
the two forms, referred to as an enolate anion, is important in
carbonyl chemistry, in large part because it is a strong nucleophile.
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Acidity of α-Hydrogen
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• Examples of -Hydrogen exchange
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The Aldol Condensation
The name aldol is derived from "aldehyde" and
"alcohol". An aldol is a β-hydroxycarbonyl
compound.
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