aldehydes and ketones - university of...
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Aldehydes and KetonesAldehydes and Ketones
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Nomenclature of Aldehydes and KetonesCommon aldehydes
H H
O
CH3 H
O
CH3CH2CH2 H
O
CH3CH2 H
O
H
O
HO HO
OH
HO
OHOMe
Methanl ethanl propanal butanal(formaldehyde) (acetaldehyde) (propionaldehyde) (n-butyraldehyde)
benzaldehyde salicylaldehyde(2-hydroxybenzenecarbaldehyde) Vanillin
cyclopentanecarbaldehyde
H H
O
CH3 H
O
CH3CH2CH2 H
O
CH3CH2 H
O
H
O
HO HO
OH
HO
OHOMe
Methanl ethanl propanal butanal(formaldehyde) (acetaldehyde) (propionaldehyde) (n-butyraldehyde)
benzaldehyde salicylaldehyde(2-hydroxybenzenecarbaldehyde) Vanillin
cyclopentanecarbaldehyde
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Common Ketones
CH3 CH3
O
CH3
OCH3
OCH3CH3
O OCH3 O
propanone (acetone)
2-butanone(ethyl methyl ketone)
3-pentanone(diethyl ketone)
cyclohexanone acetophenone(methyl phenyl ketone)
benzophenone(diphenyl ketone)
CH3 CH3
O
CH3
OCH3
OCH3CH3
O OCH3 O
propanone (acetone)
2-butanone(ethyl methyl ketone)
3-pentanone(diethyl ketone)
cyclohexanone acetophenone(methyl phenyl ketone)
benzophenone(diphenyl ketone)
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Nomenclature of aldehydes and ketones
(al) aldehyde, (one) ketonealkanes < alkenes < OH < ketone < aldehyde < acid < esterExamples
OOH
H
OO
CH3
CH3
O
CH3 O
HCH3
Cl O
CH3CH3
12345
12
34
123456
4-hydroxy-2-pentanone 3-oxobutanl 3-hexen-2-one
1
23
4 1 23
45
6
2-cholro-3-methylbutanal 2,4-dimethyl-3-hexanone
OOH
H
OO
CH3
CH3
O
CH3 O
HCH3
Cl O
CH3CH3
12345
12
34
123456
4-hydroxy-2-pentanone 3-oxobutanl 3-hexen-2-one
1
23
4 1 23
45
6
2-cholro-3-methylbutanal 2,4-dimethyl-3-hexanone
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Acyl groups
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Common aldehydes and ketones
CH3OH CH2 = O + H2
O
OH
CH3 CH3
O
Ag
600 - 700 oC
Formaldehyde
Formaldehyde is a gas (b. p. -21 oC) Formalin (37% aqueous solution of formaldehyde)
Acetaldehyde (Wacker synthesis)
2 CH2 = CH2 + O22 CH3CH = O
Pd - Cu
100 - 130 oC (bp 20 oC)
Acetone (Wacker synthesis)
2 CH3CH2 = CH2 + O22 CH3 C CH3
Pd - Cu
100 - 130 oC (bp 56 oC)From isopropylbenzene
1) O2
2) dil H2SO4
+
CH3OH CH2 = O + H2
O
OH
CH3 CH3
O
Ag
600 - 700 oC
Formaldehyde
Formaldehyde is a gas (b. p. -21 oC) Formalin (37% aqueous solution of formaldehyde)
Acetaldehyde (Wacker synthesis)
2 CH2 = CH2 + O22 CH3CH = O
Pd - Cu
100 - 130 oC (bp 20 oC)
Acetone (Wacker synthesis)
2 CH3CH2 = CH2 + O22 CH3 C CH3
Pd - Cu
100 - 130 oC (bp 56 oC)From isopropylbenzene
1) O2
2) dil H2SO4
+١١
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Synthesis of aldehydes and Ketones1) Oxidation of Alcohols
primary gives aldehydes using pyridinium chlorochromate (PCC).secondary gives ketones
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2) Friedel-Crafts
3) From Alkynes : Oxymercuration Hydration Markovnikov
OCH3
CH3COCl
AlCl3
CH3CH2C CHHgSO4, H2SO4
H2OCH3CH2C=CH2
OH
an enol
CH3CH2CCH3
O
a ketone
CH3CH2C CHHgSO4, H2SO4
H2OCH3CH2C=CH2
OH
an enol
CH3CH2CCH3
O
a ketone
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4- Aldehydes from Acid Chlorides- Lithium tri-t-butoxyaluminum hydride reduction- Rosenmund reduction
R CO
Clether
R CO
H
R CO
Cl R CO
HH2 / Pd / S
BaSO 4Rosenmund catalyst
LiAlH(O-t-bu)3R CO
Clether
R CO
H
R CO
Cl R CO
HH2 / Pd / S
BaSO 4Rosenmund catalyst
LiAlH(O-t-bu)3
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5- Ketones from Acid ChloridesAcid ChloridesGilman Reagent with
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6- Ozonolysis Alkene Cleavage
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7-Reduction of Acids and their derivatives byLithium Aluminum hydride (LAH)
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R COOR'
or
R CONH2
R CONHR'
R CONR2'
or
or1. Diisobutylaluminum
hydride
2. H3O+R COH
R COOR'
or
R CONH2
R CONHR'
R CONR2'
or
or1. Diisobutylaluminum
hydride
2. H3O+R COH
(DIBAH)
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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• 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 cannotbe 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
• Water adds rapidly to the carbonyl function of aldehydes and ketones. In most casesthe resulting hydrate (a geminal-diol) is unstable relative to the reactants and cannotbe 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
CCl3 OHOH
HChloral hydrate
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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• Uses of the reaction The reaction is usually used during the purification of
aldehydes (and any ketones that it works for). The addition compound canbe split easily to regenerate the aldehyde or ketone by treating it with eitherdilute acid or dilute alkali.
٣٢
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Reducing Agents
The reduction of an aldehydeYou get exactly the same organic product whether you use lithiumtetrahydridoaluminate or sodium tetrahydridoborate.For example, with ethanal you get ethanol:
The reduction of an aldehydeYou get exactly the same organic product whether you use lithiumtetrahydridoaluminate 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 tworeducing 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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REACTION OF ALDEHYDES AND KETONES WITH GRIGNARDREAGENTS
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The reaction between Grignard reagents and methanal
1) EtMgBr
2) H2O, H+
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 ANDKETONES
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with hydroxylamineThe product is an "oxime" - for example, ethanal oxime.
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Formation of Imines and Related CompoundsThe reaction of aldehydes and ketones with ammonia or 1º-
amines forms imine derivatives, also known as
Schiff bases, (compounds having a C=N function).
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Keto-Enol Tautomerism• Keto-enol tautomerism refers to a chemical equilibrium between a
keto form )a ketone or an aldehyde) and an enol. The enol and ketoforms are said to be tautomers of each other. The interconversion ofthe two forms involves the movement of a proton and the shifting ofbonding electrons; hence, the isomerism qualifies as tautomerism.
• A compound containing a carbonyl group (C=O) is normally in rapidequilibrium with an enol tautomer, which contains a pair of doublybonded 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 ofthe two forms, referred to as an enolate anion, is important incarbonyl chemistry, in large part because it is a strong nucleophile.
• Keto-enol tautomerism refers to a chemical equilibrium between aketo form )a ketone or an aldehyde) and an enol. The enol and ketoforms are said to be tautomers of each other. The interconversion ofthe two forms involves the movement of a proton and the shifting ofbonding electrons; hence, the isomerism qualifies as tautomerism.
• A compound containing a carbonyl group (C=O) is normally in rapidequilibrium with an enol tautomer, which contains a pair of doublybonded 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 ofthe two forms, referred to as an enolate anion, is important incarbonyl 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-hydroxycarbonylcompound.
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