Aldehydes and Ketones - University of...

Aldehydes and KetonesAldehydes and Ketones

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

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)

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

Acyl groups

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

Synthesis of aldehydes and Ketones1) Oxidation of Alcohols

primary gives aldehydes using pyridinium chlorochromate (PCC).secondary gives ketones

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

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

5- Ketones from Acid ChloridesAcid ChloridesGilman Reagent with

6- Ozonolysis Alkene Cleavage

7-Reduction of Acids and their derivatives byLithium Aluminum hydride (LAH)

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)

Naturally occuring aldehydes and Ketones

The carbonyl group

Reactions of the carbonyl group

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

Addition of Alcohols

Examples

Addition of hydrogen cyanide to aldehydes and ketones

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

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:

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.

REACTION OF ALDEHYDES AND KETONES WITH GRIGNARDREAGENTS

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+

Reaction with Acetylides

OXIDATION OF ALDEHYDES AND KETONES

ADDITION-ELIMINATION REACTIONS OF ALDEHYDES ANDKETONES

with hydroxylamineThe product is an "oxime" - for example, ethanal oxime.

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).

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.

Acidity of α-Hydrogen

• Examples of -Hydrogen exchange

The Aldol Condensation

The name aldol is derived from "aldehyde" and"alcohol". An aldol is a β-hydroxycarbonylcompound.