THE CHEMISTRYTHE CHEMISTRYOF ALDEHYDES AND OF ALDEHYDES AND

KETONESKETONES

ByByDr. Nahed NasserDr. Nahed Nasser

CONTENTSCONTENTS

• Bonding in carbonyl compounds

• Structural differences between aldehydes and ketones

• Drawing aldehydes and ketones

• Nomenclature of aldehydes and ketones

• Physical properties of aldehydes and ketones

•Preparation of aldehydes and ketones

•Reactions of adehydes and ketones

ALDEHYDES & KETONESALDEHYDES & KETONES

CARBONYL COMPOUNDSCARBONYL COMPOUNDSCarbonyl compounds contain CO group, they include aldehydes, ketones, acids and

acid derivativesBonding the carbon is sp2 hybridised and formsthree sigma (s) bonds

the unhybridised 2p orbital of carbon is overlaps with a 2p orbital of oxygen to form a pi () bond

as oxygen is more electronegative than carbon the bond is polarized

PLANAR WITH

BOND ANGLES OF 120°

P –ORBITALS

ORBITAL OVERLAP

NEW ORBITAL

The implications of these effects are :higher melting and boiling points compared to analogous alkanes lower boiling points than analogous alcohols more soluble than alkanes but less soluble than alcohols in aqueous media

Difference ALDEHYDES (RCHO) - at least one H attached to the carbonyl group thus the aldehydic group (CHO) is always terminal

KETONES RCOR’ (R and R’=alkyl or aryl )- two carbons attached to the carbonyl group

C = OH

CH3

C = OH

H

C = OCH3

CH3

C = O

C2H5

CH3

Structural differences between aldehydes Structural differences between aldehydes and ketonesand ketones

Aldehydes and ketones contains the same functional group, the carbonyl group (> C = O).

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Drawing aldehydes and ketonesDrawing aldehydes and ketones

Molecular Formula C3H6O

Structural Formula C2H5CHO CH3COCH3

Bond line formula

C = OH

C2H5

C = OCH3

CH3

O

O

H

O

NOMENCLATURE Of CARBONYL COMPOUNDSNOMENCLATURE Of CARBONYL COMPOUNDS

IUPAC Nomenclature of Aldehydes:• Find the longest continuous carbon chain contains the CHO group to get the name of the parent hydrocarbon, the ending e is then replaced by the suffix –al.

C

O

H H CH3

O

H CH3 CH2 C

O

H H3CH2CH2C C

O

H

IUPAC: Methanal Ethanal Propanal Butanal

Common: Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde

• The CHO group is assigned the number 1 position and takes precedence over other functional groups that may the present such as –OH, C=C, OR, C=O, for example:

H

O

3-Hydroxypropanal

O

2-Butenal

H

OCl

-Chlorobutyraldehyde

HO

3-ChlorobutanalIUPAC:

Common -Hydroxypropionaldehyde

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• Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde.

O

H

O

H

O2N

O

H

OH O

H

H3CO

IUPAC: Benzaldehyde 4-Nitrobenzaldehyde 2-Hydroxybenzaldehyde 4-MethoxybenzaldehydeCommnon: Salicylaldehyde Anisaldehyde

Nomenclature of Nomenclature of KetonesKetones

• Common namesCommon names: : derived by listing the alkyl substitutents attached to the carbonyl group in alphabetical order, followed by the word ketone.

• IUPAC names: IUPAC names: derived from the parent hydrocarbon and relpacing the ending –e by the suffix –one. The chain is numbred in such a way as give the lowest number to the C=O group.

IUPAC: Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone

Common: Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone

Acetone Acetophenone Benzophenone

CH3 C CH3

O

CH3 C C6H5

O

CH3 C CH=CH2

O

H5C6 C

O

C6H5

C2H5 C

O

O

C2H5

CHO

O

OH

IUPAC: Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal

PHYSICAL PROPERTIES OF KETONES AND ALDEHYDE

• Because the polarity of the carbonyl group, aldehydes and ketones are polar compounds.

• Dipole-dipole attractions,Dipole-dipole attractions, although important, are not as strong as interactions due to hydrogen bonding. As a result, the boiling points of aldehydes and ketones are higher than those of non polar alkanes, but lower than those of alcohols.

• The lower aldehydes and ketones are more soluble than alkanes but less soluble than alcohols in aqueous media

C O

C+

O-

O

C O

C

C O

H

O

H CO

Preparation of aldehydes and ketones

1- Oxidation of alcohols

2- Ozonolysis of alkenes

RCH2 OHCrO3/ pyridine

Cu / heatR

O

H

R2CH OH

CrO3/ pyridine

Cu / heat

R C R

O

i) O3

ii) Zn / H2O

CH3CH2CHO + CH3CHO

i) O3

ii) Zn / H2OO

O

Diketone

two aldehydes

3- Hydration of alkynes

4- Friedel Crafts acylation

N.B: -COR group is m-director

C C C C

OH

H

C C

H

OH

+ OH HH2SO4, HgSO4

an enol unstable carbonyl more stable

+ R

O

Cl

AlCl3R

O

• Typical aldehydes and ketones ReactionsTypical aldehydes and ketones Reactions       

Reduction (formation of alcohols)Reduction (formation of alcohols)

Nucleophilic addition reactions:

1-Addition of HCN

2- Addition of acetylide anion

3-Addtion of alcohols

4-Addition of ammonia and ammonia derivatives

5- Oxidation reactions

a) By K2Cr2O7 or KMnO4

b) By Iodoform reaction

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REACTIONS OF ALDEHYDES AND REACTIONS OF ALDEHYDES AND KETONESKETONES

1- Reduction : formation of alcohols1- Reduction : formation of alcohols

Catalytic hydrogenation

/ H

2- By nucleophilic addition of Grignard reagent to 2- By nucleophilic addition of Grignard reagent to aldehydes and ketones (formation of alcohols)aldehydes and ketones (formation of alcohols)

• Addition of RMgX to formaldehyde gives 1◦ alc.• Addition of RMgX to any other aldehyde gives 2◦ alc. • Addition of RMgX to ketones gives 3◦ alc.

R C

O

H

R CH OH

R'

R C OH

R'

R''

R C R'

O

+ R'MgX1) Dry ether

2) H2O

+ R''MgX1) Dry ether

2) H2O

CH3 C

O

H

CH3 CH

OH

C2H5+ C2H5MgX1) Dry ether

2) H2O

+ CH3MgX1) Dry ether

2) H2O

OCH3

OH

H H

O

+ RMgX1) Dry ether

2) H2O H H

OH

R

1 alcohol°

3- Addition of Hydrogen Cyanide: Formation of cynohydrins3- Addition of Hydrogen Cyanide: Formation of cynohydrins

4- Addition of alkynide ions:

R C OH

R'

CN

R C R'

O

+ HCN

O

H

+ HCN

OH

CNCyanohydrin

Benzaldehyde cyanohydrin

O

+ HCN

OH

CN

H2 / Pt

or LiAlH4 and H3O+

OH

NH2

H3O+

Heat

OH

COOH

R C C

R'

OH

C R2

R C R'

O

+

O

+

OH

C C CH3

CR2

C-Na

+

CCH3 C-Na

+

H3O+

H3O+

5- Addition of alcohols:

R C

O

R2

R C OH

R'O

R2

+ R'OH

CH3 C

O

HCH3 CH

OH

OC2H5+ C2H5OH

H+ R''OH

H+ R C OR''

R'O

R2

R2=H:

R2=Alkyl

Aldehyde

Ketone

Hemiacetal

Hemiketal

Acetal

Ketal

H+

C2H5OH

H+ CH3 CH

H5C2O

OC2H5

Hemiacetal Acetal

CH3 C

O

CH3

CH3 C

OH

OC2H5

CH3

+ C2H5OHH

+

C2H5OH

H+ CH3 C

H5C2O

OC2H5

CH3

Hemiketal Ketal

6- Addition of Ammonia and Ammonia Derivatives6- Addition of Ammonia and Ammonia Derivatives

C O

NH3C NH

Imine

NH2OH

HydroxylamineC N

OH

C N

NH2

C N

NH

C N

NH

O2N NO2

C N

NH C NH2

O

Oxime

NH2 NH2

HydrazineHydrazone

NH2 NH

PhenylhydrazonePhenylhydrazine

NH2 NH

O2N NO2

2,4-Dinitrophenylhydrazone

NH2 NH C NH2

O

SemicarbazideSemicarbazone

3- Oxidation reactions3- Oxidation reactionsa)By KMnO4 or K2Cr2O7:

Only aldehydes can be oxidized ketones resist oxidation

b) Iodoform reaction: Iodoform reaction: • This reaction gives positive result with any aldehyde or ketone has a

methyl ketone group (CH3CO) , therefore acetaldehyde is the only aldehyde gives positive iodoform test.

R-CHO or Ar-CHOKMnO4

or K2Cr2O7

RCOOH or ArCOOH

C O

CH3

R+ 3 I2 + 4 NaOH R

O

O-Na

+ + CHI3 + 3 NaI

CH3CH3

O

I2 / NaOHCH3

COONa+ CHI3

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