CHEMICAL PROPERTIES OF ALDEHYDES AND KETONES

By: Takeen KhurshidTo: Dr. Geeta Durga

Aldehydes:General formula: RCHO or RCH=O

Ketones:General formula: RCOR’ (R and R’=alkyl or aryl)

Naming Of Aldehyde:

•Select the longest continuous carbon chain that contains the C=O group and replace the ending by the suffix al.

•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.

Common name: listing the alkyl substituents attached to the carbonyl group, followed by the word ketone.IUPAC system: replace the ending –e by the suffix –one. The chain is numbered in such a way as give the lowest number to the C=O group.

Common Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone Acetone Acetophenone BenzophenoneIUPAC Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone

CH3 C CH3

O

CH3 C C6H5

O

CH3 C CH=CH2

O

H5C6 C

O

C6H5

Naming Of Ketone

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

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 nonpolar alkanes, but lower than those of alcohols.

The lower aldehydes and ketones are soluble.

C O

C

+O

-

O

C O

C

C O

H

O

H CO

C+ O-

H

H

C+ O-

H

R

C+ O-

R'

R

> >

Activity of the carbonyl group

C+ O-Nu-C O-Nu

E+

C OENu

alkane alcohol

aldehydeketone

carboxylic acid

oxidation

reductionreduction

additionproductnucleophilic

addition

CHEMICAL PROPERTIES:

Aldehydes & ketones, reactions:

1) Oxidation

2) Reduction

3) Addition of cyanide

4) Addition of derivatives of ammonia

5) Addition of alcohols

6) Condensation Reactions

7) Addition of Grignard reagents

8) (Alpha-halogenation of ketones)

9) Cannizzaro reaction

Aldehydes

and ketones

Alcohols

Lactones

and esters

Oximes

AmidesCyanohydrinsEnols and

enolate anions

Hydrazones

Alkenes

Alkanes

Ketals and thio ketals

Carboxyllic acids

1..Hydrate Formation

1- Reduction of carbonyl groupa- Addition of metal hydride

CH3O

H

2 H2 / Pd

CH3OH

CH3OH

1) NaBH4

2) H2O

C O C O-M+H C OHH+ M+H-H2O

H+

H2O

H+

O

LiAlH4

OAl

H

OH

R C

O

HR 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

HCH3 CH

OH

C2H5+ C2H5MgX1) Dry ether

2) H2O

+ CH3MgX1) Dry ether

2) H2O

O CH3

OH

b- Addition of Grignard Reagents: Formation of alcohols

c- Clemmenson reduction

d- The Wolf-kishner reduction

O

COOH HCl / Zn(Hg) COOH

HH

COOH

O

NH2NH2

COOH

N-NH2

COOH

NaOH

HH

e- Wittig reaction

C

O

+ CH2=P(C6H5)3THF

C

O-

CH2

P(C6H5)3

C

O

CH2

P(C6H5)3

C CH2 + (C6H5)3P=O

H

O

+ (Ph)3P=CH C OC2H5

O

OC2H5

O

2- Oxidation reactiona-

b- Tollenis test

c- Iodoform reaction

R-CHO or Ar-CHOKMnO4

or K2Cr2O7

RCOOH or ArCOOH

RCOO-+ 2 Ag(NH3)+2 + OH- + 2 Ag + 4 NH3 + 3 H2ORCHO

C O

CH3

R+ 3 I2 + 4 NaOH R

O

O-Na

+ + CHI3 + 3 NaI

CH3CH3

O

I2 / NaOHCH3

COONa + CHI3

R C OH

R'

CN

R C R'

O

+ HCN

O

H+ HCN

OH

CNCyanohydrin

Benzaldehyde cyanohydrin

O

+ HCN

OH

CN

H2 / Ptor LiAlH4 and H3O

+

OH

NH2

H3O+

Heat

OH

COOH

3- Addition of Hydrogen Cyanide: Formation of cynohydrins

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

CH3CH3 C

OH

OC2H5

CH3

+ C2H5OHH

+C2H5OH

H+ CH3 C

H5C2O

OC2H5

CH3

Hemiketal Ketal

4- Addition of alcohols:

C O

NH3C NH

Imine

NH2OHHydroxylamine

C 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

6- Addition of Ammonia and Ammonia Derivatives

7.ALDOL CONDENSATION

Condensation between two molecules of an Aldehyde or a ketone to form a β-hydroxyl aldehyde or a β-hydroxy ketone is known as a ALDOL CONDENSATION.

ALDOL CONDENSATION is possible only when the carbonyl compound contains atleast one α-hydrogen atom.

MECHANISM

enolate ion

An enolate ion is the anion formed when an alpha hydrogen in the molecule of an aldehyde or a ketone is removed as a hydrogen ion.

The alkoxide ion is the conjugate base of alcohols.

 Alkoxide ion  is protonated by water.

Crossed aldol condensation

In the presence of a strong base, two different molecules of aldehyde or ketone combine to form a β-hydroxyaldehyde or a β-hydroxyketone.

This reaction is called as the aldol condensation.

The enolate ion (carbanion) is the actual nucleophilic reagent.

The reaction breaks down to the following:The α-carbon of the donor attaches itself to the carbonyl carbon of the acceptor.

CH3 C

H

O CH3 C

H

O

CH2

C

H

OCH2

C

H

O

+ _ _

.. _

acceptor

donor

Step 1: Deprotonation and formation of nucleophile.

CH3CHOOH-

- CH2CHO

• Step 2: Attack by nucleophile: Formation of alkoxide ion.

C

O

H

- CH2CHO

CH

CH2CHO

O-

Step 3: Hydrolysis and formation of Aldol type product

CH

CH2CHO

O-

H-OHCH

CH2CHO

OH

+ OH-

Step 4: Intramolecular dehydration

CH

CH2CHO

OH -H2OCH

CH.CHO

Cinnamaldehyde

8- Cannizzaro reactionAldehyde which does not contain α hydrogen undergoes Cannizzaro

reaction.

CHO

+ NaOH (30 %)

+

CH2OH COO-Na+

CH

+ OH-

C

O-

OH

O

H

C

C CH2O-

+OH

O

O

H

C CH2OH

+O-

O

more stable anion