carbonyl correct

Carbonyl Compounds

Carbonyl compounds –Preparation

1.Ozonolysis

C CO3

ice-coldchloroform

C C

O O

O

H2O / H +

Zn dust

C O O C


2.Oxidation of alcohol

C O

R

CR

H

OHMnO4 / H

- +

If primary alcohol is oxidized, distill out the aldehydeimmediately. But normally aldehyde is difficult tosynthesize.


3.Acylation of benzene

C O

R

Cl

+C O

R

+ HCl

Anhy. AlCl3


4.Hydration of Alkyne

C C + H2Odil. H2SO4

HgSO4

C C

H OH

C C

H

H O

Tautomerisation

Normally, ketone is formed.


5. Decarboxylation

(RCOO)2Ca O C

R

R+ CaCO3


6.From Acid Chloride (Good method)

C O

R

Cl

+ H2

Pd / BaSO4

C O

R

H

+ HCl

It is a good method to prepare aldehyde.

Carbonyl compounds –Physical properties

Methanal is a gas, other lower members of aldehydes and ketones are liquids.

Benzenecarbaldehyde is a colourless liquid with almond smell.

Ethanal and propanone are miscible with water due to the formation of H-bond with water molecules while benzenecarbaldehyde is insoluble in water.

Carbonyl compounds –Chemical properties

1. Reduction ( to alcohol)

O CR.A.

C

OH

HR.A.: 1. Can be H2 / Pt, Ni or Pd

(also reduce C=C and CC)2. Na/ Hg in ethanol (also reduce RX)3. LiAlH4, NaBH4

(for LiAlH4, also reduce acid & acid derivative)


1.Reduction (To alkane)Clemmensen Reduction / Wolff-Kishner Reduction

O C C

H

H

a. Clemmensen reduction: Zn / Hg in conc.HClb. Wolff-Kishner reduction: NH2NH2 in NaOH


2.OxidationSpecial oxidation of aldehydeServe as a test to distinguish aldehyde from ketone. (These are very important tests)a. With Fehling’s solution

RCHO + Cu(OH)2 + NaOH RCOONa Cu2O OH2+ +


2.Oxidation (cont’d)b. With Tollen’s reagent / Silver mirror test

This is called silver mirror test.

RCHO + Ag2O + NH3

Ag(NH3)2OH(Tollen's reagent)

Tollen’s reagent is formed from silver nitrate solution and aq. ammonia

RCOONH4 + Ag + H2O


2.Oxidation (cont’d)Oxidize aldehyde to acid

C O

R

H

MnO4 / H- +

,

(or Cr2O7 / H , )2- +C O

R

OH


2.Oxidation (cont’d)Oxidize ketone to acid

C O

R

OH

CH3 C CH2CH3

Oexcess O.A.

reflux for long time

(bond breaking)

This reaction is not good method because you cannot control where the bond break.


3. Iodoform reaction

This is served as a test for CH3 C

O

, CH3 C

OH

H

CH3 C

OI2, NaOH

I3C C

OI2, NaOH

C

O

O Na- +CHI3 +

yellow ppt.


4.Nucleophilic Addition reaction

OCNu CNu OH

+OH2

CNu OH

Energy Profile

Reaction Coordinate


4.Nucleophilic Addition reaction (cont’d)Reactivity:

C O

H

H

C O

R

H

C O

R

R

C O

Ar

H

C O

Ar

Ar

Factors affecting reactivity:

Electronic FactorPositive inductive effect of alkyl group make the carbonyl carbon to be less positive.


4. Nucleophilic Addition reaction (cont’d)Factors affecting reactivity:

Electronic Factor

Benzenecarbaldehyde has low reactivity due to the loss of resonance energy when attacked by nucleophile.


4.Nucleophilic Addition reaction (cont’d)Electronic Factor

CO

H

CO

H

+

Nu

CO

HNu


4.Nucleophilic Addition reaction (cont’d)Steric FactorCarbonyl carbon change from sp2 to sp3 hybridization which leads to increase in crowding. If the R group is more bulky, the intermediate will be more unstable.


4.Nucleophilic Addition reaction (cont’d)With HCN (or KCN / H+)

OCHCN + CNC OHH2O / H

+

CHOOC OH

cyanohydrin


4.Nucleophilic Addition reaction (cont’d)With HCN (or KCN / H+)Mechanism

OCCN CNC OH

+OH2

CNC OH

OC CNC OH+ H+O

HC +CN

The carbonyl compound is regenerated when alkali is added to cyanohydrin.


4.Nucleophilic Addition reaction (cont’d)With NaHSO3

O

C + NaHSO3C

SO3Na

OH

On cooling, the bisulphite addition compound is crystallized.This reaction is a method for purification and separationof carbonyl compound (also identification). The carbonylcompound is regenerated by addition of alkali.


4.Nucleophilic Addition reaction (cont’d)With NaHSO3

O

C + NaHSO3C

SO3Na

OH

NaOHO

C


4.Nucleophilic Addition reaction (cont’d)With ROH (Ketal / Acetal formation)

O

C

R' H

C

OR

OH

R' HROH

dry HCl

ROH

dry HCl

C

OR

OR

R' H

hemiacetal acetal

O

C

R' R''

C

OR

OH

R' R''ROH

dry HCl

ROH

dry HCl

C

OR

OR

R' R''

hemiketal ketal



Carbonyl compound is regenerated if H+ is added with water.Acetal and ketal are used as a protecting group.



O COOC2H5 OH

(not possible)

O COO

+ C2H5OH

dry HCl C

OH

C

OH

COOC2H5O

OOH COO

O

O

+ C2H5OH

OH2


5.Condensation reaction

O

C + :NH2 G

NG

C + H2O


5.Condensation reaction (cont’d)Mechanism: O

C :NH2 G

NG

C + H2O

C

O

NH HG

-

+

C

OH

NH G

proton shiftNucleophilic additionfollowed by elimination


5.Condensation reaction (cont’d)With hydroxylamine

O

C :NH2 OH

NOH

C + H2O

oximeFrom aldehyde, product is aldoximeFrom ketone, product is ketoximeThey are white solids.The reaction can thus serve as a test for carbonyl compounds.


5.Condensation reaction (cont’d)With hydrazine

O

C :NH2 NH2

NNH2

C + H2O

hydrazonehydrazine


5.Condensation reaction (cont’d)With phenylhydrazine

O

C :NH2 N

HN

N

H

C+ H2O

phenylhydrazine

phenylhydrazone


5.Condensation reaction (cont’d)With 2,4-dinitrophenylhydrazine

O

C :NH2 N

H

NO2

NO2

NN

H

O2N

NO2

C + H2O

orange ppt.



This method is used for identification of original carbonyl compound by checking the melting point of the derivatives.



Criteria on choosing a suitable derivative for identification:1. Little side product

2. Reaction should be easily carried out

3. Derivatives should be easily purified.4. The difference in melting point between the derivatives of consecutive members is large.


6.With PCl5

O

CC

H

H

+ PCl5

Cl

CC

H

H

Cl

+ POCl3

alcoholic KOHreflux

C C


7.Aldol CondensationO

C

H

CH

H

H O

C

H

CH

H

Hconc. KOH

O

C

H

C

H

H

CCH3

OH

H

warming

O

C

H

C

H

CCH3

H

H2O +

Carbonyl compoundsshould contain -hydrogen

-hydrogen


7.Aldol Condensation (cont’d)Mechanism:

O

C

H

C

H

HO

O

C

H

C

O

C

H

C

O

C

H

C

O

C

H

CC

O

C

HOH2

O

C

H

CC

OH

C

H

-hydrogen


7.Aldol Condensation (cont’d)The carbonyl compounds should contain -hydrogen.The -hydrogen in carbonyl compound is quite acidic since the anion (carbanion) is resonance stabilized.

O

C

H

C

O

C

H

C


7.Aldol Condensation (cont’d) Example: O

C

H

C

H

C

H

H

C

H

H

H

C C

H

H

C

H

H

C

H

H

H

OH

H

O

C

H

CC

H

H

C

H

H

C

H

H

H

H

C

CH2CH3

O

C

H

C

H

Hconc. KOH

C

H

H

C

H

H

H

warming


Crossed aldol condensation reaction

C

O

H+ CH3CHO

conc. NaOHC

H

OH

CH2CHO


8.Cannizaro Reaction

C

O

Hconc. NaOH CH2OH C

O

ONa+

Dismutation reaction (disproportionation)Benzaldehyde (with no -H) is oxidised, and at the same time, reduced.


9.With Schiff’s ReagentOnly aldehyde will turn it purple.

Carbonyl compounds – Uses of carbonyl compounds

Uses:

1. Methanal in the manufacture of urea-methanal resin.

2. Propanone as a solvent and a raw material in the manufacture of perspex.

carbonyl correct

Documents