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

Carbonyl compounds –Preparation

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.

Carbonyl compounds –Preparation

3.Acylation of benzene

C O

R

Cl

+C O

R

+ HCl

Anhy. AlCl3

Carbonyl compounds –Preparation

4.Hydration of Alkyne

C C + H2Odil. H2SO4

HgSO4

C C

H OH

C C

H

H O

Tautomerisation

Normally, ketone is formed.

Carbonyl compounds –Preparation

5. Decarboxylation

(RCOO)2Ca O C

R

R+ CaCO3

Carbonyl compounds –Preparation

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)

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

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+ +

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

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

C O

R

H

MnO4 / H- +

,

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

R

OH

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

4.Nucleophilic Addition reaction

OCNu CNu OH

+OH2

CNu OH

Energy Profile

Reaction Coordinate

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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

CO

H

CO

H

+

Nu

CO

HNu

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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

OCHCN + CNC OHH2O / H

+

CHOOC OH

cyanohydrin

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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

O

C + NaHSO3C

SO3Na

OH

NaOHO

C

Carbonyl compounds –Chemical properties

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 compounds –Chemical properties

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

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

Carbonyl compounds –Chemical properties

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

O COOC2H5 OH

(not possible)

O COO

+ C2H5OH

dry HCl C

OH

C

OH

COOC2H5O

OOH COO

O

O

+ C2H5OH

OH2

Carbonyl compounds –Chemical properties

5.Condensation reaction

O

C + :NH2 G

NG

C + H2O

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

5.Condensation reaction (cont’d)With hydrazine

O

C :NH2 NH2

NNH2

C + H2O

hydrazonehydrazine

Carbonyl compounds –Chemical properties

5.Condensation reaction (cont’d)With phenylhydrazine

O

C :NH2 N

HN

N

H

C+ H2O

phenylhydrazine

phenylhydrazone

Carbonyl compounds –Chemical properties

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

O

C :NH2 N

H

NO2

NO2

NN

H

O2N

NO2

C + H2O

orange ppt.

Carbonyl compounds –Chemical properties

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

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

Carbonyl compounds –Chemical properties

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

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.

Carbonyl compounds –Chemical properties

6.With PCl5

O

CC

H

H

+ PCl5

Cl

CC

H

H

Cl

+ POCl3

alcoholic KOHreflux

C C

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

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

Carbonyl compounds –Chemical properties

Crossed aldol condensation reaction

C

O

H+ CH3CHO

conc. NaOHC

H

OH

CH2CHO

Carbonyl compounds –Chemical properties

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.

Carbonyl compounds –Chemical properties

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.