carbonyl correct
TRANSCRIPT
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Carbonyl Compounds
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Carbonyl compounds –Preparation
1.Ozonolysis
C CO3
ice-coldchloroform
C C
O O
O
H2O / H +
Zn dust
C O O C
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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.
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Carbonyl compounds –Preparation
3.Acylation of benzene
C O
R
Cl
+C O
R
+ HCl
Anhy. AlCl3
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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.
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Carbonyl compounds –Preparation
5. Decarboxylation
(RCOO)2Ca O C
R
R+ CaCO3
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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.
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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.
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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)
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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
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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+ +
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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
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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
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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.
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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.
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Carbonyl compounds –Chemical properties
4.Nucleophilic Addition reaction
OCNu CNu OH
+OH2
CNu OH
Energy Profile
Reaction Coordinate
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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.
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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.
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Carbonyl compounds –Chemical properties
4.Nucleophilic Addition reaction (cont’d)Electronic Factor
CO
H
CO
H
+
Nu
CO
HNu
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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.
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Carbonyl compounds –Chemical properties
4.Nucleophilic Addition reaction (cont’d)With HCN (or KCN / H+)
OCHCN + CNC OHH2O / H
+
CHOOC OH
cyanohydrin
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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.
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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.
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Carbonyl compounds –Chemical properties
4.Nucleophilic Addition reaction (cont’d)With NaHSO3
O
C + NaHSO3C
SO3Na
OH
NaOHO
C
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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
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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.
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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
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Carbonyl compounds –Chemical properties
5.Condensation reaction
O
C + :NH2 G
NG
C + H2O
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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
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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.
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Carbonyl compounds –Chemical properties
5.Condensation reaction (cont’d)With hydrazine
O
C :NH2 NH2
NNH2
C + H2O
hydrazonehydrazine
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Carbonyl compounds –Chemical properties
5.Condensation reaction (cont’d)With phenylhydrazine
O
C :NH2 N
HN
N
H
C+ H2O
phenylhydrazine
phenylhydrazone
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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.
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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.
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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.
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Carbonyl compounds –Chemical properties
6.With PCl5
O
CC
H
H
+ PCl5
Cl
CC
H
H
Cl
+ POCl3
alcoholic KOHreflux
C C
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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
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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
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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
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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
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Carbonyl compounds –Chemical properties
Crossed aldol condensation reaction
C
O
H+ CH3CHO
conc. NaOHC
H
OH
CH2CHO
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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.
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Carbonyl compounds –Chemical properties
9.With Schiff’s ReagentOnly aldehyde will turn it purple.
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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.