9 ALDEHYDES AND KETONES

9 ALDEHYDES AND KETONES
9.1 STRUCTURES AND CLASSIFICATION
-Carbonyl compounds are classified as aldehydes and ketones both
containing carbonyl group
O
R
C
H
Aldehydes
O
R
C
R’
Ketones
R and R' may be aliphatic or aromatic

9.2 NOMENCLATURE
(CH 3 ) 2 CHCHO CH 3 CH 2 COCH 3
Isobutyraldehyde
Ethyl methyl ketone -Common name
2-Methylpropanal 2-Butanone -IUPAC name
CHO
CHO
COCH 3
CH 3
Cyclohexanecarboxaldehyde
Cyclohexanecarbaldehyde
p-Tolualdehyde Acetophenone
4-Methylbenzaldehyde Phenylethanone

9.3 PHYSICAL PROPERTIES
-polar
-moderate boiling lines between ethers and
-small molecules are water soluble
alcohols
9.4 INDUSTRIAL SOURCES
-Natural source → Carbohydrates, Cinnamon, Vanilla,
Peppermint, Camphor
-From synthesis → from alcohols (1 o and 2 o )
-Mainly used as solvents, reagents, preservatives

9.5 TYPICAL REACTIONS
-Addition of Organometallic Reagents
OH
CH
CH 3 CHO ⎯⎯⎯⎯⎯⎯→ 3 MgI/Et 2 O aq.NH
⎯⎯⎯⎯→ 4 Cl
CH 3 CH-CH 3
-Addition of Cyanides
OH
C 6 H 5 CHO + NaCN/H 2 O ⎯→ C 6 H 5 CH-CN
-Addition of Alcohols
C 6 H 5 CHO + 2CH 3 OH/HCl → C 6 H 5 CH(OCH 3 ) 2 + H 2 O
-Addition of Amines and Derivatives of Ammonia
CH 3 CHO + CH 3 NH 2 /H 3 O + ⎯→ CH 3 CH=NCH 3

O
N-OH
+ HO-NH 3+ Cl - ⎯→
-Cannizzaro Reaction
1) 60%KOH
C 6 H 5 CHO ⎯⎯⎯⎯⎯→ C 6 H 5 COOH + C 6 H 5 CH 2 OH
2) H 3 O +
-Oxidation of Aldehydes
CH 3 CH 2 CH 2 CHO + KMnO 4 → CH 3 CH 2 CH 2 COOH
2Ag(NH 3 )
+
2
CH 3 CH=CHCHO ⎯⎯⎯⎯→ CH 3 CH=CHCOO - + 2Ag + 4NH 3 +
3OH -
2H 2 O

-Reduction to Alcohols
OH
1) LiAlH
C 6 H 5 COCH 3 ⎯⎯⎯⎯⎯⎯→ 4 /Et 2 O
C 6 H 5 CH-CH 3
2) H 3 O +
-Reduction to Hydrocarbons
H 2 NNH 2 /DMSO
(C 6 H 5 ) 2 CO ⎯⎯⎯⎯⎯⎯→ (C 6 H 5 ) 2 CH 2 (90%)
t-BuOK/t-BuOH
Zn(Hg)/HCl
C 6 H 5 COCH 3 ⎯⎯⎯⎯⎯→ C 6 H 5 CH 2 CH 3
heat

-Halogenation
CH 3 CH 2 COCH 3 + Br 2 /aq.HCl ⎯→ CH 3 CH 2 COCH 2 Br
-Addition of Carbanions
HO CH
aq.NaOH/10
2CH 3 CH 2 CHO ⎯⎯⎯⎯⎯⎯⎯→ o 3
C
CH 3 CH 2 CH-CH-CHO
-Electrophilic Aromatic Substitution
COCH 3 COCH 3
+ HNO 3 /H 2 SO 4 ⎯→
NO 2

9.6 LABORATORY PREPARATIONS
-From oxidation of alcohols
-From acyl chlorides
-From aromatic hydrocarbons
9.7 ANALYSIS OF CARBONYL COMPOUNDS
-Form yellow or red precipitate with ammonium derivatives
-Oxidized by cold dil.neutral KMnO 4
or CrO 3
/H 2
SO 4
-Aldehydes are distinguished from ketones by mild oxidation:
Tollens reagent or Benedict’s solution or Fehling’s solution
-Schiff test (Fuchsin-aldehyde reagent) gives reddish violet color
-Methyl ketones (Acetaldehyde) give positive iodoform test