Aldehydes and ketones are carbonyl compounds with the general formula C=O. Aldehydes have at least one hydrogen attached to the carbonyl carbon while ketones have two alkyl groups.
Esters are derived from carboxylic acids and alcohols, characterized by the RCOOR group.
Structure of Functional Groups
Aldehyde:
RCHO
(where R is an alkyl or aryl group)
Ketone:
RCOR'
Ester:
RCOOR'
Nomenclature
Aldehydes: Named with the suffix "-al". E.g.,
CH
₃
CHO is ethanal.
Ketones: Named with the suffix "-one". E.g.,
CH
₃
COCH
₃
is propanone.
Esters: Named using the alcohol-derived portion first as an alkyl group, followed by the acid-derived portion with the suffix "-oate".
E.g.,
CH
₃
COOCH
₃
is methyl ethanoate.
Preparation of Aldehydes
Aldehydes:
A.
From Primary Alcohols: By oxidizing primary alcohols using oxidizing agents like potassium dichromate (K₂Cr₂O₇) in acidic medium.
RCH
2
OH
H+K2Cr2O7
RCHO
B.
From Alkyl Halides: By hydroformylation (Rosenmund's reduction) of alkyl halides using hydrogen gas and a catalyst (typically a combination of a cobalt complex and a phosphine).
RCH
2
X + CO + H
2
→ RCHO
C.
From Nitriles: By partial hydrolysis of nitriles using water in acidic or basic medium.
RCN+2H
2
O
⟶
H + RCHO+NH
3
D.
By Ozonolysis: Alkynes undergo ozonolysis to form aldehydes.
R−CH=CH−R ′
O3
R−CHO+R ′ −CHO
Preparation of Ketones
A.
From Secondary Alcohols: By oxidizing secondary alcohols using oxidizing agents like potassium dichromate.
R
2
CHOH
H+K2Cr2O7 R
2
C=O
B.
From Acid Chlorides: Friedel-Crafts acylation of benzene using an acyl chloride in the presence of anhydrous aluminum chloride (AlCl₃) catalyst.
RCOCl + C
6
H
6
AlCl3
RCOC
6
H
5
+HCl
C.
By Ozonolysis: Alkynes undergo ozonolysis to form ketones.
R−C≡C−R ′
O3
R−CO−R ′
Also read :
Aluminum Acetate Formula
Preparation of Carboxylic Acids
a.
From Primary Alcohols: By oxidizing primary alcohols using strong oxidizing agents.
RCH
2
OH
H+K2Cr2O7 RCOOH
b.
From Aldehydes: By further oxidation of aldehydes using oxidizing agents.
RCHO+[O]→RCOOH
c.
From Nitriles: By hydrolysis of nitriles using water in acidic or basic medium.
3 RCN+2H
2
O
⟶
H + RCOOH+NH
3
d.
From Grignard Reagents: By the reaction of Grignard reagents with carbon dioxide followed by acidification.
R−Mg−X+CO
2
→RCOOMgX
RCOOMgX+H
2
O→RCOOH+Mg(OH)X
e.
From Alkylbenzenes: By vigorous oxidation of alkylbenzenes with oxidizing agents like KMnO₄.
R−C
6
H
5
+[O]→RCOOH+CO
2
+H
2
O
f.
Perkin Reaction:
C
6
H
5
COCl + C
6
H
5
CH
2
OH
⟶
C
6
H
5
COONa
C
6
H
5
COCH=C(C
6
H
5
)COOH
g.
Cannizzaro Reaction (Disproportionation of non-enolizable aldehydes):
RCHO+OH
−
→RCOOH+RCH
2
OH
Also Check:
List of Chemistry Formulas
Physical Properties
Both aldehydes and ketones are polar due to the carbonyl group, but they can't form hydrogen bonds among themselves. They have higher boiling points than hydrocarbons but lower than alcohols. Esters have a fruity smell and are used as artificial flavoring agents. They are also polar but can't form hydrogen bonds among themselves.
Also Check:
surface chemistry Formula
Chemical Properties
Nucleophilic Addition Reaction:
The partial positive charge on the carbonyl carbon makes it susceptible to nucleophilic attack.
RCHO+HCN→RCH(OH)CN
(This is the formation of cyanohydrin.)
Oxidation:
Aldehydes can be easily oxidized to carboxylic acids.
RCHO+[O]→RCOOH
Reduction:
Both aldehydes and ketones can be reduced to alcohols.
RCHO+2[H]→RCH
2
OH
′RCOR′ +2[H]→RCH
2
OHR′
Tollens' Test:
Silver mirror test.
RCHO+2[Ag(NH
3
)
2
]
+
+3OH
−
→RCOO
−
+ 2Ag+ 4NH
3
+2H
2
O.
Aldol Condensation:
For simplicity, consider the self-condensation of acetaldehyde:
2CH
3
CHO
⟶
OH−CH
3
CH(OH)CH
2
CHO → CH
3
CH=CHCHO+H
2
Clemmensen Reduction:
RCOCH
3
HCl Zn(Hg)
RCH
2
CH
3
Baeyer-Villiger Oxidation:
RC(=O)R ′ +HOOH→RCOO(R ′)+H
2
O
Decarboxylation:
2 RCOOH
heat
RH+CO
2
Reduction:
RCOOH+4[H]→RCH
2
OH
Formation of Anhydride:
2RCOOH→(RCO)
2
O + H
2
O
Hell-Volhard-Zelinsky (HVZ) Reaction:
RCH
2
COOH+Br
2
+PBr
3
→ RCHBrCOOH
