Download Carbonyl Compounds

Carbonyl Compounds
O
C
The carbonyl double bond is analogous to the alkene double
bond, i.e. the carbon involve in the double bond formation is
Sp2 hybridized.
p
C
Triginal carbon; three sp2 orbitals in a
o
plane with 120 angle between them
C
p
p orbital perpendicular
to the plane
p
p
sp2
sp2
C
p
sp2
π
120
o
C
σ
π
C
O
C
O
1.22 A
C
C
1.43 A
O
The carbonyl group has a large dipole moment
C
C
O
O
Classification
O
Aldehydes:
R = alkyl &/or aryl (except for
methanal (formaldehyde), R = H
C
R
H
O
Ketones:
R & R’ = alkyl &/or aryl
C
R
R'
Nomenclature
Aldehydes
•Systematic names are derived by replacing the terminal “e” of
the corresponding alkane with “al”.
• Trivial names are derived from the name of the
corresponding carboxylic acid by replacing the “ic” or “oic” at
the end with aldehyde
O
H3C
C
CH3
O
H
CH3CH2CH2
C
H
CH3CH2CHCH2
O
C
H
(ethane)
(butane)
ethanal
(acetic)
butanal
(butyric)
3-methylpentanal
(β
β-methylpentanoic)
acetaldehyde
butyraldehyde
β-methylpentanaldehyde
(3-methylpentane)
Ketones
•Systematic names are derived by replacing the terminal “e” of
the corresponding alkane with “one”. The chain is numbered
such that the carbonyl carbon atom is given the lowest possible
number.
• Trivial names are derived by adding ketone to the aryl or
alkyl prifix.
O
O
O
CH3
H3C
C
CH3
propanone
Dimethyl ketone
CH2CH
C
CH3
3-buten-2-one
CH3CH2CCH
CH3
2-methyl-3-pentanone
vinylmethyl ketone (ethyl isopropyl ketone)
O
O
CH3
cyclohexanone
2-methyl cyclopentanone
Aromatic ketones are called phenones and are named as
substituents of the corresponding carboxylic acid by droping
“ic” and adding “ophenone”.
O
O
C
C
CH3
(acetic)
Acetophenone
methyl phenyl ketone
(benzoic)
benzophenone
diphenyl ketone
Preparation of Aldehydes
(i) Oxidation of 1o alcohols
O
R
CH2
CrO3/pyridine
OH
R
C
H
(ii) Ozonolysis of alkenes
R
R
O3
H
H
O
R
R'
R
AcOH/Zn
R'
O
O
H
H
O
O
H
H
(iii)Reduction of Acid Chlorides
O
O
R
C
Li(tBuO)3AlH
Cl
R
C
H
mechanism
O
O
Al[OC(CH3)3]2
C
Cl
R
R
H
C
Al[OC(CH3)3]2
H
Cl
R
O
O
C
C
H
R
O
Al[OC(CH3)3]2
R
H
C
Cl
Al[OC(CH3)3]2
H
Preparation of ketones
(i) Oxidation of 2o alcohols (Na2Cr2O7 in H2SO4)
OH
R
CH
O
R'
H2CrO4
R
C
R'
mechanism
H
O
R
R
H
H
C
R'
O
O
Cr
H
OH
C
O
R'
H
OH
O
Cr
O
O
(CrVI)
H
O
H
OH2
H
H
O
R
H
R
OH
C
R'
C
O
Cr
chromate ester
O
O
+
O
Cr
O
O
R
R'
R'
O
OH
Cr
OH
O
(CrIV)
O
(ii) Ozonolysis of alkenes
R
(i) O3
O
(ii) AcOH/Zn
R'
R"
R
R"
+
O
R'''
R'
R'''
Tetrasubstituted alkenes will produce two ketones
Trisubstituted alkenes will produce one ketone and one
aldehyde
(iii) Hydration of Alkynes
O
R
C
C
H
H2SO4/H2O
2+
Hg
R
C
(enol)
H
CH2
O
R
C
CH3
(iv) From organometallic compounds
(a) Dialkyl Cadmium (R2Cd)
O
O
+
R'
Cl
R2Cd
R'
R
(b) Lithium dialkyl cuprates (R2CuLi)
O
O
+
R'
Cl
R2CuLi
R'
R
Reactions of carbonyl compounds
Two main types of reactions
(A) Reaction of the carbonyl double bond
(B) Reactions due to the acidity of the α- hydrogen
(A) Reaction of the carbonyl double bond.
The chemistry that characterizes the reactivity of the
carbonyl group is nucleophilic addition
Nu
+
O
Nu
C
O
This happens because;
C
O
O
δO
R
OH
O
δ+ R'
Nu
slow
R
C
H+
R'
R
C
fast
R.D.S.
Nu
Nu
Reactivity towards nucleophiles
R
H
O
O
H
R
H
O
R
Decreasing reactivity towards nucleophiles
WHY?
R'
General mechanisn for nucleophilic
addition
(1)
Addition under neutral or basic conditions
δO
O
(i)
R
δ+ R'
Nu
slow
R
R'
C
R.D.S.
Nu
alkoxide ion
OH
O
(ii)
R
C
R'
H+
R
C
(fast)
Nu
Nu
R'
(2) Addition under acidic conditions
H
O
H
O
(i)
O
H
R
R'
R
R'
R
H
OH
O
(ii)
Nu
R
R
C
R'
Nu
R'
R'
Examples of nucleophilic addition
(i) Addition of hydrogen cyanide (HCN)
O
OH
HCN
R
R
R'
R'
CN
cyanohydrin
Mechanism
(i) attack by CN(ii) protonation of the formed alkoxide
(ii)
Addition of alcohol (ROH)
O
O
H
OH
H
C
R
C
R'
R
R
R'
R
C
R'
OH2
R
OR"
H
R"
-H2O
C
H
R'
R
R'''
OR'''
OR'''
-H
R
C
OR"
R'
R
C
R'
OR"
hemiacetal (from aldehyde)
hemiketal (from ketone)
O
H
R"
OH
OR"
H
R'
O
O
H
C
C
R'
OR"
acetal (from aldehyde)
ketal (from ketone)
e.g.
O
C
H3C
OR'''
OH
CH3
+ CH3CH2OH
ROH
H
R
C
R'
R
OR"
ketal
OR"
hemiketal
O
C
OH
O
H
HO
CH2CH2CH2
C
H
O
OH
lactol
R'
(iii) Addition of Grignard reagents
O
OH
+
R
R'
δCH2
δ+
MgX
R
R'
R
CH2R'
Methanal ---- 1o alcohols
Aldehydes ---- 2o alcohols
Ketones
---- 3o alcohols
(iv) Addition of derivatives of ammonia (NH3)
i.e. H2N
Amines has a lone pair of electrons and will attack the carbon of
carbonyls
G
e.g.
hydrazine
H2N NH2
H2N
OH
H2N
N
H
hydroxyl amine
phenylhydrazine
OH
O
+
R
H2N
G
R
H
N
R
R
α-anino alcohol
when G = OH ---- oxime
= NH2 --- hydrazone
= NH-Ph--- Phenylhydrazone
= H or R --- imine
R
G
-H2O
C
R
N
(crystalline
compounds)
G
(v)
Olefination (Wittig reaction)
RHO and R2CO react with phosphorus ylids to yield alkenes.
Phosphorus ylids are prepared by reaction of tri-phenyl
phosphine (Ph3P) and alkyl halides (RX)
Ph3P
+
R
CH2
Ph3P
X
CH2
R
base
Ph3P
CH
R
posphorus ylid
Ph3P
R
O
O
O
C
P
Ph3P
CH
CH
R
Ph3P
CH
R
oxaphosphetane
Ph
Ph
Ph
triphenyl
phosphine
oxide
+
H
R
alkene
e.g.
O
CH2
+
CH3I +
NaOH
PPh3
mechanism
Ph3P
CH3
+
I
Ph3P
CH3
base
Ph3P
CH2
posphorus ylid
H 2C
PPh3
H2C
PPh3
CH2
O
O
Reduction of carbonyls
(i) To alcohols
O
R
R
H
aldehyde
O
R
CH2 OH
1 alcohol
o
OH
R
R
ketone
CH2 R
2o alcohol
(a) Catalytic hydrogenation -: H2/Pt or Ni or Pd
(b) Metal hydride -: LiAlH4 in ether
NaBH4 in alcohol
R
H
H
Al
H
H
+
O
H
C
R
O
R
alkoxide ion
H
OR
H
C
R
OH
(ii) To alkanes
O
R
R
R
CH2
alkane
R
(a) Hg/Zn/HCl Clemmensen Reduction
(b) NH2-NH2 / OH- Wolff-Kishner Reduction
(iii) Reductive amination
R
R
(i) NH3
O
R'
(ii) [H]
R'
C
H
amine
NH2
R'
H
C
N
R
H
R'
H
C
N
R'
H2N
O
O
R"
R
R'
N
R
R"
-H2O
R"
HO
imine
R"
R
hemiaminal
[H]
[H]
R
R'
H
C
N
H
2o amine
R"
Starting amine
Product
NH3
1o amine
R-NH2 (1o amine)
2o amine
R2-NH2 (2o amine) 3o amine
(B) REACTIONS DUE TO ACIDITY OF ΤΗΕ α-HYDROGEN
O
R
O
C
CH2
R
R
keto
O
C CH
carbanion
R
R
C
CH
R
CH
R
OH
R
C
enol
Aldol Condensation
When aldehydes react with dilute NaOH at room temp.
dimerization takes place. The product has both an aldehyde and
an alcohol function group present
O
2 R
CH2
C
H
NaOH/H2O
R
CH2
OH
R
O
CH
CH
C
H
Eg.
O
2 CH3
OH
C
NaOH/H2O
H
CH3
CH
O
CH2
C
H
Mechanism
(i) Carbanion formation
H
H
O
C
C
O
OH
H
H 2C
O
H2C
C
H
carbanion
C
H
H
(ii) Nucleophilic attack on carbonyl
O
CH3
C
O
H
+ H2C
C
H
CH3
O
O
CH CH2
C
H
alkoxide ion
(iii) Protonation
CH3
O
O
CH CH2
C
H
H
O
H
OH
O
CH CH2
C
- OH
CH3
3-hydroxybutanal
H
When ketones are used as one component in the
reaction it is called a CLAISEN-SCHMIDT reaction
O
O
C6H5
C
H
+
CH3
C
O
CH3
OH
∆
OH
O
OH
2 CH3
C
C6H5HC
CH3
CH3
C
CHC
CH3
O
CH2
C CH3
β-hydroxy ketone
CH3
OH/∆
O
CH3
CH
CH3
CH
C CH3
4-methyl-3-penten-2-one
Mechanism
O
CH3
C
OH
CH3
C
H 2C
C
H 2C
CH3
O
O
CH3
O
O
CH3 +
C
H2C
O
CH3
CH3
C
C
O
CH2
C CH3
CH3
H2O
OH
O
CH3
C
CH3
CH2
C CH3
-H2O
∆
CH3
C
CH3
O
CH2
C CH3
CH3
If the reaction mixture containing the aldol is heated
dehydration takes place.
O
H
C
OH
CH2
CH
O
CH3
-H2O
H
∆
C
CH
CH
CH3
2-butenal
(conjugated)
Cross Aldol
When an aldol reactionis done with two different aldehydes it
is called a cross aldol reaction.
O
O
C6H5
C
H
+ CH3CH2
C
OH
H
OH/H2O
C6H5C
H
H
O
C
C
H
CH3
∆
O
C6H5C
H
C
CH3
C
H
NB If the second aldehyde has an α-hydrogen then at
least four products can be formed.
O
O
H 3C
H3C
C
H
+ CH3CH2
OH
H
O
C
C
C
H
CH3
OH
H 3C
C
H
H
C
H
OH/H2O
H3CH2C
C
OH
H
O
C
C
C
H
CH3
OH
O
CH2
?
H
H3CH2C
C
H
O
CH2
C
H
H
Provide suitable mechanisms to account for the formation of
the above products.