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Chem 342 • Organic Chemistry II Need to know Reactions and Mechanisms for Exam 03
Reactions of Aldehydes and Ketones HO
O
OR
RO
OR
H+
+ 2 ROH (+ ROH) a hemiacetal
(+ ROH) (- H2O)
an acetal
Both aldehydes and ketones participate. The Wittig reagent is made from the alkyl halide by SN2 reactions.
Wittig Reaction O
Ph3P CH2
+
Ph3P O
+
phosphonium ylide 1,4-Addition O CH3NH2
O
O
NHCH3 1,2-Addition O PhMgBr
HO
O
Ph2CuLi
Ph
Gillman Reagent
O
Ph
HO
PhLi
then H3O+
Ph
then H3O+
Preparation of Carboxylic Acids Oxidation Methods CH3
O
KMnO4
KMnO4 KMnO4
OH O H
Other Methods
O OH
H3O+
C N
O OH
O
2
O C O
OH
MgBr
O
2
O O
MgBr
OH
CrO3 H3O+
O
Ag2O NH4OH
O
H3O+ OH O OH
OH
Tollen's Oxidation Chem 342
page 1
Spring 2009
Reactions of Carboxylic Acids and Derivatives Carboxylic Acids O R
OH O
R
R
SN2
O
Fischer Esterification
O R
OH O
R
limited to primary alkyl halides R
R
OCH3
LiAlH4
H
H
then H3O+
R
OH
H
H
R
OH
BH3 then H3O+
OH
OCH3 O
HA, CH3OH OH
Cl O
NaOH then CH3I OH
R
O
SOCl2
limited to inexpensive alcohol solvents methanol and ethanol most practical
selective for carboxylic acid reduction will not react with esters
Acid Chlorides O R
Cl O
R
R
Cl
R
R
Cl O
R
Cl O
R
Chem 342
OR'
R
+
pyridine•HCl
+
pyridine•HCl
NHR'
LiAlH4
H
H
then H3O+
R
OH
R'MgBr
R'
R'
then H3O+
R
OH
Adds Twice
Adds Twice
O
R'2CuLi Cl
R'
O
R'NH2, pyridine
O
O
NaCl
O R
Cl
O +
R'OH, pyridine
O
HCl
OH
R
Cl
+
O
R'CO2Na
O R
O
H2O
Adds Once R
R'
page 2
Spring 2009
Acid Anhydrides O
O O
O
R O
OR'
R O
O O O
+
pyridine•HO2CCH3
+
pyridine•HO2CCH3
O
R'NH2, pyridine
O
O
HO
O
R'OH, pyridine
O
O
+ OH
O
O
O
O
H2O
NHR'
LiAlH4
H
H
then H3O+
R
OH
R'MgBr
R'
R'
then H3O+
R
OH
Adds Twice
Adds Twice
Esters O R
then
OCH3 O
R
H3O+ H
H
R
OH
R'MgBr
R'
R'
then H3O+
R
OH
then
O OCH3
H3O+
O OCH3
then
HOCH3
Adds Twice
Adds Twice
O
DIBAL R
+ OH
LiAlH4 OCH3
R
O
H2O, NaOH
Adds Once R
H3O+
H
Amides O R
heat
NH2 O
R
O
H2O, H3O+
NH2
OH
LiAlH4
H
H
then H3O+
R
NH2
Adds Twice - Nitrogen is retained.
Carbonyl Alpha Substitution O
O Br2 CH3CO2H
Chem 342
O Br
pyridine E2 elimination
page 3
Spring 2009
1) Br2
O OH
PBr3
O OH
2) H2O Br
O
O
I2, NaOH CH3
O
+
CHI3
iodoform precipitate
Enolate Alkylation O
O
1) LDA 2) O
Br
NaOH, CH3OH
O
O
CH3I
dialkylation, doing a second reaction with the product and the electrophile, is often a problem
O
CH3
Malonic Ester Synthesis O Ph
Br
+
O
O
EtO
OEt
Ph
OEt
O
H3O+, Heat
NaOEt, EtOH
+ CO2
O
EtO
OH
Ph
Acetoacetic Ester Synthesis O H3 C
NaOEt EtOH
O
O H3 C
OEt R
H3O+, Heat
O OEt
O H3 C
+ CO2
R
Br R
Aldol Reaction (We may not get all the way to this point by Monday. The exam will cover reactions through Monday’s lecture so please check where we end on that day.) O
NaOEt EtOH
H
O
O
O
EtOH
O
H
H
O
OH
H aldol
O
NaOEt EtOH
O
heat 22% OH
Chem 342
page 4
O
-H2O
Spring 2009
NEED TO KNOW MECHANISM Mechanism for Acetal Formation
HA
O
H O
HO R
H O
H O
H O R
R
O
O
HA
H
R
H O
O
R
Hemiacetal
resonance structures
O
H O
A
-H2O
A R
R
H O
R OH
O
O
R O
R
R
resonance structures
NEED TO KNOW MECHANISM Fischer Esterification O R
OH
HA OH
R
R'OH
OH
H HO OR' R
OH
A
HO OR' R
OH
HA
A
O R
Chem 342
OR'
OH R
OR'
page 5
HO OR'
HO OR'
R
R
OH H
Spring 2009
NEED TO KNOW MECHANISMS Acid Catalyzed Hydrolysis O
H
HA
H
O
OCH3
H2O
O
OCH3
H O H OCH3
H O
OCH3
H O
A
O H OCH3 HA
O
H
A
H
O
OH
H O
O
OH
OH
O H OCH3 H
- HOCH3
BEST METHOD Base Catalyzed Hydrolysis (Saponification) O
OH
O
O
OH
OCH3
O OH
OCH3
+
OCH3
O
Rapid acidbase reaction takes place
O
HA (cat)
R
NH2
+
HOCH3
Carboxylate is a thermodynamic sink and makes the reaction essentiall non-reversible. To get the carboxylic acid, add acid to protonate.
O R
H2O
Amide Hydrolysis
OH
NEED TO KNOW MECHANISMS Acid Catalyzed Hydrolysis O
