Reactions of Acyl Halides: Examples
A base is required to
trap the HCl byproduct.
byproduct
A suitable reagent/base is pyridine (1 equivalent).
TEA
Excess amine
E
i
traps HCl
TEA = Triethylamine (a tertiary amine) – another suitable base/reagent.
Synthesis of Esters and Amides
1)
2)
Generally use acid chlorides (or anhydrides) since they are more
reactive than either esters or amides as starting materials.
In addition, generally use a nucleophilic amine such as pyridine as a
reagent/catalyst.
O
R
O
Cl
N
3)
R
C
+N
-
O
Cl
R
+
N
+ Cl-
cannot become neutral
therefore- reactive amide
Why does this work?
a. Pyridine is a good nucleophile.
b. Chloride is a good leaving group.
c
c.
The positively charged nitrogen intermediate (acyl pyridinium
ion) activates the carbonyl group of the acyl compound for
subsequent nucleophilic attack (catalyses the process).
Synthesis of Esters and Amides
1)
Weak nucleophiles (e.g. an alcohol) can attack the acyl pyridinium
ion. Pyridine then functions as a reagent and reacts with the
liberated proton/acid. This affords an ester as the reaction product.
O
R
+
O-
N
R
C
N
+
+O
H
H
O
R
R'
O
O
R
R
H
OR'
N
+
N
+
OR'
+
H
Synthesis of Esters and Amides
1)
Same/similar mechanism for amide formation (the weak nucleophile
is a ammonia, a primary amine or a secondary amine) …
O
R
+
O -
N
R
H
H
C
+
+N
H
N
N
R
H R'
O
O
R
R
NR'
N
H
+
+
N
H
+
NR'
H H