20.3 Nucleophilic Substitution in Acyl Chlorides

1
20.3Nucleophilic Substitutionin Acyl Chlorides
2
General Mechanism for Nucleophilic Acyl
Substitution
involves formation and dissociationof a
tetrahedral intermediate
HY
-HX
3
Preparation of Acyl Chlorides
from carboxylic acids and thionyl
chloride(Section 12.7)
SOCl2


SO2
HCl
heat
(90)
4
Reactions of Acyl Chlorides
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Reactions of Acyl Chlorides
Acyl chlorides react with carboxylic acids to
giveacid anhydrides


HCl
6
Reactions of Acyl Chlorides
Acyl chlorides react with carboxylic acids to
giveacid anhydrides


HCl
via
7
Example

pyridine
(78-83)
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Reactions of Acyl Chlorides
Acyl chlorides react with alcohols to give esters


R'OH
HCl
9
Reactions of Acyl Chlorides
Acyl chlorides react with alcohols to give esters


R'OH
HCl
via
10
Example
pyridine

(CH3)3COH
(80)
11
Reactions of Acyl Chlorides
Acyl chlorides react with ammonia and aminesto
give amides


R'2NH
H2O
HO

Cl
12
Reactions of Acyl Chlorides
Acyl chlorides react with ammonia and aminesto
give amides


R'2NH
H2O
HO

Cl
via
13
Example
NaOH

H2O
(87-91)
14
Reactions of Acyl Chlorides
Acyl chlorides react with water to
givecarboxylic acids (carboxylate ion in base)


H2O
HCl


2HO
Cl

H2O
15
Reactions of Acyl Chlorides
Acyl chlorides react with water to
givecarboxylic acids (carboxylate ion in base)


H2O
HCl
via
16
Example


H2O
HCl
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Reactivity

• Acyl chlorides undergo nucleophilic substitution
  much faster than alkyl chlorides.

C6H5CH2Cl
Relative rates ofhydrolysis (25C)
1,000
1
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20.4Preparation ofCarboxylic Acid Anhydrides

• Anhydrides can be prepared from acyl chlorides as
  described in Table 20.2

19
Some anhydrides are industrial chemicals
Aceticanhydride
Phthalicanhydride
Maleicanhydride
20
From dicarboxylic acids

• Cyclic anhydrides with 5- and 6-membered rings
  can be prepared by dehydration of dicarboxylic
  acids

H2O
(89)
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20.5Reactions ofCarboxylic Acid Anhydrides

• Table 20.3

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Reactions of Anhydrides
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Reactions of Acid Anhydrides
Carboxylic acid anhydrides react with alcoholsto
give esters


R'OH

• normally, symmetrical anhydrides are used(both R
  groups the same)
• reaction can be carried out in presence of
  pyridine (a base) or it can be catalyzed by acids

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Reactions of Acid Anhydrides
Carboxylic acid anhydrides react with alcoholsto
give esters


R'OH
via
25
Example
H2SO4
(60)
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Reactions of Acid Anhydrides
Acid anhydrides react with ammonia and aminesto
give amides


2R'2NH
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Reactions of Acid Anhydrides
Acid anhydrides react with ammonia and aminesto
give amides


2R'2NH
via
28
Example

(98)
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Reactions of Acid Anhydrides
Acid anhydrides react with water to
givecarboxylic acids (carboxylate ion in base)

H2O
2RCOH


2HO
2RCO
H2O
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Reactions of Acid Anhydrides
Acid anhydrides react with water to
givecarboxylic acids (carboxylate ion in base)

H2O
2RCOH
31
Example

H2O