Post on 03-Nov-2019
transcript
22.17
Synthetic Transformations
of Aryl Diazonium Salts
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
Ar OH
Ar I
Ar F
Ar Br Ar Cl
Ar CN
Preparation of Phenols
Ar N N +
Ar OH
H2O, heat
Example
2. H2O, heat
(CH3)2CH NH2
1. NaNO2, H2SO4
H2O, 0-5°C
(CH3)2CH OH
(73%)
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
Ar OH
Ar I
Ar F
Ar Br Ar Cl
Ar CN
Preparation of Aryl Iodides
Ar N N +
Ar I
reaction of an aryl diazonium salt with
potassium iodide
KI
Example
2. KI, room temp.
1. NaNO2, HCl
H2O, 0-5°C
(72-83%)
NH2
Br
I
Br
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
Ar OH
Ar I
Ar F
Ar Br Ar Cl
Ar CN
Preparation of Aryl Fluorides
Ar N N +
Ar F
heat the tetrafluoroborate salt of a diazonium ion;
process is called the Schiemann reaction
Example
(68%)
NH2
CCH2CH3
O
2. HBF4
1. NaNO2, HCl,
H2O, 0-5°C
3. heat
F
CCH2CH3
O
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
Ar OH
Ar I
Ar F
Ar Br Ar Cl
Ar CN
Preparation of Aryl Chlorides and Bromides
Ar N N +
Ar Br Ar Cl
aryl chlorides and aryl bromides are prepared by
heating a diazonium salt with copper(I) chloride or
bromide
substitutions of diazonium salts that use copper(I)
halides are called Sandmeyer reactions
Example
(68-71%)
NH2
NO2
2. CuCl, heat
1. NaNO2, HCl,
H2O, 0-5°C
Cl
NO2
Example
(89-95%)
2. CuBr, heat
1. NaNO2, HBr,
H2O, 0-10°C
NH2
Cl
Br
Cl
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
Ar OH
Ar I
Ar F
Ar Br Ar Cl
Ar CN
Preparation of Aryl Nitriles
Ar N N +
Ar CN
aryl nitriles are prepared by heating a diazonium
salt with copper(I) cyanide
this is another type of Sandmeyer reaction
Example
(64-70%)
2. CuCN, heat
1. NaNO2, HCl,
H2O, 0°C
NH2
CH3
CN
CH3
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
Ar OH
Ar I
Ar F
Ar Br Ar Cl
Ar CN
Transformations of Aryl Diazonium Salts
Ar N N +
Ar H
hypophosphorous acid (H3PO2) reduces diazonium
salts; ethanol does the same thing
this is called reductive deamination
Example
(70-75%)
NaNO2, H2SO4,
H3PO2
NH2
CH3 CH3
Value of Diazonium Salts
1) allows introduction of substituents such as
OH, F, I, and CN on the ring
2) allows preparation of otherwise difficultly
accessible substitution patterns
Example
Br
Br Br
NH2
Br
Br
Br
(74-77%)
NaNO2, H2SO4,
H2O, CH3CH2OH
NH2
Br2
H2O
(100%)
22.18
Azo Coupling
Azo Coupling
Diazonium salts are weak electrophiles.
React with strongly activated aromatic
compounds by electrophilic aromatic
substitution.
Ar N N +
Ar' H + Ar N N Ar'
an azo compound
Ar' must bear a strongly electron-releasing group
such as OH, OR, or NR2.
Example
OH
+ C6H5N N +
OH
N NC6H5
Cl–