Transcript Document 7683931

22.16
Nitrosation of Alkylamines
Nitrite Ion, Nitrous Acid, and Nitrosyl Cation
– ••
•• O
••
••
O ••
N
••
H
+
H
••
O
••
+
H
• O ••
•
H
O ••
N
H
H
••
••
+
••
N
+
+
•• O
••
O ••
H
••
N
••
O ••
Nitrosyl Cation and Nitrosation
••
N
+
••
O ••
Nitrosyl Cation and Nitrosation
+
N
N ••
+
••
••
O ••
N
••
N
+
••
O ••
Nitrosation of Secondary Alkylamines
+
N
••
••
O ••
N
•• N
H
H
O ••
N
+
H
N ••
••
••
+
••
N
+
••
O ••
+
nitrosation of
secondary amines
gives an N-nitroso
amine
Example
••
(CH3)2NH
NaNO2, HCl
H2O
••
(CH3)2N
••
N
(88-90%)
••
O ••
Some N-Nitroso Amines
(CH3)2N
N
O
N-nitrosodimethylamine
(leather tanning)
N
N
N
N
O
N-nitrosopyrrolidine
(nitrite-cured bacon)
N
O
N-nitrosonornicotine
(tobacco smoke)
Nitrosation of Primary Alkylamines
R
H
+
N
R
••
N
••
O ••
•• N
H
H
H
N ••
H
+
••
N
+
••
O ••
O ••
N
+
H
R
••
••
+
analogous to
nitrosation of
secondary amines
to this point
Nitrosation of Primary Alkylamines
R
•• N
••
N
••
O ••
H
this species reacts further
Nitrosation of Primary Alkylamines
R
•• N
H
••
N
•• +
H
+
R
•• N
O
H
H
••
N
••
O ••
Nitrosation of Primary Alkylamines
R
•• N
••
N
•• +
O
H
H
R
•• N
H
+
••
N
••
O ••
H
Nitrosation of Primary Alkylamines
R
•• N
R
••
N
••
O ••
H
H
+
•• N
H
••
N
O ••
+
H
Nitrosation of Primary Alkylamines
R
•• N
H
••
N
O ••
+
H
Nitrosation of Primary Alkylamines
nitrosation of a
primary alkylamine
gives an alkyl
diazonium ion
process is called
diazotization
H
R
+
N
N ••
+
•• O ••
H
R
•• N
H
••
N
O ••
+
H
Alkyl Diazonium Ions
+ + •N
R
•
N ••
alkyl diazonium ions
readily lose N2 to
give carbocations
R
+
N
N ••
Example: Nitrosation of 1,1-Dimethylpropylamine
NH2
OH
+
N
HONO
H2O
– N2
+
(80%)
+
Fig. 22.5 (p 890)
(3%)
N
(2%)
Nitrosation of Tertiary Alkylamines
There is no useful chemistry associated with the
nitrosation of tertiary alkylamines.
R
R
R
R
+
N
N ••
R
R
••
N
••
O ••
22.17
Nitrosation of Arylamines
Nitrosation of Tertiary Arylamines
reaction that occurs is
electrophilic aromatic substitution
N(CH2CH3)2
1. NaNO2, HCl,
H2O, 8°C
N(CH2CH3)2
2. HO–
N
(95%)
O
Nitrosation of N-Alkylarylamines
similar to secondary alkylamines;
gives N-nitroso amines
NaNO2, HCl,
H2O, 10°C
NHCH3
N
O
NCH3
(87-93%)
Nitrosation of Primary Arylamines
gives aryl diazonium ions
aryl diazonium ions are much more stable than
alkyl diazonium ions
most aryl diazonium ions are stable under the
conditions of their formation (0-10°C)
Nitrosation of Primary Arylamines
gives aryl diazonium ions
aryl diazonium ions are much more stable than
alkyl diazonium ions
most aryl diazonium ions are stable under the
conditions of their formation (0-10°C)
+
RN
+
ArN
N
N
fast
+
R
+ N2
slow
+
Ar
+ N2
Example:
(CH3)2CH
NH2
NaNO2, H2SO4
H2O, 0-5°C
(CH3)2CH
+
N
N HSO4–
Synthetic Origin of Aryl Diazonium Salts
Ar
H
Ar
NO2
Ar
NH2
Ar
+
N
N
22.18
Synthetic Transformations of Aryl Diazonium Salts
Transformations of Aryl Diazonium Salts
Ar
Ar
Cl
Ar
CN
+
N
Ar
Ar
Ar
F
Ar
I
N
H
Ar
Br
OH
Preparation of Phenols
hydrolysis of a diazonium salt
+
N
Ar
N
H2O, heat
Ar
OH
Example
NH2
(CH3)2CH
1. NaNO2, H2SO4
H2O, 0-5°C
2. H2O, heat
OH
(CH3)2CH
(73%)
Transformations of Aryl Diazonium Salts
Ar
Ar
Cl
Ar
CN
+
N
Ar
Ar
Ar
F
Ar
I
N
H
Ar
Br
OH
Preparation of Aryl Iodides
reaction of an aryl diazonium salt with
potassium iodide
Ar
+
N
N
KI
Ar
I
Example
NH2
Br
1. NaNO2, HCl
H2O, 0-5°C
I
Br
2. KI, room temp.
(72-83%)
Transformations of Aryl Diazonium Salts
Ar
Ar
Cl
Ar
CN
+
N
Ar
Ar
Ar
F
Ar
I
N
H
Ar
Br
OH
Preparation of Aryl Fluorides
Ar
Ar
+
N
F
N
heat the tetrafluoroborate salt of a diazonium ion;
process is called the Schiemann reaction
Example
NH2
1. NaNO2, HCl,
H2O, 0-5°C
CCH2CH3
O
2. HBF4
3. heat
F
CCH2CH3
O
(68%)
Transformations of Aryl Diazonium Salts
Ar
Ar
Cl
Ar
CN
+
N
Ar
Ar
Ar
F
Ar
I
N
H
Ar
Br
OH
Preparation of Aryl Chlorides and Bromides
Ar
Cl
Ar
Ar
+
N
Br
N
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
NH2
1. NaNO2, HCl,
H2O, 0-5°C
NO2
2. CuCl, heat
Cl
NO2
(68-71%)
Example
NH2
Cl
1. NaNO2, HBr,
H2O, 0-10°C
Br
Cl
2. CuBr, heat
(89-95%)
Transformations of Aryl Diazonium Salts
Ar
Ar
Cl
Ar
CN
+
N
Ar
Ar
Ar
F
Ar
I
N
H
Ar
Br
OH
Preparation of Aryl Nitriles
Ar
CN
Ar
+
N
N
aryl nitriles are prepared by heating a diazonium
salt with copper(I) cyanide
this is another type of Sandmeyer reaction
Example
NH2
CH3
1. NaNO2, HCl,
H2O, 0°C
CN
CH3
2. CuCN, heat
(64-70%)
Transformations of Aryl Diazonium Salts
Ar
Ar
Cl
Ar
CN
+
N
Ar
Ar
Ar
F
Ar
I
N
H
Ar
Br
OH
Transformations of Aryl Diazonium Salts
hypophosphorous acid (H3PO2) reduces diazonium
salts; ethanol does the same thing
this is called reductive deamination
Ar
Ar
H
+
N
N
Example
NH2
CH3
NaNO2, H2SO4,
H3PO2
CH3
(70-75%)
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
NH2
NH2
Br2
NaNO2, H2SO4,
Br H O, CH CH OH
2
3
2
Br
H2O
Br
Br
Br
(100%)
Br
(74-77%)
22.19
Azo Coupling
Azo Coupling
Diazonium salts are weak electrophiles.
React with strongly activated aromatic
compounds by electrophilic aromatic
substitution.
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–