22.15 Nitrosation of Alkylamines

1
22.15Nitrosation of Alkylamines
2
Nitrite Ion, Nitrous Acid, and Nitrosyl Cation
3
Nitrosyl Cation and Nitrosation
4
Nitrosyl Cation and Nitrosation

5
Nitrosation of Secondary Alkylamines

• nitrosation of secondary amines gives an
  N-nitroso amine

6
Example
NaNO2, HCl

H2O
(88-90)
7
Some N-Nitroso Amines
8
Nitrosation of Primary Alkylamines

• analogous to nitrosation of secondary amines to
  this point

9
Nitrosation of Primary Alkylamines
R
H

• this species reacts further

10
Nitrosation of Primary Alkylamines

• nitrosation of a primary alkylamine gives an
  alkyl diazonium ion
• process is called diazotization

11
Alkyl Diazonium Ions

• alkyl diazonium ions readily lose N2 to give
  carbocations

12
Example Nitrosation of 1,1-Dimethylpropylamine
13
Nitrosation of Tertiary Alkylamines

• There is no useful chemistry associated with the
  nitrosation of tertiary alkylamines.

14
22.16Nitrosation of Arylamines
15
Nitrosation of Tertiary Arylamines

• reaction that occurs is electrophilic aromatic
  substitution

16
Nitrosation of N-Alkylarylamines

• similar to secondary alkylamines
• gives N-nitroso amines

NaNO2, HCl,H2O, 10C
17
Nitrosation of Primary Arylamines

• gives aryl diazonium ions
• aryl diazonium ions are much more stable
  thanalkyl diazonium ions
• most aryl diazonium ions are stable under the
  conditions of their formation (0-10C)

18
Example
HSO4
19
Synthetic Origin of Aryl Diazonium Salts
20
22.17Synthetic TransformationsofAryl Diazonium
Salts
21
Transformations of Aryl Diazonium Salts
22
Preparation of Phenols
H2O, heat
23
Example
1. NaNO2, H2SO4 H2O, 0-5C
2. H2O, heat
(73)
24
Transformations of Aryl Diazonium Salts
25
Preparation of Aryl Iodides

• reaction of an aryl diazonium salt with potassium
  iodide

KI
26
Example
I
1. NaNO2, HCl H2O, 0-5C
Br
2. KI, room temp.
(72-83)
27
Transformations of Aryl Diazonium Salts
28
Preparation of Aryl Fluorides

• heat the tetrafluoroborate salt of a diazonium
  ion
• process is called the Schiemann reaction

29
Example
1. NaNO2, HCl, H2O, 0-5C
2. HBF4
3. heat
(68)
30
Transformations of Aryl Diazonium Salts
31
Preparation of Aryl Chlorides and Bromides

• 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

32
Example
NH2
Cl
1. NaNO2, HCl, H2O, 0-5C
2. CuCl, heat
NO2
NO2
(68-71)
33
Example
1. NaNO2, HBr, H2O, 0-10C
Br
Cl
2. CuBr, heat
(89-95)
34
Transformations of Aryl Diazonium Salts
35
Preparation of Aryl Nitriles

• aryl nitriles are prepared by heating a diazonium
  salt with copper(I) cyanide
• this is another type of Sandmeyer reaction

36
Example
1. NaNO2, HCl, H2O, 0C
CN
CH3
2. CuCN, heat
(64-70)
37
Transformations of Aryl Diazonium Salts
38
Transformations of Aryl Diazonium Salts

• hypophosphorous acid (H3PO2) reduces diazonium
  salts ethanol does the same thing
• this is called reductive deamination

39
Example
NaNO2, H2SO4, H3PO2
(70-75)
40
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

41
Example
42
22.18Azo Coupling
43
Azo Coupling

• Diazonium salts are weak electrophiles.
• React with strongly activated aromatic compounds
  by electrophilic aromatic substitution.

44
Example

Cl
45
Section 22.19Spectroscopic Analysis of Amines
46
Infrared Spectroscopy

• the NH stretching band appears in the
  range3000-3500 cm-1
• primary amines give two peaks in this region,
  onefor a symmetrical stretching vibration, the
  other foran antisymmetrical stretch

47
Infrared Spectroscopy

• primary amines give two NH stretching peaks,
  secondary amines give one

48
1H NMR

• compare chemical shifts in

49
13C NMR

• Carbons bonded to N are more shielded than those
  bonded to O.

CH3NH2
CH3OH
50
UV-VIS
An amino group on a benzene ring shifts ?maxto
longer wavelength. Protonation of N causesUV
spectrum to resemble that of benzene.
?max204 nm256 nm
?max230 nm280 nm
?max203 nm254 nm
51
Mass Spectrometry

• Compounds that contain only C, H, and O have
  even molecular weights. If an odd number of N
  atoms is present, the molecular weight is odd.
• A molecular-ion peak with an odd m/z value
  suggests that the sample being analyzed contains
  N.

52
Mass Spectrometry

• Nitrogen stabilizes carbocations, which drives
  the fragmentation pathways.

e
53
Mass Spectrometry

• Nitrogen stabilizes carbocations, which drives
  the fragmentation pathways.

e
54
End of Chapter 22