Nitrogen compounds

1
Nitrogen compounds

• (Chapter 37)

2
Nitrogen containing compound

• T.N.T.
• Proteins
• Enzymes
• Drugs

3
Amines

• Aliphatic
• 1o amine
• 2o amine
• 3o amine
• 4o ammonium cpds
• Aromatic

R-NH2
4
IUPAC names

• CH3NH2 Methanamine
• (CH3)2NH N-methylmethanamine
• (CH3)3N N,N-dimethylmethanamine
• C6H5NH2 Phenylamine (aniline)

5
Formation of amines

• Alkylation of NH3
• RX NH3 ? R-NH2 R2-NH R3N R4NX-
• (NH3 in large excess, 1o amine as main product)
• 1o Amine from Amides and Nitriles
• R-C?N ? RCH2NH2 (H2/Ni or LiAlH4)
• RCONH2 ? RCH2NH2(LiAlH4 /ether than H)

6
Formation of Amines

• C6H5-NO2 ? C6H5-NH2
• Reducing agent
• H2/Ni
• or
• HCl,Fe (or Zn, Sn, SnCl2) then OH-

7
Basicity of Amines
NH3 pKb 4.74
CH3NH2 3.36
CH3CH2NH2 3.25
CH3CH2CH2NH2 3.33
(CH3)2NH 3.28
(CH3)3N 4.30
C6H5NH2 9.4
8
Basicity of Amines
Order of basicity 2o gt 1o gt 3o gt NH3 gt
C6H5NH2 Why?
9
Explanation

• Solvation of protonated amine in water by
  hydrogen bonding (more H, better solvation)
• NH3gt1ogt2ogt3o

H2O
H2O
H2O
10
Explanation

• Effect of the inductive electron push of the R
  groups
• Increase the basicity
• Stabilize the alkylammonium ion
• 3ogt2ogt1ogtNH3

11
Explanation

• Lone pair e- partly incorporated into benzene
  ring
• Less ready for protonation

12
Reactions

• Salt Formation

?
13
Reactions

• Amide Formation

14
Reaction with Nitrous acid

• HNO2 prepared by NaNO2 HCl
• 1o aliphatic amines

15
Reaction with Nitrous acid

• 1o aromatic amine

(stable at temp.lt5oC, greater stability by
dispersing charge into the benzene ring)
16
Mechanism
-H2O
H
-H

H
..
..

Ar
NH
N
O
Ar
N
N
OH
Ar
N
N
OH2
..

-H2O

Ar
N
N
Ar
N
N
17
Stability of Ar-N?N
18
Benzenediazonium salt

• C6H5-N2 Cl-
• C-N bond heavily polarized away from benzene ring
• C atom accept Nu (against the norm of aromatic
  chemistry)
• Has considerable synthetic value

19
Benzenediazonium salt

• Can be replaced by a variety of function groups
• High yield
• No multiple substitution

20
Coupling reaction
Orange II, Azo dye (1876) Also serve as a
test for 1o aromatic amine