Nitrogen Compounds

Nitrogen compounds (Chapter 37)

Nitrogen containing compound    

T.N.T. Proteins Enzymes Drugs

CH3 NO2

NO2

NO2

Amines 

Aliphatic    



1o amine 2o amine 3o amine 4o ammonium cpds

R-NH2 R-N-H R’

Aromatic NH2

R-N-R” R’ R + R-N-R” BrR’

IUPAC names 

CH3NH2



(CH3)2NH N-methylmethanamine





Methanamine

(CH3)3N N,Ndimethylmethanamine C6H5NH2 Phenylamine (aniline)

Formation of amines 

Alkylation of NH3 RX + NH3 → R-NH2 + R2-NH + R3N + R4N+X(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+)

Formation of Amines 

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

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

Basicity of Amines R H N:

H H O

H

R

H N H H

Order of basicity: 2o > 1o > 3o > NH3 > C6H5NH2 Why?

+ OH-

Explanation 



Solvation of protonated amine in water by hydrogen bondingH2O (more H, better solvation) NH3>1o>2o>3o

R

+

H N H H H2O

H2O

Explanation 

Effect of the inductive electron push of the R groups 





Increase the basicity Stabilize the alkylammonium ion

3o>2o>1o>NH3

R R N: R R

+

R N H R

Explanation 



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

..

NH2 ..-

+

NH2

Reactions 

Salt Formation NH2 + HCl

NH2 + H2O + NaCl

NH3+ ClNaOH ?

Reactions 

Amide Formation

O O R-NH2 + CH3CCl → CH3CNHR + HCl O O R-NH2 + C6H5CCl → C6H5CNHR + HCl High m.p. Used in identification

Reaction with Nitrous acid 

HNO2 prepared by NaNO2 + HCl



1o aliphatic amines RNH2 + NaNO2 + HCl → [R←N+≡N]ClAliphatic ROH H O Diazonium salt 2 -H+ (unstable) R+ + N2 C=C (evolution of N2 serves Xas a test for 1o amine) R-X

Reaction with Nitrous acid 

1o aromatic amine NH2 + NaNO2 + HCl →

N+≡N Cl-

(stable at temp.<5oC, greater stability by dispersing charge into the benzene ring)

Mechanism .. HO N

H+

H + O 2 .. .. Ar NH2 + N+ O O

Ar NH N -H2O

.. O ..

+ Ar N N:

N

-H2O N+ O

.. O

+ Ar NH2 N

Ar N N

N .. O

O -H+

.. H+ + OH Ar N N OH2

+ Ar N N:

Stability of Ar-N+≡N

+

N

N:

Benzenediazonium salt  





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

Benzenediazonium salt 

 

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

CuCl ArCl CuBr

ArBr

Ar-N2+ CuCN ArCN + N2 IH2O

ArI ArOH

Coupling reaction .. N=N+:

OH 1

+

ONaOH

(Napthalen-2-ol)

Ice cold 1

N+= N-

HO

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