1. BY HARJEET GUJRAL ASSOCIATE PROFESSOR GOVT. COLLEGE ROPAR
REACTIONS OF AMINES BY
HARJEET GUJRAL
ASSOCIATE PROFESSOR
GOVT. COLLEGE ROPAR

2. Amines, reactions Amines are similar to ammonia in their reactions.
Like ammonia, amines are basic.
Like ammonia, amines are nucleophilic and react with alkyl halides, acid chlorides, and carbonyl compounds.
The aromatic amines are highly reactive in electrophilic aromatic substitution.

3. Amine, reactions:
As bases
Alkylation
Reductive amination
Conversion into amides
EAS
Hofmann elimination from quarternary ammonium salts
Reactions with nitrous acid

4. As bases
a) with acids
b) relative base strength
c) Kb
d) effect of groups on base strength

5. WITH ACIDS
Amines react with acids to form quaternary ammonium salt.

6. RELATIVE BASE STRENGTH
RNH2 > NH3 > ArNH2
Kb ionization of the base in water
:Base H2O H:Base OH-
Kb = [ H:Base+ ] [ OH- ] / [ :Base ] Kb
aliphatic amines – 10-4
ammonia 1.8 x 10-5
anilines or less

7. Why are aliphatic amines more basic than ammonia?
NH H2O  NH OH-
R-NH H2O  R-NH OH-
The alkyl group, -R, is an electron donating group. The donation of electrons helps to stabilize the ammonium ion by decreasing the positive charge, lowering the ΔH, shifting the ionization farther to the right and increasing the basicity.

8. Why are aromatic amines less basic than aliphatic amines?
R-NH H2O  R-NH OH-
resonance stabilization of the free base, increases the ΔH, shifts the ionization to the left, decreasing base strength.

9. Effect of substituent groups on base strength:
Electron donating groups will stabilize the anilinium ion, decreasing the ΔH, shifting the ionization farther to the right and making the compound a stronger base.
Electron withdrawing groups destabilize the anilinium ion, increasing the ΔH, shifting the ionization towards the reactants, making the compound a weaker base.

10. Common substituent groups:
-NH2, -NHR, -NR2
-OH
-OR
-NHCOCH electron donating
-C6H5 groups -R -H -X
-CHO, -COR
-SO3H electron withdrawing
-COOH, -COOR groups
-CN
-NR3+
-NO2

11. Number the following in decreasing order of base strength (let #1 = most basic, etc.

12. 2. Alkylation (ammonolysis of alkyl halides)

14. 3. Reductive amination

16. Conversion into amides
R-NH RCOCl  RCONHR HCl
1o N-subst. amide
R2NH RCOCl  RCONR HCl
2o N,N-disubst. amide
R3N RCOCl  NR 3o

18. Conversion into sulfonamides
R-NH ArSO2Cl  ArSO2NHR HCl
1o N-subst.sulfonamide
R2NH ArSO2Cl  ArSO2NR HCl
2o N,N-disubst.sufonamide
R3N ArSO2Cl  NR

19. Schotten-Baumann technique: reactions of aromatic acid chlorides are sped up by the addition of base.
R-NH ArSO2Cl + KOH  ArSO2NHR
1o acidic
ArSO2NR
water soluble salt
R2NH ArSO2Cl KOH  ArSO2NR HCl
2o N,N-disubst.sufonamide
water insoluble

20. Hinsberg Test: unknown amine + benzenesulfonyl chloride, KOH (aq)
Reacts to produce a clear solution and then gives a ppt upon acidification  primary amine.
Reacts to produce a ppt  secondary amine.
Doesn’t react  tertiary amine.

22. EAS
-NH2, -NHR, -NR2 are powerful activating groups and ortho/para directors
a) nitration
b) sulfonation
c) halogenation
d) Friedel-Crafts alkylation
e) Friedel-Crafts acylation
f) coupling with diazonium salts
g) nitrosation

23. a) nitration

24. b) sulfonation

25. c) halogenation

26. Swimming pool test kit for chlorine:

27. Friedel-Crafts alkylation
NR with –NH2, -NHR, -NR2

28. Friedel-Crafts acylation
NR with –NH2, -NHR, -NR2

29. g) nitrosation

30. h) coupling with diazonium salts  azo dyes

31. Hofmann elimination from quarternary hydroxides
step 1, exhaustive methylation  4o salt
step 2, reaction with Ag2O  4o hydroxide + AgX
step 3, heat to eliminate  alkene(s) + R3N

33. 7. Reactions with nitrous acid

34. note: 90% of all tested nitrosamines are carcinogenic in man
note: 90% of all tested nitrosamines are carcinogenic in man. Many nitrosamine cancers are organ specific. For example, dimethylnitrosamine causes liver cancer while the nitrosamines in tobacco smoke cause lung cancer.
Sodium nitrite (“cure”) is used as a preservative in meats such as bacon, bologna, hot dogs, etc. to kill the organism responsible for botulism poisoning. In the stomach, the nitrous acid produced from sodium nitrite can react with secondary and tertiary amines to form nitrosamines. To reduce the formation of nitrosamines, ascorbic acid (Vitamin C) is now added to foods cured with sodium nitrite.
Nitrosamines are also found in beer!