1. CHEMISTRY OF NITROGEN CONTAINING COMPOUNDS

2. Session Objectives Introduction nitro compounds Nomenclature
Structure and physical properties
Preparation of nitro compounds
Chemical reactions
Cyanides and isocyanides
General method of preparation
Physical and chemical properties
7. Diazo compounds

3. Preparation of nitro compounds
Aliphatic nitro compounds
Vapour phase nitration of alkanes
Treatment of alkyl halides with alcoholic AgNO3
Oxidation of t-alkyl amines with KMnO4.
2. Aromatic nitro compounds

4. Vapour phase nitration of alkanes
Hydrocarbons on heating with fuming nitric acid at K are converted into nitroalkanes.
This method is important in the commercial production of nitro compounds.

5. Treatment of alkyl halides with alcoholic AgNO3
Iodoalkanes on treatment with alcoholic AgNO2 are converted into nitroalkanes besides alkylnitriles.

6. Limitations
(i) Aromatic nitro compounds cannot be prepared by this method because of the less reactivity of aryl halide towards nucleophilic substitution.
(ii) This method is not suitable for the large scale preparation of nitro compounds.

7. Oxidation of t-alkyl amines with KMnO4
The amine must be primary and —NH2 group should be attached to a tertiary carbon.

8. Aromatic nitro compounds
Nitration is performed with a mixture of concentrated nitric and sulphuric acid (source of nitronium ion).

9. Reactions of nitro compounds
In aromatic and aliphatic nitro compounds, notro group undergoes similar reactions.
Reduction
i) Catalytic reduction: easily reduced by catalytic hydrogenation using Pd/C catalyst in ethanol.

10. Reduction in neutral medium
(iii) Reduction in neutral medium: Zinc dust and ammonium chloride convert nitro benzene to corresponding hydroxylamine.

11. Reduction with LiAlH4
Aliphatic nitro-compounds are reduced to primary amines with LiAlH4.
Aromatic nitro-comopunds on reduction with LiAlH4 give azo compounds.

12. Reduction in basic medium
Forms different products depending on reducing reagent

13. Reductive removal of nitro group
Nitro group can be removed from aromatic ring via reduction to amine followed by deoxidization with HNO2 and then reductive removal of the diazonium group using sodium borohydride or hypo phosphorus acid/Cu+ mixture.

14. Electrophilic substitution
The nitro group strongly deactivates the benzene ring towards electrophilic substitution.
Required strong conditions.

15. Nucleophilic substitution
Nitro group facilitates the nucleophilic substitution by stabilising the intermediate carbanion as depicted below.

16. Diazonium Salts
The diazonium salts are represented by general formula ArN2+X–, where Ar stands for the aryl group and X may be any anion such as
obtained by adding the suffix diazonium to the parent compound and is further followed by the name of the anion, e.g.
Nomenclature

18. Preparation of diazonium salts
1. Obtained by treatment of primary aromatic amine dissolved in cold aqueous mineral acid with sodium nitrite.
The conversion of primary amine into a diazonium salt is called diazotisation.

19. Chemical properties of diazonium salts
Arenediazonium salts are highly reactive compounds due to excellent leaving ability of the diazo group as nitrogen gas, N2.
Their chemical reactions may be classified into two types.
(i). Reactions in which the –N2X is completely replaced.
(ii). Reactions in which the nitrogen atoms are retained.

20. Reactions in which the –N2X is completely replaced
1. Replacement by –Cl, –Br and –CN (Sandmeyer reaction)

21. 2. Replacement by iodine
3. Replacement by fluorine — Balz-Schiemann reaction

22. Reactions in which the nitrogen atoms are retained
1. Reduction to arylhydrazines
This reduction can be brought about by a number of reagents such as stannous chloride-hydrochloric acid, sodium sulphite, sodium hydrosulphide and even electrolytically.

23. Vigorous reducing agent such as Zn/HCl is used, the product is an aromatic amine.

24. Cyanides
Cyanides
Cynanides are considered to be the derivatives of hydrogen cyanide (HCN) in which H atom is replaced by alkyl or aryl group. These are also known as nitriles or carbonitriles.

25. General Methods of Preparation
1. From alkyl halide
2. By dehydration of primary amides

26. Physical properties 1. Physical state and smell:
The lower members of the family are colourless liquids whereas the higher members are crystalline solids. They are stable compounds with pleasant smell.
2. Boiling point:
Due to the presence of polar group in the molecules, they have high dipole moment and consequently high melting and boiling points.

27. Solubility: The lower cyanides are soluble in water due to the tendency of their molecules to form hydrogen bond with water molecules.
With the increase in molecular mass, the bulk of the non-polar portion (i.e. R–) increases and consequently, solubility in water decreases.
However, the cyanides are fairly soluble in organic solvents.

28. Chemical properties 1. Hydrolysis:
Hydrolysed in acidic as well as in basic solution to give amides as the initial products. Exhaustive hydrolysis form carboxylic acid.

29. By using alcohol under acidic conditions, an ester is obtained.

30. Reduction
Nitriles need relatively stronger reagents for reduction. Catalytic hydrogenation in presence of Raneys nickel or on reduction with LiAlH4 nitriles are reduced to primary amines.

31. Isocyanides
Isocyanides are structural isomers of alkyl cyanides. In these compounds, the group is linked to the alkyl or aryl group through N atom. They have general formula

32. Nomenclature
In common system, these are generally named by adding a prefix iso before the name of the isomeric alkyl nitriles.
They are also called alkyl carbylamines.
In IUPAC system, isocyanides are named as alkyl isocyanides.
CH3CH2NC Ethyl isocyanide

33. General Methods of Preparation
1. From alkyl halide
2. From primary amines (Carbylamine reaction)
+ 3KCl + 3H2O

34. Physical properties Physical state, smell:
Isocyanides are colourless liquids with very unpleasant smell.
Boiling point:
They are relatively less polar in comparison with isomeric cyanides. Consequently, their melting and boiling points are relatively low in comparison with the cyanides of same molecular mass.

35. Solubility:
They are not very soluble in water. This is due to the reason that nitrogen atom does not have a lone pair of electrons and hence cannot form H-bonds.

36. Chemical properties 1. Addition of water:
Acid catalysed addition of water gives alkyl formamide derivative.
2. Reduction with LAH: reduced to N-methyl amines.