1. Chemistry

2. Organic compounds with functional groups containing nitrogen-I Session

3. Session Objectives 1.Introduction nitro compounds 2.Nomenclature 3.Structure and physical properties 4.Preparation of nitro compounds 5.Chemical reactions 6.Cyanides and isocyanides General method of preparation Physical and chemical properties 7.Diazo compounds General method of preparation Physical and chemical properties

4. Preparation of nitro compounds 1.Aliphatic nitro compounds Vapour phase nitration of alkanes Treatment of alkyl halides with alcoholic AgNO 3 Oxidation of t-alkyl amines with KMnO 4. 2.Aromatic nitro compounds

5. Vapour phase nitration of alkanes Hydrocarbons on heating with fuming nitric acid at 693-793 K are converted into nitroalkanes. This method is important in the commercial production of nitro compounds.

6. Treatment of alkyl halides with alcoholic AgNO 3 Iodoalkanes on treatment with alcoholic AgNO 2 are converted into nitroalkanes besides alkylnitriles. 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 KMnO 4 The amine must be primary and —NH 2 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 acidic medium (ii) By metal in acidic solutions: Metals(Fe, Sn and Zn) and HCl are used for reducing a nitro group to an amino group.

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

12. Reduction with LiAlH 4 Aliphatic nitro-compounds are reduced to primary amines with LiAlH 4. Aromatic nitro-comopunds on reduction with LiAlH 4 give azo compounds.

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

14. Selective reduction One nitro group can be reduced without affecting the second group on benzene ring using ammonium sulphide orsodium polysulphide.

15. Reductive removal of nitro group Nitro group can be removed from aromatic ring via reduction to amine followed by deoxidization with HNO 2 and then reductive removal of the diazonium group using sodium borohydride or hypo phosphorus acid/Cu + mixture.

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

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

18. Acidic nature of alpha hydrogen atom Alpha hydrogen atom in aliphatic nitro compounds becomes acidic due to the electron withdrawing nature of nitro group. Gives aldol condensation with carbonyl compounds which on dehydration gives unsaturated nitro compound.

19. Hydrolysis of aliphatic nitro compounds Primary nitro-compounds are hydrolysed by boiling HCl or by 85% H 2 SO 4 to a carboxylic acid and hydroxylamine. Secondary nitro-compounds are hydrolysed by boiling hydrochloric acid to ketones and nitrous oxide. Tertiary nitro-compounds are generally unaffected by HCl.

20. Diazonium Salts The diazonium salts are represented by general formula ArN 2 + X –, where Ar stands for the aryl group and X may be any anion such as Nomenclature obtained by adding the suffix diazonium to the parent compound and is further followed by the name of the anion, e.g.

21. 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. 2. Nitrite esters formed from alcohols and nitrous acid are also used to generate diazonium salt on treatment with aromatic primary amines.

22. Chemical properties of diazonium salts Arenediazonium salts are highly reactive compounds due to excellent leaving ability of the diazo group as nitrogen gas, N 2. Their chemical reactions may be classified into two types. (i). Reactions in which the –N 2 X is completely replaced. (ii). Reactions in which the nitrogen atoms are retained.

23. Reactions in which the –N 2 X is completely replaced 1. Replacement by –Cl, –Br and –CN (Sandmeyer reaction) 2. Replacement by iodine

24. Reactions in which the –N 2 X is completely replaced 3. Replacement by fluorine — Balz-Schiemann reaction 4. Replacement by nitro group 5. Replacement by hydroxyl group

25. Reactions in which the –N 2 X is completely replaced 6. Replacement by hydrogen atom 8. Replacement by an aryl group Gomberg-Bachmann reaction

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

27. Reactions in which the nitrogen atoms are retained 2. Coupling reactions Diazonium salts are weak electrophiles and they react with highly reactive aromatic compounds such as phenols, napthols and aromatic amines to form highly coloured azo compounds which are used as dyes.

28. 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. Nomenclature

29. General Methods of Preparation 1. From alkyl halide Aryl cyanides cannot be prepared by this method since aryl halides are almost unreactive towards nucleophillic substitution reaction. 2. By dehydration of primary amides In this reaction, ammonium salts of carboxylic acids can be used instead of amides.

30. General Methods of Preparation 3. By dehydration of aldoximes with P 2 O 5 or acetic anhydride 4. From Grignard reagent 5. From aryl diazonium salt This reaction is a special case of Sandmeyer reaction or Gattermann reaction.

31. 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.

32. Physical properties 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.

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

34. Chemical properties 4. Alcoholysis Reaction with Grignard reagent

35. Chemical properties Reduction Nitriles need relatively stronger reagents for reduction. Catalytic hydrogenation in presence of Raneys nickel or on reduction with LiAlH 4 nitriles are reduced to primary amines.

36. 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 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. CH 3 CH 2 NCEthyl isocyanide

37. General Methods of Preparation 1. From alkyl halide 2. From primary amines (Carbylamine reaction) + 3KCl + 3H 2 O

38. 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. 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.

39. Chemical properties 1.Addition of water: Acid catalysed addition of water gives alkyl formamide derivative. 2. Reduction with LAH: reduced to N-methyl amines. 3. Oxidation: On reaction with HgO or with ozone as well as with halogen and dimethylsulphoxide, oxidised to isocyanates

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