1. Chemistry

2. Alkyl and Aryl halides–1

3. Session objectives 1.Classification 2.Nature of C — X bond 3.Preparation of alkyl halides 4.Physical and chemical properties of alkyl halides 5.Substitution reaction: S N 1 and S N 2 reactions

4. Elimination reaction E 1 E 2 E1 c B Ei

5. E1 Mechanism

6. Elimination reaction 3° > 2° > 1° > CH 3 Rate = k[RX] 1

7. E2 Rate = k[RX] [Base] = k[CH 3 CH 2 Cl]

8. E1 cB carbanion stabilization by the participation of –R (conjugation), –I effect etc. Mechanism

9. Ei Observed for pyrolytic elimination for xanthates (Tschugaev’s reaction), esters, oxides of amines (Cope’s reaction) which produces alkene. It occurs intramolecularly through the formation of a transition state, when they are heated.

10. Comparison between E1 and E2

12. Polyhalogen compounds Dichloromethane (CH 2 Cl 2 ) Colourless sweet smelling volatile liquid. It has low boiling point (313 k) and inflammable; used as a solvent in extraction in food and pharmaceutical industries. Vicinal dihalide When two halogen atoms are attached to adjacent carbon atoms, the compound is called vicinal dihalide. 1, 2-dichloroethane e.g.,

13. Polyhalogen compounds Geminal dihalide When two halogen atoms are attached to the same carbon atom, the compound is called geminal dihalide e.g. H 3 C – CHCl 2 1,1-dichloroethane

14. Polyhalogen compounds Chloroform (CHCl 3 ) Methods of preparation (1) By chlorination of methane (2)By reduction of carbon tetra chloride

15. Polyhalogen compounds (3) From ethyl alcohol

16. Polyhalogen compounds (4) From acetone

17. Properties (1)Sweet smelling liquid, boiling point 61° C. (2) Oxidation Stored in dark coloured bottled because on oxidation chloroform gives phosgene gas which is poisonous 1% C 2 H 5 OH is added while storing chloroform

18. Properties (3) Reduction (4) Chlorination (5) Hydrolysis (6) Nitration

19. Properties (7)Reaction with acetone (8) Dehalogenation (9) Carbylamine reaction

20. Iodoform (CHI 3 ) Preparation

21. properties 1.Yellow solid melting point 119° C. 2.Chemical properties of iodoform are same as that of chloroform. 3.Chlorine and bromine can replace iodine in iodoform reaction to give CHCl 3 and CHBr 3 respectively. The reaction is called haloform reaction.

22. Carbon tetrachloride Preparation Properties (1) Colourless liquid, boiling point 350 K.

23. Uses (1) Used as fire extinguisher. Trade name is pyrene. At 773 K it is hydrolysed by water vapours into phosgene gas. Therefore, the room should be well ventilated after using CCl 4 as fire extinguisher. (2) Industrial solvent for oils, fats, resins etc.

24. Thank you