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Chemistry

Chemistry. Alkynes. Session objectives. 1. Preparation of alkynes by (a) Kolbe’s method (b) dehydrohalogenation of vicinal dihalide (c) dehydrohalogenation of geminal dihalide 2. Chemical reactions of alkyne (a) Addition of halogen, hydrogenhalides. (b) Ozonolysis

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Chemistry

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  1. Chemistry

  2. Alkynes

  3. Session objectives 1. Preparation of alkynes by(a) Kolbe’s method (b) dehydrohalogenation of vicinal dihalide (c) dehydrohalogenation of geminal dihalide 2. Chemical reactions of alkyne (a) Addition of halogen, hydrogenhalides. (b) Ozonolysis 3. Confirmatory test for alkyne

  4. General characteristics of alkynes • General formula CnH2n–2 • sp hybridization • C–C bond length 1.2 A0 • Shows chain and functional isomerism

  5. Chain isomerism Functional group isomerism

  6. Preparation Kolbe electrolysis

  7. Dehydrohalogenation of vicinal dihalides From gem dihalides

  8. Miscellaneous methods Miscellaneous methodsFrom CaC2 Lime

  9. Chemical properties Addition Reactions (i) Addition of hydrogen

  10. Chemical properties Lindlar catalyst (H2/Pd/BaSO4) partially reduces a disubstituted alkyne to a cis-alkene. Trans-2-butene

  11. Chemical properties Addition of halogens Addition of hydrogen halides

  12. Mechanism

  13. Addition of water

  14. Hydroboration oxidation

  15. Oxidation of alkynes

  16. Ozonolysis of alkynes

  17. Formation of alkynides

  18. Formation of alkynides

  19. Acidity of Alkynes Ethyl anion Acetylide anions Vinyl anion

  20. Acidity of Alkynes sodium. acetylide

  21. Acidity of Alkynes The order of boiling point among hydrocarbons is alkynes > alkenes > alkanes. These hydrocarbons also possess low dipole moment. Acetylene having two hydrogen atoms is more acidic than a mono substituted acetylene.

  22. Class exercise

  23. Class exercise 1 How will you effect the following conversions? Solution: (a) (i) Cl2 + hn (ii) Wurtz reaction (iii) Cl2 + hn (iv) alc. KOH, heat (b) (i) HgSO4, H2SO4 (20%) Hence, the answer is (c)

  24. Class exercise 2 Write the structural formula of the main organic product. Solution: Hence, the answer is (b)

  25. Solution

  26. Class exercise 3 Give a chemical test to distinguish between 1-butyne and 2-butyne. Solution: 1 butyne will give white ppt. with ammonical AgNO3.

  27. Class exercise 4 A cylinder contains one of the following gases — propyne, propene, propane. What chemical test would you apply to identify the gases? Solution: AgNO3 (ammonical) is used for alkyne, alk. KMnO4, and heat is applied for alkene. No reaction takes place with propane with the above mentioned reagents.

  28. Class exercise 5 Write the product of the following reaction. Solution: CH3CH2CHO

  29. Class exercise 6 What reaction of an appropriate alkyne would lead to the following product? Solution:

  30. Class exercise 7 An organic compound (A) having molecular formula when treated with NaNH2/ NH3 followed by reactionwith n-propyl bromide yielded (B) . Compound (A) gives a ketone (C)when treated with acidified HgSO4.(B) on oxidation with hot alk. KMnO4gives two isomeric acids (D) and (E). Deduce structures from (A) to (E). Solution:

  31. Class exercise 8 Write the correct product of the following reaction. Product Solution: Cl2CHCHO

  32. Class exercise 9 Write the products of the following reaction. C is CO2 D is C2H5CO2HE is H2O F is HCOOH G is C2H5COOH Solution:

  33. Class exercise 10 Write the intermediate steps of the following reaction Solution:

  34. Solution

  35. Thank you

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