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Ozonolysis

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Degradation of alkenes using ozone as an oxidizing agent.

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Ozonolysis

  1. 1. OZONOLYSIS Prepared By Dr. Krishnaswamy. G Faculty DOS & R in Organic Chemistry Tumkur University Tumakuru 1
  2. 2. Oxidative cleavage of carbon-carbon double bond using ozone as an oxidizing agent is called Ozonolysis. The reaction is performed in common organic solvents such as Dichloromethane (or) Methanol (or) Acetone at -78o C. 2 R1 R3 R2 R4 R1 R3 R2 R4 O O O3 Work Up
  3. 3. Ozonolysis of carbon-carbon double takes place through ozonide intermediate followed by work up results in the formation of respective products. Work up in the ozonolysis may be divided into three categories. 3 (1) Reductive work up using mild reducing agents such as Me2S (or) PPh3 (or) Zn dust. (2) Reductive work up using strong reducing agents such as LiAlH4 (or) NaBH4. (3) Oxidative work up using oxidizing agents such as H2O2 (or) O2.
  4. 4. 4 (1) Reductive work up using mild reducing agents such as Me2S (or) PPh3 (or) Zn dust produces aldehyde and ketone. R1 R3 R2 H R1 R3 R2 H O O O3 Mild Reductive Work Up R1 R3 R2 H O O O Me2S/PPh3/ Zn dust [Ozonide]
  5. 5. 5 (2) Reductive work up using strong reducing agents such as LiAlH4 (or) NaBH4 produces alcohols. R1 R3 R2 H R1 R3 R2 OH HO O3 Strong Reductive Work Up R1 R3 R2 H O O O LiAlH4/ NaBH4 [Ozonide]
  6. 6. 6 (3) Oxidative work up using oxidizing agents such as H2O2 (or) O2 provides carboxylic acids. R1 R3 R2 H R1 R3 R2 OH O O O3 Oxidative Work Up R1 R3 R2 H O O O H2O2/ O2 [Ozonide]
  7. 7. Ozone inserts to the alkene by 1, 3-dipolar cycloaddition to form primary ozonide, which is highly unstable and undergoes retro 1, 3-dipolar cycloaddition to form carbonyl and carbonyl oxide. 7 R R' O R O O Primary Ozonide O O O O O O R' O R O O R' Carbonyl Carbonyl oxide 1, 3-Dipolar cycloaddition Retro 1, 3-Dipolar cycloaddition 1, 3-dipole Mechanism
  8. 8. 8 Carbonyl oxide which has a dipole undergoes once again 1, 3 – dipolar cycloaddition reaction with carbonyl to for the stable ozonide. O O O R' Carbonyl Carbonyl oxide R O O O R R'1, 3-Dipolar cycloaddition Ozonide 1, 3-dipole
  9. 9. 9 The stable ozonide reacts with reducing (or) oxidizing agents to give desired products. O O O R R' Ozonide S Me Me O O R R' S O MeMe
  10. 10. Ozonolysis of simple allenes leads to the formation of two carbonyl fragments and carbon monoxide. 10 C C C R1 R3 R2 R4 C O R1 R3 O C R2 R4 CO O3 Ozonolysis of alkynes leads to the formation of either acid anhydrides or a diketone. C C O3 C C O O O C C O O C C O O O Diketone Anhydride Work Up

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