Ozonolysis

OZONOLYSIS ADVANCED ORGANIC CHEMISTRY, MPHARM ,

1. Presented By Shubham S harma M .Pharm (1 sem ) (Pharmaceutical Chemistry) Roll No-20029 Presented To Dr. Ashok K umar Yadav UGC Assistant Professor UIPS, Panjab University OZONOLYSIS

2. CONTENTS INTRODUCTION MECHANISM ( OF ALKENES) REAGENTS USED OZONOLYSIS OF ALKYNES TYPES OF OZONOLYSIS SYNTHETIC APPLICATIONS

3. INTRODUCTION Ozonolysis was invented by Christian Friedrich Schönbein in 1840. Ozonolysis refers to the organic chemical reaction where ozone is employed to cleave the unsaturated bonds of alkenes, alkynes, and azo compounds (compounds with the functional diazenyl functional group). Oxidation of alkenes with the help of ozone can give alcohols, aldehydes, ketones, or carboxylic acids. Alkynes undergo ozonolysis to give diketones. If water is present in the reaction, the diketone undergoes hydrolysis to yield two carboxylic acids. For azo compounds, the ozonolysis yields nitrosamines.

4. Electrophillic addition of ozone to the carbon carbon bond forms the molozonide intermediate. Electrophillic addition of ozone to the carbon carbon bond forms the molozonide intermediate.

5. re R earrangment

6. MECHANISM Ozonolysis mechanism proceeds via an oxidative cleavage reaction. The ozone not only breaks the carbon pi bond but also the carbon-carbon sigma bond. It involves the attack of ozone on the given reactant to form an ozonide . To eliminate the oxygen in this intermediate stage, zinc dust is employed (since it forms zinc oxide with the oxygen).  The final product will depend upon the type of reactant used as well as on the type of ozonolysis(type of agent used).

7. O ZONOLYSIS Oxidative cleavage of carbon carbon double bond using ozone as an oxidizing agent is called ozonolysis. As in these reaction whenever reducing agents (Oxidizing agents can also be used , will seen in typeS of ozonolysis) such as zinc , dimethyl sulfide is used then such ozonolysis is termed as reductive ozonolysis. Ozone is a very reactive allotrope of oxygen. The reaction of ozone with  alkenes  and alkynes causes the oxidative cleaving of the alkene or alkyne.  Oxidizing agent can also be used however then product will change

8. Continued…………. Ozone is produced by passing dry oxygen into ozonisers (which contains certain electric discharge) .   Only 5 to 10 percent of oxygen get converted into ozone . Example of some of the ozonisers are S iemen’s ozoniser , and B rodie’s ozoniser .

9. OTHE ALWAYS USE MILD REDUCING AGNETS DURING OZONOLYSIS

10. Ozonolysis of alkynes Alkynes undergo ozonolysis to give an acid anhydride or a diketone as the final product. The fragmentation is not complete in this reaction (alkenes undergo complete fragmentation). No reducing agents are required as a simple aqueous workup is followed.

11. TYPES OF OZONOLYSIS Alkenes can undergo ozonolysis to form alcohols, aldehydes, ketones, or carboxylic acids. The general procedure uses a solution of alkene in methanol. Ozone is bubbled through this solution at approximately 780 Celsius. When the solution turns blue, the alkene is consumed (the blue colour comes from the unreacted ozone). Other indicators of the endpoint of the reaction include potassium iodide solution. Once the ozone is added to the reaction mixture, a reagent must be added to convert the ozonide to the required carbonyl derivative . For this conversion, 2 techniques can be employed : Reductive Workup Oxidative Workup

12. Oxidative Workup When oxidant hydrogen peroxide is used instead of zinc or dimethyl sulfide to treat the ozonide , the aldehydes formed are oxidized to carboxylic acids. Potassium Permanganate in the presence of hot acid can also be used in the oxidative workup.

13. Reductive Workup Here, the ozonide is treated with mild reducing agents such as dimethyl sulfide and zinc metal with water. The ozonide is reduced as shown below . However, reductive workup conditions see a lot more use when compared to oxidative workup conditions. In these workup conditions, triphenylphosphine , thiourea , zinc dust, and dimethyl sulfide can be used to produce aldehydes or ketones. 

14. SYNTHETIC APPLICATIONS S ynthesis of aldehydes and ketones. This is one of the best method for the location of double bonds in the unknown alkenes . Ozonolysis of ketene dimer gives a very unstable compound that can be observed only at low temperatures (–78 °C or below). It has two carbonyl bands in the IR and reacts with amines to give amides, so it looks like an anhydride(as malonic anhydride can’t be made directly from malonic acid).

15. 5. Ozonolysis of oleic acid is an important route to azelaic acid. The coproduct is nonanoic acid. 6. In the synthesis of various other drugs.