Epoxide, nomenclature, synthesis, ring opening, regio-selectivity

Epoxide nomenclature, ring-opening and regioselectivity, synthesis, acid catalysed ring-opening of epoxides, base catalysed ring-opening of epoxides

1. Subject: Organic Chemistry. Teacher In charge: Dr. V. Sridharan. Topic: Epoxides: synthesis and ring opening. Presented by: Zeeshan Nazir. Roll Number: 3940319. Department of Chemistry and Chemical Sciences . CENTRAL UNIVERSITY OF JAMMU.

2. Contents Introduction. Nomenclature of epoxides . Synthesis of epoxides. Acid catalysed ring opening of epoxides. Base catalysed ring opening of epoxides. Regiochemistry of epoxide ring opening.

3. Definition. Epoxide: cyclic ether with a three-membered ring. The basic structure of an epoxide contains an oxygen atom attached to two adjacent carbon atoms of a hydrocarbon . Strain in the ring makes it more reactive than ethers.

4. Nomenclature. 1. 2. 3. 4. 5. 6. 1 2 1 2 3 1 2 3 4 5 1,2-epoxy ethane or Oxirane 1,2-epoxy propane or Methyl Oxirane 2,3-epoxy-2,3-dimethyl Pentane 1 2 3 or 2-ethyl-2,3,3-trimethyl Oxirane 1 2 3 4 5 6 1,2-Epoxy-1-methyl cyclohexane 1 2 3 2-chloromethyl-1,2-epoxy propane 1 2 3 4 5 6 3,4-Epoxy-4-ethyl-2-methyl hexane

5. Synthesis

6. 1. Epoxidation of Alkenes. Most widely used method. Alkene reacts with an organic peroxy acid. Peroxy acid: A peroxy acid is an acid which contains an acidic –OOH group. Some common Peroxy acids: 1. Peroxy acetic acid. 2. Peroxy benzoic acid.

7. Alkene Peroxy acid Epoxide Carboxylic acid Most often used Peroxy acids; MCPBA: Meta - ChloroPeroxyBenzoic Acid. MMPP: Magnesium MonoPeroxyPhthalate. General Reaction of Epoxidation.

8. Mechanism. Alkene Peroxy acid Epoxide Carboxylic acid Peroxy acid transfers an oxygen atom to the alkene in a cyclic, single-step mechanism.

9. The epoxidation of alkenes with peroxy acids is stereospecific: 1. cis -2-Butene yields only cis -2,3-dimethyloxirane 2. trans -2-butene yields only the racemic trans -2,3-dimethyloxiranes Enantiomeric trans -2,3-dimethyloxiranes

10. 2. Via halohydrins (Intramolecular Williamson ether synthesis). Halohydrin: Hydroxyl and the halogen are bonded to adjacent carbon atoms. e.g: Reaction:

11. Mechanism. The base deprotonates the alcohol forming an alkoxide intermediate that has enhanced nucleophilicity. An intramolecular S N 2 reaction where the alkoxide nucleophile attacks the electrophilic C displacing the leaving group, the halide ion.

12. Ring Opening

13. 1. Acid Catalysed. + + + +

14. E.g:

15. 2. Base catalysed. + +

16. E.g:

17. Regiochemistry examples

18. + + Methyl Oxirane 1-Ethoxy-2-propanol If the epoxide is unsymmetrical epoxide, the nucleophile attacks primarily at the less substituted carbon atom in base catalysed ring opening.

19. Thank You.