PHOTO-OXIDATION

PHOTO-OXIDATION

1. PHOTO-OXIDATION

2. INTRODUCTION Oxidation under the influence of the light or radiant energy. Formation of radicals that induces oxidation of the material. Excited singlet or triplet states .

3. Photosensitiser This is especially useful in providing a new group of potentially new reactive molecules. Aldehydes and ketones Requirements of photosensitiser It must be excited by the irradiation used. Present in sufficient concentration and absorb more strongly than the other reactants so that it is the major light absorber. Energy of triplet state of sensitiser must be greater than that of the reactant. Must be able to transmit energy to reactant.

4. Benzophenone Acetophenone Fluorenone Benzene Naphthaleine Biacetyl Benzil

5. Main steps of photo-oxidation Initiation Propagation Branching Termination

6. PHOTO-OXIDATION REACTIONS

7. 1. Formation of peroxy compound. Irradiating the parent organic compound in the presence of oxygen and a sensitizer. Reaction occurs by the excitation of the sensitizer to its triplet state. Either the triplet abstracts a hydrogen atom from the substrate to form a radical which then reacts with oxygen, or it interact with the oxygen molecule.

8. 2. Conjugated dienes yield cyclic peroxides in a reaction of Diels- Alder type.

9. 3. Oxidative coupling of aromatic compounds

10. 4. Formation of polycyclic compound

11. 5. Photo-oxidation of cholesterol

12. 6. Photo-oxidation of polymers Light is absorbed by a polymer - photochemical reactions can occur as a result of activation of a polymer macromolecule to its excited singlet or triplet states. Chemical change that reduces the polymer's molecular weight.

13. REFERENCE Principles of organic synthesis – R.O.C. Normann . Organic reation and mechanism – V.K ahluwalia . https://www.researchgate.net/figure/Plausible-photodegradation-mechanisms-occurring-in-PLA-Mechanism-a-photolysis_fig5_28972767 https://onlinelibrary.wiley.com/doi/pdf/10.1002/ps.278010021 https://www.sciencedirect.com/science/article/pii/0014305777900957