Photo-oxidation involves the oxidation of materials under the influence of light or radiant energy. It requires a photosensitizer that absorbs light strongly and can transfer energy to reactants. Main steps include initiation by excitation of the photosensitizer, propagation by reaction of radicals formed with oxygen, and termination. Specific photo-oxidation reactions include the formation of peroxy compounds, cyclic peroxides from conjugated dienes, oxidative coupling of aromatics, and formation of polycyclic compounds and changes to polymers.

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
1. It must be excited by the irradiation used.
2. Present in sufficient concentration and absorb more strongly
than the other reactants so that it is the major light absorber.
3. Energy of triplet state of sensitiser must be greater than that
of the reactant.
4. Must be able to transmit energy to reactant.

4. • Benzophenone
• Acetophenone
• Fluorenone
• Benzene
• Naphthaleine
• Biacetyl
• Benzil

5. Main steps of photo-oxidation
1. Initiation
2. Propagation
3. Branching
4. Termination

8. PHOTO-OXIDATION REACTIONS

9. 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.

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

13. 3. Oxidative coupling of aromatic
compounds

15. 4. Formation of polycyclic compound

16. 5. Photo-oxidation of cholesterol

18. 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.

20. 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/0014305777
900957