Photoreduction in organic compounds

1. PHOTO-REDUCTION
SAMEEN FATIMA
ROLL NO: 908529

2. CONTENT
 PHOTOREDUCTION IN ORGANIC COMPOUNDS
 CARBONYL COMPOUNDS
 PHOTOREDUCTION IN KETONES
 NITRO COMPOUNDS
 PHOTOREDUCTION IN AROMATIC
COMPOUNDS
 PHOTO-REDUCTION/PHOTOHALOGENATION
 POLYMERIZATION VIA PHOTOREDUCTION
 DEFINITION

3. DEFINITION
• The chemical reduction which is influenced by under control
of photons / light energy is called photo reduction. 1
• A reduction reaction induced by light. 2
Photo-reduction is defined as the addition of one or more
electrons to photo-excited species or the photochemical
hydrogenation of a substance. 3
4

4. Photoreduction in ketones: Ketones photoreduction can be take
place by hydrogen atom donars for example secondary alcohol
and tertiary amines. In these reactions the photoexcited specie
reacts with a suitable hydrogen donor (like alcohol with α
hydrogen, toluene, even cyclohexane). The radical formed may
react with other hydrogen donor to form alcohol or other
reaction partner.
CARBONYL COMPOUNDS: Photo-reduction
5

5. When H2Se used in the photoreduction of carbonyl
compound.
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6. Nitro compounds:
In the photo-reduction of nitro compounds the hydrogen
donor is needed, if hydrogen donor is not present then the
photo-fragmentation is done instead of photo reduction.

7. MECHANISM:
7

8. COMPOUNDS: The following example is the classical
reaction that is done by photochemical process, the
preparation of the formation of 1, 1, 2, 2-tetraphenyl-
1,2-ethanediol ((3), benzopinacol).
PHOTOREDUCTION IN AROMATIC
8

9. MECHANISM: The reaction of benzophenone in the
triplet excited state with isopropanol to produce
diphenylketyl radical and dimethylketyl radical is an
example of photoreduction.
The dimethylketyl radical produced transfer a hydrogen
atom to benzophenone in ground state to produce
another dipheny ketyl radical. It is interesting to know
that only one photon is needed to convert both reactants
into product.

10. 9
Many hydrocarbons benzene, naphthalene, anthracene,
biphenyls react with amine to give reduction product. The
above example is the best photo-reduced product in aromatic
compounds. Mostly these reactions are initiated by the
transfer of electron lone pair orbital from nitrogen to the half-
filled highest bonding molecular orbital of excited aromatic
compound.

11. 10

12. • PHOTOREDUCTION/PHOTODEHALOGENATION:
The replacement of halogen atom with hydrogen atom in the
presence of hydrogen donor is very interesting alternative to
Raney nickel catalyzed reduction. As we see in the following
example; Irradiation of 2-bromophenol in
propan-2-ol leads to the 90% chemical
yield (phenol) via radical mechanism
scheme.
11

13. Polymerization via photo-reduction: The
photoreduction is used in the polymerization in such a
way that the initiator is produced by this reduction that is
further react with the monomer to form the polymer.
12

14. REFERENCE
1. Photoreduction Definition & Meaning - Merriam-Webster
2. https://www.collinsdictionary.com/dictionary/english/photoreduction
3. https://www.slideshare.net/RabiaAziz6/photo-redox-reactions
4. Postgraduate chemistry series: Photochemistry of Organic Compounds: From
Concepts to Practice by Petr Klan and Jakob Wirz, pg # 230
5. Postgraduate chemistry series: Photochemistry of Organic Compounds: From
Concepts to Practice by Petr Klan and Jakob Wirz, pg # 296
6. https://www.slideshare.net/RabiaAziz6/photo-redox-reactions
7. Postgraduate chemistry series: Photochemistry of Organic Compounds: From
Concepts to Practice by Petr Klan and Jakob Wirz, pg # 362
8. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Basic_Principles_
of_Organic_Chemistry_(Roberts_and_Caserio)/28%3A_Photochemistry/28.03
%3A_Organic_Photochemistry#:~:text=Photoreduction%20of%20Diaryl%20Ket
ones,-
9. https://slideplayer.com/slide/13159506/
10. Photochemistry and pericyclic reaction, 3rd addition by Jagdamba Singh and
Jaya Singh pg # 263
11. Postgraduate chemistry series: Photochemistry of Organic Compounds: From
Concepts to Practice by Petr Klan and Jakob Wirz, pg # 399
12. Postgraduate chemistry series: Photochemistry of Organic Compounds: From
Concepts to Practice by Petr Klan and Jakob Wirz, pg # 434 and 435

15. THANK YOU