1) The document discusses various reagents used in organic synthesis, including phase transfer catalysts, crown ethers, and methods for converting alkenes to epoxides and diols. 2) Phase transfer catalysts facilitate reactions between substances in different phases by shuttling reactants between phases, while crown ethers selectively bind to specific ions due to their ring structure. 3) Common methods for converting alkenes include epoxidation, which introduces an oxygen atom to form an epoxide, and dihydroxylation, which adds two hydroxyl groups to form vicinal diols.

1. Reagents in organic
synthesis
Presented By:
Harsh
Msc(Industrial Chemistry)
1st Year
Under the supervision
:
DR. BHAVANA
Dr. S. S. Bhatnagar University Institute of Chemical Engineering &
Technology
Panjab University

2. My Topics
•Phase Transfer catalyst
•Crown
Ether
•Conversion of Alkenes to Epoxides
And Diols

3. PHASE TRANSFER
CATALYST
(PTC)

4. Introduction:**
- PTC, or Phase Transfer Catalysis, is a chemical technique used to
facilitate reactions between substances in different phases, often
between aqueous and organic phases. It's significant because it enables
reactions that would be otherwise challenging due to immiscibility
between the reactants. PTC works by using a phase transfer catalyst,
which is a compound that can shuttle ions or molecules from one phase
to another.

5. **Mechanism and Principles:**
- The mechanism of PTC involves the phase transfer catalyst forming a
complex with one of the reactants, thus making it soluble in the
otherwise immiscible phase. This enhances the collision frequency
between reactants, promoting the reaction. Key principles include:
- Solubility enhancement: The catalyst increases the solubility of the
reactants in the phase where they are typically insoluble.
- Ion pairing: The catalyst forms ion pairs with charged reactants,
making them soluble and facilitating reactions.
**Applications:**
- PTC is widely applied in organic synthesis. For instance:
- Nucleophilic substitutions: It's used to convert alkyl halides into more
reactive species by transferring halide ions to the organic phase.
- Quaternization reactions: PTC is crucial in the synthesis of quaternary
ammonium salts.
- In industry, PTC is employed in the production of pharmaceuticals,
agrochemicals, and specialty chemicals due to its ability to improve
reaction rates and selectivity.

7. **Advantages and Limitations:**
- Advantages of PTC include increased yield, reduced waste generation,
and improved selectivity by minimizing side reactions.
- Limitations include the need to select appropriate catalysts, potential
contamination from the catalyst, and the environmental impact of some
catalysts.
**Recent Developments:**
- Recent advancements in PTC include the development of more
efficient and sustainable catalysts, such as surfactant-based catalysts
and biodegradable catalysts. Researchers are also exploring PTC's
applications in green chemistry to reduce the environmental impact of
chemical processes.

8. CROWN ETHER

9. **Introduction:**
- Crown ethers are a class of cyclic compounds containing oxygen
atoms, typically arranged in a crown-shaped ring. Their significance lies
in their ability to selectively bind to specific ions or molecules due to
their crown-like structure.

10. **Structural Variations:**
- The structural variations in crown ethers primarily involve altering the
ring size and the number of oxygen atoms. Smaller rings may be more
selective for smaller ions, while larger rings can accommodate larger
ions.

11. **Applications:**
- Crown ethers have a wide range of applications, including:
- Ion-selective electrodes: They are used to measure specific ions in
solution.
- Phase transfer catalysis: Crown ethers can enhance the transfer of
ions between phases in reactions.
- Host-guest chemistry: They form complexes with cations, making
them valuable in molecular recognition and supramolecular chemistry.
**Synthesis:**
- Crown ethers are typically synthesized by reacting a suitable precursor
compound with a strong base in the presence of a suitable crown-
forming agent. The choice of precursor and conditions can determine
the size and structure of the crown ether formed.

12. **Notable Examples:**
- Notable examples of crown ethers include 18-crown-6 and dibenzo-18-
crown-6. 18-crown-6 is known for its ability to complex with alkali metal
ions, making it useful in ion-selective electrodes and phase transfer
catalysis. Dibenzo-18-crown-6 has applications in molecular recognition
and has been studied for its binding properties.
Dibenzo 18-crown-
6

13. CONVERSION OF
AKLENES TO EXPOXIDES
AND DIOLS

14. **Introduction:**
- The conversion of alkenes to epoxides and diols is crucial in organic
synthesis as it introduces oxygen atoms into molecules, creating
valuable functional groups. These functional groups are found in a wide
range of chemicals and pharmaceuticals.

15. **Epoxidation:**
- Epoxidation is a reaction that introduces an oxygen atom between the
two carbons of a carbon-carbon double bond, forming a three-
membered ring called an epoxide. Common reagents include
peroxyacids, peroxides, and metal catalysts. The mechanism typically
involves the attack of the electrophilic oxygen species on the double
bond.

16. **Dihydroxylation:**
- Dihydroxylation adds two hydroxyl (-OH) groups across a carbon-
carbon double bond. Common reagents for dihydroxylation include
osmium tetroxide (OsO₄) and potassium permanganate (KMnO₄) in the
presence of a suitable co-reagent like NMO (N-methylmorpholine N-
oxide). The reaction proceeds through a syn addition mechanism,
leading to the formation of vicinal diols.

17. **Applications:**
- Epoxides and diols have versatile applications, including:
- Pharmaceuticals: They are key intermediates in the synthesis of
various drugs.
- Polymers: Epoxides are used in epoxy resins for coatings, adhesives,
and composites.
- Fine chemicals: They are employed in the synthesis of specialty
chemicals.
**Recent Advances:**
- Recent advancements in alkene conversion to epoxides and diols
nclude the development of more selective and environmentally friendly
reagents, as well as the exploration of enzymatic methods for
dihydroxylation reactions.