SUPERHEATING EFFECTS OF MICROWAVE .pptx

Advanced organic chemistry 2
superheating effects of
microwave, effects of solvents in microwave assisted
synthesis, microwave technology in process optimization, its
applications in various organic reactions and heterocycles
synthesis

1. SUPERHEATING EFFECTS OF MICROWAVE PRESENTED BY: KANNAN PHARMACEUTICAL CHEMISTRY( 2 ND SEM ) JAMIA HAMDARD UNIVERSITY

2. Topics to discuss SUPERHEATING EFFECTS OF MICROWAVE 1 EFFECTS OF SOLVENTS IN MICROWAVE ASSISTED SYNTHESIS 2 Microwave technology in process optimization 3 TYPES OF MICROWAVE ASSISTED ORGANIC REACTIONS 4 APPLICATIONS OF MICROWAVE ASSISSTED REACTIONS 5

3. SUPERHEATING EFFECTS OF MICROWAVE 3 1 Superheating (sometimes referred to as boiling retardation or boiling delay) is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling. When a liquid is heated by microwaves, the temperature increases rapidly to reach a steady temperature while refluxing. It happens that this steady state temperature can be up to 40 K higher than the boiling point of the liquid. The bulk temperature of a microwaved solvent under boiling depends on many factors: physical properties of the solvent, reactor geometry, mass flow, heat flow, and electric field distribution.

4. EFFECTS OF SOLVENTS IN MICROWAVE ASSISTED SYNTHESIS 2 Every solvent and reagent will absorb microwave energy differently. They each have a different degree of polarity within the molecule, and therefore, will be affected either more or less by the changing microwave field. A solvent that is more polar, for example, will have a stronger dipole to cause more rotational movement in an effort to align with the changing field. A compound that is less polar, however, will not be as disturbed by the changes of the field and, therefore, will not absorb as much microwave energy.

5. 3 1.*Higher Yields*: Microwave heating often leads to higher yields by promoting more complete reactions and minimizing side products. 2.*Speed and Efficiency*: Microwave heating accelerates reaction rates, reducing reaction times from hours to minutes or even seconds. 3.*Energy Efficiency*: Microwave heating is often more energy-efficient than conventional heating methods since it directly heats the reaction mixture rather than heating the surrounding environment. 4.*Improved Selectivity*: This selectivity optimization is crucial for industries where product purity is paramount, such as pharmaceuticals and fine chemicals. 5.*Green Chemistry*: Microwave-assisted reactions can be more environmentally friendly by reducing solvent usage, lowering waste generation, and minimizing the need for harsh reaction conditions. This adherence to green chemistry principles aligns with sustainability goals and regulatory requirements. MICROWAVE ASSISTED REACTIONS IN PROCESS OPTIMIZATION

6. TYPES OF MICROWAVE ASSISTED ORGANIC REACTIONS 4 It is possible to carry out a number of microwave organic syntheses. These syntheses are grouped in the following three categories: Microwave-assisted reactions in water. 2) Microwave-assisted reactions in organic solvents. 3) Microwave solvent-free reactions (solid state reactions).

7. Microwave assisted reactions in water 5 1. Hofmann elimination In this method, normally quaternary ammonium salts are heated at high temperature and the yield of the product is low. Use of microwave irradiation has led to high-yielding synthesis of a thermally unstable Hofmann elimination product. In this water-chloroform system is used.

8. 2. Hydrolysis 1)Hydrolysis of Benzyl Chloride Hydrolysis of benzyl chloride with water in microwave oven gives 97% yield of benzyl alcohol in 3 min. The usual hydrolysis in normal way takes about 35 min. 2) Hydrolysis of Benzamide The usual hydrolysis of benzamide takes 1 hr. However, under microwave conditions, the hydrolysis is completed in 7 min giving 99% yield of benzoic acid.

9. 3. Oxidation of toluene Oxidation of toluene with KMn04 under normal conditions of refluxing takes 10-12 hr compared to reaction in microwave conditions, which takes only 5 min and the yield is 40% 4. Oxidation of alcohols A number of primary alcohols can be oxidised to the corresponding carboxylic acid using sodium tungstate as catalyst in 30% aqueous hydrogen peroxide.

10. Microwave assisted reactions in organic solvents Esterification: Reaction of Carboxylic Acid and Alcohol A mixture of benzoic acid and n-propanol on heating in a microwave oven for 6 min in presence of catalytic amount of cone. sulphuric acid gives propylbenzoate . 6

11. 2. Fries Rearrangement Fries rearrangement is a useful method for the preparation of phenolic ketones and is usually carried out by heating a mixture of substrate and aluminium chloride. A mixture of p- cresyl acetate and anhydrous aluminium chloride are heated in dry chlorobenzene in a sealed tube in a microwave oven for 2 min to give 85% yield of the product 3. Decarboxylation Conventional decarboxylation of carboxylic acids involves refluxing in quinolone in presence of copper chromite and the yields are low. However, in the presence of microwaves, decarboxylation takes place in much shorter time.

12. 4. Synthesis of Chalcones Microwaves have been used for the synthesis of chalcones and related enones . Considerable rate enhancement is observed, bringing down the reaction time from hours to minutes in improved yield.

13. Microwave assisted solvent free reactions (solid state reactions) Deacetylation Aldehydes, phenols and alcohols are protected by acetylation. After the reaction, the deacetylation of the product is carried out usually under acidic or basic conditions; the process takes long time and the yields are low. Use of microwave irradiation reduces the time of deacetylation and the yields are good. 7

14. 2. Aromatic Nucleophilic Substitutions Formation of Substituted Triazines Aromatic nucleophilic substitutions are carried out using sodium phenoxide and 1,3,5-trichlorotriazine under microwave irradiation (6 min). The products, 1,3,5-triarlyoxytriazines are obtained in 85–90% yields. 3. O-Alkylation Preparations of ethers were carried out from β- naphthol using benzyl bromide and 1-butyl-3- methylimidazolium tetrafluoroborate under microwave irradiation (6-12 min) the products were isolated in 75-90% yields.

15. 4. N- Alkylations N- Alkylations under microwave irradiation using phase transfer catalysts occupy a unique place in organic chemistry. Bogdal and co-workers reported the synthesis of N-alkyl phthalimides using phthalimide, alkyl halides, potassium carbonate and TBAB; giving products in 45–98% yields. 5. Saponification of Esters Hindered esters which take 5 hr under classical heating with alkali can be easily saponified under microwave irradiation using KOH- Aliquat

16. 5. Alkylation of Reactive Methylene Compounds Efficient and rapid alkylation of compounds containing reactive methylene group (e.g., ethylacetoacetate ) can be achieved in a microwave oven, using tetrabutyl ammonium chloride (TBAC) as PTC (phase transfer catalyst) without solvent.

17. 8 Application of Microwave in material Chemistry The use of microwave for synthesis of inorganic solid is very efficient and useful technique in material chemistry. Microwave has been used in preparation of ceramics 2. Preparation of catalyst under microwave irradiation Synthesis of a high permeance NaA zeolite YBa2Cu3O7-X membrane was prepared from an aluminate and silicate sodium with molar ratio of 5 SiO2 : Al2O3: 50Na2O:1000H2O in a modified domestic microwave oven operating at 2450 MHz in 15 min. 3. Application of Microwave Technology for Nanotechnology Today nanotechnology is being applied in the fields of synthesis of single-site catalyst, antimicrobial nanocomposites, fire retardant materials, novel electro-optical devices, sensors, ultra soft magnets and also in the area of drug delivery systems. APPLICATIONS OF MICROWAVE ASSISSTED REACTIONS

18. 4. Application of Microwave in polymer synthesis The synthesis of polyacrylamide(PAM) was studied under microwave irradiation. PAM is used as a flocculating agent in waste water treatment. 5. Analytical Chemistry Microwave irradiations are routinely used for sample digestion and solvent extraction techniques. They have also been put to use for gravimetric, moisture determination and to find out enthalpy of vaporization of solvents. 6. Microwave irradiation in waste management Microwave heating is plying an important role in treatment of domestic and hazardous industrial and nuclear waste.

19. APPLICATIONS IN HETEROCYCLES SYNTHESIS AND ORGANIC REACTIONS 1. Fischer Indole Synthesis: Reaction Overview: Microwave heating accelerates Fischer indole synthesis from aryl hydrazines and carbonyl compounds, offering rapid access to indole derivatives. Applications: Indoles are key structural motifs in pharmaceuticals, agrochemicals, and materials science due to their diverse biological activities and functional versatility. 9

20. 2. Pyrazole Synthesis: Microwave Conditions: Efficient pyrazole synthesis under microwave irradiation involves condensation reactions between hydrazines and 1,3-dicarbonyl compounds. Applications: Pyrazoles serve as important pharmacophores in medicinal chemistry, agrochemicals, and materials science, with applications in drug discovery and materials design.

21. 3. Pyridine and Pyrimidine Synthesis: Microwave-Assisted Reactions: Microwave heating accelerates condensation reactions for pyridine and pyrimidine formation, such as Hantzsch synthesis or multicomponent reactions. Applications: Pyridines and pyrimidines are prevalent in pharmaceuticals, herbicides, and materials science, showcasing diverse biological activities and functional properties.

22. Diels-Alder Reactions: Microwave-assisted Diels-Alder reactions facilitate rapid cycloadditions between dienes and dienophiles, leading to fused heterocyclic frameworks with high regio- and stereoselectivity. Rapid Cyclization Reactions: Microwave heating accelerates ring closure reactions, cyclizations , and cycloadditions involved in heterocycle formation, reducing reaction times and improving yields. Facilitated Aromatic Substitutions : Microwave conditions promote rapid aromatic substitutions (e.g., electrophilic aromatic substitution) in heterocyclic systems, enabling efficient functionalization and diversification of heterocyclic scaffolds.

23. CHALLENGES OF MICROWAVE ASSISTED REACTIONS 10 *Temperature Control*: Microwaves can heat reactants unevenly, leading to localized hotspots and potential thermal runaway. *Pressure Build-Up*: Certain reactions may generate gases, causing pressure build-up in closed vessels, which must be carefully managed to avoid accidents. *Reaction Selectivity*: Microwaves can sometimes promote side reactions or alter selectivity compared to conventional heating methods. *Scalability*: Scaling up microwave reactions from lab to industrial scale can be challenging due to variations in equipment and heating efficiencies.

24. 5. *Safety Concerns*: Handling of potentially hazardous reagents under microwave conditions requires strict safety protocols. 6. *Reaction Monitoring*: Monitoring reaction progress in real-time can be difficult, requiring specialized equipment. 7. *Equipment Compatibility*: Not all reaction vessels and equipment are suitable for microwave heating, limiting the scope of reactions that can be performed.Addressing these challenges often involves a combination of experimental optimization, equipment modification, and careful process design.

25. REFERENCES Surati , M.A., Jauhari , S. & Desai, K.R. 2012, 'A brief review: Microwave assisted organic reaction', Scholars Research Library, vol. 4, no. 1, pp. 645-661. ➡ Grewal, A.S., Kumar, K., Redhu , S. & Bhardwaj, S. 2013, 'MICROWAVE ASSISTED SYNTHESIS: A GREEN CHEMISTRY APPROACH', International Research Journal of Pharmaceutical and Applied Sciences (IRJPAS), vol. 3, no. 5, pp. 278-285. Ahluwalia, V.K. & Kidwai, M. 2004. New trends in Green Chemistry: Microwave Induced Green Synthesis. Anamaya Publishers, New Delhi. 263 pp. ► https://shodhganga.inflibnet.ac.in/bitstream/10603/3197/8/08_chapter%201.pdf 11

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