ultrasound assisted reaction 2.pptx

Ultrasound assisted reaction
M. PHARM. 1ST YEAR
2ND SEMESTER
PHARMACUTICAL CHEMISTRY

1. Department of Pharmaceutical Sciences Rashtrasant Tukadoji Maharaj Nagpur University Nagpur-440033 Topic : Types of Sonochemical (Heterogeneous Liquid-liquid & Liquid – Solid Reaction) And its Synthetic Application Presented By- Tahmina Khan M. Pharm. 1 st Year (Pharmaceutical Chemistry)

2. 2 Content Introduction Types Of Sonochemistry- Heterogenous Solid /Liquid Phase Reaction. Heterogeneous Liquid/Liquid Phase Reaction . Synthetic Applications References

3. 3 ULTRASOUND Ultrasound is defined by the American National Standard Institute as “sound at frequencies greater the 20Hz” Ultrasound is sound wave with frequencies higher than the upper audible limit of human being. The normal range of hearing is between 16Hz to 16kHz, and ultrasound is generally considered to lie between 20kHz to 500MHz. Ultrasound is no different from normal [audible] sound in its physical properties, expect in that human cannot hear it.

4. 4 SONOCHEMISTRY The introduction of ultrasound in chemistry is known as sonochemistry. Sonochemistry is a branch of chemistry dealing with the chemical effects and application of ultrasonic waves i.e sound with frequencies above 20KHz (20,000 cycle per second) that lies beyond the upper limit of human hearing through the frequencies can be extended up to 100MHz that’s especially affects on chemical activity.

5. 5 TYPES OF SONOCHEMICAL REACTION ..

6. 6 HETEROGENOUS SOLID/LIQUID PHASE REACTION - In heterogeneous reactions, involving solids dispersed in liquids, the overall reactivity will depend upon the available reactive surface area. Ultrasonically induced enhancements in the chemical reactivity that are observed in such heterogeneous systems are because of cleaning action of ultrasound. This cleaning action causes “pitting” of the surface of the solid, which acts both to expose new surface to the reagents and increase the effective surface area available for reaction.

7. 7 Two processes causes the pitting- The implosion of cavitation bubbles formed from seed nuclei on the surface. Micro streaming of a jet of solvents on to the surface when a cavitation bubble collapses in the solvent close to it. Example- There are two types of reaction involving solid/liquid interfaces : Those in which the solid is a reagent and is consumed in the process, and Those in which the solid often a metal-functions as a catalyst.

8. 8 Classic use of ultrasound with solid as reagent is the preparation of a Grignard reagent – an organo-magnesium halide . A long-standing problem associated with Grignard reagent synthesis is that in order to facilitate reaction between the organic halide and the metal in an ether solvent all the reagents must be dry and the surface of the magnesium must be clean and oxide free.
Ultrasonic irradiation gives initiation in under four minutes even in damp, technical-grade ether without the addition of activators used in conventional synthesis

9. 9 An example of solid metal functioning as a catalyst addition of hydrogen to an unsaturated compound – Catalytic Hydrogenation . Sonication at room temperature for the total hydrogenation of diphenylacetylene (2 hours) appear to be almost as good as those obtained under traditional reflux conditions and are substantially better than obtained with stirring at 25°C (6 hours )

10. 10 HETEROGENOUS LIQUID/LIQUID PHASE REACTION - Ultrasound generates extremely fine emulsions from mixtures of immiscible liquids. One of the main consequences of these emulsions is increase in the interfacial contact area between the liquids and increase in the region over which any reaction between species dissolved in the liquids can take place. This emulsification also leads to the use of ultrasound in place of phase transfer catalyst. Disruption of phase boundary (highly efficient emulsification ) At a liquid \ liquid interface

11. 11 An additional feature of sonication is that the sonicated emulsion is continuously subject to mechanical vibration – enhancing any transfer between phases. A good example of this type of application is to be found in the use of a whistle reactor to enhance the hydrolysis of commercially important oils, fats, and waxes. Under Sonochemical conditions the hydrolyses can be carried out at lower temperatures, resulting in cleaner and good yield of products.

12. 12 SYNTHETIC APPLICATIONS Esterification : The esterification is generally carried out in the presence of catalyst like sulphuric acid. Reaction requires longer time, and yields are very low. A simple procedure for the esterification of a variety of carboxylic acids with different alcohol at ambient temperature using ultrasound is reported.

13. 13 2 .Saponification : Ester hydrolysis is frequently affected under aggressive conditions. It can be conducted under milder condition when sonication is used. Ex : methyl 1-2,4-dimethylbenzoate on saponification (20KHz) gives 2,4 dimethyl benzoic acid 94% compared to 15% yield by normal process of heating with aqueous alkali (60 min).

14. 14 Cannizzaro reaction : Under heterogeneous conditions catalyzed by barium hydroxide is considerably accelerated by low intensity ultrasound. The yield 100% after 10 min where as no reaction is observed without the use of ultrasound.

15. 15 Ullmann-type coupling reactions : The Ullmann-type coupling reaction occurs at a lower temperature and shorter time in almost quantitative yield with probe sonication.

16. 16 Applications of Sonochemistry Sonochemistry has been used for synthesis of composites for energy storage applications nanoparticles, gold and platinum nanoparticles etc.
Synthesis of Cu 2 O-Graphene, graphene oxide- Fe 2 O 3 for lithium ion battery electrodes. Primary/Binary/Ternary nanocomposites which gave good specific capacitance, power energy density and cyclic stability applicable for electrode material in Supercapacitors:
Ultrasound finds its application in biomedical devices. Sonoporation : Enhancement in permeation due to acoustic cavitation and thus used for modifying the permeability of cell plasma membrane. It is mainly used to allow the uptake of molecules like DNA into the cell. Sonolysis : Application in purifying water because of formation of reactive species when ultrasound reacts with water.

17. 17 References James Clark And Duncan Macquarrie . Handbook of green chemistry and technology;2002; 372-393.
Sonochemistry (Application of ultrasound in chemical Synthesis and reactions): A Review part I; Az. J. Pharm Sci. Vol. 53, March, 2016
Sonochemistry Advantages and Application –A Review. Research gate publication.

18. Thank you