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Workshop for Secondary School Teachers

Experiments of Microscale Organic Chemistry. Workshop for Secondary School Teachers. Dr. W M TSUI Department of Chemistry, HKUST. Outline. Introduction of Microscale Organic Chemistry Introduction of designing experimental procedures Microscale Organic Glassware

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Workshop for Secondary School Teachers

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  1. Experiments of Microscale Organic Chemistry Workshop for Secondary School Teachers Dr. W M TSUI Department of Chemistry, HKUST

  2. Outline • Introduction of Microscale Organic Chemistry • Introduction of designing experimental procedures • Microscale Organic Glassware • Techniques in Microscale Organic Experiments: • Solvent /Reagent Dispensing, Reaction Setup • Liquid-Liquid Extraction, Filtration • Purification methods • Characterization Method of Organic Compounds • Experiment highlights

  3. Organic synthesis & natural products synthesis • Complex and fascinating molecular structures can be assembled from simple starting materials. • Designed molecular frameworks containing carbon atoms in combination with H, O, N, S, and halogens, can be synthesized on demand and tested for various applications.

  4. Organic synthesis & natural products synthesis • These useful compounds range from biological tools and medicines to high-value materials for cosmetics, computers and useful devices

  5. Introduction of Microscale Organic Chemistry • Had been gradually recognized and adopted at secondary school level • Handle with small quantities of chemical substances

  6. Macroscale vs. Microscale

  7. Advantages • Require smaller storage area • Save laboratory space • Reduce amount of chemical waste • Improve laboratory safety (smaller amount of …) • Shorter reaction time (efficient heat transfer…) • Save time for preparation and work up • More time for evaluation and communication • ………….

  8. Microscale Organic Glassware • Various designs http://www.sigmaaldrich.com/labware/glassware-catalog/glassware-kits-microscale.html

  9. Microscale Organic Glassware • All-purpose kit: 9

  10. Designing experimental procedures • Stage 1: Setup reaction • Experimental setup, Temperature, Time, Catalyst, Solvent • Stage 2: Isolation of crude product • Solvent extraction, Filtration, Precipitation • Stage 3: Purification of crude product • Distillation, Recrystallization, Sublimation • Stage 4: Characterization • Melting point, Boiling point, IR, MS

  11. Technique: Transfer of reagent/dispensing of solvent • Macroscale: • Measuring cylinder • Beaker • Conical flask • Dropping funnel • Microscale: • Syringe • Needle • Septum 1.0 mL Syringe Medical Syringe Sterile Luer Slip 1ml

  12. Technique: Setup for Organic Synthesis • Organic Synthesis: Formation and breaking of C-C bond, C-O bond, C-H bond, C-X bond, etc. • Reflux: for long reaction time Macroscale reflux setup

  13. Technique: Microscale Experiment Setup • Microscale Organic Synthesis: Water condenser Microscale Condenser, Threaded Water out • Reagents (+ catalyst) • Anti-bumping granules • Water in Microscale Round-Bottom Flasks, Threaded • Sand bath Microscalereflux setup

  14. Technique: Microscale Experiment Setup • Microscale Organic Synthesis: Air condenser • Reagents (+ catalyst) • Anti-bumping granules Microscale Round-Bottom Flasks, Threaded Microscale reflux setup

  15. filter paper Isolation Technique: Filtration • Vacuum filtration: • Probably the most common type of filtration used by chemists. The funnel used for this method is called Hirsch funnel. This funnel has a flat disc inside which is made from porous ceramic materials

  16. Isolation Technique: Filtration • Pipette filtration: • For small quantity of crystals

  17. Isolation Technique: Liquid-liquid Extraction • Partition coefficient • Solubility in solvents Separatory funnel Screw cap Test tube

  18. Purification Technique: Distillation • For liquids with various volatilities Macroscale distillation setup Microscale distillation setup

  19. Purification Technique: Sublimation • For solids Microscalesublimation setup Macroscalesublimation setup

  20. Temperature controlled by depth in sand Purification Technique: Recrystallization • For solids • Various Solubility Macroscale 250mL Conical flask Microscale 5mL Conical flask Microscale 5mL Reaction tube

  21. Purification Technique: Recrystallization • Steps in Recrystallization: • Dissolution (various choice of Solvent) • Hot Filtration • Decolorization • Crystallization • Collection

  22. Purification Technique: Recrystallization • The general idea is to follow the “like dissolves like” principle, e.g. compounds containing hydroxyl groups are best recrystallized from hydroxy-containing solvents

  23. Methods for crystallization Ice bath • 2

  24. Purification Technique: Recrystallization • Crystallization • Slow cooling: the easiest method and works for most cases • Scratching: induced crystallization by scratching the inside of the beaker or flask with a glass stirring rod. This will produce microscopic fragments of glass that may act as surfaces on which crystal growth can begin • Seeding: taking a small crystal from the original solid or the other groups and dropping them into the solution

  25. Characterization of organic compound • Melting point / melting point apparatus • Simplest and most common characterization method for solid organic compounds • Purity check • Affordable

  26. Characterization of organic compound • Boiling point / distillation apparatus • Simplest and most common characterization method for liquid organic compounds • Purity check • Affordable

  27. Characterization of organic compound • Infrared spectrum • Infrared spectrophotometer • Absorption of infrared electromagnetic radiation • Information of functional groups

  28. Characterization of organic compound • To allow passage of IR, most sample cuvettes have mineral salt windows [Caution! Avoid high humidity.] • Transmission limit: • NaCl 650cm-1 • KBr 350cm-1 • CsI 56 μm (200cm-1)

  29. Characterization of organic compound

  30. Characterization of organic compound • Functional groups can be identified • Infrared spectrum of acetone

  31. Characterization of organic compound • Mass spectrum / mass spectrometer • mass-to-charge ratio of molecular ion Picture from http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch13ms.html

  32. Characterization of organic compound • Mass-to-charge ratio: • Molecular ion • Fragmentation pattern of molecular ion

  33. Characterization of organic compound • Decane (C10H22) • Molecular ion at m/z = 142 • 142-29 = 113 • 113-14 = 99 • etc

  34. Characterization of organic compound • Acetone (C3H6O) • Molecular ion at m/z = 58 43 –15 58 –28 15

  35. Experiment 1: Microscale separation of components in a mixture 3 components caffeine p-dimethoxybenzene acetaminophen Separation based on their different physical and chemical properties

  36. Experiment 1: Microscale separation of components in a mixture • Step 1: Solubility test • Technique: Solid-liquid extraction (Filtration) • Step 2: Acid-base chemistry • Technique: Liquid-liquid extraction, Pipette filtration, Evaporation • Step 3: Purity check • Technique: TLC analysis

  37. Experiment 1: Microscale separation of components in a mixture • Step 1: Solubility test • water, dichloromethane, hexane soluble Insoluble Slightly soluble Powder

  38. Experiment 1: Microscale separation of components in a mixture • Solid-liquid extraction (Filtration)

  39. Experiment 1: Microscale separation of components in a mixture • Step 2: Acid-base chemistry basic neutral HCl NaOH aq org org

  40. Experiment 1: Microscale separation of components in a mixture • Liquid-liquid extraction • Release pressure • Which layer on the top? • Test by adding water

  41. Experiment 1: Microscale separation of components in a mixture • Some water will be transferred into the organic phase because of the partial miscibility of the organic phase and water  Organic solution contaminated with traces of water. Water • brine works to pull the water from the organic layer to the water layer

  42. Experiment 1: Microscale separation of components in a mixture • Dry by anhydrous Na2SO4 (Preliminary purification) Pipette filtration

  43. Experiment 1: Microscale separation of components in a mixture • Evaporation Needle Compressed air

  44. Experiment 1: Microscale separation of components in a mixture • Step 3: Purity check • Thin layer chromatography (TLC)

  45. Experiment 1: Microscale separation of components in a mixture • Thin layer chromatography (TLC) Chromatography: Separation of compounds by the distribution between two phases – Mobile phase & Stationary phase

  46. stationary phase (TLC plate: Silica gel) Sample mixture mobile phase (solvent) Experiment 1: Microscale separation of components in a mixture

  47. Experiment 1: Microscale separation of components in a mixture

  48. Experiment 2:Catalytic Hydrogenation of Methyl Oleate • Organic Synthesis by Hydrogenation • Microscale Experiment Setup • Reagents: • Methyl oleate, H2, Palladium on charcoal, Methanol H2(g) Catalyst: Pd/C methyl oleate methyl stearate

  49. Catalytic Hydrogenation of Methyl Oleate Syringe instead of dropping funnel • Setup: • Generation of hydrogen gas as reagent • Use of septum • Use of needles • Use of syringe H2(g) HCl(aq) Zn metal in 5mL flask 5mL flask

  50. Catalytic Hydrogenation of Methyl Oleate • Collect H2 into a inverted measuring cylinder Syringe instead of dropping funnel H2(g) HCl(aq) Zn metal in 5mL flask 5mL flask

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