Docstoc

Experiments of Microscale Organic chemistry

Document Sample
Experiments of Microscale Organic chemistry Powered By Docstoc
					    Experiments of Microscale
    Organic Chemistry

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



                                 Outline
2


           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
                                                        Department of Chemistry



        Organic synthesis & natural products synthesis
3




       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.
                                                       Department of Chemistry



    Organic synthesis & natural products synthesis
4




       These useful compounds range from biological tools
        and medicines to high-value materials for cosmetics,
        computers and useful devices

                         O       OH                O        OH
                             C                          C
                 NaOH                  (CH3CO)2O
           OH                     OH                             O        O
                                                                     C
                 CO2                                                 CH3

                                                       aspirin
                                                       Department of Chemistry



    Introduction of Microscale Organic Chemistry
5




       Had been gradually recognized and adopted at
        secondary school level
       Handle with small quantities of chemical substances
                                          Department of Chemistry



    Macroscale vs. Microscale
6




                     Macroscale     Microscale

     Quantities of     5-100 g      0.005-0.5 g
      chemicals
     Glasswares      25 - 500 mL   Microscale kit
                                      (<5mL)
       Cost per      $100-1000       $10-100
      experiment
                                                     Department of Chemistry




    Advantages
7




    1.   Require smaller storage area
    2.   Save laboratory space
    3.   Reduce amount of chemical waste
    4.   Improve laboratory safety (smaller amount of …)
    5.   Shorter reaction time (efficient heat transfer…)
    6.   Save time for preparation and work up
    7.   More time for evaluation and communication
    8.   ………….
                                                                                       Department of Chemistry



       Microscale Organic Glassware
 8


          Various designs




http://www.sigmaaldrich.com/labware/glassware-catalog/glassware-kits-microscale.html
                               Department of Chemistry



Microscale Organic Glassware
   All-purpose kit:




                                             9
                                                                    Department of Chemistry



         Designing experimental procedures
10



        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
                                                   Department of Chemistry

                             Technique:
11
         Transfer of reagent/dispensing of solvent
        Macroscale:
          Measuring   cylinder
          Beaker
          Conicalflask
          Dropping funnel

        Microscale:              1.0 mL Syringe
          Syringe
          Needle
          Septum
                                        Department of Chemistry



     Technique: Setup for Organic Synthesis
12


        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
                                                                  Department of Chemistry



     Technique: Microscale Experiment Setup
13


        Microscale Organic Synthesis:                             Microscale
                                                                   Condenser, Threaded
         Water condenser
                         Reagents (+ catalyst)                         Water out

                         Anti-bumping granules
                                     Microscale Round-Bottom
                                                                        Water in
                                     Flasks, Threaded




                     Sand bath
                                                          Microscale
                                                         reflux setup
                                                                  Department of Chemistry



     Technique: Microscale Experiment Setup
14



        Microscale Organic Synthesis: Air condenser
        Reagents (+ catalyst)
        Anti-bumping granules




                                              Microscale Round-
                                              Bottom Flasks,
                                              Threaded
                                 Microscale reflux setup
                                       Department of Chemistry



     Isolation Technique: Filtration
15


      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
                                       Department of Chemistry



     Isolation Technique: Filtration
16


      Pipette filtration:
      For small quantity of

       crystals
                                                       Department of Chemistry



     Isolation Technique: Liquid-liquid Extraction
17


        Partition coefficient
        Solubility in solvents




                                              Separatory
                                  Screw cap   funnel
                                  Test tube
                                                                  Department of Chemistry



         Purification Technique: Distillation
18


        For liquids with various volatilities




           Macroscale distillation setup         Microscale distillation setup
                                                             Department of Chemistry



     Purification Technique: Sublimation
19


        For solids




                                             Microscale sublimation setup
              Macroscale sublimation setup
                                                 Department of Chemistry



     Purification Technique: Recrystallization
20


        For solids
        Various Solubility




     Temperature
     controlled by
     depth in sand
              Microscale      Macroscale      Microscale
              5mL             250mL           5mL
              Reaction tube   Conical flask   Conical flask
                                                    Department of Chemistry



     Purification Technique: Recrystallization
21


         Steps in Recrystallization:
     1.   Dissolution (various choice of Solvent)
     2.   Hot Filtration
     3.   Decolorization
     4.   Crystallization
     5.   Collection
                                                                     Department of Chemistry



     Purification Technique: Recrystallization
22


        The general idea is to follow the “like dissolves like”
         principle, e.g. compounds containing hydroxyl groups
         are best recrystallized from hydroxy-containing solvents

            Class of compound    Suggested solvents

            Hydrocarbons         Light petroleum, pentane, cyclohexane and
                                 toluene
            Ethers               Diethyl ether and dichloromethane
            Halides              Dichloromethane
            Carbonyl compounds   Ethyl acetate and acetone
            Alcohols, acids      Ethanol
            Salts                Water
                                 Department of Chemistry



Methods for crystallization
    23
                              Ice bath
   2
                                                         Department of Chemistry



     Purification Technique: Recrystallization
24


        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
                                   Department of Chemistry



     Characterization of organic compound
25



    Melting point / melting
     point apparatus
  Simplest and most common
   characterization method for
   solid organic compounds
  Purity check

  Affordable
                                         Department of Chemistry



         Characterization of organic compound
26




        Boiling point / distillation
         apparatus
          Simplest and most common
           characterization method for
           liquid organic compounds
          Purity check

          Affordable
                                       Department of Chemistry



     Characterization of organic compound
27



        Infrared spectrum
          Infrared
           spectrophotometer
          Absorption of infrared
           electromagnetic radiation
          Information of functional
           groups
                                                   Department of Chemistry



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)
                                                                            Department of Chemistry



         Characterization of organic compound
29


           Bond   Base Value   Strength / Shape Comments

     1     C=O    1715         s, "finger"    Exact position depends on type of carbonyl

     2     O-H    3600         s, broad       Broad due to hydrogen bonding

     3     N-H    3500         m              Can tell primary from secondary

     4     C-O    1100         s              Also check for O–H and C=O
                               w alkene       Alkene w due to low polarity
     5     C=C    1650
                               m-s aromatic   Aromatic usually in pairs
     6     CΞC    2150         w, sharp       Most obvious in terminal alkynes
                                              As hybridisation of C changes sp3-sp2-sp,
     7     C-H    3000         s
                                              the frequency increases
                                              Characteristic since little else around this
     8     CΞN    2250         m, sharp
                                              value
                                                      Department of Chemistry



     Characterization of organic compound
30


        Functional groups can be identified




                      Infrared spectrum of acetone
                                                                                       Department of Chemistry



     Characterization of organic compound
31


        Mass spectrum / mass spectrometer
        mass-to-charge ratio of molecular ion




                              Picture from http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch13ms.html
                                                                                Department of Chemistry



     Characterization of organic compound
32


        Mass-to-charge ratio:
          Molecular ion
          Fragmentation pattern of
           molecular ion

                             The ion obtained by the loss of an electron from
            Molecular ion
                             the molecule
            M+               Symbol often given to the molecular ion
                             +ve charged species with an odd number of
            Radical cation
                             electrons
                             Lighter cations formed by the decomposition of
            Fragment ions    the molecular ion.
                             These often correspond to stable carbcations.
                                         Department of Chemistry



     Characterization of organic compound
33


                               Decane (C10H22)
                               Molecular ion at
                                m/z = 142

                               142-29 = 113
                               113-14 = 99
                               etc
                                                Department of Chemistry



     Characterization of organic compound
34


        Acetone (C3H6O)
        Molecular ion at m/z = 58
                   O
                                           43
                   C
             H3C       CH3
                                           –15          58
                                     –28

                               15
                                                         Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
35



     3 components




        caffeine         p-dimethoxybenzene         acetaminophen

                   Separation based on their different
                    physical and chemical properties
                                                           Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
36



    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
                                                             Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
37


        Step 1: Solubility test
          water,   dichloromethane, hexane

                           Insoluble                          soluble




         Powder                           Slightly soluble
                                                 Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
38


         Solid-liquid extraction (Filtration)
                                                  Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
39


        Step 2: Acid-base chemistry

                       basic                            neutral

                                            HCl




                     NaOH
              org                      aq               org
                                            Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
40



        Liquid-liquid extraction
          Release  pressure
          Which layer on the top?

          Test by adding water
                                                                                Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
41


         Some water will be
                                                     p-                        Sodium




                                           organic




                                                                     aqueous
          transferred into the                       dimethoxy-                chloride
          organic phase because                      benzene
          of the partial miscibility
          of the organic phase and                   Diethyl ether
          water  Organic                                 Water
          solution contaminated
                                           brine works to pull the
          with traces of water.
                                            water from the organic
                                            layer to the water layer
                                                       Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
42


         Dry by anhydrous Na2SO4 (Preliminary purification)




                           Pipette filtration
                                             Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
43


        Evaporation




                                    Needle
                       Compressed
                           air
                                                Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
44


         Step 3: Purity check
           Thin   layer chromatography (TLC)
                                                     Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
45


        Thin layer chromatography (TLC)



                              Chromatography:
                              Separation of compounds by the
                              distribution between two phases –
                              Mobile phase & Stationary phase
                                               Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
46




     stationary
     phase                    Sample mixture
     (TLC plate:
      Silica gel)



                    mobile phase (solvent)
                                             Department of Chemistry

                      Experiment 1:
     Microscale separation of components in a mixture
47
                                                              Department of Chemistry

                        Experiment 2:
          Catalytic Hydrogenation of Methyl Oleate
48


      Organic Synthesis by Hydrogenation
      Microscale Experiment Setup


                                    H2(g)
         methyl oleate                                methyl stearate
                                Catalyst: Pd/C




        Reagents:
          Methyl   oleate, H2, Palladium on charcoal, Methanol
                                                     Department of Chemistry



     Catalytic Hydrogenation of Methyl Oleate
49

                                           Syringe instead of
        Setup:                            dropping funnel

          Generationof hydrogen
                                   H2(g)
          gas as reagent                                         HCl(aq)



          Use of septum
          Use of needles
          Use of syringe
                                                     Zn metal in
                                                     5mL flask
                              5mL flask
                                                Department of Chemistry



     Catalytic Hydrogenation of Methyl Oleate
50



    Collect H2                      Syringe instead of
                             H2(g)   dropping funnel
     into a
     inverted                                               HCl(aq)
     measuring
     cylinder



                                                Zn metal in
                                                5mL flask

                                            5mL flask
                                           Department of Chemistry



     Catalytic Hydrogenation of Methyl Oleate
51


        Beginning of
                                   H2(g)
         synthetic reaction




                                                      Methyl oleate
                                                      + methanol
        Use of syringe
         + needle
                                           Department of Chemistry



     Catalytic Hydrogenation of Methyl Oleate
52




                             Use of parafilm to
                              prevent leakage
                                                              Department of Chemistry



     Catalytic Hydrogenation of Methyl Oleate
53




        Workup:
            Filter off Pd/C
            Evaporate excess CH3OH
            Purification of methyl stearate
                 Isolation of second crop of product (by adding H2O to
                 filtrate)

        Characterization
            Melting point determination

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:10
posted:11/18/2012
language:English
pages:53