Organic Chemistry 351 Sample Lab Report

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Organic Chemistry 351 Sample Lab Report Powered By Docstoc
					          Friedel-Crafts Acylation: Acetylferrocene and Diacetylferrocene

Introduction:

The purpose of this lab is to prepare acetylferrocene and diacetylferrocene from
ferrocene, acetyl chloride, and aluminum chloride. The reaction is a classic example of
Friedel-Crafts acylation. Acetyl chloride reacts with the aluminum chloride to produce
the electrophilic acylium ion. Once the acylium ion is produced, the nucleophilic
aromatic ring(s) of ferrocene donate electrons to the electrophilic acylium ion resulting in
an aromatic carbocation. The aromatic carbocation is then stabilized by loss of a proton
to a chloride ion (which came from AlCl4-), to give AlCl3 and HCl as side products.
Once the products have been formed, they will be analyzed by TLC. The products will
then be separated by column chromatography. Once separated, the products will be
analyzed by melting point and IR spectroscopy.

Overall Reaction:




         Table 1: Physical Constants of Important Chemicals
                          Physical Constants
                         molecular
                                       density     b.p.        m.p.
     Compound             weight
                                       (g/mL)      (°C)        (°C)
                          (g/mol)
 Aluminum Chloride        133.34        n/a        n/a          190
   acetyl chloride        78.50         1.11       51           n/a
      ferrocene           186.04        n/a        249          173
   acetylferrocene        228.07        n/a        n/a         81-83
  diacetylferrocene       270.10        n/a        n/a        122-128
Chemical Procedure:

   1- Assemble the apparatus drawn above (the glassware should be clean and dry
      before use).
         a. Attach a tared 5 mL conical vial with a spin vane to a Claisen adaptor.
         b. One of the Claisen heads should be connected to a drying tube filled with
             cotton and blue CaCl2. Any used pink dessicant should be recycled and
             put in the used dessicant container.
         c. The other Claisen head should have a septum and lid over the top. (See
             Figure 1.)




      Figure 1: Apparatus used for the Friedel-Crafts Acylation reaction.


   2- To the vial add 150 mg anhydrous AlCl3 and about 2.5 mL of methylene chloride
       (solvent).
   3- To the vial add ~80 L acetyl chloride (density 1.11 g/mL) via automatic delivery
       pipet
   4- Then add a ferrocene solution made with ~100 mg ferrocene dissolved in 1.5 mL
       CH2Cl2.
   5- Important: you should observe a purple colored solution. Please advise the
       instructor if your solution is not purple.
   6- Allow the reaction to stir at room temperature for 15 minutes.
   7- Quench the reaction by transferring the solution to a centrifuge tube (test tube
       with screw cap lid) with 5.0 mL of cold water.
   8- Neutralize this solution with 6.0 M NaOH by adding ~3 drops at a time and
       shaking the solution after each addition.
   9- Check the pH with litmus paper until the solution is neutralized (~15 drops of
       base will be needed).
   10- Extract the solution with three 3 mL portions of CH2Cl2.
   11- Dry (remove residual water) the CH2Cl2 layers by addition of anhydrous Na2SO4.
   12- Transfer the dried solution to a tared Erlenmeyer flask.
13- Remove a small portion for TLC analysis next week.
14- Remove solvent by boiling off the methylene chloride in the hood.
15- Weigh the crude product.

   END OF FIRST WEEK


16- Analyze the reaction mixture (sample taken before) by TLC using CH2Cl2 as the
    mobile phase.The product is now purified by column chromatography (use dry
    alumina):
17- Dissolve the crude product in ~0.5 mL CH2Cl2 and mix with 300 mg of alumina
    in a beaker. If there is a lot of residual solvent, heat CAREFULLY in the
    hood (it tends to bump). If there is not a lot of residual solvent, let it air dry.
18- We will make two columns for chromatography because generally we would
    overload one column with the amount of material that we have generated.
    Construct two columns in pasteur pipets: (glass wool plug, then 1/8” sand, at least
    1”alumina, ½ of the alumina-product mixture, 1/8”alumina).Remember to leave
    a little bit of space at the top of the column for solvent. (See Figure 2.)




      Figure 2: Setup for the column used to purify the crude product.

19- Elute columns with pure hexane until unreacted ferrocene (usually a faint yellow
    color) exits the column.
20- Once you are confident that all of the unreacted ferrocene has exited the column,
    elute with 1:1 CH2Cl2/hexane until acetylferrocene exits the column.
21- Elute columns with 9:1 CH2Cl2/CH3OH until diacetylferrocene exits the column.
22- Collect each band separately.
23- Spot a new TLC plate with the material in each flask to verify separation and
    purity of products. Combine like fractions.
24- Remove the solvent from the products by heating in the hood until products are
    dry.
   25- Weigh each product.
   26- Obtain the melting points of each product (acetylferrocene m.p. 81-83oC,
       diacetylferrocene m.p. 125-127oC).
   27- Obtain the IR spectra for each product.

IR of Ferrocene:




IR of Acetylferrocene:
IR of Diacetylferrocene:




Assigned Questions:

1.    Show an arrow pushing mechanism for the formation of the monoacetyl
      ferrocene.
2.    Produce a diagram of your TLC plate with the spots shown and the Rf values on
      the diagram.
3.    Report your percent yield of each product and show the appropriate calculations.
4.    Explain the role of anhydrous sodium sulfate.
5.    Why do we extract with three 3-mL portions of methylene chloride instead of a
      single 9 mL portion (it has nothing to do with the volume capacity of the
      glassware).
6.    Why does the disubstituted product require a 9:1 solvent mixture of
      CH2Cl2/CH3OH instead of 1:1 of CH2Cl2/hexane or pure hexane?
7.    Attach your IR spectra and summarize the results.
8.    Report both the experimental and actual melting points of monoacetylferrocene
      and diacetylferrocene.

				
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