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a. Draw figures over-viewing the apparatus/procedure for (a)vacuum filtration and (b) hot gravity filtration, two techniquesused in this protocol. Briefly explain why the two methods are usedin the specific steps of the procedure, contrasting the goals ofeach method.

b. What is the purpose of the CaCl2 drying tube? What chemicalreaction is it preventing (please supply a mechanism).

c. Draw the product and detailed electron-pushing mechanismfor a slightly different reaction: benzene (not ferrocene) beingtreated with chlorine and FeCl3 to generate chlorobenzene.

d. Based on the structures of the starting material andproduct, draw predicted TLCs of: (1) a complete reaction and (2) anincomplete reaction. (We’ll pretend the TLC is done at 10:1 H:E,but that is irrelevant for this question).

Reaction

1. Begin to heat asand bath (to 80-90 0C)set on top of a stir plate while preparing the following reactionmixture. Proper temperature control is crucial in this reaction!Carefully try to avoid going over 90 0C.Only use thermometers that read up to 200 0C.(Thermometers reading only to 110 0Cmay explode!)

2. Place 1.5gferrocene in a 25 mL round-bottom flask containing amagnetic stirbar.Cork-stopper the

flask.The magnetic stir bar should be ~1cm long for optimal stirring (2cmstirbars do not stir well).

1. In a fume hood,add 5.0 mL acetic anhydride and 1.0 mL of 85% phosphoric acid tothe flask. The mixture should heat up and darken in color. Looselycork the flask again temporarily.

2. Construct acalcium chloride drying tube: insert glass wool into a macroscaledrying tube, add a ~1-2 inch layer of CaCl2on top. Affix tothe flask with a Keck clip.

3. Heat thereaction mixture, with stirring, in the 80-90 0Csand bath prepared in step 1. Heat for 15-20 minutes. A visual wayto monitor the reaction is transformation from darkred to deeppurple.

4. Remove flaskfrom sand bath for TLC analysis.

5. Follow thereaction by TLC (10:1 H:E). (TLC: ferrocene SM on left, reaction onright, cospot in the

   middle). If thereaction is incomplete, you may continue heating. (but keep thetemperature 80-90 0C)

   1. Pour thereaction mixture directly onto 25g (~60mL) ice in a 200 mL beaker,rinsing the flask with H2O(2 x 5 ml). (A black residue may remain in the flask, leave itbehind). Stir the orange-brown mixture with a glass rod for a fewminutes. Any insoluble black material present in your reactionmixture will be removed in the following steps.

      1. Add 37.5 mL of3M aqueous NaOH solution. Check the pH – most students will observepH 9-13 which is good.

      2. Stir the mixturewell and crush any lumps, affording the product as a brownsuspension.

      3. Allow themixture to stand for ~10 min, then collect the crude product byvacuum filtration. Continue to

         pull air throughthe product for a few minutes to dry it. Finish the drying processby pressing the solid

         product betweentwo sheets of filter paper or paper towels.

      4. Save a smallamount of crude product for TLC analysis (perhaps in your ceramictray for TLC samples)

      5. Transfer thecrude product to a 50 ml ERLF and add 20 mL of hexanes. Gently boilfor 3-5 minutes

         withgentleswirling todissolve the product, then decant the dark-orange solution intoanother Erlenmeyer flask, leaving behind any black gummy substance.(If considerable solvent has evaporated, add more hexane to avoidproduct loss)

      6. To the hotsolution, add a small spatula-full of decolorizing carbon (no morethan 100mg), adding more will decrease your yield. Heat withswirling, (i.e. keep the mixture hot!), and then quickly perform ahot gravity filtration to remove the decolorizing carbon, into anew clean/dry 50 ml ERLF. (using a short- stem plastic funnel, not the long-stem glassfunnel!)

      7. Set the flaskaside to cool slowly. Red-brown needles of acetylferrocene shouldbegin to form. Once the flask has reached room temperature, cool itin ice. Collect the crystalline product by vacuum filtration,washing with a small quantity of cold hexanes, and dry it bycontinuing to pull air through it for a few minutes.

      8. Re-analyze yourcrude and recrystallized products by TLC.
         Consider spotting left=SM (ferrocene), middle=crude product,right=purified product.

         (noco-spotting necessary in this experiment).

      9. Place yourproduct in a labeled class sample (20 g vial) of thismaterial.

      Only if yourmixture is acidic (pH < 7), add small amounts of sodiumbicarbonate until

      your pH is ~8-9.(Very few, if any students will not have to add sodiumbicarbonate).