XL Friedel-Crafts Reaction, Mono- and Diacctylferroccne

A. Reaction

CH3COCI

AICI,

COCH, COCH,

COCH.,

B. ProcedureThe methylene chloride has already been dried and the acetyl chloride has been freshly

distilled. Work rapidly with the aluminum chloride to prevent deactivation by moisture inthe air. Dig down into the bottle. The material on top is often just aluminum oxide fromhydrolysis. To check the activity of aluminum chloride, drop a little into water and see if itfizzes and gives off smoke.

The reaction equipment consists of a 5 mL vial, spin vane, Claisen head, drying tubefilled with calcium chloride, a septum cap, and a syringe. All glassware must be dry. Weigh,directly into the reaction vial, 150 mg of anhydrous aluminum chloride. Then add 2 mL ofdry methylene chloride followed by 80 |iL (88 mg, 1.1 mmole) of acetyl chloride. Stirbriefly and then, using a syringe, add gradually through the septum a solution of 100 mg(0.54 mmoles) of ferrocene dissolved in about 1.5 mL of methylene chloride. Stir for about1/2 hour. The solution is sampled occasionally for TLC analysis.

Thin Layer Chromatography. Remove a small sample of the reaction mixture witha Pasteur pipet A silica gel plate is spotted with a methylene chloride solution of the startingferrocene and then, about a centimeter away, with a sample of the reaction mixture. Place theplate in the developing chamber using pure methylene chloride as the developing agent.Make sure that the level of the developer in the beaker does not come above the level of thespot on the plate. Develop the plate for a few minutes using pure methylene chloride as thedeveloping agent. The spots on the developed plate are quite visible and so no visualizationtechniques need be employed. You should see two spots, one for the mono- and the other forthe diacetylferrocene. A trace of unsubstituted ferrocene may also be present.

After about 1/2 hour, the reaction mixture is transferred to a 12 mL centrifuge tubecontaining about 5 mL of cold water. Rinse the reaction flask with methylene chloride andcombine with the-material in the tube. Add a solution of NaOH until the aqueous top layer isabout neutral. Take off the methylene chloride layer with a Pasteur pipet and place it in a 25mL flask. Extract the aqueous mixture in the tube with three 1 mL portions of methylenechloride and add these extracts to the flask. Dry the methylene chloride with about 300 mgof magnesium sulfate. The dried solution is transferred to another flask using a Pasteur filterpipet. Wash the magnesium sulfate wi th a small amount of methylene chloride and add thisto the flask. Evaporate the solution to about 3 mL. and transfer the solution to a 5 mL vial.Continue to evaporate until the solution is on ly about 1/2 mL and then add 300 mg of alu-mina (activity HI). Continue to evaporate to dryness. Be careful not to blow the fine powderout of the flask by the stream of nitrogen.

C. Separation and Purification by Column ChromatographyPreparation of the column. The column consists of a 25 mL burette with a Teflon

stopcock. Remove the stopcock and cut a small circle of filter paper that will just cover thetop of the stopcock and block the hole. Then insert the stopcock with the filter paper cover-ing the hole. Fasten the column in an upright position and add about 1/2 cm of sand. Thecolumn is now ready for packing. The success of this separation depends entirely on howcarefully you pack the column. Add slowly the alumina (activity HI) through a small fun-nel while tapping the column briskly. (I tap using a plastic centrifuge tube.) Continueadding the packing while tapping all around. The object is to get a very uniform packing.You can't tap it too much. If you don't do this very well, the alumina will not pack properly,the solution will channel down the column, and the separation will not be clean. Use about10 cm of packing. Then add the product-alumina mixture to the top of the column, pack, andthen add another cm of straight alumina on top.

Operation of the column. Close the stopcock and add hexane to the column, carefullyat first so as not to disturb the top of the column, and then fill up the column. Open thestopcock and allow the hexane to run through. Start collecting fractions in a 10 mL gradua-ted cylinder. A trace of unreacted ferrocene will run through first and will be in the first 5mL. When the effluent becomes clear, close the stopcock and using a Pasteur pipet removethe liquid from the top of the column down to the alumina. Then add a 50-50 mixture ofhexane-methylene chloride. Open the stopcock and begin a new collection. When theorange monoacetylferrocene begins to emerge, switch flasks and collect the fraction. Ifeverything is working well, the monoacetylferrocene should all come out in the next 20 mLleaving the orange diacetylferrocene as a band on the column. When effluent turns clearagain, close the stopcock and remove the liquid from the top of the column as before. Nowadd pure methylene chloride and begin collecting again. The diacetylferrocene will come outof the column in about the next 20 mL.

Isolation of the Fractions. Place each of the two fractions in 25 mL Erlenmeyerflasks and evaporate under a stream of nitrogen to a volume of about 3 or 4 mL. Transfer thesolutions quantitatively to 5 mL vials and continue to evaporate to dryness. Run TLC to con-firm purity. Sublime the product under vacuum using the sublimator at a block temperatureof about 150°C. Weigh and run the IR spectrum.

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D. Report: Acylation of Ferrocene

Name

Chemical Reaction:

Reagents:

Products:

Date Exp. No.

Compound Mol Wt. Density Wt., mg Vol. nL mmole

Compound

Acetylferrocene

Diacetylferrocene

Mol Wt. Wt., mgTheory

mmolTheory

WL.mgActual

mmoleActual

Total No. of mmoles yield

Melting Point ranges

Acetylferrocene

Percent yield.

Diacetylferrocene

°C

*C

Infrared Data. Evidence for the confirmation of structure. Attach IR spectra.

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