Chapter 33 Friedel crafts Acylation of Ferrocene: Acetyllerrocene 353 then is ad

Question

Chapter 33 Friedel crafts Acylation of Ferrocene: Acetyllerrocene 353 then is added to acetic The crude product isolated by filtration and then chromatographed on alumina. This is an excellent system to observe separation on a column because the unreacted fer rocene is yellow and the acetyl product is orange Procedure In a 25-mL round-bottomed flask place 3.0 g of ferrocene, 10.0 mL of acetic anhydride, and 2.0 mL of 85% phosphoric acid. Equip the flask with a reflux condenser and a calcium chloride drying tube. Warm the flask gently on the steam bath while swirling to dissolve the ferrocene, then heat strongly for 10 min more. Pour the reaction mixture onto 50 g of crushed ice in a 400-mL beaker and rinse the flask with 10 mL of ice water. Stir the mixture for a few minutes glass rod, add 75 mL of 3 M sodium hydroxide solution (the solution should still be acidic), then add solid sodium bicarbonate (be careful of foaming) until the remaining acid has been neutralized. Stir and crush all lumps, allow the mixture to stand for 20 min. then collect the product by suction filtration. Press the crude material as dry as possible between sheets of filter paper, save a few crystals for thin-layer chromatography, transfer the remainder to an Erlenmeyer flask, and add 40 mL of hexane or ligroin to the flask. Boil the solvent on the steam bath for a few minutes, then decant the dark-orange solution into another Erlenmeyer flask, leaving a gummy residue of polymeric material. Treat the solution with decolorizing charcoal and filter it through a fluted filter paper placed in a warm stemless funnel into an appropriately sized Erlenmeyer flask. Evaporate the solvent (use an aspi- rator tube; see Fig. 8.5) until the volume is about 20 mL. Set the flask aside to cool slowly to room temperature. Beautiful rosettes of dark orange-red nee- dles of acetylferrocene will form. After the product has been cooled in ice. collect it on a Buchner funnel and wash the crystals with a small quantity of cold solvent. Pure acetylferrocene has mp 84-85°C. Your yield should be about 1 g. Analyze your product by thin-layer chromatography. Dissolve very small samples of pure ferrocene, the crude reaction mixture, and recrystallized acetylferrocene, each in a few drops of toluene: spot the three solutions with microcapillaries on silica gel plates; and develop the chromatogram with 3:1 toluene-absolute ethanol. Visualize the spots under a UV lamp, if the silica gel has a fluorescent indicator, or by adsorption of iodine vapor. Do you detect unre- acted ferrocene in the reaction mixture and/or a spot that might be attributed to diacetylferrocene? Cleaning Up The reaction mixture filtrate can be flushed down the drain Unused recrystallization and thin-layer chromatography solvents should be placed in the organic solvents container. The decolorizing charcoal of solvent, can be placed in the nonhazard

Explanation / Answer

FLOW CHART TO THE ABOVE PROCEDURE

Step 1
Take a 25 ml round bottom flask and add 3 g of ferrocene, 10 ml of accetic anhydride and 2ml of 85% phosphoric acid

Step 2
Set up the flask with reflux condenser and a calciul chloride drying tube

Step 3
Warm the flask gently on the steam bath followed by heating strongly for 10 mins

Step 4
Pour the reaction mixture onto 50 g of crushed ice in a separate 400 ml beaker and rinse the flask with 10 ml ice water

Step 5
While stirring the mixture with glass rod add 75 ml of 3M NaOH solution followed by adding sodium bi carbonate ( no foam shuld be formed)

Step 6
Keep stiring and crush all the lumps. Leave the mixture untouched for 20 mins

Step 7
Collect the product by suction filtration

Step 8
Dry the product by pressing it in between a filter paper

Step 9
Take aside few crystals for chromatography. And put the rest to an erlenmeyer flask followed by adding 40 ml of hexane or ligroin to the flask

Step 10
Boil the solvent on steam bath for few minutes.

Step 11
Decant the solution to another erlenmeyer flask, be careful with the left over residue of the polymeric material

Step 12
Treat the solution with decolorizing charcoal and filter it with a filter paper fitted in a steamless funnel to a proper sized erlenmeyer flask

Step 13
Evaporate the solvent until 20 ml volume remains

Step 14
Cool down the flask to room temperature

Step 15
Collect the dark orange red coloured needles of acetlyferrocene and cool it on ice.

Step 16
Rinse the cooled product with cold solvent

Step 17
Weigh your product and note it down

Step 18
Analyze your product by thin layer chromatography for that take 3 test tubes. In 1st test tube add pure ferrocene. In 2nd add crude reaction mixture and in 3rd add recrystallized acetylferrocene.

Step 19
Add few drops of toluene in each of the test tubes

Step 20
Spot the three solutions with microcapillaries on silica gel plate and develop the chromatogram with 3:1 toluene- absolute ethanol

Step 21
Visualize the spots under U-V lamp and check for fluorescent colour.

Step 22
Flush down the drain the filterate reaction mixture

Step 23
Place the unused recrystallization and chromatography solvents back in the organic solvent container.

Step 24
Place the decolourized charcoal, once free of solvent in the solid waste container

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