The Friedel-Crafts Reaction: Acetylation of Ferrocene

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Ferrocene was acetylated in acetic anhydride and phosphoric acid. It proceeded via a Friedel-Crafts reaction without the use of organic solvents or strong Lewis acid.

Operations and Observations
A mixture of ferrocene (1.5 g, 0.008 mol), acetic anhydride (5 mL) and phosphoric acid (1 mL 85%) was heated over a steam bath until all the ferrocene dissolved and the mixture darkened from orange to dark red. The mixture was then refluxed with a calcium chloride drying tube for ten minutes and left to cool for an hour taking on a dark almost black colour. The reaction mixture was then poured onto ice (60 mL) and stirred to form brown mixture with some greenish black precipitate. Aqueous sodium hydroxide (37.5 mL, 3M) was added to the mixture and solid sodium bicarbonate was added until the mixture was neutralised. The mixture was left to stand for an hour with stirring before the crude product was collected with vacuum filtration.The product was air dried for a couple of minutes then boiled with hexane (20 mL) leaving behind a brown- black gummy substance. The product was then decolourised with activated charcoal and recrystallized from hexane to give dark orange crystals (0.51 g, 27%, m.p. 84°C; lit. m.p. 81-86 ºC). A TLC plate was used to compare the ferrocene, the crude product and the recrystallised product. The ferrocene had an Rf value of approximately 0.8, the recrystallised product had an Rf of approximately 0.3 and the crude product contained both as well as a small amount of violet impurity with a Rf value slightly higher than the product which was not present elsewhere.

There was a lot of the black insoluble material in the mixture and at times it appeared to be a slightly greenish colour in solution. The greenish colour could be due to the presence of Fe (II) ions in the solution. If there were Fe (II) ions loose in the solution then the gummy substance could contain a...
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