last updated Friday, February 12, 2016

1. General

Review the following topics: NMR spectroscopy, Infrared spectroscopy, Recrystallization, Flash chromatography

2. Experiment

Safety notes:  Acetic acid anhydride are very corrosive.

In the initial stage of the reaction, ferrocene is dissolved in acetic acid anhydride and Amberlyst A15 is added. The reaction mixture is then heated to 75-80 oC on a water bath. Higher temperatures and longer reaction times usually lead to a lot of byproducts (i.e., diacetylferrocene, oxidation products)!

After the reaction is completed, the reaction mixture is poured into water. The pH-value has to be adjusted to pH=5-7 using solid sodium bicarbonate (Careful!). It is highly advisable to use a large beaker here (~400 mL). The resulting mixture is extracted with ethyl acetate. The dark-brown or purple solid/oil that does not dissolve in ethyl acetate is not of interest to us!

The solution is usually very dark red (or brown) at this point, which makes it difficult to observe the phase separation. Depending on the conditions, it can also take some time to observe a phase separation.

The crude product is purified by column chromatography. The stationary phase is wet with petroleum ether. The crude product is suspended in a mixture of petroleum ether:ethyl acetate (95:5). The same solvent is initially used elute the unreacted ferrocene off the column. Afterwards, a mixture of petroleum ether:ethyl acetate (80:20) is added to elute the mono-acylation product off the column.

Important: When applying the crude product to the column, the entire sample should be applied, and not only a small portion. Also, the polarity of the solvent used for this step should be as low as possible ), which implies that the student cannot use pure ethyl acetate for this purpose (why)?.

In some cases the tip of the burette clogs up. In order to minimize this problem, the tip should be rinsed regularly with a little EtOAc to remove the deposited solid. In addition, it is also helpful to place the tip in the upper part of the test tube to immerse it in the solvent vapors which also reduces the evaporation of the solvent. This problem often occurs when the elution is too fast or too slow.

The fractions containing the final product are combined and the solvent removed without overheating the sample. Any impurity in FcAc causes problems in the next project. Try to isolate as much as possible FcAc in order to have sufficient starting material for the independent project.

Note: Fc stands for "Fe(C5H5)(C5H4)"

Other resources: Youtube Videos Part1 Part2