Acetylation of Ferrocene, Part Two

On Thursday 9-22-11, we had to redo the acetylation part of the ferrocene lab because it did not work the first time. The GC of our product did not yield anything, so we decided to try a different procedure to make the same product. This new procedure was scaled up considerably so we hoped that there would be enough of our product to run tests on.

We began by adding ferrocene, acetic anhydride, and phosphoric acid in a round bottom flask and placing this flask in a sandbath with an air condenser hooked up to a steady flow of argon gas. We heated and stirred it until the temperature reached 100 degrees Celsius, and then heated it for 10 minutes after that.

When we took the flask off to empty the precipitate, we found that in addition to the precipitate, we had a tar-like black substance stuck on the bottom of the flask. It had actually formed around our stir bar, so the stir bar was probably not stirring for a long time before we realized it! We did have some precipitate so we washed that into a large beaker of ice and waited for the ice to melt before we added some sodium hydrogen carbonate until the solution stopped bubbling with the addition of the base. This took a huge amount of NaHCO3 (around 7 grams) and by this time, the solution was starting to look like we were just boiling a beaker of mud. Once in the ice bath, it started to look a little better. It looked like a brown precipitate in a reddish solution.

We suction filtered it and got a large amount of brown precipitate, which we then used to make a GC sample, an IR sample, and a Mel temp sample.

The trouble is, we didn't get the GC yet due to technical difficulties and the Mel temp gave a melting point of about 59 degrees Celsius while pure acetylated ferrocene has a recorded melting point of about 81 degrees Celsius.

We thought that maybe there were impurities in the sample causing the melting point aberration, so we decided to recrystallize our product. We did this by adding the minimum amount of petroleum ether to our sample to make most of it dissolve. We then decanted the clear yellowish liquid (which was the product dissolved in the pet ether) into a clean beaker and let it sit overnight. After the night was up, the ether had all evaporated off and a layer of orange crystals was left on the side of the beaker--this was our pure product.

Unfortunately, a Mel temp test of the pure product gave us the same results as the unpurified product, so at this point we need our GC to give us some proof of acetylation. We know from the drastically lower melting point that there is a new chemical formed from this reaction, we just don't know what it is!