Finishing Ferrocene and Beginning Benzene

FINALLY...we got our acetylation of ferrocene to work. We ran the GC on Tuesday 9-27-11 and the highest peak on the spectrum was monoacetylated ferrocene. That is the most compelling evidence we have, and the only evidence we have that still contradicts the presence of monoacetylated ferrocene is the low melting point we got. However, 3 out of 4 isn't bad! That successfully finishes the ferrocene lab, which is good because we have gotten tired of writing about it!

Along with finishing ferrocene, we finished our purple crystals lab on Tuesday. Allen was responsible for this while I (Emily!) was working on other things. He did the isolation like with the benzene inclusion compound, but this time it was just the pure [Ni(en)2(NCS)2] crystals without any benzene added to it. These crystals took so long to grow, and even after five weeks, there were still only a couple of crystals in the vial (nothing like the vial full of benzene crystals we got). We finally decided to purify them and take the melting point since they didn't seem to be growing any more crystals. After the isolation, we got some very pretty dark purple crystals:

These actually look nothing like the benzene inclusion crystals, which were not shiny and dark purple but more dull and light purple. They were also much smaller crystals than these. Here's a picture of the benzene crystals to jog your memory:

We massed the new crystals so we could find percent yield for the lab report, and then we took the melting point, which ended up being above 220 degrees Celsius (that is the limit on our thermometer, so we couldn't get more precise than that!).

Since those two things didn't take much time, we were able to set up our first reaction for our final project. We are doing our project on Cr-Arenes, in which Cr(CO)6 is reacted with an arene in a solvent mixture of dibutyl ether and THF. There are so many arenes to choose from, but we just picked 6 of them to try and synthesize, purify, and characterize. The first arene we wanted to try was benzene.

We set up a three neck flask exactly the same as in the synthesis of ferrocene except with a condenser on the middle neck of the flask:

The condenser is needed to air-cool the reaction so the solvent doesn't boil away. We vacuumed and argon-filled the flask three times and then left the argon running throughout the experiment. We then added in the two solvents via syringe. We added 8 ml of dibutyl ether and 1 ml of THF.

 Now we needed to bubble argon through the solvents to get rid of any oxygen that might ruin the reaction. We "adapted" a disposable syringe to fit into a hose from the rack and stuck the needle through the septum so that the argon bubbled through the solvents. It actually looked like the solvents were boiling because of the gas bubbles:

While this was bubbling, we got 1 g of Cr(CO)6 (which is a white solid) and measured out 1 ml of benzene in a syringe. We had to take the septum out before we could add these two reactants plus a stir bar, so we just replaced the septum with a greased glass stopper. We had to wire down all the attachments and the hoses to prevent any accidents. After that was done, we turned on the stirring mechanism on the hot plate, and turned the heating mantle on to 4. Once it started refluxing, the color of the solution changed quickly from clear with the white Cr(CO)6 floating around undissolved to a light yellow-green color:

Since we have been reading about these complexes, we have seen that they usually have a yellow or orangish color so this color change was a good sign! We left the lab on Tuesday night feeling pretty confident that we would just let it stir for 20 hours, and we would come back on Wednesday to a perfect product that we could purify and characterize.