Another Cr Arene Reaction

On Thursday 11-17-11 we stopped heating the reaction of 4-trifluoromethylaniline that had been going for four days. It was a reddish-orange liquid that was cloudy. We vacuum-filtered it to see if we could get a precipitate out of it, and we did get a large amount of a dark yellow precipitate:

The filtrate was still a little bit cloudy and was still a red-orange color and this is what we put in the IR to test:

The tabulated data said that there should be two peaks: one at 1977 inverse centimeters and one at 1898 inverse centimeters. Our IR showed two peaks that were almost exactly in these two positions, so this reaction was a successful one! That makes three successful reactions so far, and one that we have gotten peaks for but have no data to compare it to.

We decided to set up another reaction for fluorobenzene since we didn't get good data from the last time. We set it up the same way but we used different amounts of reactants, since we have found that we have a better success rate when we have chromium hexacarbonyl in excess. The only problem with this is that it collects in the condenser if there is excess, but we try and collect it after the reaction is done because it can be vacuum-sublimated and used again. Here is an example of the Cr(CO)6 collecting in a ring around the middle of the condenser:

This time, we added 8 ml of dibutyl ether, 1 ml of THF, 1 ml of fluorobenzene, and 1.018 g of chromium hexacarbonyl and began stirring and heating on Thursday afternoon. It turned a light yellow color:

For the rest of that day's lab, we worked on the Spartan calculations that go along with our project. Unfortunately, there is more to this project than just doing a bunch of cool reactions! Our question we are asking is: how does the identity of the arene change the nature of the bonding in the complex? We are going to use Spartan images to try and demonstrate the effects of electron-withdrawing and electron-donating substituents on the complex.

The heat on our reaction was a little higher than usual because on Friday the inside of the flask and halfway up the condenser was blackened, but the reaction was still refluxing so we turned the heat down and let it go over the weekend.