Solvent Transfer Lab

In this lab, we followed a very explicit procedure in order to learn how to do a solvent transfer on the vacuum line. We made a THF complex with CrCl3. We put 0.1 mmol of the CrCl3 and a stir bar in a flask attached to the vacuum line. The flask was a two-neck flask with a septum in the other neck. We vacuumed the flask and then filled it with argon gas, and then repeated this cycle. We added 8 ml of anhydrous THF to the flask via the syringe through the septum. In a separate round bottom flask, we put 2 ml of chlorotrimethylsilane and attached this flask to the vacuum line. We degassed this flask by doing three "freeze-pump-thaw" cycles. To do this, we had to freeze the flask in liquid nitrogen:

We then turned the valve to "open" to evacuate the flask of any gas, and then closed the valve and let the flask to warm to room temperature. Once the liquid in the flask was unfrozen, we froze it again and repeated the process. This took a long time to do!

We then performed a vacuum distillation, in which we froze the contents of the two-necked flask in liquid nitrogen and then opened the two-necked flask to the vacuum manifold. We also opened the round-bottom flask to the vacuum manifold so that the two flasks were open to each other, but not to the main pump. We could see that the chlorotrimethylsilane was leaving the round-bottom flask and entering the frozen solution in the two-neck flask because the amount of liquid in the small round-bottom flask decreased as time went on.

Once all the liquid had gone out of the round-bottom flask, we let the solution warm to room temperature and observed the color change of the solution from a light pink to a dark pink color.

It was supposed to change from green to pink, but somehow our solution in the two-neck flask turned pink before it was supposed to (before we even added the chlorotrimethylsilane). We then removed any unreacted materials by opening the flask to the vacuum manifold. This was a very useful technique to learn, even though we didn't really see the color-change that we were supposed to in the reaction.