Characterization of para-phenylenediamine chromium tricarbonyl

On Thursday 12-1-11, we tested our final complex to see if we formed the desired product. The solution, which turned yellow after we began heating, was now a dark brown color that had a dark brown solid in it.

 (at beginning of reaction)

(after reaction was completed)

We vacuum-filtered the solid out of the liquid and tested the liquid in the IR. We didn't really get any peaks with the liquid, so we decided to test the solid. There were a couple of small yellow crystals in the dark brown solid which led us to believe that our desired product was contained in the solid. 

We had the idea of extracting the solid with methylene chloride four times, and we did this by mixing all of the solid into about 20 ml of methylene chloride and then vacuum-filtering out the remaining solid that hadn't dissolved in the methylene chloride. We added the remaining solid to another 20 ml of methylene chloride and repeated the process twice. We could tell that it was working because the methylene chloride turned yellow as we did this, and the amount of solid lessened with each extraction.

We added a boiling chip to the extracts and reduced the volume until there were only about 5 ml left in the hopes that this would give us more intense peaks. When we tested this liquid in the IR, there were very small peaks that correlated almost exactly to the literature values for this complex (we had 1954 and 1862 cm-1 while the literature values were 1954 and 1862 cm-1). We could then consider our final synthesis a success!!

For the last week of the semester, we worked on putting all the aspects of our labs and our project together so that we could present them in one portfolio. Overall, we had an awesome semester! We learned a ton of new lab techniques and worked together to make our project a complete success, with 6 out of 6 complexes synthesized. We got to see a variety of different inorganic compounds (all pretty colors, of course!) and we developed a new appreciation for organometallic compounds such as our Cr Arenes. We in Purple Chrome wish that you could have as much fun reading this blog as we had doing the experiments we wrote about!

Final Cr Arene!

On Tuesday 11-22-11 we tested the fluorobenzene chromium tricarbonyl that had been reacting for 5 days. We were a little apprehensive because this is what the flask looked like after it had burnt the preceding week:

When we took out the stopper, there was a greenish liquid in it, and there also looked to be a precipitate in it. We took out some of the liquid and tested it in the IR. The tabulated frequencies were 1982 and 1903 inverse centimeters. We got two peaks in the IR; one was at 1913 and the other was at 1985. These were so close to the tabulated data that we considered this reaction a success! We then vacuum-filtered the product to separate the liquid from the solid. The liquid was actually a dark yellow-green color once the precipitate was taken out:

The precipitate was light green in color, and we kept it in case we had time to recrystallize it and get pure crystals:

There were insoluble black specks in it like there were in the benzene chromium tricarbonyl, but we got rid of these easily when we dissolved the solid in methylene chloride to recrystallize it.

The next Tuesday (11-29-11) we set up the reaction for our last Cr Arene. This time, the arene was para-phenylenediamine. Since nitrogen-containing groups are electron-donating and this one has two amines on it, it shouldn't take very long to react!
We set up the two neck flask and gas condenser like all the other experiments, and vacuum-filled and argon-filled it. We added the solvents (10.1 ml of dibutyl ether and 1.05 ml of THF) to the flask through the septum and then we bubbled argon through the solvent to remove any oxygen. Since the para-phenylenediamine is so reactive, we needed to make sure that we had a completely inert atmosphere for the reaction. To do this, we cut the end off a syringe and stuck it into a tube attached to the vacuum line. Then we opened the gas valve and allowed the argon to flow through the syringe needle. We placed the syringe needle into the solvent and then added an exit needle to relieve the pressure (we had to close the stopcock on the gas inlet valve in order to get the gas to bubble in the solvent because the incoming pressure was too much, so we needed to have some way for the extra pressure to escape). We let the gas bubble through for 10 minutes and then we removed the exit needle and the syringe.
We removed the septum and added a stir bar, 0.330 g of chromium hexacarbonyl, and 0.160 g of para-phenylenediamine. We placed a greased stopper into the neck and began heating and stirring the reaction. We are going to leave this one react for two days because we can check it Thursday during lab, which will be a little less than 48 hours. As soon as the reaction reached reflux, it turned a bright yellow color, like many of the other reactions before. Tomorrow we get to check it out and see if we were successful for our final reaction of the semester!

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.

Purifying our Wild Card Project

On Tuesday 11-15-11 we purified Part A of our recently redone Wild Card Project. Where the last time, we just poured the 5 20-ml portions of methylene chloride over the green solid while filtering the whole time, this time we decided to stir the green solid into the methylene chloride and then vacuum filter the solution to get the undissolved impure solid back out. We then replaced the filter paper with a new one and put the left-over green solid into another portion of methylene chloride. We vacuumed it and repeated this process for three more portions of methylene chloride. We knew we were dissolving the green solid in the solvent because after we were done extracting it, we had very little of the green solid left so most of it must have gone into the solution which was now yellow. We then added a boiling chip to the solution and heated it until most of the solvent evaporated.

Once this was done, we stuck it in an ice bath and hoped that we would see some crystals forming. The last time, this didn't really happen so we were hoping that we would get lucky this time! There was some solid in the beaker and we let the rest of the methylene chloride evaporate off so that the crystals would form. We finally did get a slightly shimmery yellow-orange powder that we figured was our pure product, and we got a lot of it, so we don't have to worry about not having enough to run tests this time. Here is the pure product:

The melting point of the pure product was 198 degrees Celsius. The melting point of Part B of the Wild Card was slightly lower at 140 degrees Celsius.

Wild Card (again) and A New Arene

The next lab day, Thurday 11-10-11, we decided that Purple Chrome needed to divide and conquer. Elom and Allen worked on redoing the Wild Card (both parts in one day...ambitious!) while I (Emily) set up a new Cr Arene reaction. First up: the Wild Card.

The procedure we followed was the same as the one that we followed for the previous experiment with a little bit of creative tweaking. The masses of ruthenium chloride, diazald, and triphenyl phosphine were all the same as we used before. The Diazald from Part A was not dissolving, so an extra 6 ml of ethanol was added to the solution. Part A went very quickly and we ended up getting the same green precipitate as we did the last time once we cooled the flask down to room temperature. Here it is, just filtered out of the solution:

We took this as a good sign that this was actually what we were supposed to get, because we reproduced the same result as we had the last time we did it!

Extra ethanol was also added to the solutions of ruthenium chloride and Diazald in Part B of the experiment to get them to dissolve, so we had a lot more solution than we did the last time. Everything went well until we got to the part where we had to add the triethylamine to the solution until it turned a deep purple color. This was REALLY hard to see the last time, and this time was no different. We added the 1 ml that it said in the book, but the color that it turned did not look that purple. It looked more reddish-brown than anything.

How are we supposed to see a change from dark brown to deep purple? We thought that maybe this time we needed to add more triethylamine, so we added 4.5 ml total this time, which was 3.5 ml more than we added the last time. We also gave it an extra 5 minutes of reflux time because of all the extra solvent in the flask. When we let it cool to room temperature, we had hardly any precipitate at all! We had a couple flecks of the same coppery solid as we did the last time, as well as an unknown lump of black (possibly burned) solid. Thank goodness we still had a lot of the precipitate left from the first time we did it, so we can use that. We will have to do IRs on these to see what we got, and hopefully we get better results than we did the last time!

Now for the Cr Arene reaction:
The next arene we decided to do was 4-trifluoromethylaniline. The reaction hints for our project indicated that this one might take 2-4 days to react, so we set it up on a Thursday so it could run all weekend. We set up the flask and did the vacuum/argon-fill as usual. We added 8 ml of dibutyl ether and 1 ml of THF to the flask. Then we added 0.4 ml of the arene and 1.079 g of the chromium hexacarbonyl. We started stirring and heating that day, and it turned a light yellow color:

Overnight, there was a collection of yellow in the condenser and it looked like the reaction might be losing some solvent from the level of liquid in the flask. We shut it off over the weekend, and then the next Monday we added 2 ml more of solvent and regreased the connections in the setup. The reaction then was heated non-stop until Thursday afternoon (11-17-11).

Next Arene: Fluorobenzene

On Tuesday 11-8-11, we started another reaction for our project and this time the arene was fluorobenzene. We chose this arene because we read that electron-withdrawing substituents (such as fluorine) on the ring will make the reaction proceed more slowly, and can sometimes stop the reaction from happening at all. From what we saw, one fluorine on the ring would only make the reaction a little bit slower, so we decided to try it. We found a procedure for the reaction that used large amounts of all the reactants, so we scaled it down to fit with the microscale approach we were taking to the project.

We set up the flask and did the vacuum/argon-fill procedure again, the same as all the ones before.

We added 10 ml of dibutyl ether and 1 ml of THF to the flask via syringe through the septum, and then we took the septum out and added 1.67 ml of fluorobenzene and 0.167 g of chromium hexacarbonyl to the flask. We started heating it and stirring it and let it sit overnight because the procedure we found said to let it heat for 24 hours. It started turning  green and there was a little bit of green solid that formed on the bottom when we started heating it:

We have found that the color change to green or yellow is always a good sign in this reaction!
We let it run for 24 hours and then tested it, but the IR didn't have the characteristic peaks of the solution. It may have been because of the IR which has been on the fritz lately, but more likely it was because it didn't have enough time to react, so we decided to try this one over again once we got a few more reactions done that were successful.

We also tried to get IRs for the Wild Card Project on this Tuesday, but we couldn't do the KBr pellet method, so we had to try dissolving the solids in something that wouldn't show up in the IR. We tried both of them in methylene chloride, but we didn't get anything conclusive from the IRs. Unfortunately, we didn't have a lot of solid from Part A in the first place, and after this we completely ran out. We decided that we would also do the Wild Card Project again to see if our yield was better for Part A (and to also see if Part B would still yield that coppery precipitate or if it would actually give us a gray precipitate like it says in the book!).

Since the IR wasn't being very helpful in our characterizations, we spent a little time trying to see if we could get GC-MS for two of our Cr Arenes (N,N-diethylaniline and methyl-3,5-dimethoxybenzoate) and the two parts of the Wild Card. Unfortunately, we ran all four samples twice, but we didn't get any conclusive peaks in the GC-MS. When we consulted Dr. Daryle Fish on this problem, he told us that maybe the products just weren't volatile enough to get good data from the GC-MS. This was a little bit of a waste of time, but we got to learn how to set up a method in the GC-MS that is tailored to our specific sample, so we did learn something useful that day!

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.