Week 2 - Almost Up and Running

This week, I set up the practices I would need to run my experiments. On Monday, I created more MnO₂ and flash dried it to send off to the XRD. I also created known concentrations of 4-chloroaniline solutions to create a calibration curve for the HPLC. Unfortunately, I overlooked a key step in my experimental procedure. When I perform my experiments, the aqueous solution will be extracted from our extraction vessel and diluted to half concentration with methanol. This is because our HPLC runs with 50/50 methanol/water, and we want our sample to match our HPLC’s composition. However, this dilution also means that the actual concentration of the amine in solution will be halved when prepared for the HPLC. To counteract this, I simply need to create known aqueous concentrations for the calibration curve, and then halve them with methanol. This way, no extra calculations need to be performed. I forgot to halve the concentration of my original solutions for the calibration curve, and so had to remake these solutions later in the week.

On Tuesday, I corrected this mistake and prepared solutions of the correct concentrations, and created a usable calibration curve for our 4-chloroaniline experiments. I then created more MnO₂ for use in my experiments. On Wednesday, I was able to run my first reaction experiment. Unfortunately, this wound up being more of a trial run than an actual experiment, as I needed to refine a few techniques. My experiments involve preparing a solution of known concentration MnO₂ in buffer in a sealed reaction vial. Then, the amine of interest is injected at a known concentration and constantly agitated. At specific times, a sample is drawn out from the reaction vial, and then pushed through a filter into aliquots for the HPLC. The filter removes the MnO₂ from the solution, and ensures the oxidation reaction stops, allowing me to accurately measure amine concentration against time. This relationship of concentration versus time will allow us to characterize our reaction’s kinetics.

It took me all Wednesday to perfect the techniques used in our experimental setup, so I ran my first true experiment on Thursday. The experiment ran smoothly, and I was excited to see our results. However, the results were highly perplexing. At the first time point, one minute in to the reaction, the HPLC showed no 4-chloroaniline left. This was confusing because I had run our experiment at conditions similar to those we had studied in the literature. None of those papers suggested the reaction should have run to completion in less than one minute, so I knew something unexplained was occurring. I respiked the reaction vessel with the same amount of 4-chloroaniline, but again, the HPLC recorded no 4-chloroaniline at one minute. At the end of the day, I added 4-chloroaniline to the reactor again, but at an order of magnitude higher concentration than I had injected earlier. This finally showed a signal at the one minute mark.

Another researcher had the HPLC reserved for Friday, so I could not run additional experiments to compare to Thursday’s results. I spent much of Friday preparing stock solutions of future amines of interest, and generally getting my supplies cleaned and ready for future use. Next week will be interesting as I try to puzzle out my results.