Foreign Perspectives

Somehow we’ve reached the final day in the lab. This is when a lot of people realise that we should have been a bit more organised earlier in the week and be much further on than we are right now.

As we’ve moved through the steps in the preparation, the quantities and yields have dropped somewhat. The 100% return from the phosphonium salt was the best, and by the third second stage of the main line of the experiment I’m down to 27%. Not disastrously bad by itself but since the final stage of the experiment in the afternoon has a much, much lower yield I eventually found myself with just enough product to put through the IR and GC and put everything left into the NMR with fingers crossed that it was enough.

In practice a number of people didn’t manage to complete the final stage and some others ended up with nothing so having enough to test was a plus point. As one of my fellow students pointed out, it would have taken the moths a serious amount of time to produce even that amount.

The evening session was to allow us to prepare our presentations but after a long couple of days the numbers dropped quite quickly and I ended up with only a draft of the first slide and the IR analysis of the second so it’ll be an early start to get the presentation done in the morning. To give me a bit more time with that, I packed the case tonight.

Everyone was much more organised today and acquired the various items quite early on so there were quite so many delays in trying to track down stuff for each stage of the experiment. Just as well, since as the morning progressed those on option A or B were once more working on the same methods albeit with the option A people slightly ahead of the game as the overall process was quicker.

My set-up started to look more like a “proper” chemistry experiment as the clear liquids and white solids were replaced with a range of different coloured ones culminated in a thick black oily gunge in my case. No more of the four hour breaks today and instead it was fairly constant activity.

No tutorials tonight as it was the SXR344 pub crawl around assorted York bars with the last stragglers returning well after 1am.

Tuesday was a leap into unknown territory as we were all working on our own experiments. Having 44 separate experiments running rather than 22 made for a lot of slowing down as we all fought for the same pieces of glassware, chemicals and time from tutors and the York lab people. The net effect was that I didn’t get underway until rather later than anticipated.

To start with I was one of those using the “option A” method for the first stage of the experiment. That in itself was something of a challenge as it required rather larger than usual quantities of reagents with volumes measured in litres and made it feel like a small industrial process rather than a teaching lab scale. We originally thought that we’d be fighting over the two litre flasks at the end of the first stage but in practice our staggered starting times meant that it all went quite smoothly. This particular option is a little peculiar as once it gets going there’s a four hour reflux period followed by a flurry of activity and it’s done; the other option needs a good deal more constant attention. Overall, this option fits quite nicely into the day so, in principle, could be completed in one day.

That four hour break means that you can get going on preparing the phosphonium salt. This needs a little more thought as the salt you need usually isn’t the same one as you prepared earlier in the week so I needed the hex rather than pent variety; not everybody noticed that though. If you were really organised you could probably get that salt prepared on Tuesday but I think most people were working on it into Thursday morning. It would be worthwhile to try and get it done the first day as otherwise the final day can be quite hectic.

The evening tutorials covered how to write up a lab notebook which was quite different to my style for sure although I had good comments back on the first notebook this morning. Also covered or rather not covered was the EMA: we don’t get that ’til the last practical session is completed so don’t know what we’re aiming for yet.

Things kicked off much quicker this morning as we’d already checked all the glassware yesterday and we’d a better handle on where things were and what to do with them.

Starting with the carboethoxymethylenetriphenylposphorane that we’d made yesterday the plan was to prepare our alkene using ethanol as our reagent (the others starting from the same product used different reagents). There would have been more time between steps today but we were performing a direct synthesis and one using competing reagents so the second synthesis filled the gaps in the first which made for a very full day.

Reaching the end of this stage of the synthesis meant that it was time to analyse the end product using NMR spectroscopy, Infrared spectroscopy and gas chromatography. In practical terms, few people managed to complete the analyses as the various tests weren’t run until quite late in the afternoon so there wasn’t much time to do the analysis before we had to hand in our lab notebooks for assessment. Yup, on this course they actually do check your lab notebooks. This first assessment doesn’t count towards the final mark though and it’s intended to give us pointers as to how to do better when we’re writing up the second lab notebook which does count towards the final exam.

Tonights tutorial discussed our overall results as we’ll need to know how best to make a double bond that’s either E or Z. Also, we’d to pick which of the three substances we’d like to have a go at preparing (queen substance, farnesol and an insect pheromone). We’re going for the pheromone basically because loads of people started off choosing the  queen substance and farnesol is covered in some detail in the pre-course notes already.

Catering-wise, the lunch lets things down and the breakfast and dinner are excellent.

The day got off to a relatively slow start as it took quite a while to check that we’d all the various items of glassware on the checklist and that they were clean.

Our first experiment was to prepare carboethoxymethylenetriphenylposphorane from carboethoxymethyltriphenylphosphonium bromide. That requires a fair number of steps and helps a lot in getting back into the swing of practical chemistry with steps ranging from the simple dissolving of various chemicals, handling assorted chemicals that are toxic, irritants, flammable or indeed all of the above, separating out two different layers of chemicals, evaporating to get rid of solvents and finally weighing what you’ve made to see how efficient your methods were. Along the way, we picked up where the various solvents and reagents were in the lab, built increasingly fancy structures with the clamps, wrote it all down in a lab notebook and finished up with an overall yield of 87% which is pretty amazing. Since we weren’t fully up to speed that ended up taking most of the day and was quite a busy one.

All of us doing the stabilised Wittig procedure followed the above starting approach but we broke up into about half a dozen separate teams later in the afternoon as we used a variety of different reagents to make our alkene.

Catering-wise, the breakfast was excellent with a full English breakfast cooked quite nicely. Lunch was a bit of a let-down as it’s just sandwiches with tea/coffee. The evening lectures were optional with one on interpreting NMR spectra and the other on retro-synthetic analysis (which went way too quickly over the material for me so it’s just as well that the notes will be on the forum in due course).