Wednesday, 23 February 2011

Midweek Blues

I arrived slightly later than I would have liked this morning due to the fact I may or may not have had one too many midweek lagers last night.
After a coffee (the Nespresso machine in our office has been taking a bit of a hammering this week) and still feeling slightly the worse for wear, I proceeded to start my day’s work. First up was a lithium aluminium hydride (LithAl for the British readership) reduction, a reaction that always works but is also always a pain to do. There just isn’t an interesting way of slowly adding powdered LiAlH4 to a THF solution of the compound in question over the course of half an hour or more and you definitely can’t do it too quickly for fear of getting boiling THF and lithium salts all over your fumehood. Anyway, that reaction was set up and heated to reflux for the majority of the day. I then set about working up some catalyst runs I set up yesterday. I somehow completely failed to purify anything in the first column I did so the other three I have to do were shelved until tomorrow when I’m hopefully in a better mood.

I brought my laptop to work this morning with the intention of spending some of my spare time writing up the experimental section of my thesis. I did not in fact manage any of this today but I did install a piece of software which I had never heard of, Mendeley. Essentially, it’s a reference organiser much like Endnote (a piece of software I never really got on with) which is really user-friendly with a lot of genuinely helpful features. Finally, and best of all, it’s completely free of charge. I recommend giving it a try if you are going to be writing a thesis in the next few years. 

Anyway, back to the chemistry. Having spent 20 minutes adding NaOH solution to my reduction, I then proceeded to go through the standard workup. Extract organics into diethyl ether, wash with brine, dry with magnesium sulfate and then filter and remove solvent. Easy right? I first proceeded to find the only blocked sinter funnel in the lab and attempted to use that. I then found the wettest sinter funnel in the lab and looked on in horror as my nice clear solution went decidedly cloudy on its way through the sinter. Drying it again and removing the solvent gave me something resembling pure product which I promptly left on my bench ready for tomorrow where I will probably throw it all over the floor and have to start over. It’s shaping up to be one of those weeks.



    syringe driver??

  2. Is there a particular reason for adding the LAH to the substrate...more conventionally you'd do it the other way round.

    I've always found that LAH pellets are much more reliable than powder. Reflux pellets in solvent for a while, till they're nicely powdered, then cool and add substrate dissolved in same solvent.

    I've heard tell of Mendeley; I'll have to give it a look.

  3. Next time you have to deal with LAH, try the Merlic work-up:
    also, Rochelle's salt solution is really helpful to dissolve Al salts!

  4. what Bartleby said- it's much easier to slowly add your substrate (via addition funnel or whatever) to a stirred solution of LAH.

  5. I literally have no idea why I wrote it that way round. What I in fact did today was add a solution of my substrate to a stirred suspension of LAH.

    One work-up which works quite well is adding a minimum amount of water to quench your reaction and then adding sodium sulfate and stirring for half an hour. Simple filtration then gives a dry solution. It's not great for large scale but on small scale it works a treat.

    As for LAH solution, the only thing I've used that for is to prepare alane (AlH3) by adding the solution to AlCl3. I think it's a bit expensive for everyday use!

  6. Sylvia Winstead19 July 2013 at 07:48

    There are things that we really find it hard to do while doing masters thesis and/or phd dissertation. But, in the end of the day, it was good that everything went well. Anyway, I do hope everything went well with your thesis. I know that you really did great for it.