Jan 11, 2010

Microwave Chemistry

I just thought I would put down a few lines on some microwave chemistry and hopefully gain some outside views as well. This all comes from a paper that my old boss recently published in Aust. J. Chem. regarding some pretty neat synthesis of quinolones and napthyridones by using microwave irradiation to replace the original FVT (flash vacuum thermolysis) methods.

As an undergrad I spent my honours year pounding on the CEM Discover microwave unit and I am so glad I did. The reactions I did in the microwave (when they worked) were so fast and I did so many more reactions in so little time that it really didn't seem fair on the other poor undergrads, like MSG, who had to do the good organic stuff in the fume hood. I kind of regret it too as I didn't really learn all that much in terms of lab technique among other things. However, I still love to use the microwave as much as I can, which is rarely now :(.

The use of the microwave for reactions such as simple esterification of carboxylic acids is a good example of MAOS (microwave assissted organic synthesis). The reaction takes no time at all and workup is no problem. But sometimes you just can't get the results you want from microwave reactions either. For example, some researchers in the past use trusty old kitchen microwaves for their MAOS and unfortunately this made replication of their experiments quite difficult in other labs. The generation of hotspots in the rotating microwave ovens is virtually limited in units like the CEM but at the same time the CEM is prone to generating a lot of heat in a short amount of time and you can really nuke a reaction and expensive materials if you aren't careful.

Another interesting part of the CEM discover microwave is the nitrogen inlet valve for "power cooling" the concept behind this being that if you cool the reaction while irradiating it you can put more microwave energy (in effect a greater vibration of the molecules in the reaction chamber) into the reaction and therefore speed the reaction up. However, in my experience the heat of the reaction was required to have the reaction proceed. Anyway, I am keen to have any outside input made as to how anyone else uses the microwave for reactions as this was deemed to be "the way of the future" in organic chemistry but we are yet to see the full implement of microwave reactions in our lab and I sure haven't been reading all that many journals with MAOS included.


  1. That CEM has copped a pounding from me thats for sure. I had it heating 50 mL of toluene at 300W for 6 hours at a time. The machine always crapped out half way with power source errors. Eventually had to put in one of those carbide widget things because the dielectric constant of toluene is so crap.

  2. yeah you can also just use graphite powder but that stuff gets everywhere and is nowhere near as cool as a "Widget"

  3. Labchimp, I think I gave that CEM the most loving. Remember when I melted glass..

  4. TMTCl = trimethyltin chloride?

  5. interesting to know about the microwave chemistry, i did not know too much thing about it