Friday, May 30, 2014

Rene Peters Date of birth: August 26, 1971 Position: Professor, Institut fuer Organische Chemie, Universitae t Stuttgart

Well, it was either do a post on one of these foolish author profiles, or read the other review in this issue, which was an Janus structures, but I decided I needed some desperate brushing up on organic chem instead.

Let's see here... well, this author is Western since in his picture he is not wearing a tie and looking official and determined like the Angewandte profiles of the Chinese scientists. Also, obsessed with wolves and dogs that are similar enough to wolves (his husky). I can't really share anything there since a wolf is just some pack mammal that spends most of its life cold and hungry and being beat up by the Alpha, unless it is the Alpha and then it has to suffer constant psychological stress of keeping the others who want its job at bay. Nothing against pack animals. Humans are also pack animals, but at least we figured out a way to have a constant food supply and to hear our homes reliably. At least this time around they didn't ask him what piece of equipment he would be, although I suppose what car would you like to be is also not much of an inspiring question.

Still, this profile is a bit better than the Kim one from last week since you do get some very small insights into the person. I find the music and literature questions to be the most useful. However, since I don't know how music is tied to anything, I leave that stuff for others, especially when answers are Ozzy Osbourne and Concert Pianist, though I did have an image of a scene from 'This is Spinal Tap' after that one. The books are a great one since 'War and Peace' and 'Perfume' are highly philosophical works, where the first one describes people trying to find personal meaning in events that are greater than them and that sweep them along, and the second one is basically a parable from the early 20th century history and the relationship of society to a genius personality, despite it taking place in 17th century France. After all, Grenouille was a genius in creating perfumes and despite his personal inadequacies and repulsion felt towards him, all his mistakes and crimes are forgiven when people smell one of his inventions. So, Haber is forgiven for creating poison gas for use during wartime because he invented the ammonia synthesis process and was a chemistry genius, and this could explain how Germans were so enamored with a certain personality in the 1930s who was a political genius and turned the country's economy and pride in itself around, with many reasonable people ignoring the less palatable parts of his policy.

Well, I still don't know anything about Rene Peters really, except that he likes to read good literature and reading. And by the way, you should Read 'War and Peace' and 'Perfume' as well. Certainly beats setting up another experiment after a 10 hour workday. You're probably tired anyways and you will forget to add something and it will fail anyways. Might as well read 30 pages of 'War and Peace'.

Donor-Acceptor Cyclopropanes

Now this one is not my area of expertise... but it's closer than carbon-fibers, though due to my last job that could be a little debatable. The background for the review is laid out very nicely in simple terms in the introduction, namely that a cyclopropane has a lot of ring strain, and reactions that open up the ring or expand it are thermodynamically favored. Nonetheless, it's quite a stable motif and in general it's hard to to get a simple cyclopropane to react. However, when one carbon is substituted by an electron accepting group, and another one by an electron donating one, then you can draw convincing zwitterionic resonance structures with the ring being open, and now, it's a lot easier to get things to insert inside like a double bond, a keteone, a nucleophile, or an electophile. The possibilities are many and after a very nice introduction, the review quickly delves into the details one well organized topic after another, based on the substrate. It's the donor-acceptor motif that makes cyclopropanes such a powerful precursor for making large ring structures. The use of chiral ligands for a catalyst that can further activate the acceptor gives access to enantioselective transformations and you can obtain something that looks like a complicated natural product from something that looks like a deceptively simple cyclopropane.

It did remind me of my undergraduate organic classes, about how you could certainly memorize the reactions, or you could try and push the electrons around since all of organic chemistry is basically about adding an acid to a base. For the latter two substrates mentioned above, the nucleophile will attack the more positive site on the resonance structure of the donor-acceptor cyclopropane, and hydride transfer will occur to the more negative site to complete the reaction. Even though the products can get pretty complicated, and you often need a pen and some paper to scetch out the right product, it's pretty easy to figure out the mechanism and what is happening. It can get pretty complicated to follow in your head once you get one catalyst activated cyclopropane opening up and inserting into another one, and even though the review does give some intermediates (and in the case of that reaction it is essential to draw one intermediate), you really have to draw it out yourself on paper to see how to get from the starting materials to the product based on which partially negatively charged carbon attacks the partially positive charged carbon on the other cyclopropane.

So, going through the review was a bit hard at first, but eventually it all started to click in my head and I was following electron movement and even the most complicated transformation became easy to follow. That why, despite the awesomeness of the review, Section 3.3. and Scheme 14 is the part that stands out where I got stumped. This is on cycloadditons of alkenes to a cyclopropane to make a five membered ring. There a tin catalyst is used and if the aryl substituting one of the cyclopropyl carbons is electron donating, you get one regioselectivity, but if it's not you get another. I really got stuck on this for a while, because the scheme was suggesting that electronics are a factor, but the aryl is always the electron donating group no matter what the substituent, compared to the acceptor that has two CO2Me groups... surely it is sterics which should be the driving force for the product here? And the scheme doesn't mention the subustituents on the alkene and I was too lazy to look up the original papers... Anyways, I decided that since you get the other product at -30 degrees, then that's where sterics predominate, but it doesn't help that in that case the aryl can't be too donating as well, since you lower reactivity of the cyclopropane. The moment you increase it a bit, you only get the other isomer (even at -30 I assume?). Well eventually, I decided to move on, since thinking about it too much would lead me to look up the original paper and I did mention that I was lazy above. I suppose that my reading through of giant reviews on topics that are not related to mine is not laziness then. Maybe masochism of some sort? Doesn't feel exactly like that though...

Anyways, cycloaddition of nitrones and allenes got me back in the mood, and I found Scheme 15 to be particularly elegant (right below that Scheme 14 that stumped me for a bit). You get a really cool and complicated bicyclic structure of just a plain old cyclopropane with an intermolecular allene addition based on the conditions. The ring enlargement section 4, and especially 4.3, shows how you can get something that really looks like a natural product from a cyclopropane in Scheme 24. It's all really impressive actually, and as the authors mention, a lot of the results are really recent as the field is undergoing a Renaissance. Plus, there are still not many results about making six and seven membered rings (even though there was a section about 3+3 cycloaddition). However, one minor quibble which is very much evident in that last Scheme 24 that I spoke just so glowing about at the start of this paragraph, is that cyclopropanes like compound 115, which lead to complicated products such as 120, are themselves sort of complicated. I'm not disputing that the reactions are very elegant and you can get complex products with lots of stereocenters under mild conditions through the judicial use of catalysts, but, you know. 115 looks really hard to make on its own. Plus a lot of these really complex transformations need an acceptor, which in most of the cases is two CO2Me groups. How are you going to get rid of these methyl ester groups if you don't want them in your final product?

Maybe new ways of making cyclopropanes from metal carbines will become a really hot field in the future and my point will be moot. Or maybe I don't know enough about organic chemistry and it really is not a problem to have all these strange acceptors hanging off of your final product. Whatever the case, I have really enjoyed reading this review and it definitely revived some atrophied part of my organic electron pushing brain mass. Kudos to the authors, a recently tenured German professor and two of his students. I will definitely not be dissuaded to look at paper after I see an abstract with some cyclopropane, a few lines, and some crazy looking complex product, in the future. After all, it's only a simple Donor-Acceptor cyclopropane reaction.

"A New Golden Age for Donor–Acceptor Cyclopropanes
Tobias F. Schneider, Johannes Kaschel, and Daniel B. Werz"

DOI: 10.1002/anie.201309886

Wednesday, May 21, 2014

Dongho Kim
Date of birth: November 1, 1957
Position: Professor, Department of Chemistry, Yonsei University

After that really long review on carbon fibers, that still invades my dreams (well, I hope not, but my waking thoughts from time to time anyways), I need a break post and that's provided by the 'biography' of Dongho Kim from the same issue. Now, Angewandte biographies are all professional and you don't really learn anything about the person, like what it was like to study chemistry during the time of dictatorship in South Korea and the threat from the north that was credible at the time. Sometimes you get something interesting in regards to how the person chose to go into chemistry and later become a professor, but most of the time not really, and that's the case here as well. I'm pretty aware of the dissonance between useless anecdotes in a general Angewandte biography and a person's real-life experiences from the coverage of my post-doc advisor.

Nothing too interesting here, and the answer to 'what you would like to be if you were a piece of equipment' really nails the lack of useful anecdotal information here. If someone ever asks me that, I will tell them "I would like to be a $*^#ing futuristic android. So that I can do everything I do now but better and I will never die, and you would be afraid of me."

Anyways, Monet and Beethoven might be the staple of any Western oriented education for the upwardly mobile... but what's really interesting is the 'going hiking in a spare hour'. Really? I hike a lot and a one hour hike is not a real hike. And there is no way you're going to be drinking a beer after a long desert or mountain hike that took most of the day. It will destroy you.

It doesn't sound like a hike... but like a pleasant stroll. Still, this made me look up Yonsei University in Seoul on Google Earth, and it does have a pretty large forest park next to it and the pictures from it are pretty nice. So, I'm willing to believe that professor Kim goes there in a spare hour, but it's still a stroll. Not a hike.

DOI: 10.1002/anie.201311143

Tuesday, May 20, 2014

Carbon Fibers: Precursor Systems, Processing, Structure, and Properties

  1. Dr.  Erik Frank, 
  2. Dipl.-Chem. Lisa M. Steudle, 
  3. Dr. Denis Ingildeev, 
  4. Dipl.-Chem. Johanna M. Spörl and
  5. Prof. Michael R. Buchmeiser*  
Angewandte Chemie International Edition
Volume 53Issue 21pages 5262–5298May 19, 2014

This topic is completely outside of my area of expertise. I bet I'm going to be starting many a post with this sentence on this blog, so it seems like something appropriate to start this blog with. But yes, carbon fibers. The picture that first popped into my head was a string of something made out of stretchy carbon, like a polyethylene bag, but spun into some sort of fibers to make a sweater. The first sentence of the review mentions that these are things that are 92% at least made of carbon and later it's mentioned that they can be incorporated into textiles, so I was on the right track, if not completely wrong in the end anyways.

  1. I made a point of not checking the Wikipedia entry on 'carbon fibers' until after finishing the review. But maybe I should have since it complements the article very well, especially in terms of polyacrylonitrile (PAN) that is used for making most of carbon fibers today.
So carbon fibers. Basically you take an ordered material, such as PAN, or some sort of tar pitch that is sort of polymeric, or even cellulose, and as I learned at the end even polyethylene. Now you have to spin this material into fibers with a big spooling machine, and the way this is done, with solvents, with additives, or without all that, and depending on the shape of the vessel and the speed of the spinning, will give you fibers that hopefully won't fuze together at the end. Afterwards this material is heated until heteroatoms are lost and you're mostly left with carbon. Then the temperature is increased to as much as a couple thousand degrees Celsius in order to turn the stuff into a material that is mostly graphite, but is sort of bent and has some hole features. That turns out to be key in fibers having these high tensile strengths. They end up being used in composite materials with plastics and make them much, much stronger.  

The review is very detailed and goes into the steps that are needed to turn PAN into a cyclyzed and dehydrogenated polymer that is ready for carbonizing… but then you have to oxidize it or the carbonization process won't take place properly. The oxygen leaves with some hydrogens and also helps HCN to leave (getting rid of that pesky nitrogen part and getting the carbon content high). Sounds like an enormous industrial undertaking, and it was, as you start realizing as you go through this 30 page review.
PAN precursors very were successful, but people are always interested in using renewable sources (such as pitch from coal… okay maybe not that section) such as cellulose. It turns out that cellulose needs to be spun very orderly before carbonizing to have a chance and it still doesn't compete so well with PAN (has anyone tried chitosan?). Lignin sounded like a better plan to me by the time I got to that section, since lignin has less heteroatoms to start with and seems to me to be better set up for carbonization than cellulose which really loses a lot of weight as CO due to the high oxygen content. However, lignin gave really bad results and was a big disappointment in terms of the section as well. It sounded like reminiscing by the primary PI with no pictures and anecdotes with paragraphs that took up half a page or more. This section almost killed me with its writing style and practical failures. That is, until I made it past it and got to the PE section where the results seem to be a bit better. Plus PE allows to make carbon fibers with weird shapes…

One thing I forgot to mention is that obviously carbonizing this stuff in an oxygen atmosphere is not done too often since your carbon will burn and fly away as carbon monoxide or dioxide, and the atmosphere affects the graphitization of the fibers. The last section is actually pretty fun and it talks about the structure of the final stuff with some pretty hypothetical schematics of what they look like. Plus, I realized that Raman spectroscopy is a good way to determine the level of carbonization and that it's possible to take an X-Ray of a carbon fiber… but solid state NMR with magic angle spinning still sounds (and looks from the date in the review) more reasonable.
I don't have any wish to make my summary of this 30 page review to get to record proportions, especially since this is my very first post. So… in the end, if you don't know much about carbon fibers, you're probably better off with reading Wikipedia. You will definitely learn more from reading the review and it will definitely be more memorable. But, you know… 32 pages. They really went overboard in some places, and especially in that lignin section. Still, I bet it's a useful summary for the many excellent scientists in industry, and some in academia I guess, who are working in this very important area that I am ashamed to say I was ignorant of before.
I do not check the biographies of the authors before finishing the review. That way lies madness, and by madness I mean time-wastage. Afterwards, I checked and it's a PI with two students, and two people who work at a specialty institute for carbon fibers. They are Germans, which sounds about right as this is one of those countries (along with the States and Japan like I learned from the review) that are capable of funding these huge research efforts into these products that have very clear industrial applications but require a lot of development.