One last trick for this *%$&ing Grignard reaction. Sonication is sometimes used to activate the magnesium surface. Ultra-high frequency sound waves are pulsed in a small pool of water. The reaction vessel is submerged in the water and the sound waves cause small bubbles on the surface of the magnesium. These bubles collapse with considerable localized force, and in an ideal situation, activate the surface of the metal. I'll cut to the chase and mention that this did not work either, frustrating me to no end. I am done with Victor Grignard and his ways.
Just because I am giving up on the Grignard reaction and Rieke magnesium does not mean I am admitting defeat here. The magnesium complex was never an object of attainment, merely a means to an end. The object is to get cobalt on the ligand in a high-yielding manner under reasonable reaction conditions; I simply need to try new means to achieve my end. Next up? We run kitty-corner on the periodic table and pound the ligand with a little lithium.
Showing posts with label research trial. Show all posts
Showing posts with label research trial. Show all posts
February 18, 2009
February 11, 2009
Teflon tape to seal joints
I wanted to find a way to reflux under inert conditions without drawing silicon grease into the reaction flask. I tried using some Teflon tape in between the joints. This sort of worked, but sort of didn't. When I tested the the seal it held better vacuum than ground glass on ground glass, but unfortunately it was not as good as a greased joint. I tried to make a better seal with a little more pressure. With enough pressure the tape in the joint became translucent, looking as thought it almost would form a perfect seal. With a little more pressure I cracked the glass into millions of little pieces, cutting my hand in several places and making a mess of tiny glass shards in my hood. I do not recommend this method.
January 19, 2009
Grignard Reaction
François Auguste Victor Grignard enjoyed his heyday in the late 19th and early 20th centuries. In his spare time, when he and Franz Haber weren't trying to figure out how to kill each other with phosgene, he played around with Mg and halogenated reagents. The ubiquitity of this reaction is attested to in the quote "...every chemist has carried out the Grignard reaction at least once in his lifetime..." by M. S. Kharasch and O. Reinmuth in Grignard reactions of Non-Metallic Substances (Prentice-Hall, New York, 1954). It was true in the '50s and is still true today. Although the Grignard reagent is a very useful synthetic tool for organic chemistry, it is actually most chemistry student's first attempt at becoming an organometallic chemist. Things usually go poorly, in part because the TA's are organic chemists themselves, ill trained at how to handle the air and moisture sensitive reagents, but mostly because the organic chemistry laboratory is ill-equip to handle such sensitive manipulations. These experiments, often set up for failure, are the last of many student's attempts to become interested in organometallic chemistry. This is unfair, due mostly to the great amount of voodoo required to get a desirable reaction in the first place.
I have spent a considerable amount of time recently trying to make my ligand into a Grignard reagent so as to assist in metallating with cobalt. Things have not been going well. This reaction has been attempted at least 10 times now with varying levels of success. The two most successful attempts have occurred January 6th and previously on December 8th. Suspiciously, these days coincided with a moon phase of waxing gibbous. I am not proposing that the phase of the moon determines the outcome of this reaction, but I am not willing it rule it out yet either.
The typical reason for a Grignard reaction to not proceed as desired is a lack of "activity" of the Mg. This is usually directly related to the amount of exposed surface area of Mg in the zero oxidation state. The same principle is true of making contacts in electronics; anyone who has torn a flashlight apart can see the contact where the circuit of the battery is completed. If the contact is dirty (black copper oxide or green copper carbonate) one need simply rub it with some sand paper to expose the copper metal in order to make a good contact. Several tricks for activating Mg turnings have been tried in the work I'm currently attempting.
Pre-treat the Mg: The Mg turnings which exist in our storage cabinet turned out to be pretty awful and disgusting. I wish I had noticed this before I started to use them, but hopefully you can learn from my mistakes. Not really knowing what pure, uncorroded elemental magnesium should look like, I thought the Mg was clean enough, and nothing a crystal of I2 couldn't take care of (see below). Simply looking at a metal to judge the level of corrosion is like having perfect pitch. Some people think they can sing a C note on demand but few people actually can. The safe bet is that any metal which has been sitting around has some tarnish or corrosion to it. I washed a portion of the Mg with 1 M hydrochloric acid to shine it up. This is an exothermic reaction which gets pretty warm (and also evolves H2 gas) so I had a bucket of ice water nearby just in case. After that I gave it a few thorough rinses with deionized water and then anhydrous diethyl ether. Just to be sure this stuff was dry before I took it into the Ar box I left it under vacuum in a sand bath at 130 C overnight. The difference is pretty clear. On the left are the Mg chips as they were in the store room. On the right are the same chips after washing. Like I said, I'm embarrassed to admit I even tried using the unwashed chips. At the time I thought this hadn't worked. More on that later.
I2 crystals: The typical activation reagent used in Grignard reagents is to add a small crystal of iodine. Iodine is used because it is a solid at room temperature, so it is easier to use than bromine or chlorine, although these would presumably have the same effect. The iodine reacts easily with the surface of the magnesium, and after the small amount of I2 is consumed, fresh Mg surface is left exposed to react with your halogenated reagent. Small amounts of preformed Grignard reagent are sometimes used in this same manner, although I did not attempt them myself with this reaction. After using I2 I was still isolating protonated reagent at the end of the reaction, which at the time made me think I was getting some water into the reaction somewhere. I was also having reactivity problems. As I followed the reaction by NMR I noticed that the Grignard product was slow to form, and soon after it did I would see the protonated product.
Heat: In order to speed things along I was heating the reaction and using THF as a solvent so that I could use higher temperatures. (Diethyl ether is the typical reagent, but THF boils about 30 C higher.) Heating a Grignard is not usually advised, as the formation of Grignard reagents is usually exothermic, and therefor performed at room temperature or sometimes in an ice bath.
Drying/Activating Mg: Frustrated with the prospect of water somehow getting into the reaction, I decided to use a qualitative indicator to ensure everything I was adding to the pot was dry. I made up a soluton of sodium naphthalenide. (Simply 1:1 Na metal and naphthalene in THF, about 0.1 M.) After stirring for a few hours all the water will have reacted with the Na and the solution will be dark green. I slowly added the dark green solution to Mg chips stirring in THF until the reaction solution remained pale green, indicating that the Mg was activated and no water existed in the pot. This still gave me slow reactions, and after heating protonated product was still apparent.
At this point I am running out of tricks, but there is one more, to be discussed in another post. As it turns out the Grignard reagent that was forming had the Mg stabilized by a THF when it was isolated, and in solution it was no doubt solvated. Most Grignard reagents are only stable in solution, but probably what happened was the Grignard was activating the alpha proton on THF either at high temperatures or while being isolated. I tried all of the above with diethyl ether as well, but no luck... the reaction does not get hot enough to go to product at the temperatures accessable using ether. The next trick? Rieke Magnesium.
I have spent a considerable amount of time recently trying to make my ligand into a Grignard reagent so as to assist in metallating with cobalt. Things have not been going well. This reaction has been attempted at least 10 times now with varying levels of success. The two most successful attempts have occurred January 6th and previously on December 8th. Suspiciously, these days coincided with a moon phase of waxing gibbous. I am not proposing that the phase of the moon determines the outcome of this reaction, but I am not willing it rule it out yet either.
The typical reason for a Grignard reaction to not proceed as desired is a lack of "activity" of the Mg. This is usually directly related to the amount of exposed surface area of Mg in the zero oxidation state. The same principle is true of making contacts in electronics; anyone who has torn a flashlight apart can see the contact where the circuit of the battery is completed. If the contact is dirty (black copper oxide or green copper carbonate) one need simply rub it with some sand paper to expose the copper metal in order to make a good contact. Several tricks for activating Mg turnings have been tried in the work I'm currently attempting.
Pre-treat the Mg: The Mg turnings which exist in our storage cabinet turned out to be pretty awful and disgusting. I wish I had noticed this before I started to use them, but hopefully you can learn from my mistakes. Not really knowing what pure, uncorroded elemental magnesium should look like, I thought the Mg was clean enough, and nothing a crystal of I2 couldn't take care of (see below). Simply looking at a metal to judge the level of corrosion is like having perfect pitch. Some people think they can sing a C note on demand but few people actually can. The safe bet is that any metal which has been sitting around has some tarnish or corrosion to it. I washed a portion of the Mg with 1 M hydrochloric acid to shine it up. This is an exothermic reaction which gets pretty warm (and also evolves H2 gas) so I had a bucket of ice water nearby just in case. After that I gave it a few thorough rinses with deionized water and then anhydrous diethyl ether. Just to be sure this stuff was dry before I took it into the Ar box I left it under vacuum in a sand bath at 130 C overnight. The difference is pretty clear. On the left are the Mg chips as they were in the store room. On the right are the same chips after washing. Like I said, I'm embarrassed to admit I even tried using the unwashed chips. At the time I thought this hadn't worked. More on that later.
I2 crystals: The typical activation reagent used in Grignard reagents is to add a small crystal of iodine. Iodine is used because it is a solid at room temperature, so it is easier to use than bromine or chlorine, although these would presumably have the same effect. The iodine reacts easily with the surface of the magnesium, and after the small amount of I2 is consumed, fresh Mg surface is left exposed to react with your halogenated reagent. Small amounts of preformed Grignard reagent are sometimes used in this same manner, although I did not attempt them myself with this reaction. After using I2 I was still isolating protonated reagent at the end of the reaction, which at the time made me think I was getting some water into the reaction somewhere. I was also having reactivity problems. As I followed the reaction by NMR I noticed that the Grignard product was slow to form, and soon after it did I would see the protonated product.
Heat: In order to speed things along I was heating the reaction and using THF as a solvent so that I could use higher temperatures. (Diethyl ether is the typical reagent, but THF boils about 30 C higher.) Heating a Grignard is not usually advised, as the formation of Grignard reagents is usually exothermic, and therefor performed at room temperature or sometimes in an ice bath.
Drying/Activating Mg: Frustrated with the prospect of water somehow getting into the reaction, I decided to use a qualitative indicator to ensure everything I was adding to the pot was dry. I made up a soluton of sodium naphthalenide. (Simply 1:1 Na metal and naphthalene in THF, about 0.1 M.) After stirring for a few hours all the water will have reacted with the Na and the solution will be dark green. I slowly added the dark green solution to Mg chips stirring in THF until the reaction solution remained pale green, indicating that the Mg was activated and no water existed in the pot. This still gave me slow reactions, and after heating protonated product was still apparent.
At this point I am running out of tricks, but there is one more, to be discussed in another post. As it turns out the Grignard reagent that was forming had the Mg stabilized by a THF when it was isolated, and in solution it was no doubt solvated. Most Grignard reagents are only stable in solution, but probably what happened was the Grignard was activating the alpha proton on THF either at high temperatures or while being isolated. I tried all of the above with diethyl ether as well, but no luck... the reaction does not get hot enough to go to product at the temperatures accessable using ether. The next trick? Rieke Magnesium.
February 10, 2008
glassy toluene
Well, the blue crystals didn't diffract. That's not the current problem though.
I'm trying to do low temperature NMR with deuterium enriched samples. This requires adding and removing H2, HD, or D2 gas from a sample in an NMR tube in succession by doing repetitions of degassing. Essentially you remove gas dissolved in a liquid sample by removing the gas in the headspace of the sample, which draws out gas in solution into the headspace. To prevent the solvent from evaporating you need to have it frozen.
The solvent is toluene, which freezes at about -90 C. To degass it you need to freeze it in liquid nitrogen (temperature about -200 C). The quirk is that toluene forms a glass initially when forming a solid and then "cracks" as it cools further. As it cools the solid shrinks, forming a good amount of pressure on the inside, which isn't as cold as the outside closer to the liquid nitrogen. This pressure comes to a head with a loud crack that sounds like breaking glass. Since the toluene is in a glass tube, this makes for some scary moments as your degassing. The toluene in my tube cracked several times, but I was doing a lot of cycles, so I got complacent, and I was just getting to the end of the deuteration, the toluene crack shocked the glass too much and that was the end of that.
That mistake sent me back about four days. I supposed I needed to make some new starting material anyway, but I was hoping to bang out that one last good result.
I'm trying to do low temperature NMR with deuterium enriched samples. This requires adding and removing H2, HD, or D2 gas from a sample in an NMR tube in succession by doing repetitions of degassing. Essentially you remove gas dissolved in a liquid sample by removing the gas in the headspace of the sample, which draws out gas in solution into the headspace. To prevent the solvent from evaporating you need to have it frozen.
The solvent is toluene, which freezes at about -90 C. To degass it you need to freeze it in liquid nitrogen (temperature about -200 C). The quirk is that toluene forms a glass initially when forming a solid and then "cracks" as it cools further. As it cools the solid shrinks, forming a good amount of pressure on the inside, which isn't as cold as the outside closer to the liquid nitrogen. This pressure comes to a head with a loud crack that sounds like breaking glass. Since the toluene is in a glass tube, this makes for some scary moments as your degassing. The toluene in my tube cracked several times, but I was doing a lot of cycles, so I got complacent, and I was just getting to the end of the deuteration, the toluene crack shocked the glass too much and that was the end of that.
That mistake sent me back about four days. I supposed I needed to make some new starting material anyway, but I was hoping to bang out that one last good result.
January 21, 2008
those effing xtls
Of all the bogus crap I have to put up with in the lab. I grew more "crystals" from the same solution that didn't diffract well enough. Instead of taking them right over to the crystallographer, I had enough to take and NMR and then, if pure, enough to send off for elemental analysis. So I took the NMR. Starting material. Effing A, D.
Nothing is more frustrating than spending large amounts of time and effort on purifying starting materials that were apparently only dirtied with extraneous reagent.
Nothing is more frustrating than spending large amounts of time and effort on purifying starting materials that were apparently only dirtied with extraneous reagent.
January 16, 2008
bogus crystals
Well, the crystals didn't diffract well enough to even get the space group. The crystallographer suspected that they crystals were twinned. Very dissapointing, as this was going to be a good solid page in the paper I was writing. All hope is not lost however, as there are still several crystallization methods that are still under consideration and the distinct possibility that the original mess could give me a non-twinned cyrstal. It would help if the argon-box freezer would stay cold for more than a day at a time.
December 16, 2007
mixed bag
New paper has been first drafted. Heller recently tore it apart (from abroad even!) and sent it back, notifying me that he prefers separated Results and Discussion sections. I personally enjoy discussing my results as they come up, it leads to less confusion for the reader who might not want to read the whole paper (most readers are of this type.) Doesn't matter much, what does is that several of the claims in the paper were found to be untrue while Heller was in Europe. This will result in frantic synthesis of materials and copious amounts of low temperature high field heteronuclear NMR. On the upside is better to have something you thought didn't work turn out to work. Much better than having someone else contradict you in the literature. A good catch, and perhaps another try at a new crystal structure. It seems as though this new product is temperature sensitive, although not terribly so (stable in an ice/water bath.) This could lead to some interesting antics with the crystallographer.
August 1, 2007
Ir recycling step 5.1
The thermal shock on the crucibles has proved to be too much. Recall that the Meker burner did not generate enough heat to reduce the ash mixture to elemental material and salts, but it did come close. The solution then, or so I thought, was to use more Meker burners set up in a tripodal fasion. This (I patted myself on the back a few times for this) would allow greater control over slow heating as well as provide more actual area on on the crucible which was being heated so as to not develop "hot spots" on the crucible itself (slow heating is ineffective if the thermal shock is due to one area of the crucible expanding while another cool area does not.)
I set up (painstakingly) a couple of stands with Meker burners perfectly in place for the tripod along with the crucible at the optimal height and then started up all the Meker burners at the lowest possible gas flow. I increased the gas flow slowly on each of the burners over the course of about twenty mintues, carefully monitoring all of the surroundings to make sure they were not overheating.
Long story short the heat load was too much for the dry powder fire extinguisher which comes standard on all of the hoods in the lab. The heat triggered nozzle fired fine yellowish powder all over myself, the setup I was so proud of and half of the lab. A picture (of course) of the misery will follow shortly after I get it off of Krista's camera.
I set up (painstakingly) a couple of stands with Meker burners perfectly in place for the tripod along with the crucible at the optimal height and then started up all the Meker burners at the lowest possible gas flow. I increased the gas flow slowly on each of the burners over the course of about twenty mintues, carefully monitoring all of the surroundings to make sure they were not overheating.
Long story short the heat load was too much for the dry powder fire extinguisher which comes standard on all of the hoods in the lab. The heat triggered nozzle fired fine yellowish powder all over myself, the setup I was so proud of and half of the lab. A picture (of course) of the misery will follow shortly after I get it off of Krista's camera.
June 1, 2007
update
After some gentle urging from an adoring fan, a quick update, although not much of interest has happened.
I've been working carefully on two projects, a new ligand synthesis, and isolating some final compounds for what I hope will soon become a complete body of work, ready to be written up and published.
The new ligand synthesis is slow, as stated before its only useful solubility is in pyridine, and once the deprotonation is accomplished it is no longer soluble in this either. After trying to get the arms on the ligand it resolublizes, but only to show in NMR that the deprotonation was not complete, even after overnight sonication. The solution in this case is the cook it good and hard for a couple days. So that is where my NMR tube sits right now, trying to deprotonate the starting material, bathed in 120C oil, bumping away.
The other final synthesis I have been messing with has been postponed until I can completely purify the starting materials. Its this kind of fervid obsession with purity is probably the cause of most OCD which chemists experience outside of the lab. For instance, I am constantly skeptical that the dish washer we have actually gets the dishes clean. This is a manifestation of a fear that my lab mates simply rinse their glassware and place it on the drying rack, which requires me to wash every piece of glassware I use thoroughly before I use it, even if I pull it right out of the drawer.
Some of the booted material has gone from red to deep blue-green, and partially soluble in hexane. I've thrown together some crystallization chambers to see what's really in there after my stuff hits the air. One is a slow evaporation of a saturated hexanes solution, the other is a vapor diffusion of hexanes into a nearly saturated THF solution.
On the positive side of things, the lab has acquired a wiffle bat and some wiffle balls. The good weather and large lawn outside the chemistry hall has drawn us out on several occasions to take our frustrations out on each other in a non-deconstructive manner. I highly recommend this for graduate students everywhere.
I've been working carefully on two projects, a new ligand synthesis, and isolating some final compounds for what I hope will soon become a complete body of work, ready to be written up and published.
The new ligand synthesis is slow, as stated before its only useful solubility is in pyridine, and once the deprotonation is accomplished it is no longer soluble in this either. After trying to get the arms on the ligand it resolublizes, but only to show in NMR that the deprotonation was not complete, even after overnight sonication. The solution in this case is the cook it good and hard for a couple days. So that is where my NMR tube sits right now, trying to deprotonate the starting material, bathed in 120C oil, bumping away.
The other final synthesis I have been messing with has been postponed until I can completely purify the starting materials. Its this kind of fervid obsession with purity is probably the cause of most OCD which chemists experience outside of the lab. For instance, I am constantly skeptical that the dish washer we have actually gets the dishes clean. This is a manifestation of a fear that my lab mates simply rinse their glassware and place it on the drying rack, which requires me to wash every piece of glassware I use thoroughly before I use it, even if I pull it right out of the drawer.
Some of the booted material has gone from red to deep blue-green, and partially soluble in hexane. I've thrown together some crystallization chambers to see what's really in there after my stuff hits the air. One is a slow evaporation of a saturated hexanes solution, the other is a vapor diffusion of hexanes into a nearly saturated THF solution.
On the positive side of things, the lab has acquired a wiffle bat and some wiffle balls. The good weather and large lawn outside the chemistry hall has drawn us out on several occasions to take our frustrations out on each other in a non-deconstructive manner. I highly recommend this for graduate students everywhere.
May 25, 2007
pyridine
The ligand that I've been working on (the A+B = C+D thing in a previous post) has been one tough cookie to crumble. The main reason for this is (I think) that the solubility of the starting material is pretty poor in THF, which is the solvent of choice for analogues of the target compound. The smart move here is to switch to a better solvent. After testing solubility of the starting material in a number of different solvents (THF, fluorobenzene, nitromethane, glyme, pyridine, DMSO, and methylene chloride) it turns out that this stuff is soluble only in pyridine and DMSO. DMSO is a great solvent if you never want to isolate your product again. Everything is soluble in DMSO. I'm soluble in DMSO. It boils somewhere up around 180C which doesn't really make it strippable. This leaves pyridine, which is what I've been using, but I can't say I'm terribly excited about this either. It stinks(if you can smell it, you're not working carefully enough), its tough to dry, tough to vacuum transfer and is particular bad for gentlemen such as myself, if you know what I mean. (For those that don't know, pyridine could be used as a very effective male sterilizer, so long as you don't mind not having lungs, a liver, or several other major organs as well.) The upshot of all this is that when I get frustrated trying to get the pyridine to pump over in time for me to get down to my NMR time, I can't throw the bomb to the floor in frustration for consideration of my future kin.
May 18, 2007
in the opposite direction
I've spent the last two weeks working on new compounds, one is a variation on a ligand we've been using here, and the other is a new metal complex. After a considerable amount of effort I have made (I think) both of them, but they are so unstable they fall apart into starting material. That is to say, there is more than one way to make these things. Say I can get complex P (the desired product) either starting with A + B or C + D. What I have essentially done is found a way to fleetingly make P from A + B but ultimately what I have done is to make C and D from A + B in a really fantastically expensive and time consuming way. Not that this is uncommon, but to have it occur to two different projects at the same time is extraordinarily frustrating.
May 8, 2007
wrong
Things have not improved. Our chemical storage refrigerator stopped working over the weekend. There are two reasons to keep chemicals in a cold storage refrigerator: it will decompose to something else or it has a very low boiling point and could generate enough pressure in a closed container to explode at room temperature. This means that you need to have an explosion-proof fridge, just in case. And we did, (luckily nothing blew up) but it also makes repair or replacement a much more expensive proposition for the lab.
In better news I should get my line back tomorrow.
In better news I should get my line back tomorrow.
May 3, 2007
sash troubles
The cable which supports the counter weight for the sash on my fume hood snapped yesterday. This is a minor inconvenience compared to the other myriad of poor fortune which has befallen the lab in the last week. My Schlenk line is going to the glassblower on Tuesday (hopefully it will be in tip top condition upon its return.) To boot, Jake's line got completely wrecked and Derrik's sash had a crack in the safety glass, which the fellow's who came to fix my sash insisted also needed to be taken care of by ES&H regulations, so his line is down as well. For those of you keeping score, that leave two functional Schlenk lines - one of which is only half functional - for 8 lab members. Oh - and the facilities manager who came to check up on the sash progress noticed that some of the clamps we were using to hold the Schlenk lines up were wrapped in asbestos tape, so they were confiscated. Goody goody. Things can only improve from here.
April 30, 2007
crystals and dissapointment
Well, a picture of the crystals just to show you how big they were. Unfortunately the camera I was using does not take very good close-up shots. There are two whole crystals shown in the J. Young tube, with a penny for size comparison. These were blocky, and I could actually tell you the space group just by looking at the facets on the crystals if I were to take the time to look them up. Unfortunately careful 11B and 13C NMR analysis indicates almost certainly that these are not what I thought they were, and to boot, they are pretty common and easy to obtain, which explains why I got such huge crystals.
April 25, 2007
Liquid pearl
For reasons I may explain later (or not, it doesn't matter) I was converting some phloroglucinol to 3,5-dihydroxybenzenesulfonate. The prep calls for diluting the aqueous solution with ethanol in order for the product to crystallize overnight. Whatever, this didn't happen. After a few other attempts I evaporated all of the solvent and then tried to dissolve it into a minimum of water, which didn't work at all for some unknown reason (it was soluble in water to start out with - maybe a pH issue). It did give a suspension which looked remarkably like liquid pearl. Pretty as it is, this stuff turns out to be nearly impossible to filter because the particles are so fine. These particles are however, soluble in neat ethanol, and hopefully some crystals can be coaxed out of solution this way.
April 20, 2007
Long time, no work
Sorry to disappoint the many many fans who I know attentively watch this blog on a daily basis. The promising reaction I spoke of nearly a month ago now? No crystals, just some gummy crap at the bottom of the vial. Where has our fearless author been this past month? Well, for the first part of it I was feverishly working on a research proposal project as a requirement for staying in the graduate program. The proposal outlines the synthetic plan necessary to synthesize Moebius molecules. I rendered a computer simulation of the molecule for the conclusion, and I've included it here.
Obviously its not going to really look red and blue, thats just the coloring used to define the rails and rungs of the Moebius strip. I haven't gotten much feedback on the proposal yet from my committee, but I figure that no news is good news in this particular case. Professor Heller did at least acknowledge it and said he liked the proposal. Good enough for me.
So that covers the first two weeks of my absence, the last two weeks have been spent feverishly preparing for group meeting which I gave yesterday. Mostly this was spent trying to scrape together some results in the wee bit of time I had left in between finishing the proposal and giving the group meeting presentation. All in all I thought it went rather well, and now its time to settle back into some solid, non-feverishly done research.
Obviously its not going to really look red and blue, thats just the coloring used to define the rails and rungs of the Moebius strip. I haven't gotten much feedback on the proposal yet from my committee, but I figure that no news is good news in this particular case. Professor Heller did at least acknowledge it and said he liked the proposal. Good enough for me.So that covers the first two weeks of my absence, the last two weeks have been spent feverishly preparing for group meeting which I gave yesterday. Mostly this was spent trying to scrape together some results in the wee bit of time I had left in between finishing the proposal and giving the group meeting presentation. All in all I thought it went rather well, and now its time to settle back into some solid, non-feverishly done research.
March 22, 2007
THF solvent bomb
After improperly refilling the tetrahydrofuran solvent bomb, the color of the sodium benzophenone ketal was no longer dark purple, not even bright blue or even green, it was yellow, indicating a total loss of the flask's integrity. I emptied the bomb and quenched the remaining sodium. In the process of vacuum transferring new THF into the freshly made bomb flask, the convection in the condensed THF was so strong that it created a little fountain in the center of the bomb, with a well about 1 cm deep and spray that came up and spattered the sides of the flask. I called over Jake and Derrik to look at it but they were not as impressed with it as I was. Regardless, its a very pretty blue color.
March 19, 2007
stir plate repair
We don't have enough working stir plates. I attempted to repair one by stripping it down and washing the moving parts with hexane. No dice. I regreased it with some Loctite N-5000 (the packaging proudly proclaims "Nickel-based anti-seize lubricant for the Nuclear Power Industry") but still, no dice. I began removing parts I thought looked extraneous. This worked somewhat, and as it turns out the piece that was obstructing the bar magnet was the cooling fan. When I say it worked "somewhat" I mean that it worked until the motor overheated and seized, in spite of the newly applied Ni-based nuclear power grease. At the very least this is now a valid state of disrepair to warrant tossing the old plate and ordering a new one. A view of the carnage...
The pieces in the foreground are some of the amputated bits. The washer and lock washer appeared to have no purpose whatsoever. The shiny bits are what remains of the cooling fan after being torn out of the middle of the stir plate.
The pieces in the foreground are some of the amputated bits. The washer and lock washer appeared to have no purpose whatsoever. The shiny bits are what remains of the cooling fan after being torn out of the middle of the stir plate.
March 5, 2007
Sublimation mixed results
After taking care of the details such as fixing thermometers and getting dry NMR solvent, the results of the purification are in. A partial success! The final material is more pure in that there are fewer products present (3 as opposed to 7) however only about 50% product, down from about 75%. Looks like I'll have to make a new batch from scratch.
March 4, 2007
wet NMR solvents
The deuterated benzene bomb in the lab is dried using CaH2, which should be a pretty effective drying agent. I prefer it to NaK alloy, mostly because you don't have to worry about the flask exploding after you finish transferring all of the solvent off. The downside is that you miss the pleasure of the deep purple color of the NaK benzophenone ketyl which tells you definitively that your solvent is indeed H2O free. After several crappy NMR spectra using the C6D6 over CaH2, a blank spectrum confirmed that my solvent was wet. I made a new bomb and then quenched the leftovers. (No fizz, of course.) The new bomb has a much whiter color to it than the wet bomb, which only brings to my attention three other solvent bombs in the lab sporting a depressingly dark grey color. SEP? you betcha. Maybe now I'll be able to tell if the sublimation worked or not.
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