Co is apparently ferromagnetic. Who knew? Not me, until I talked to one of the students from the lab downstairs. Dunno why it was so surprising, on the surface I was thinking that iron was the only ferromagnetic material. I knew this wasn't true already though, because I've used gadolinium before and we also have a number of neodymium magnets in the lab. Silly silly silly.
This came about while trying to make finely divided cobalt powder in the same manner that Rieke Mg is synthesized. Whether this actually produced Reike Co or not is not certain, but it certainly didn't work for what I wanted it to. I did not spend a whole lot of time sorting out the rubble, but I did notice the Co particles lining up on the magnetic field lines of the stir bar. Weird.
January 28, 2009
January 21, 2009
schlenk line pt 2
A good working space is tantamount to good productivity. Schlenk lines are generally mounted on some sort of support, most typically a metal cage. (VWR lists these as "lattices" or "lab frames".) The cage serves not only as a support for the Schlenk line, but also as space to connect reaction vessels using clamps while they are being used. Most everything in the hood is held together with fasteners. The cage itself and other permanent fixtures are attached using smaller 90 degree frame connectors which are tightened down using small Allen wrench. Other items such as reaction vessels are attached on a temporary basis using thumb screws. When I first arrived at the Heller lab the hood assigned to me had a cage made of stainless steel and aluminum rods, fixed directly to the back of the hood. When I moved my work space the new hood was a mish-mash of rusty steel, corroded aluminum, and about half constructed with fiberglass rods. Totally unacceptable. This was totally disassembled and a new cage was constructed using only metal rods. No individual pictures exist of only the cage, but the reader should take note of the underlying structure in future pictures.
January 20, 2009
Reike Magnesium (Mg*)
In order to get my Grignard reactions to work even a little bit, I've been heating them considerably. This was fine when I was working in THF, as I would usually heat them to 70 C or so. The bomb flasks I'm using can handle the extra pressure (THF boils at 65 C). Now I'm using diethyl ether as a solvent to prevent activation of the alpha hydrogen in THF; unfortunately this means I'm restricted to lower temperatures. I tried to calculate the pressure I would build up in the flask while heating the ether to 70 C. I didn't get the number exactly, but suffice to say it's more than I'm comfortable with having in my hood. So the next great idea is to lower the required temperature by using "highly activated magnesium powder" also known as Reike Magnesium. (The abbreviation commonly used is Mg*.) This is made simply by reducing Mg-dihalide to elemental magnesium using a strong reductant, usually an alkali metal. The easiest way I can see to make this is to stir up the MgCl2 with potassium metal in THF while refluxing. Potassium melts at a slightly lower temperature than THF boils, so the molten potassium reacts quite easily with the MgCl2.
Rieke Magnesium is called such because Ruben D. Rieke has championed this form of magnesium as a route to generally inaccessable Grignard reactions. He has also commercialized this process, you can see his outfit here if you like. I browsed the website myself, and noticed a little grammatical mistake that I'll now make light of.
Often times my students, and occasionally even my well learned labmates, will do what is called "verbification". (This word actually shows up in several on line dictionaries now, very depressing) That is, they take a noun and use it as a verb to imply action of the noun on a subject in an obvious manner. One of the most common nouns which is subjected to verbification in the lab is "cannula", a long metal tube used to transfer liquids between reactions vessels while excluding the outside atmosphere. Often the transfer process is reffered to by the slur "cannulate". This appears in Rieke's website...
No need for a drybox or a solvent still. Simply cannulate Rieke® Metals in THF into a reaction flask under an atmosphere of argon or nitrogen.
I have been telling my students (and labmates) that "cannulate" is not a word, although you can in fact transfer something using a cannula. I was amused to see this grammatical miscue on a commercial website. Upon further investigation it turns out "cannulate" is actually a word, but it refers to the act of puncturing with a cannula, not transfering a vessel's contents. A near-miss for the author's of Ruben's website, but a miss for sure. As I tell my students quite often while they struggle to pronounce words like meridional, molybdenum, mesitylene; part of being educated is sounding educated.
Rieke Magnesium is called such because Ruben D. Rieke has championed this form of magnesium as a route to generally inaccessable Grignard reactions. He has also commercialized this process, you can see his outfit here if you like. I browsed the website myself, and noticed a little grammatical mistake that I'll now make light of.
Often times my students, and occasionally even my well learned labmates, will do what is called "verbification". (This word actually shows up in several on line dictionaries now, very depressing) That is, they take a noun and use it as a verb to imply action of the noun on a subject in an obvious manner. One of the most common nouns which is subjected to verbification in the lab is "cannula", a long metal tube used to transfer liquids between reactions vessels while excluding the outside atmosphere. Often the transfer process is reffered to by the slur "cannulate". This appears in Rieke's website...
No need for a drybox or a solvent still. Simply cannulate Rieke® Metals in THF into a reaction flask under an atmosphere of argon or nitrogen.
I have been telling my students (and labmates) that "cannulate" is not a word, although you can in fact transfer something using a cannula. I was amused to see this grammatical miscue on a commercial website. Upon further investigation it turns out "cannulate" is actually a word, but it refers to the act of puncturing with a cannula, not transfering a vessel's contents. A near-miss for the author's of Ruben's website, but a miss for sure. As I tell my students quite often while they struggle to pronounce words like meridional, molybdenum, mesitylene; part of being educated is sounding educated.
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.
January 14, 2009
Building a Schlenk Line pt 1
A good Schlenk line starts with a good plan. In the figure I'm showing the basic sketch of the type of Schlenk lines used in the Heller Lab. This is scheme one of four and shows only the basic outline of the order we put in to the glassblower. There are five pages to the full schematic, one of written instructions and four of figures such as this one detailing the types of tubing, joints, lengths and thicknesses of glass etc. Either you are only a mildly interested reader and don't want to sift through pages of schematics or you are intimately interested and want to make a close copy. If you're the latter you should contact me, I might be willing to give it up (for a price). I will make a couple of suggestions as far as types of joints. The O-ring joints (the three joints in the bottom right of the figure which looks like bulges in the glass tubing) are all Urry-type O-ring joints. What are "Urry" joints, you ask? The glassblower who fabricated this glassware for us didn't know either. "Does that mean, 'eh, I need this in an 'urry'"? Well, no, it means that there is a raised edge running in the middle of the groove. When the clamp is tightened down the ridge presses against the O-ring which makes a better seal. This is particularly helpful when the joint is being removed frequently, as it ought to be if you are emptying the trap out every night. Dirt inevitably gets onto the O-ring and the Urry-joint will make a much better seal with a slightly dirty O-ring than a simple grooved joint will. As it turns out, there's not many glass manufacturers who make a simple groove anymore, but if you happen to get a hold of one save yourself some time and toil; drop it on the floor right now.
There's a design flaw in the sketch above. Its not terrible, but embarassing that it made it all the way through to the final product without getting caught. I'll mention it next time.
January 13, 2009
sublimation apparatus
I've used the sublimation apparatus before and had it work, but never like this. Labmate Krista was purifying some starting material (I think it was some type of imidazole) and got some real gemstones. This first picture shows you basic air-free sublimation device.The Teflon pin and black hose on the top left of the device connect it to the Schlenk line so that the atmosphere inside the sublimator can be cleared of air and either inert gas (argon for us) or vaccuum can be maintained. Doing a sublimation under vaccuum lowers the temperature at which the sublimation has to take place. The heating mantle on the bottom, although rusty and corroded, heats the oil bath (the opaque mess in the beaker which ought to be clear and colorless) which keeps the impure imidazole hot. Under vaccuum the imidazole is below the triple point, so as it is heated it vaporizes into the atmosphere of the sublimator. The vapors are cooled on the cold finger (peice of glass sticking down into the middle of the sublimator) which is kept cold by cold water flowing through it (through the two hoses on top). Upon very close inspection the astute observer will notice that the water is flowing backwards in this particular setup. Since the crystals Krista was growing were so spectacular, I asked if this was on purpose. Normally you would want the water to be coldest at the very bottom of the sublimator and have it warm up as it exited. Krista assured me that this wasn't skill, merely a silly little mistake. It is absolutely amazing that these crystals came out as well as they did given that the setup appears to be thrown together in someones basement using spare parts and grease someone cleaned out of their griddle. But there you have it. For those of you who are looking at the scale of these crystals, unimpressed, it is true that when most people think of crystals they are thinking of quartz crystals in their local curiosity shoppe. Well rubbish, those cyrstals took thousands of years to make, and Krista had these nailed out in less than a day; much more impressive.
January 7, 2009
Neglect, and Building a Schlenk Line
Once again, the blog has fallen by the wayside. Upon signing in after a long hiatus I found a comment asking about building a Schlenk line. I started talking about this then stopped, long before the conclusion of Schlenk line building was completed. This seems as good as any reason to resume this disscussion, which I'll start again from the beginning. later....
In other fantastic news, I recieved a new digital camera from my in-laws. This camera has a fantastic macro function and should provide some pretty stellar photos for the blog.
In other fantastic news, I recieved a new digital camera from my in-laws. This camera has a fantastic macro function and should provide some pretty stellar photos for the blog.
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