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.

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.

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.

pleochroism

Pleochroism occurs when a crystal absorbs light differently along different orientations within the crystal. Meaning, when looking down one axis of the crystal, light enters randomly polarized (there is no preference for the direction that the amplitudes of the waves are travelling). As the light passes through the crystal, only light which is in a particular orientation is absorbed, allowing other light to pass through. When this occurs for a particular band of visible light, you get crystals that are differently colored when viewed along different directions. This is all very confusing. The best explanation I could find on the web after a brief search is still a bit confusing, but much more elegantly worded with a touch of bad grammar. They're Spanish, so I will give them a free pass. I cut some tiny pieces of the crystal with a razor and tried to line them up so you can see the two different colors. These two crystal fragments (right) were cut from the same single crystal (largest crystal from the left picture). These are technically dichroic because they display only two colors, although pleochroism would only be used for crystals which displayed three different colors, but this is never called "trichroic" for some reason.

red or green?

The crystals diffract. It has been really difficult figuring out just what color these crystals are. The compound is paramagnetic, so the color is very deep. It looks like a reddish purple color when it is in solution, but the crystals came out almost with a green color when looked at the right way. I took them to the crystallographer who informed me that the crystals are dichroic, and this explains the confusion in the colors. For now, a crummy picture of the crystals and one of the diffraction slices... later, hopefully, pictures showing the dichroism and little more discussion on just what dichroism is and how it works. A resounding success by any measure. X-ray quality crystals were grown from a slowly cooled n-hexane solution.

Soxhlet success!

The extractor did wonderfully. The green substance from a couple posts ago was much less pure than I had hoped, consisting mostly of a blue substance (identity yet unknown, but not starting material.) There are three pretty distinct colors here, the yellow substance in the top sample tube is the desired product. The bottom tube is the mystery blue compound. I feel like I should spend a little time figuring out what this is so that I can avoid making it in the future. The middle tube is the original sample from the crude mix, composed of both compounds. I forget whether or not I had claimed the green compound in my color checklist, but if I did, it was unwarranted. Instead, I have made a yellow compound (which I can claim) and a blue compound (which I am not claiming yet as it is not properly identified.)

crystals

Some pretty sweet dark red/purple (or dark green!) crystals have come my way. More on these later as I procure a better camera. The camera on the cell phone does these beauties no justice.

Soxhlet Extractor

The Soxhlet extractor is one neat peice of equipment. It is used in conjunction with a solvent in which what you want is slightly soluble, and what you don't want is totally insoluble. The advantage is that you end up using significantly less solvent in the extraction process, and once it is up and running, it can be left unattended for long periods of time. The matter for extraction is the green powder I posted in the previous blog entry. The setup is shown to the right. I'm using n-hexane as a solvent in this extraction, which is collected in the round bottom flask. This was vacuum transferred into the extractor using the Teflon pin you can see in the top left of the photo. The black hose is connected to the Schlenk line. I did not backfill the extractor with inert gas, which means I can operate the extractor at lower energy (longer times between filling the bucket with ice). At the bottom is a stir plate with a heating element. I keep a pretty vigorous stir going to prevent the hexane from bumping. The dish around the round bottom flask is empty in the picture, but I filled it with water and set the temperature on the heating element to be just around 25-30 C. (The hexane will cool as it is evaporated, so you have to put heat back into the system. The bucket is filled with ice water. One hose connects the pump to the cold finger and the other drains back into the bucket. All of the green material from the previous post is inside the paper thimbles you can see in the center of the extractor. The large glass tube on the far left is the vapor transfer tube. "Warm" hexane vapor travels up this tube at about 30 C and condenses on the cold finger, which is at about 0 C (from the ice bath). As the liquid condenses it drips down onto the paper thimbles holding the material. The material I want (light yellow green color) is dissolved. Eventually the level of solvent in the extraction chamber reaches above the bend in the return tube. This is the small squiggly tube in between the vapor transfer tube and the extraction chamber. When this happens the solution in the extraction chamber is siphoned back down the return tube into the round bottom, leaving behind the insoluble materials. This process is repeated a couple hundred times, concentrating the desired material down in the bottom flask. All in all a pretty nifty piece of equipment!

green

The camera is OK. Nothing spectacular but I think it will do just fine for the blog.

I'm working with some cobalt compounds being ligated with a Grignard pro-ligand. The CoCl2 is pretty typical starting material, and is pure blue when totally anhydrous. When it's wet the color becomes a pink/purple color. The ligand starts with a halide which is reacted with Mg to form the Grignard reagent, all of which are colorless. When the cobalt dichloride and Grignard are mixed the color of the solution turns from blue to deep green in minutes. The final product is pale green color, almost yellow, so there's probably still a lot of impurity in the solution. The first picture is of the solids after stripping the solvent. It looks pretty gooey, but after a bit of scraping its powdery in the bottom of the bomb flask. This material will have to be extracted in order to remove the magnesium salts and unreacted CoCl2. More to come of this in a bit.

problem solved

Procrastination comes through once again. While feverishly losing bids on ebay for a crummy but not too crummy digital camera, I've allowed my cell phone plan to run its course. For simply agreeing to pay a monthly fee for another two years, Verizon will graciously throw in a new phone. Who could pass this up? The little bonus is that the new phone comes with a 1.3 MP camera, more than enough for my blogging needs. We'll try this phone camera out for a while and see if it really is cut out for the job.

It's also come to my attention that I had a series of posts going on both iridium recycling and on building a Schlenk line from scratch, both of which have been neglected. I'll get back around to these soon.

colors and technological needs

My chemistry has turned away from iridium towards cobalt. This means cheaper starting materials and harder characterizations, but it also means a whole new spectrum of colors. I've been getting some really nice blues and greens, some of which are even new products. I made a pretty wierd two coordinate cobalt bis-amide complex which was initially a dark black mess. A little sublimation however, cleaned that right up to a bright green color.

Usually I would have a photo here so that you could enjoy this coloration with me, but I haven't been able to fanagle the camera from home. I think I could benifit greatly from a cheap used camera bought off ebay which I could keep in the lab. Unfortunately I haven't been able to locate a camera as cheaply as I'd like which will still take decent quality pictures.

I guess for now you'll just have to trust me that the colors are as nice as I say they are.