Melgar
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High-pressure hydrogenation for super cheap! But will it work?
So, I had an idea for getting high-pressure hydrogen inside a pressure vessel without using any sort of high-pressure gas-transfer mechanisms. It
wouldn't be the most accurate thing in the world, but it seems like it could work.
Essentially, you take septum vials (no rubber septa though! that poisons catalysts from the sulfur!) like this:
http://www.ebay.com/itm/252284342183
And weight them at the bottom, so the top always points up when it's in liquid. Then put chunks of lithium in the vial, and cover those chunks with
wax. Add extra wax on top of that once it hardens, just to be safe. Now add water to the vial. You'll notice that the wax has prevented the water
and the lithium from reacting. Cut a slit in the septum, so that it could release any pressure inside it, but probably wouldn't leak if the pressures
were the same on both sides. You can probably see where this is going. Anyway, get your pressure vessel (ideally with a pressure gauge installed on
it), put the vial inside along with your reactants and solvents, and then seal it up tight.
Now, you'll probably want to dig a hole in the ground and put a jug full of very hot water in that hole. Have some cinder blocks or concrete slabs
handy. Drop the pressure vessel into the hot water, and then put the cinder blocks over the hole. If nothing explodes in the time it would take the
water to cool off, check the pressure vessel and make sure that the pressure is appropriately high, but not ridiculously high. At this point, you can
probably agitate it or do whatever else you need to. You could even add more vials if you had to. Obviously, it would only work for reactions that
can reach the melting point of wax without any problems, but that would be most of the hydrogenation reactions that I know of.
So, any potential problems with this? (The hole and the cinder blocks was kind of a joke, but not entirely)
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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Dr.Bob
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Given that they are 2 ml vials, it will be hard to generate much H2. I can think of some safer ideas. My theory is that the more complex and more
parts, the worse things are. Most hydrogenations are done at 40 psi, so it is not hard to generate that safely. The biggest challenge is purging
the reaction with nitrogen at the end without setting anything on fire. That can be difficult, even with decent equipment, as I have know a few
people to have the reaction catch fire when they did not purge it properly.
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Chemetix
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With 2mls of working volume, I can't imagine anything other than GC or LC-ms that would determine if the reaction worked or not. There's some
microprep ninja skills needed to get this to be practical.
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zed
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Umm. Well.....I've never set one on fire, but it can happen.
Your catalyst is charged with hydrogen, probably in a flammable liquid, and if a little bit of catalyst is stuck to your vessel wall, where it drys
out while being exposed to atmospheric O2..... There may be a fire. And, that could occur regardless of of an initial N2 purge.
Back in the day, I would try to siphon out product, without opening the vessel, then evacuate the excess H2 with vacuum, and finally.... quench the
catalyst with H20. About the time I got the catalyst covered with water, I would breath a sigh of relief....and pretty much stop worrying.
The majority of hydrogenations I attempted were at ~STP. I just utilized a very active catalyst , prepared via injecting Chloroplatinic acid in
ethanol, into ethanolic NaBH4.
Thereafter, you can use NaBH4 to generate the hydrogen you require for your reduction.
Very simple to do. And....cheap enough too, if you can acquire NaBH4 in bulk.
The procedure was invented by Brown. Works well, but I see few references to it nowadays.
Too bad! Brown did some great work. In fact, I'm gonna go study, and refresh myself on his apparatus and procedures.
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