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madcease
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I think the Parr Shaker type apparatus is much better than the stirring type correct me if im wrong but when using some catalysts it tends to be very
pyrophoric such as Rayney Nickel which if stirred the catalyst has a tendency to sit on side walls without being in solution whereas the shaker is
always saturated and gives no chance to ignite.
Very interesting patent Zed. I have another type of apparatus that can be built very easily like the previous UC Berkeley, Chemistry Library stirred
apparatus you found which used to be on Rhodium. Just have to find it ill post the link once done so.
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Sauron
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Hmm, I have no refs for direct combination of Li, Al, and 2 H2. How much heat and pressure? I am constrained to 1900 psi and something <400 C. with
the equipment I have at hand.
Merck, Brauer, etc give only the prep from 4 LiH + AlCl3 in Et2O which may consume LiH but requires neither autoclave nor H2.
It's academic for me as I have a lot of LAH and when I want more, I order it.
LiH is no joy to prepare if you have to. Even to use the commercial LiH in prep of LAH requires grinding, best done under N2 in a special ball mill in
anhydrous Et2O - whiclso sounds like great fun for all.
[Edited on 31-3-2009 by Sauron]
Attachment: ja01197a061.pdf (180kB)
This file has been downloaded 2765 times
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Sauron
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There is only one y in Raney.
My personal approach to separation of pyrophoric catalysts from solutions after reduction is to do the filtration and transfer in an inert atmosphere
glove box with an airlock and tus avoiding any exposure of the catalyst to air.
All else is russian roulette.
Magpie, re direct attachment of main high pressure H2 cyclinder to reaction bottle, that is still onjectionable even if you run a long gas line. Why?
Think of the reaction bottle, particularly the H2-rich catalyst, as a match, the H2 line as a very fast fuze and the H2 tank as a bomb.
At the bare minimum a flash arrester needs to be interposed. And even then I like a small secondary tank at low pressure better. The Parr tanks are
brass. 100 psig is a little more than 6 arm. and a liter of H2 # 6 atm isn't much.
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zed
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I'll see if I can dig up a reference. I'm pretty sure I know what book it is in, it's just a question of finding the book. Surrounded by books. Not
as many as I used to have, but still too many. Like, maybe 10,000 or so.
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madcease
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Is there a reason why Parr Inst sell mainly the shaker type and not stirred type?
Seems as if shaker is the way to go instead of a stirred apparatus.
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Sauron
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Parr makes a very wide range of pressure reactors, mostly stirred, medium and high pressure autoclaves. The shaker type hydrogenator is really a very
minor product of theirs
They also make stirred low pressure glass reactors, calorimeters and a variety of other instruments and equipment.
Do a google on "parr pressure reactors" to get to their home page. If you register and create a password to go with your email address you can access
their brochures and manuals, exploded drawings, parts lists etc.
They are not cheap!! but sometimes you can find a bargain on labx or a generic auction site like ebay.
Zed, according to Ullmann's, the LiH + AlCl3 method is the only industrially employed method of making LAH.
They do mention two other methods, hot used:
2 LiH + 2Al + 3 H2 -> 2 LiAlH4
at unspecified and unreferenced elevated temp and pressure. This probably what you were thinking of.
and by metathesis:
NaAlH4 + LiCl -> LiAlH4 + NaCl
The requisite sodium aluminum hydride can be produced from Na, Al and 2 H2 at 100-200 C and 1450-2900 psi according to a series of patents held by the
Ethyl Corporation. Best done in hydrocarbon solvent and in presence of trimethylaluminum catalyst, what fun. My Parr tops out at 1900 psi.
It can also be prepared from
4 NaH + AlCl3 -> NaAlH4 + 3 NaCl
E. C. Ashby: "The Chemistry of Complex Aluminohydrides," Adv. Inorg. Chem. Radiochem. 8 (1966) 283 – 335.
Sodium hydride is easier to come by and cheaper than lithium hydride but just as much of a pain to prepare.
Attachment: US4045545.pdf (231kB)
This file has been downloaded 650 times
[Edited on 31-3-2009 by Sauron]
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Magpie
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Think of the reaction bottle, particularly the H2-rich catalyst, as a match, the H2 line as a very fast fuze and the H2 tank as a bomb.
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Sauron, I think it is more reasonable to think of the H2 rich catalyst as a bunsen burner with the line just a conduit to the high pressure supply.
Without O2 the H2 does nothing.
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Sauron
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But your Bunsen is in a bucket of petrol and there's air and vapor all round,
You can do it your way, just remind me not to visit when you are hydrogenating.
Anyway, here is the improved Ethyl Corp. patent describing lower pressure (700-1500 psig) two stage preparation (140 and 80 C) of NaAlH4 from Na, Al,
and 2 H2.
Remember, sodium aluminum hydride metathesizes with LiCl to LiAlH4. So if you have an ordinary autoclave like mine and can get or make Na metal, Al
powder and H2 cylinder you can make your own LAH in a 2 step procedure with only LiCl.
BTW despite the broad claims in the above patents, Ethyl Corp does not make LAH this or any other way, and while they make NaAlH4 on a modest scale,
there is no demand for it in bulk. From this I surmise that the direct combination of the elements is not so practicable for LAH directly, as the
"omefficient" prep from 4 LiH and AlCl3 remains the only manufacuring process in use after 65 years.
LiCl can of course be electrolyzed and Li metal recovered and hydrogenated back to LiH or used in another manner so the "wastefulness" of the process
has perhaps been overstated for purposes of patent prosecution.
Attachment: US4512966.pdf (210kB)
This file has been downloaded 660 times
[Edited on 31-3-2009 by Sauron]
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zed
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Indeed that was the procedure I found.
From "Advanced Inorganic Chemistry" pg 339, 4th Edition, 1980, By Cotton and Wilkinson.
" However, for AlH4 the sodium salt can be obtained by direct interaction:
Na + Al + 2H2 -------------------------------------------------> NaAlH4"
150C/2000 p.s.i./24h/ in THF
The NaAlH4 may be used directly(some actually prefer it to LiAlH4 due to ease of post reaction workup)......or it may be precipitated by the addition
of Toluene.
The NaAlH4 may then be efficiently converted to the Lithium salt.
NaAlH4 + LiCl ---------------------------------------->NaCl (solid ppt) + LiAlH4
Et2O
Nice thing about obtaining a Parr high pressure reactor. Once you have one, most things are do-able.
Thank you for the Patent links, Sauron. I did not have those.
************************************************
As a side note.....My understanding is that at lower temperatures the Parr reactor can withstand higher pressures.
Parr vessels are often rated as 1900psi at 350C. At 150C they can withstand somewhat more pressure. I believe Parr provides a table or graph
somewhere that describes that pressure/temperature relationship.
*Wow, just read that Ashby Patent. Pretty Nice. Much better than the method I was familiar with.
[Edited on 1-4-2009 by zed]
[Edited on 1-4-2009 by zed]
[Edited on 1-4-2009 by zed]
[Edited on 1-4-2009 by zed]
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Sauron
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Now read the Nelson followup patent.
-- toluene preferred solvent
-- triethylaluminum catalyst (pyrophoric liquid, formerly used in military flamethrower M3 and ignites as soon as it hits air)
-- 14o C first stage, 80 C second stage
-- 1000 psig H2 pressure
First stage forms Na3AlH6, second stage NaAlH4.
Reason why ethers shunned is that NaAlH4 is unstable in ethers, and the ethers are hard to completely remove from solid. At least per patent. This
does not appear to be a problem with LAH production from LiH and AlCl3 in ether.
This does appear to do the trick. A one pot two stage prep from the elements in toluene, then an easy metathesis in eyjer. The trialkyl aluminum is a
minor hassle, practice your airless technique and handle under inert atmosphere. Syringe, transfer line, usual drill. The solvent with
triethylaluminum inside is reusable. That helps.
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zed
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Actually, somewhere in Ashby's patents, it suggests that the catalyst can be formed in-situ. I like that idea.
Overall, the procedures look pretty good.
I have no current use for any of the products, but it is nice to know they can be manufactured if need be.
Nelson's patent suggests about 2lbs of NaAlH4 were produced per 1 gallon of reactor capacity. In a 400 gallon reactor, about 750lbs of product was
produced.
So by extrapolation, in a single run, in a 1 liter Parr reactor about 1/2 Lb of NaAlH4 could be produced.
THAT is practical.
Thank you again for sharing your research with us.
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Sauron
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De nada, it was interesting to find out.
I have no doubt that Li, Al, and H2 will combine under conditions were the Li is a melt dispersed as sand in toluene and the H2 is under pressure.
It's just a question of how much pressure, and how long the reaction time. On a bench scale I don't mind if it takes 24 hrs. Throughput is a process
engineer's problem and not that of a synthesist. Li metal is easy to buy, I have maybe 500 g wire in oil. It's a lot cheaper than LiH and need not be
wet-milled in Et2O under N2.
BUT on the other hand I have maybe 12 Kg Na and it is a LOT cheaper. So there is little point in swimming upstream.
Zed, while the ealier patent (Ashby) does mention making catalyst in situ. he was referring to sodium alkyl or similar monovalent metal alkyls.
Unfortunately things are not that simple for trialkyl aluminums and the patents are quite specific about triethylamuminum being the catalyst of
choice.
It is commercially available as a 25% wt solution in toluene, this is almost certainly not an accident.
What happens when you react alkyl halide (say ethyl bromide) with Al is that you get a mixture of ethylaluminum dibromide and diethylaluminum bromide.
These cannot readily be separated. However the ethylaluminum dibromide can be reduced with Na metal to the diethylaluminum bromide and this then
purified and converted to triethylaluminum in decent overall yield.
Better is to incorporate the reducing agent into the aluminum as an alloy, thus 30% Mg 70% Al alloy turnings are reacted with EtBr and the resulting
Et2ALBr reduced with Na to Et3Al. See Brauer above. Also here is the original 1940 paper from JOC.
[Edited on 1-4-2009 by Sauron]
Attachment: jo01208a004.pdf (221kB)
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Sauron
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Sorry, here are the pages from Brauer describing prep of diethylaluminum bromide and triethylaluminum from Al/Mg "magnalium" 70/30 alloy turnings (Dow
Chemical).
Attachment: Pages from brauer_ocr.pdf (91kB)
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madcease
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If one is to build one of these pressure shakers/stirrers, should there be a pressure relief valve attached to the apparatus like a pressure cooker
which if for some reason pressures go over 50-60PSI then the relief valve will open causing no breakage of glass.
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Sauron
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Such devices are common for high pressure steel autoclaves but are not used on shaken or stirred glass hydrogenators which are by nature of the
vessels limited to 30-60 psig depending on size of the bottle.
The 250 ml and 500 ml Parr bottles max 60 psi
The 1 L and 2 L machine made Parr bottles 40 psi I think
The costlier hand blown 2 L Parr bottle and the steel 2 L Parr bottle 60 psi.
We are only talkin 4 atmospheres here. As H2 is taken up pressure drops so normally the highest pressure is at the onset. Sometimes there is an
exotherm, and external cooling jackers are abailable. Sometimes heating is necessary and thermocouple monitored PID controller mantles are also
available.
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Sauron
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Since this thread is about Parr shakers, rather than making LAH, I have started a new thread about making LAH so please let's allow this older thread
to return to topic. Thanks.
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zed
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Ah, back to Parr Shakers! I don't disparage them. They have their place. But, under some conditions, an ordinary filter flask, equipt with a
magnetic stir bar, driven by a modern stir plate, is superior.
In the past, for hydrogenations, such setups, achieved results approximately equivalent to those achieved with shaker units.
Magnetic de-coupling of the stir-bar, at higher speeds, limited reaction rates. At high rpm, the turbulence created in the stirred solution, would
overwhelm the magnetic bond between the the stir-bar, and the drive magnets in the stir plate.
This old problem, caused my charming young Granddaughter, Munchkinkiss, to design a simple little experiment using alternative stir bars. She
figured....Stronger magnets=Stronger coupling.
So, she got herself some stronger magnets to use as stir bars. And, low and behold, by using modern, super-strong Neodymium Alloy Magnets as
Stir-bars, formerly undreamed of turbulence can be achieved. They don't break loose easily!
Ordinary stir-bar stirring? Dust-devil.
Stirring with Neodymium Magnet? Full-force Hurricane. Lots of gas entrainment.
I've never seen a Parr shaker that could equal it.
Neodymium Alloy magnets, which are usually only nickel plated, may need extra coating to render them sufficiently inert to corrosive reagents, and of
course, they demagnetize at high temperatures.
If your hydrogenation can be achieved at relatively normal temperatures, Neodymium stir-bars may be the way to go.
A Parr shaker retails for 3-4 Thousand dollars, while you can purchase a parcel of ten 1/4 inch by 1 inch Neodymium magnets, for about $16.00
including postage. Link two, end on end, and create a 1/4 inch by 2 inch magnet, that will produce good turbulence and gas entrainment, in a 2000
ml filter flask containing 1000 mls of liquid.
Stable at a fairly high RPM too.
If you still have doubts, observe the even greater turbulence and gas entrainment, achieved by a Neodymium Cylinder magnet, 1/2 inch by 2 inchs,
spinning at high RPM. Your doubts will be erased.
A parcel of four, 1/2 inch by 2 inch N48 Neodymium Cylinder Magnets retails for about $30.00 including postage.
[Edited on 1-5-2009 by zed]
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Sauron
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No one in their right mind buys Parr anything new except spares. Parr shakers go for a song on the used market. I payd $300 for my 3911\\In fact I
have less than $2K ib my 1 L Parr stirred heated SS autoclave which is somewhere in mid 5 figures new and rated for 1900 psig @ 350 C
The temp controller for mantle for Parr shaker vessels is restricted to 80 C. Some hydrogenations do call for heating and some are qute exothermic.
Those thick walled filter flasks were never designed as pressure vessels, and never designed to be heated. They were designed for aspirator reduced
pressure of substantilly less than 1 atm negative pressure, typically more like 50-100 torr.
The Parr glass vessels are rated, depending on size and type, to between 30 psig and 60 psig @ 80 C. In fact they are indicidually tested to 10 atm
(150 psi) at the factory.
Ace pressure vessels are rated to 50 psi.
In neiter case dothey warranty due to the nature of glass.
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zed
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An interesting premise. Since I've had filter flasks quite hot, at 200C to 300C, under fairly high vacuum, and never had a mishap, my experience has
been that they are pretty durable.
That however, was in the past. What currently manufactured glassware is capable of, may be a different matter.
At any rate, I wasn't suggesting significant pressure. Nor was I suggesting the use of heat.
Most of my personal experience has been with small scale "Brown" type hydrogenations.
Basically STP condition hydrogenations, using very active catalyst, in Erlenmeyer type flasks or Filter flasks.
In that environment, greater magnetic coupling, via Neodymium Alloy stir-bars, allows for more vigorous stirring, and highly improved gas entrainment.
Still to be addressed, is the question, "How much internal pressure can a modern filter flask withstand?" This would be nice to know!
Currently, I have no idea. But, I'm going to research it.
Hopefully, someone somewhere knows, and I won't have to burst a bunch of filter flasks to find out.
Glassware is so expensive now.
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jimwig
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they appear to be gone
craZy jiM wGGns
--packrat, professional bum. -- once just tired
now REtired.
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Sauron
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Zed, I have no headache with the use of a filter flask for a 1 atm hydrogenation at room temperature.
That would for example be fine for removing Z-protecting groups from amino acids or peptides with H2 and Pd black- an old method but a good one.
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zed
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I'll try to find out more about pressure and temperature capability. Naturally, I wouldn't suggest trying to push the limits if the filter flasks
can't take it.
It would be nice if they can take a little pressure. The shape of the Erlenmeyer flask is very advantageous for the entrainment of gas via stir bar.
It is unfortunate that the shape may have less than optimal strength for containing
pressurized gas.
Of course, stainless steel vessels can also be used for stir-bar hydrogenations, and stainless can take more pressure.
But to date, I've haven't seen spin bars create really good gas entrainment in high-pressure vessels. The inch thick stainless steel bottoms,
prevent the strong magnetic coupling required. Too much distance between the drive magnets and the spin bar.
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Sauron
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Dedicated autoclaves are generally either packed-gland direct drive stirred, or magnetically coupled at the top (lid) - mine is packed gland sealed,
belt driven continuously variable speed, I forget the top end, it's on the Parr sire. Of course this is not a dedicated hydrogenation apparatus. I's
more versatile than that. Still, there's a gas inlet.
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benzylchloride1
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I recently purchased an older Parr model 3911 pressure reactor from a surplus store for $17.00. It came with everything besides the glass reaction
bottle and a hydrogen cylinder. It appears to be in excellent condition, but required some cleaning. Now I just have to rent a hydrogen cylinder,
purchase tubing, regulator and pressure bottle
Amateur NMR spectroscopist
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entropy51
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Quote: Originally posted by benzylchloride1  | | I recently purchased an older Parr model 3911 pressure reactor from a surplus store for $17.00. It came with everything besides the glass reaction
bottle and a hydrogen cylinder. It appears to be in excellent condition, but required some cleaning. Now I just have to rent a hydrogen cylinder,
purchase tubing, regulator and pressure bottle |
Nice find! Now you have catalyst-induced hydrogen fires like the rest of us.
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