cfourforever
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Safety precautions when working with LAH (First time)
I'm going to perform a reduction Using 50g of LAH. The only problem is, this is my first time working with the compound. What kind of safety
requirements should be undertaken?
( I'm currently enrolled in high school, and just stated chemistry as such I only have a basic understanding so spelling things out for me would be
helpful)
1. First i'm going to Dissolve 50g of LAH in 200ml Tetrahydrofuran (THF), I understand this is going to get hot, how hot?
2. Going to be working in my bedroom in my parents house with low humidity. I want to work with an ice bath under my reaction vessel but i'm worried
about the LAH coming in contact with the H2O on accident or increasing the humidity in the room. Is this right or just silly?
3 Next I will add my LAH Dissolved in THF to a pressure equalizing addition funnel connected to the top of my reaction flask that contains my
undisclosed compound that happens to be an alkene (also dissolved in THF)
4. Then, wearing a full face mask, gloves and lab gear I will SLOWLY drip my LAH into the RBF containing the alkene. I understand hydrogen and heat
will be evolved. Will this be too much for my bedroom? how much heat will there be? I have a window and plan on opening it
Thanks in advance.
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Metacelsus
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Really, don't burn your house down!
Can you try it on a smaller scale first?
Can you try different reducing agents? (Pd/C + H2 will reduce alkenes, but I'm not sure about your secret substrate)
If you have to do it, can you at least do it outside?
By the way, LAH does not reduce simple alkenes. Might you be working with a conjugated nitroalkene?
[Edited on 22-10-2014 by Cheddite Cheese]
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cfourforever
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Might you be working with a conjugated nitroalkene? Yes it is
I have heard a lot about about this Pd/c + H2 reduction in books, Google and such but have yet to visualize how to turn this into a practical
application, plus I already have the LAH so might as well use it.
So you would definitely work outside?
Thanks,
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NexusDNA
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I understand you've already paid for the LAH and all, but really... LAH is not really appropriate to be used at your bedroom. I'm being euphemistic.
If you are really not considering changing to some other chemical, do a test run outside, and be careful.
If I were you I'd look for NaBH4 followed by Zn dust. You can find patents on that. Pd/C is of course safer but not cheap.
Also, if I were you, I'd choose a better topic for your first thread, or a forum more suited to your needs. You understand this is not a clandestine
chem forum, yes? Good luck.
Bromine, definitely bromine.
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cfourforever
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All of my questions have been safety related
I'm not asking any questions on how to make anything illegal. Plus your asserting, without knowing, that my conjugated nitroalkene reduction product
will be illegal. That's not very nice.
All I want to know is more about safety protocol regarding LAH. I can't find good information on search.
I have heard some people say that I MUST work under inert atmosphere, where others have said that its not necessary.
How much heat and hydrogen gas are we talking about here. A beans and broccoli kind of gassing or something more like a Auschwitz kind of gassing.
Thanks again,
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Texium
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Alright, well, you've just had two people who seem to know what they're talking about strongly suggest not using LAH, so you can do what you wish with
that helpful advice I guess. It looks to me like the best thing to do would be to listen to them and not use LAH in your bedroom.
And the reason that they're asserting that you're making something illegal is most likely because you refer to your nitroalkene as an "undisclosed
compound." Talk like that and you can expect to be questioned. Don't act all surprised and offended about it. If you're really not concerned, just
explain exactly what you're doing. The extra information can always help anyway.
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HgDinis25
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If you're really serious about this you need to think this through first.
I assume you already know a bit about LAH, like it's daring desire to kill you.
Anyway, if you MUST work with it don't do it outside, in an uncontrolled environment. Doing it there has the advantage that, should anything cath
fire, your possessions are safely away. But think about all the uncontrolled variables: the wind carring humidity and all sorts of watery crap, bugs,
the nearby tree that likes to dispense leaves (non dry) etc etc
If you MUST use it prepare your room first. Use a dehumidifier and let it run a few hours before starting to work. Make sure all the equipment you're
going to use is water free. After your workplace and equipment is verified, check your reagents. They should be as water free as possible.
During the reaction, as you stated, H2 will be evolved. Only open your window at that time.
Make sure that, during the entire process, you have a fail switch. I recomend having a safe place to put the LAH and the things burning because of it,
like a metal bin (a large one). Also, clean the area outside, below your window, and isolate it. That's where your metal bin is going to land after
the fire has started and, hopefully, you''ve contained it in the metal bin.
Use Latex gloves. Make sure to use leather gloves too. If you have fire retardent clothing, time to wear it.
Do you really want to do this?
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j_sum1
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Quote: Originally posted by HgDinis25  | If you're really serious about this you need to think this through first.
I assume you already know a bit about LAH, like it's daring desire to kill you.
Anyway, if you MUST work with it don't do it outside, in an uncontrolled environment. |
I assume you mean do do it outside!
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gdflp
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No, he means don't. Finish reading the sentence, humidity and other unknown factors outside can cause potentially dangerous mishaps with LAH.
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Metacelsus
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I'd rather have it likely catch fire outside than possibly catch fire in my house!
Anyway, some tips:
1) Make sure your glassware is completely dry (like Grignard dry) beforehand.
2) Use the ice bath. The risk of overheating is greater than the risk of the ice bath water getting in the reaction.
3) Have good ventilation (to dissipate hydrogen and solvent vapors).
4) Add the LAH to the THF slowly, and stop adding it for a while if it gets too hot.
5) Do a small test run first.
6) Be prepared for it to catch on fire despite these precautions.
Do your parents know what you're planning, and, if so, do they approve of it?
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DJF90
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Where do I start... as others have said, use a safer substitute and find somewhere more suited to do lab work. Never do an unfamiliar reaction on
such a large scale. This enables you to define the process on ca 1g, determine how strong the exotherms are on a scale that isn't too dangerous, work
out how long the reaction is expected to take, and determine the best way to work it up and isolate product. It also allows you to observe any
potential problems before you scale up, e.g. the formation of a thick precipitate (may require more solvent to provide mobility).
One thing that no-one here has picked up on is the ratio of solvent to LAH you're intending to use. There is nowhere near enough solvent there.
You're proposing a ca 6.25 molar solution, which is not,possible: LAH is not that soluble in THF. Having seen LAH reactions done on 20 L scale, and
having heard from colleagues about fires they've had with the reagent on that scale, I can safely say this is not suited to someone of your skill
level. When using LAH powder, inert atmosphere is a necessity. The solid is charged to a flask under inert gas, and the apparatus arranged for reflux.
The flask is cooled in an ice bath, and quickly (in one portion, with appropriate stirring) all of the THF (I'd suggest targeting a 2 or 2.5 M
solution) is added don the condenser (cooling water ON!). The dissolution of LAH is extremely exothermic, and you'll find that even with the ice bath
you'll hit reflux!
The solution if required for addition to your substrate will have to be transferred to pressure equalising funnel via cannula (aldrich sell nice
chemflex lines for this sorta thing...). Preferably (if it is safer and does not affect the chemistry) the substrate is added to the prepared
solution.
Your reaction should not generate hydrogen unless your solvent is wet, or you have an acidic proton on your substrate (e.g. phenol). The workup
however will generate plenty, and this is,something else you should have an understanding of. Quenching a LAH reaction is not an easy task for those
inexperienced with it. There are numerous ways of doing so. Do NOT use ethyl acetate. Diethyl ether saturated with water is one way. Solid sodium
sulfate decahydrate (glaubers salt) is another. Some people charge water or saturated ammonium chloride. Then theres the Feiser's method. I've heard
you can add 6eq. NaF then water to get a filterable solid (cryolite?). Personal preference is a solution of rochelle's salt, although it can take a
while to give two clear phases.
To recap: Don't do this. If you really have to (you don't) then do some small scale tests first. Use,more THF. Find a safer alternative if you can.
Don't destroy your parent's house... they will NOT be pleased.
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careysub
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Here is an account of a recent fatal lab accident involving tert-butyllithium:
http://cen.acs.org/articles/87/i31/Learning-UCLA.html
When you dissolve LAH in THF you have created something very similar - a highly volatile spontaneously combustible incendiary.
It could also be compared perhaps to triethylaluminum (TEA), which is used as an actual incendiary weapon:
http://en.wikipedia.org/wiki/Triethylaluminium
While not the same compound, the reactivity of TEA is instructive. Here is a professor demonstrating the combustion of 1 mL (0.8 grams) of the stuff:
https://www.youtube.com/watch?v=TwlrU5dgryk
Now imagine 60 times that amount plus your solvent going up.
[Edited on 23-10-2014 by careysub]
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Loptr
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I think it's ironic considering his nickname, cfourforever, i.e. C4 (explosive) forever, with the fact that it will most likely go up in his face.
I don't have any experience with LAH, but I have heard tales of it being friction sensitive when previously exposed to a non-inert atmosphere.
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Bert
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cfourforever
The ONLY reason this isn't going to detritus is the excellent safety advice members are giving you- Young, dumb and full of cum as you are, please
stop and listen to them BEFORE your parents first have a house fire, an idiot child in a burn ward or body bag to worry about, and then lose your home
under drug war spawned property forfeiture laws if this is in USA.
[Edited on 23-10-2014 by Bert]
Rapopart’s Rules for critical commentary:
1. Attempt to re-express your target’s position so clearly, vividly and fairly that your target says: “Thanks, I wish I’d thought of putting it
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2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
Anatol Rapoport was a Russian-born American mathematical psychologist (1911-2007).
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bbartlog
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Two other bits of advice, assuming you decide to go ahead with this:
1) Have a fire extinguisher handy and some idea of how to use it.
2) An open window, by itself, is almost useless; you don't know which way the wind is going to be blowing. If you want to substitute an open window
for a fume hood, at least get a window fan (blowing outward). I had such a setup for a while (with a remote for the fan, so I could turn it on from
the doorway as I was exiting the room, if need be), and while it was no substitute for a proper hood it at least allowed me to clear the room of
noxious gases within a reasonable timeframe, and ensure that they didn't diffuse in to the rest of the house too much.
The less you bet, the more you lose when you win.
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Loptr
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| Quote: Originally posted by bbartlog | Two other bits of advice, assuming you decide to go ahead with this:
1) Have a fire extinguisher handy and some idea of how to use it.
2) An open window, by itself, is almost useless; you don't know which way the wind is going to be blowing. If you want to substitute an open window
for a fume hood, at least get a window fan (blowing outward). I had such a setup for a while (with a remote for the fan, so I could turn it on from
the doorway as I was exiting the room, if need be), and while it was no substitute for a proper hood it at least allowed me to clear the room of
noxious gases within a reasonable timeframe, and ensure that they didn't diffuse in to the rest of the house too much. |
Also, not just any fire extinguisher is advisable, since there are different types and I am pretty sure you would want some sort of dry chemical.
http://www.femalifesafety.org/types-of-extinguishers.html
http://www.falckproductions.com/resources/fire-safety-and-fi...
[Edited on 23-10-2014 by Loptr]
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zed
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It's better to have a mentor to instruct you during such a dangerous first encounter.
At the very least, try a preliminary run of this reduction, using only 1/2 a gram of hydride.
Fifty grams of LAlH4 is a lot, not a little. Explosive ignition, with solvent, will permanently spoil your looks for the main drag. If you live.
Moreover, you will find life as a "crispy critter" unimaginably horrible. I mean, what with your face and all of your fingers being burned off, and
everything.
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