FireLion3
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Is Raney Nickel inherently flamable, or only after pressure reactions?
I've read quite a bit about handling Raney Nickel, and a number of sources say it can just spontaneously ignite in the air. Wouldn't this only be true
if it was previously used in a pressure hydrogenation? Would transfer hydrogenations pose the same hazard since there is no free hydrogen ever stuck
in the catalyst?
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Metacelsus
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Both in transfer hydrogenations and in hydrogenations with gaseous hydrogen, the catalysts adsorbs the hydrogen. I expect similar danger with transfer
and regular hydrogenations.
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FireLion3
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I had understood that transfer hydrogenations take place under the mechanisms of oxidative addition and reductive elemination, and that the hydrogen
never actually leaves its source, it is instead only transferred when both the receiver and the donor are both touching the catalyst simultaneously.
The only cases I have seen warning over the flammability of Raney Ni was when it is used in pressure hydrogenations.
Of similar consequence, other Nickel Catalysts such as coordination complexes are often used for transfer hydrogenations without any risk for
ignition, granted, the mechanisms are slightly different. A touch unrelated, but it is interesting to me is that both zero valent nickel and the
nickel cation are capable of transfer hydrogenation.
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Dr.Bob
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Ranet Nickel itself can burn, just like zinc, magnesium or other finely powdered metals, which is why it is sold as a slurry in water. Since it is
stored in water, it is usually not an issue, and mostly if measured out as a slurry. Once dried, it is flammable, just as any other fine metal
powder, so best to filter it wet or handle away from other chemicals. But once any catalytic metal is exposed to H2, it becomes more dangerous, best
to purge with N2 or cycle through a few vacuum N2 cycles to remove the excess H2 before handling.
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zed
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Raney Nickel is generally produced by by the action of a base on an Aluminum-Nickle alloy. Dissolving Aluminum in such a manner produces hydrogen.
So, the presence of hydrogen on Raney Nickel, must be assumed. It is inherently flammable.
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FireLion3
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Guys I am getting some Raney Nickel from a supplier, 93% Ni 7% Aluminum. They only sell it as a fine powder, 50 micron size.
Is combustion a legitimate risk I have to think about when using or storing this? What are we talking about here? A small fire? Or a lab shattering
explosion?
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Dr.Bob
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I don't think there is any risk of an explosion from just Raney Nickel. Adding it to some compounds, like hydrazine, or other reducing agents, can
cause decomposition, which can be quite reactive, so that could be dangerous if not done slowly and best under a nitrogen atmosphere, but I can done
small ones without much purging. But it certainly can catch fire from exposure to air, with or without any other chemicals around. Filtering to
dryness in air is the cause of most fires.
I have used it many times for reductions, and most of mine were in ethanol, and I simply filter the reaction, and then wash the solids with ethanol
quickly, then water to help keep them wet. If your product is water sensitive, just have another collection flask ready to collect the water wash
into.
Once the filtrate is collected, I then wash the solids into a vial or bottle with some rinse water, and then keep the spent nickel as a slurry in
water. As you fill the bottle, you can decant off some water to keep the bottle from overflowing but as long as there is any water over the top of
the nickel, it should be fine. I may be overly cautious, but I have not ever had a problem, and I often get 90+% yields from my Raney Ni reductions.
It works quite well for easy reductions like aromatic nitro to amine, but it not as reactive for some other groups.
[Edited on 10-12-2014 by Dr.Bob]
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FireLion3
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I'm not worried about storing it post reaction. I am more concerned with storing the unused Raney Ni. I will be receiving a presumably mylar-sealed
bag of it. Will it be safe for me to transfer this to a standard plastic reagent container and store it there until use?
Used portions will be stored under water.
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Ozone
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I have had Raney nickel catch fire several times. This usually happens when filtering it out (solvent evaporates quickly and poof). I have also
observed the residue to catch fire in bomb reactions (again, solvent evaporates and poof), and when a slurry in an unlabeled container was tossed in
the trash on lab-cleanup day (wasn't me, but the firetrucks came out for that one).
It will catch fire if allowed to dry in air straight as it comes from the bottle. It is even more touchy after a reaction. The presence of flammables
nearby should be avoided.
In all cases with finely divided metals, Al hydrides (cyanoborohydride and STAB are pretty laid back) and/or most organometallics--don't plan to react
in case of fire, plan on having one. This is especially true with Zn, Al and Li alkyls.
All of the Raney nickel I have ever received came from the supplier in a wide-mouth plastic bottle under water. It will stay that way nicely almost
forever, SFAIK. We kept it in the refrigerator.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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CuReUS
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Quote: Originally posted by FireLion3  | Guys I am getting some Raney Nickel from a supplier, 93% Ni 7% Aluminum. They only sell it as a fine powder, 50 micron size.
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IIRC ,the ratio of Ni:Al is usually 1:1
if there is so little Al ,the alloy will not become very porous , and not a lot of H2 will be liberated as only the Al will react with the
NaOH ,not nickel
http://www.webelements.com/nickel/chemistry.html
read under "reaction of nickel with bases"
for the importance of Al in raney nickel read this
http://chemistry.stackexchange.com/questions/14695/differenc...
are you getting the 7% Al grade because you want a less reactive and more selective catalyst ?
[Edited on 10-12-2014 by CuReUS]
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FireLion3
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The supplier is an industrial factory supplier and they said this ratio is a very standard ratio used in the industry. I'm not sure why else they
would just have this ratio mixed laying around.
The reactions I am going to be doing do not require Raney Nickel Explicitly. Normal nickel works just as well as long as it is Ni 0. Ni 0 without
aluminum also works for transfer hydrogenations, I think the Aluminum just helps activate it?
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S.C. Wack
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He didn't say it was Raney alloy. He called it Raney Ni, which probably does always have some Al in it, when made from the usual alloy.
If it comes in a bag and isn't under water and doesn't have a bunch of hazardous shipping labels on it...it's probably not very reactive.
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WChase501
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It is flammable no matter what.
"Playing God" is false, Nothing in our Universe is impossible, you just need to know the method of doing whatever you want to. Knowledge is
everything.
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