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YT2095
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LiAlH4 vs NaBH4
I`m going to placing an order soon for further stock.
is there much of a difference between LiAlH4 and NaBH4?
the Borohydride seems to be generaly a more stable (less risky) chem to store/use, and that`s always a good thing.
but are there any chemical advantages between one or the other?
they both seem to do more or less the same job.
so I`de like your opinions/advice before I make my choice.
Thanks each 
edit: also, what conc of HF(aq) is the most frequently used in general chemistry?
for instance Dillute (38%) nitric acid I get through more than my conc stuff.
[Edited on 11-11-2006 by YT2095]
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Eclectic
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LiAlH4 explodes when it hits water, NaBH4 doesn't.
If you don't know that much, you shouldn't be messing with either (or ether).
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YT2095
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if I was planning on putting it in water to generate H2, I can think of less expensive ways to that!
Why do you think I stated about the borohydride being less risky?
Now, any chance you can actualy Answer my question(s) as opposed to making bold statements of the bloody Obvious!?
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Nicodem
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| Quote: | Originally posted by YT2095
is there much of a difference between LiAlH4 and NaBH4?
...
they both seem to do more or less the same job. |
They nearly don't do the same job and they have anything but similar properties. You do not seem to know exactly what you are dealing with, so stay
away from LiAlH4 and buy NaBH4 instead. (Besides, I can't imagine a chemical supplier that would sell LiAlH4 to an individual.)
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YT2095
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by,"More or less" seem to do the same job (probably badly worded on my part) I meant as powerfull Reductors.
these 2 were reccomended to me as agents to decarboxylate benzoic acid.
I`m all for keeping the risk factor here as low as possible also, However I Am now curious more than before, what the difference is betwen these 2
agents for such operations?
and you`re quite right, I don`t exactly know too much about these as I`ve never used either of them Yet.
that`s why I`m asking
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Nicodem
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| Quote: | Originally posted by YT2095
these 2 were reccomended to me as agents to decarboxylate benzoic acid. |
What are you talking about? Neither LiAlH4 or NaBH4 decarboxylate anything.
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matei
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NaBH4 is not as powerful a reducing agent as LiAlH4 and is also more selective (e.g. normally it doesn't reduce esters but reduces ketones etc.). I'll
post a link to very good on this subject on the "New Books" thread.
Anyway I'd advise against using LiAlH4 in a home lab (in our lab LiAlH4 ignited spontaneously a few times when being taken out of its container).
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YT2095
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| Quote: | Originally posted by matei
Anyway I'd advise against using LiAlH4 in a home lab (in our lab LiAlH4 ignited spontaneously a few times when being taken out of its container).
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in that case then, I don`t want it around here at all 
my days of enjoying that sort of thing are long gone!
Nicodem, yeah, I was told it would work, although I`ve long since forgoten the source, I do have the note written down here with me, however after
what I`ve just read, the BoroHydride seems to be the chem of choice regardless.
I knew asking you guys First would be the right thing to do
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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woelen
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NaBH4 is the best choice. I also have some of this and it is a very neat reductor, also in aqueous environments. LiAlH4 is somewhat too extreme to my
opinion. I have Na-metal and I notice, that I hardly use it, because of the hassle of using it. LiAlH4 is more extreme than Na-metal, so I think you
will not use it much in your experiments. NaBH4 on the other hand is still a chemical, which can be handled easily. It dissolves in water quite well
and slowly releases bubbles of hydrogen. In alkaline solution it is somewhat more stable, in acidic solutions, it gives off hydrogen vigorously. NaBH4
is capable of releasing many metals from their salts. Even iron is released from its compounds.
If you look for good aqueous reductors, then you also definitely should order some sodium dithionite, Na2S2O4. This compound also is a very strong
reductor, but be careful with it, it can ignite in air, especially when somewhat humid. When dry, this stuff is stable, when humid, it absorbs oxygen
from the air, and this reaction releases a lot of heat, which can be so much, that it ignites. I myself never had this, but it is something you should
keep in mind, when using sodium dithionite. But, I really recommend you to order some of this as well.
Finally, I also suggest you to order some zinc metal, coarsely powdered. Zinc is a very good reductor, even better than Na2S2O4 and NaBH4. Zinc can
accomplish reactions, which Na2S2O4 and NaBH4 cannot accomplish. E.g. zinc can reduce chromium (III) ions to the +2 oxidation state and vanadium can
be reduced to the +3 and even +2 oxidation states. Both Na2S2O4 and NaBH4 cannot accomplish this. I would not order the ultrafine powder, because that
is pyrophoric. I have 500 grams of coarse zinc powder and I use it very often, it is one of my favorite chems. It also is cheap.
Keep NaBH4 and Na2S2O4 in very tightly closed containers, preferrably a second container around the inner container. NaBH4 is air-sensitive and if not
stored well, it slowly is oxidized by oxygen from the air, converting it to tame basic borate. Na2S2O4 is easily oxidized to sulfite or sulfate.
---------------------------------------------------------
YT2095, please do NOT order any HF. Really, you don't want that, if you value your health. Again, don't buy any HF.
If you really want to experiment with fluorides, then order some NaF (or even better: KF, which dissolves a little easier) and use that with dilute
acids to make dilute HF. Waterfree NaF or KF also can be interesting in conjuntion with H2SO4 to do some anhydrous fluoride experiments, but also
here, be VERY careful.
I advice much more strongly against HF than LiAlH4. HF simply does not belong to the set of home chems.
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The_Davster
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I think you meant that LiAlH4 would reduce benzoic to phenol, not decarboxylate. I have never used LiAlH4(yet) but have heard many horror stories
about it. On the other hand there are many organic reductions which will only proceed with LiAlH4 and not with NaBH4. Reducing benzoic acid to
phenol is one of those.
Unfortunatly Woelen, the good inorganic reducers do not carry over as well to organic as one would like. There are many organic reductions with zinc,
and some with dithionite(but it is a rather novel reducing agent to my knowledge), and there is definatly more literature on the use of borohydride
and aluminum hydride in reductions.
I suppose HF could be used at home, if you are using less than 5% solutions of it and have a tube of Ca-gluconate gell in your pocket at all times
while working with it. But it is definatly not something I would be comfortable with. Go with making dilute solutions when needed like Woelen said,
then you avoid storing the stuff as well. I avoid the stuff as much as possible, even the flourides I have I have not even used yet. I am more
comfortable with stuff like Mn2O7
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ziqquratu
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Something I've been told is that dilute solutions can in some respects be more of a hazard than the concentrated. This is because the LD50 is fairly
low, and a dilute solution can give a toxic dose just as well as a concentrated one. The difference is, it's relatively easy to miss the fact that you
just spilled a bit of the dilute stuff on yourself, allowing a longer exposure time, as opposed to the concentrated stuff which begins to burn very
quickly, alerting you to the spill and allowing you to respond faster.
Also, if using HF, yes absolutely have Ca-gluconate on hand. But personally, in case of a spill, I'd be taking myself to see a doctor ASAP just to be
sure, 'cause HF toxicity sounds like a rather unpleasant way to go...
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Eclectic
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There is a book on borohydride and aluminohydride reductions recently posted in reference...
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dapper
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HF
HF acid is something I don't want to get anywhere near, unless I absolutely have to. Painlessly dissolves you, and kills you..
Another thing that come to mind as scaring the piss out of me.. methyl mercury
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12AX7
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Painlessly? That's not how I heard it!
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Jdurg
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Honestly, HF is bad but I think it gets blown out of proportion quite a bit in terms of its toxicity. Having some of it spilled on you is dangerous
and you want to avoid it, but it doesn't mean certain and instant death. A good friend of mine has his doctorate in chemistry and works for a battery
company. During his postgrad work someone in his lab was using anhydrous HF and somehow had a great deal of it splashed onto her face. He admitted
that it was quite frightening, but they just washed it off and took her to the local Emergency Room and there were no lasting effects.
If you know what you are working with you can use HF quite safely. The thing is, there isn't a whole lot out there that does require HF and HF only
so few people get the chance to work with it. I would honestly be more concerned about having concentrated nitric acid around than I would HF.
\"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists of the unmistakable scent of broccoli, and usually
requires wiping afterwards.\"
http://maddox.xmission.com. |
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Magpie
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I have had the fun of using both LiAlH4 and NaBH4 in organic lab. I remember that in both cases I treated them with respect as powerful reagents. I
accidently spilled a little LiAlH4 over the sink when cleaning up. I remember a surprisingly violent reaction when it hit the water in the sink.
HF is the active ingredient in an etchant for glass sold in craft shops. It is somewhat surprising that this is available to the general public in
today's litigious climate.
Edit: When I checked my notebook I see that I have not used LiAlH4. The chemical that reacted violently in the sink was AlCl3 I believe.
[Edited on 13-11-2006 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Waffles
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| Quote: | Originally posted by Jdurg
Honestly, HF is bad but I think it gets blown out of proportion quite a bit in terms of its toxicity. Having some of it spilled on you is dangerous
and you want to avoid it, but it doesn't mean certain and instant death. A good friend of mine has his doctorate in chemistry and works for a battery
company. During his postgrad work someone in his lab was using anhydrous HF and somehow had a great deal of it splashed onto her face. He admitted
that it was quite frightening, but they just washed it off and took her to the local Emergency Room and there were no lasting effects.
If you know what you are working with you can use HF quite safely. The thing is, there isn't a whole lot out there that does require HF and HF only
so few people get the chance to work with it. I would honestly be more concerned about having concentrated nitric acid around than I would HF.
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I think the reason HF gets such a bad rap is because of its sneakiness. If you are working with the strong stuff, and you get a little hole in your
glove, and just keep working for an hour or two since it doesn't hurt for awhile, and not even realize- you can easily get acute hypocalcemia from
that. Most strong acids just burn your skin, fuck up your tissue. HF has the potential to be kill without a fuss, even under fairly controlled
laboratory conditions- better to blow the danger up a bit rather than play it down, no?
\"…\'tis man\'s perdition to be safe, when for the truth he ought to die.\"
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YT2095
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Thanks each
I`ll stick to the Borohydride and the KF salt, the plan is work through my AS and A2 chemistry text books stage at a time, Doing the experiments
outlined therein, to get a better understanding and hopefully leave no Gaps in knowledge (I have quite a few).
also the fact that the Borohydride is sufficiently powerfull enough to rip the metals from their salts is Ideal, up to yet I`m either Plating out,
thermit or displacement reactions with Mg or Zn, this can lead to significant contamination.
the second part of my goal is to collect/extract as many of the elements as possible towards my element collection, mineral shops are a fairly good
source of the raw materials and ores (as are beaches on holiday).
as for Conc Nitric vs HF, I have conc nitric here, and it`s never been an ounce of trouble, it`s quite well behaved although I don`t have cause to use it much, I get through about a litre of the 38%
stuff every couple of months though (much more usefull).
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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woelen
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| Quote: | Originally posted by Jdurg
If you know what you are working with you can use HF quite safely. The thing is, there isn't a whole lot out there that does require HF and HF only
so few people get the chance to work with it. I would honestly be more concerned about having concentrated nitric acid around than I would HF.
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I strongly disagree with this. Nitric acid of course also must be treated with respect, but it is not nearly as toxic as HF. Nitric acid at least is a
"honest" chem. It burns everything quickly and visibly. It also reacts violently with many chemicals and as such clearly shows its dangers.
HF on the other hand is really nasty. I once did an experiment with it (see my webpage, the KMnO4/H2SO4/NaF experiment) and white fumes of HF were
produced. These fumes were not really alarming, and even are less irritating than similar fumes of HCl. In the meantime they can do increadible damage
to you. Also, HF has longterm effects, while HCl and HNO3 do not have those effects.
In the past, quite a few great chemists were severely poisoned, not by HNO3, H2SO4 or HCl, but by HF. Some to name: Davies, Moissan (first person who
made elemental fluorine). Apparently, some of these great chemists have suffered great pains from fluoride poisoning.
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Jdurg
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Well I had a nice long reply all set to go but the forum software decided to crap out on me, so I'll just put up the succinct version.
HF is a nasty chemical and I'm not arguing that. I am simply arguing the mythical proportions to which this chemical is regarded in terms of danger.
This is a direct result of HF being used so very infrequently as there are virtually no reactions that require HF and only HF that most people come
across. When something isn't used that often people's imaginations begin to work overtime.  Again, HF is incredibly nasty and if you don't know what you're doing (which many people don't) you can get seriously
hurt. However, hundreds of thousands of people across the world use it daily in their jobs (Glass etchers, refridgerant producers) and they don't
seem to have any higher incidence of death and dismembermant than any other chemistry jobs.
Again, if you know what you are doing then it is a perfectly safe compound to work with. If you don't know what you're doing, then you shouldn't be
touching it. The same can be said for concentrated acids, many organic compounds, etc. etc.
As for the HF versus HNO3 dangers, when you've seen an entire stock room fill with NOx vapors thanks to a leaky HNO3 bottle you'd see where I'm coming
from. (The entire room was filled with the vapors and there was a serious fear that random fires would start breaking out thanks to the strong
oxidizing properties of NOx. HF wouldn't have caused that danger).
\"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists of the unmistakable scent of broccoli, and usually
requires wiping afterwards.\"
http://maddox.xmission.com. |
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YT2095
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I had a 500ml plastic bottle of HF in my early teens, I had no idea of it`s dangers in the way I do as an adult, I just simply treated it as any other
acid (I actualy found it quite Boring for the most part too).
I`m still here to tell about this, and with no ill effects at all.
to ME conc HNO3 was THE Acid! that was my idea of what an acid "Should" be like (I was only 14).
I guess in That respect I was "lucky"? I knew nothing about its Toxicity at all, it was just AN acid to me, and treated as such.
I still think the idea of using the salt and making it in situ is a little safer though, I`de sooner have to pick up a dropped crystal than a blob of
the acid
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Waffles
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| Quote: | Originally posted by woelen
In the past, quite a few great chemists were severely poisoned, not by HNO3, H2SO4 or HCl, but by HF. Some to name: Davies, Moissan (first person who
made elemental fluorine). Apparently, some of these great chemists have suffered great pains from fluoride poisoning. |
I love reading about the antics of the first chemists who isolated and experimented with fluorine and HF gas. And by antics I mean horrible deaths and
painful disabilities.
\"…\'tis man\'s perdition to be safe, when for the truth he ought to die.\"
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YT2095
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We ALL stand on the shoulders of Giants!
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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vulture
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LiAlH4 is hazardous if you pour water or acid over it, yes. Just work neatly, clean up everything it comes into contact with and plan your stuff. It
was surprisingly easy to work with it considering all the horror stories I've heard. Same goes for NaH.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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garage chemist
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LiAlH4 will reduce benzoic acid to benzyl alcohol, not to phenol.
If you want to decarboxylate benzoic acid, you have to heat its sodium salt with NaOH or Ca(OH)2. See the benzene thread for this, as benzene is the
product of this decarboxylation.
LiAlH4 usage brings with it the problem that the solvent (Diethyl ether or THF) in which the reduction will be carried out must be ABSOLUTELY dry. It
has to stand over sodium wire for several weeks (or use better drying agents like NaH and CaH2) and must be distilled in a distillation setup which is
flushed with dried inert gas and protected with a drying tube against atmospherical moisture.
I have long been unable to achieve the extreme dryness which is necessary to do LiAlH4 reductions. Even Grignards have much lower requirements for
dryness.
If the solvent isn't dry enough, it will fizz upon addition of the LiAlH4 to the solvent, and the LiAlH4 is hydrolyzed and lost.
The standard concentration of HF is 38-40%. This is the constant boiling acid, like with 21% HCl.
38% HF does not fume at ordinary conditions and outgasses only small amounts of HF, which is a good thing.
Needless to say, this acid is still extremely dangerous and skin contact can very well lead to loss of the affected body part.
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