I want to test the activity of different batches of LAH that I have. I'm thinking of adding a small measured amount to dried THF and then adding water
drop by drop, watching to see when bubbling stops, measuring the amount of water used and then calculating.
One thing I'm wondering is -- I'm not going to be completely sure when the THF is completely dry, so some of the LAH might get affected by residual
water.
Has anyone tried this?bfesser - 31-7-2013 at 19:02
<img src="../scipics/_warn.png" /> These procedures can be hazardous! <img src="../scipics/_warn.png" />
<strong><a
href="http://www.sigmaaldrich.com/etc/medialib/docs/Aldrich/Bulletin/al_techbull_al123.Par.0001.File.tmp/al_techbull_al123.pdf"
target="_blank">Quantitative Analysis of Active Metals and Metal Hydrides via Gas Buret</a></strong> <img src="../scipics/_pdf.png"
/> (Aldrich Technical Bulletin AL-123)
<strong>Determination of Lithium Aluminum Hydride in Solution</strong>. J.A. Krynitsky , J.E. Johnson , H.W. Carhart.
<em>Anal. Chem.</em>, <strong>1948</strong>, 20 (4), pp 311–312. DOI: <a href="http://dx.doi.org/10.1021/ac60016a010"
target="_blank">10.1021/ac60016a010</a> <img src="../scipics/_ext.png" />
<strong>Iodometric determination of lithium aluminium hydride</strong>. H. Felkin. <em>Bulletin de la Société Chimique de
France</em> 18 (<strong>1951</strong>: 347-348.
<a href="viewthread.php?tid=25035&page=2#pid294290">[papers requested]</a>soma - 8-8-2013 at 13:20
Thanks for the input.
Any thoughts about the method I suggested? -- putting a weighed amount of the LAH in THF and neutralizing with H2O drop by drop until it stops
bubbling - measuring the amount of water needed and then calculating?
testing LAH
soma - 9-8-2013 at 11:06
(I also posted this to Chemistry in General)
I want to test the activity of different batches of LAH that I have. I'm thinking of adding a small measured amount to dried THF and then adding water
drop by drop, watching to see when bubbling stops, measuring the amount of water used and then calculating.
One thing I'm wondering is -- I'm not going to be completely sure when the THF is completely dry, so some of the LAH might get affected by residual
water.
Has anyone tried this?Bot0nist - 9-8-2013 at 11:08
Dont crosspost.!bfesser - 9-8-2013 at 11:20
The gas burette method I posted above is facile and proven. Why are you wasting time trying to come up with something less accurate?soma - 9-8-2013 at 11:38
The gas burette method I posted above is facile and proven. Why are you wasting time trying to come up with something less accurate?
I don't have some of the equipment for the gas burette method whereas the equipment for the method I'm suggesting doesn't require any new equipment. I
don't need an extremely accurate reading - just a general idea of how much excess LAH I'm going to need to be sure I get 100% reaction.
Also, it's not clear to me what they are saying to do.
"To obtain an accurate reading of the volume of hydrogen gas produced, the water level in the side tube H must be coplanar with the water level in
the buret I. Consequently, more hydrogen gas must be forced over into the buret to raise the water level in the side tube until it corresponds to the
water level in te buret. This is easily accomplished be quickly lowering the leveling bulb J to a point below the outlet of the side tube in the buret
and then raising the leveling bulb to its original position. The lowering and raisingof the leveling bulb are repeated until the water levels in the
side tube, buret and leveling bulb are all coplanar. The final buret reading is then taken as illustrated in Fig. 1
[Edited on 9-8-2013 by soma]
[Edited on 9-8-2013 by soma]soma - 24-12-2013 at 14:47
Anyone tried this:
Titrate THF or ether solutions of lithium aluminium hydride with 9-fluorenone.
E. Brown, A. Lézé, J. Touet Tetrahedron Lett. 1991, 32, 4309. chemrox - 26-12-2013 at 16:54
I don't want to buy 9-fluorenone. Are any of these stocks showing signs of deterioration? Turning from metallic gray to ashy looking powder?
BTW the fire extinguishers for metal hydrides run ~ 6-800 US. Sand is a lot cheaper.
[Edited on 27-12-2013 by chemrox]soma - 27-12-2013 at 21:50
I got some that was from Alfa Aesar through a 3rd party (it was still in the Alfa packing). I was very surprised to find that they didn't have a
recloseable metal container to put the unused powder back into-- just a plastic bag. I wrapped the bag in 2 ziplocks and put it into a cardboard
container with a plastic lid.
It seems like the LAH I got about 2 years before this one (in a glass bottle) is less decomposed than this one (after about a year.) It still looks
like a grey powder though.
: 347-348.