organicchemist25
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LAH handling concern after searching before asking
SO, I will be taking on my first LAH reduction with a styrene. It will be approximately 20-25 grams of LAH after some calculations, but no more than
25g because that's all I received. I am anxious and nervous at the same time. It is the first reaction I really have gotten worked up over, and
rightfully so....at least to me and my level. We never did an LAH reduction in ochem I or II. We did a lot on paper and exams, but that does not
prepare one for its use by any means.
I've done numerous Grignards with success and handle diethyl ether and THF pretty frequently in my fume hood with proper hood ventilation along with
properly drying over sodium and freshly distilling, but LAH is still concerning me.
Ok, first off, I have had the LAH in the same container I purchased it in 4-5 months ago and still in the vacuum sealed foil bag from the
manufacturer, Sigma. I am not sure if we are allowed to name drop, so, if not, I apologize ahead of time and will comply from here on out.
It has been in my lab with only air conditioning when I go out to do experiments etc. I have since been keeping it on a controlled climate constantly
( 75 F / 24 C ) and will just keep the lab climate controlled year round. Reagents and solvents are too expensive not to just pay ~30$ a month to
keep room temperature.
1.. Is the LAH still ok if it was subjected to 2 months of summer heat even though it is sealed and vacuumed sealed around the content package?
2.. It is humid in my region on the east coast, usa. It averages 90 degrees currently and humidity is high (~90-100%) for sure, almost always. Is
there a maximum humidity threshold to open exposure? I know its moisture sensitive. Would a minute or two in open air be ok in the fume hood as I add
it to a DRY flask with DRY THF freshly distilled, while being flushed with nitrogen?
3.. I know its very exothermic upon addition to the THF, so is there a rate to add or bubbling to subside per addition of small quantities?
4.. Once its in THF is it a lot "safer"? Like can I relax a little when I know its in solution?
5.. I think this is last question. I may think of something else later up until I move forward. I have a small utility room (but the only serious
negative is its attached to my house) but would it be best to run a dehumidifier for a day or two, keep it closed up, add the LAH in a pretty dry
room, get it into solution, then resume in the lab? I don't want this to sound like a foolish question...I'm totally against the house, but just
asking if I used it for a few minutes with low ambient moisture and proper fire gear, ie blanket, extinguisher, sand, as well as all of my safety
apparatus, too. The glassware would be dry and so will the THF and I have a portable tank of N2. There just wouldn't be a fume hood
I have always appreciated everyone's feedback and input..Im sorry this is a long one, but this will be a big leap for me. I just
want to make damn sure, as much as anyone of us can, to keep it under control and feel like I fully understand it.
The lab is insured, but I still want my stuff and to be unharmed inthis progression.
Thank you all
*If I left something critical out or a concern or tip, PLEASE share with me..
[Edited on 11-8-2018 by organicchemist25]
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Metacelsus
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For the first time, I would suggest doing it on a smaller scale than 25 grams.
LAH should be OK for a few minutes in the air.
The most dangerous part of doing a LAH reduction, in my opinion, is quenching the remaining LAH during workup. What's your plan for this?
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Tsjerk
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Exactly what Metacelsus is saying. Start with a reaction using about a gram of LiAlH4
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organicchemist25
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Sorry, that I left the quenching work-up step out.
For each gram of LAH I use I’ll add dropwise (SLOWLY) one mL of dH2O at zero degree C followed by one mL of 15% aqeuous NaOH and, finally, another 3
mL of dH2O. Then filter the resulting solid and rinse the solid with plenty of ether and evaporate in my rotovap. I also read to additionally add
anhydrous Magnesium sulfate? If MgSO4 should be added, at what point should I add that?
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organicchemist25
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Thank you both for the great advice! I appreciate it very much. I’ll scale it down quite a bit. I may try 2-2.5 grams, but that’s 10x smaller
scale.
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Tsjerk
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Why don't you start with half a gram? You can preform the reaction five times compaired with the 2.5 grams. The percentage of loss during work-up will
be a bit higher with snake quantities but if you screw up a larger quantity it sucks harder.
My experience is that the quality of work goes up exponentially when repeating an experiment
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