Author Topic: Short Questions Thread  (Read 10820 times)

Enkidu

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Re: Short Questions Thread
« Reply #640 on: October 21, 2010, 03:58:38 PM »
Sitting class today something struck me.  Why haven't meth cooks just taken to oxidizing ephedrine with chromic acid or bleach, then performing a clemens reduction?

I think you'd have to protect the amine, but I'm not really sure. no1uno would probably know more.

akcom

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Re: Short Questions Thread
« Reply #641 on: October 21, 2010, 07:00:12 PM »
I've got some old benzoquinone that has not been stored properly (not under vacuum, but still bagged and away from light).  Would recrystallization be a decent way to remove whatever shit has formed?  If so, any recommendations on solvents + volumes?  I've seen petroleum ether in lit, along with the suggestion of 91% IPA.  Not a shot in hell I'm sublimating this stuff.

tregar

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Re: Short Questions Thread
« Reply #642 on: October 22, 2010, 05:40:22 PM »
it couldn't hurt to recrystallize it, give it a shot. I think this same question was asked a time or two at the old hive, if you search you may find an answer there as well. If after recrystallizing it...and once it's dry...you then find that you can't stand to be around it, then congrats...it is back to it's old stinky intolerable self, albleit perhaps 10 to 20% loss.

jon

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Re: Short Questions Thread
« Reply #643 on: October 22, 2010, 07:17:26 PM »
^ oerlikon
no it's worthless if you plan to do a williamson ether synthesis you will get all kinds of side reactions namely aldol condensations.
if you reductively aminate it you would have to protect that amine from alkylation.
« Last Edit: October 22, 2010, 07:23:02 PM by jon »

jon

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Re: Short Questions Thread
« Reply #644 on: October 22, 2010, 07:20:40 PM »
^goldmember that's an  interesting question i don't have an answer for

solidstone

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Re: Short Questions Thread
« Reply #645 on: October 22, 2010, 09:24:10 PM »
So, I've been curious how well this works or if it works and if not why not.

NaBr + HCl --->  HBr + NaCl

this has always seemed a viable route to HBr over the counter, and the difference in electronegativity would suggest this reaction occurs.  does it?  and how well does it proceed.

Vesp

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Re: Short Questions Thread
« Reply #646 on: October 22, 2010, 09:27:51 PM »
It is going to form in an equilibrium - so really "nothing" AFAIK changes when HCl is added to NaBr solution since H+ and Cl- are in one solution, and Na+ and Br- are in another.

You would have to separate them out using something such as distillation, solvent extraction (?) or crystallization?

I don't know if it would be an effective method of producing HBr, but depending on how one isolated it or what it was going to be used for - it might be useful. Depends on what you have available to yourself.
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Enkidu

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Re: Short Questions Thread
« Reply #647 on: October 22, 2010, 09:36:08 PM »
No, you can't make hydrobromic acid like that because hydrogen bromide is a stronger acid than hydrogen chloride..

Vesp

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Re: Short Questions Thread
« Reply #648 on: October 22, 2010, 09:50:46 PM »
No, you can't make hydrobromic acid like that because hydrogen bromide is a stronger acid than hydrogen chloride..

While HBr is a stronger acid, I don't think that is necessarily relavent when it comes to producing HBr from HCl - The electrotivity of the chloride is stronger than the bromide, isn't it? So it would favor being with the sodium, IIRC

It would be tricky to do, but it isn't impossible.
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Enkidu

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Re: Short Questions Thread
« Reply #649 on: October 22, 2010, 10:42:11 PM »
HCl + H2O <-->>> Cl- + H3O+
HCl + Br- <<<--> Cl- + HBr
HCl + Br- + H2O <-->>> Cl- + Br- + H3O+

No, Vesp. Electonegativity is simply a measure of electron affinity - and all the electrons have already been taken from the sodium atoms and hydrogen atoms and given to the the halides. (We are working with ionic bonding.) Strong acids completely dissociate in soln, and you have, at this point, a mixture of ions floating around in solution. You can imagine the proton jumping from a water molecule to a bromide to a chloride. The proton will want to sit around where the situation is most favorable, i.e., where the conjugate acid is the weakest. So the order is H2O > Br- > Cl-. Since we are dealing with an equilibrium, you can manipulate it in a variety of ways. If you can find a way to remove the chloride ions from the solution, then you have a shot at isolating the hydrobromic acid. As it stands, from a practical point of view, there is no way to achieve this isolation.

Why would an atom with a high electroNEGATIVity (it wants electons) be attracted to a POSITIVe ion?

Chlorine is a stronger oxidizer than bromine due to the difference in electronegativity, but that is a completely different topic.
« Last Edit: October 22, 2010, 10:46:03 PM by Enkidu »

solidstone

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Re: Short Questions Thread
« Reply #650 on: October 22, 2010, 11:12:24 PM »
I guess this would be my answer to how to get HBr.

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Enkidu

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Re: Short Questions Thread
« Reply #651 on: October 22, 2010, 11:16:33 PM »
You should not use sulfuric acid because it will oxidize quite a bit of bromide to bromine.

solidstone

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Re: Short Questions Thread
« Reply #652 on: October 22, 2010, 11:42:27 PM »
I believe that is why he is using an ice bath to limit the reaction.  What would be your method for preparing HBr, I'm open to suggestions

Sedit

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Re: Short Questions Thread
« Reply #653 on: October 22, 2010, 11:49:29 PM »
You should not use sulfuric acid because it will oxidize quite a bit of bromide to bromine.

H2SO4 is only a strong oxidizing acid at concentrations roughly 75% and up. Below this threshold its oxidation abilitys do not pose so much of an issue.  50% Sulfuric acid will only turn slightly orange when mixed with NaBr and if chilled and the addition is handled slowly this is even less of an issue.

H3PO4 is the standard for making HBr from NaBr but I am considering using Toluene sulfonic acid in the near future since this is a solid, strong non oxidising acid as well.
« Last Edit: October 22, 2010, 11:51:07 PM by Sedit »
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solidstone

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Re: Short Questions Thread
« Reply #654 on: October 23, 2010, 12:36:29 AM »
Could you outline the procedure for making HBr from 85% phosphoric.  I guess I'm just asking if one reagent is to be in excess and if you purify through distillation.  This would be very helpful to me.  Thankyou

Sedit

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Re: Short Questions Thread
« Reply #655 on: October 23, 2010, 01:24:15 AM »
There are many places online that detail this procedure better then I could explain it. Its relatively straight forward.
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solidstone

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Re: Short Questions Thread
« Reply #656 on: November 02, 2010, 06:40:17 AM »
Just curious if chlorobenzene could be used with ferric chloride and acetone for a friedel craft route to phenylacetone.

Enkidu

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Re: Short Questions Thread
« Reply #657 on: November 02, 2010, 06:47:50 AM »
Nope.


« Last Edit: November 02, 2010, 06:49:44 AM by Enkidu »

Evilblaze

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Re: Short Questions Thread
« Reply #658 on: November 08, 2010, 08:18:29 PM »


Hello everyone. I would have a question in chemistry....

There would be a compound (4 nitro 2,5 dimethoxy phenylacetone) and the goal would be to turn this into DON (4 nitro 2,5 dimethoxy amphetamine).

My ideas:
-turn the ketone into an imine with an ammonium salt. Or maybe with hydroxylamine to an oxime.
-reduce this imine/oxime to amine with something what won't damage the  nitro on teh aromatic ring.

Any ideas? Or any references?

As I readed NaBH4 would be a good reducing agent for the second step. The only question would be that will it reduce the oxime to amine (I would prefer to make an oxime, because hydroxylamine is a relative "clean" chemical and an oxime is a bit more stable than an imine) and will it damage the nitro group on the other side of the molecule?

Thanks!

atara

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Re: Short Questions Thread
« Reply #659 on: November 09, 2010, 07:13:32 PM »
Zinc borohydride / pyridine is the only thing I think would have the appropriate selectivity.
http://proj3.sinica.edu.tw/~chem/servxx6/files/paper_8139_1269159644.pdf
Quote
Aryl aldoxime with a substituted nitro group showed a selectivity and was readily reduced using two molar equivalents of reagent without affecting the nitro group (entry 5), but with further molar amounts of the reagent the simultaneous reduction of the nitro group took place.

Stoichiometry, stoichiometry, stoichiometry.

http://www.erowid.org/archive/rhodium/pdf/zinc.borohydride.pdf -- gives the preparation of zinc borohydride

« Last Edit: November 09, 2010, 07:37:25 PM by atara »