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Author: Subject: The Short Questions Thread (4)
DubaiAmateurRocketry
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[*] posted on 18-1-2014 at 02:21


Where is the supplier ? my search engine is filled with trichloroacetyl isocyanate..
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alexleyenda
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[*] posted on 18-1-2014 at 21:18


I know that black rubber stoppers do not resist to nitric acid and I was wondering what else I should avoid using with them, I could not find informations about it. Same question for cork stoppers, what chemicals should be avoided with cork stoppers? Thank you

[Edited on 19-1-2014 by alexleyenda]
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[*] posted on 22-1-2014 at 06:42


Quote: Originally posted by alexleyenda  
I know that black rubber stoppers do not resist to nitric acid and I was wondering what else I should avoid using with them, I could not find informations about it. Same question for cork stoppers, what chemicals should be avoided with cork stoppers? Thank you

[Edited on 19-1-2014 by alexleyenda]


Acids burn cork stoppers.

Cork stoppers wrapped well in PTFE tape, not the cheapest thinnest kind but 0,2mm min. thickness and wider is better too, those corks withstand about everything and can in case just be re-wrapped.
If using stopppers with holes the tape has to be wound through this to make it perfect.

My preferred connector actually, the elasticity is often advantageous too.



My question is thouh:

Will a hybrid combination of neodym and electromagnet prevent loss of magnetisation in the neaodym part at higher temperatures and still have the combined power? f course some iron is to be included in this, say and iron pot with the neodym in it and a coil around the pot.

thx
/ORG




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alexleyenda
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[*] posted on 22-1-2014 at 11:36


Thank you, and interesting question I cannot answer :)
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[*] posted on 22-1-2014 at 13:21


How do you guys purify your vitamins and what not from store bought pills? In specific I want to know about inositol, PABA, and nicotinic acid (niacin).



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[*] posted on 22-1-2014 at 16:18


Sublimnation of PABA (340°C)

liquid-liquid extraction of nicotinic acid using DMSO?
(http://lxsrv7.oru.edu/~alang/onsc/solubility/allsolvents.php...)

inositol could also be extracted using liquid-liquid extraction
(not a real reference, but http://www.researchgate.net/post/Does_anyone_know_about_solu...)

the purification technique really depends on what you're using it for
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thebean
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[*] posted on 22-1-2014 at 17:04


The PABA sublimation will come in handy but liquid-liquid extraction isn't useful seeing as I'm removing insoluble binders from the pills. Recrystallization from water solution would work fine but whenever I do it with inositol I seem to destroy the inositol, so I'm nervous about destroying what little inositol and nicotinic acid I have left.



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[*] posted on 23-1-2014 at 12:56
Question


Does anyone know of any preparations of solid hydronium salts or a discussion of them in literature?

Wikipedia mentions they do indeed exist, but only gives a few odd and exotic examples.

[Edited on 1/23/2014 by Sublimatus]
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[*] posted on 23-1-2014 at 13:31


Quote: Originally posted by Sublimatus  
Does anyone know of any preparations of solid hydronium salts or a discussion of them in literature?

Wikipedia mentions they do indeed exist, but only gives a few odd and exotic examples.


There are quite a few solid strong acid monohydrates that are in fact solid hydronium salts. For example p-toluenesulfonic acid monohydrate is hydronium p-toluenesulfonate. Indicative of it being a salt is that the monohydrate's melting point is considerably higher than the anhydrous acid. Perchloric acid monohydrate is similar.




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[*] posted on 23-1-2014 at 13:39


Thanks, UC.

I've actually made p-toluenesulfonic acid monohydrate, but never considered it from that perspective.

If anyone can point me to preparations for similar salts, I'd be excited to read them.
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[*] posted on 23-1-2014 at 13:40


Most hydronium salts are probably thought of as acid monohydrates, whatever their structure. If you look at the phase diagram of nitric acid/water mixtures:

You will see the bump marked "NAM" (nitric acid monohydrate). This is a solid that melts at about 238 K (-35 oC), and I would assume that there is extensive hydrogen bonding between the hydronium ion and the nitrate ion (I expect that it'd be closer to being hydronium nitrate than a water molecule hydrogen bonded to nitric acid).

Actually, this paper http://peer.ccsd.cnrs.fr/docs/00/71/66/36/PDF/PEER_stage2_10... references an X-ray crystal structure, and says that it is indeed made of hydronium and nitrate ions.

ETA: Ninja'd by UC!

[Edited on 23-1-2014 by DraconicAcid]




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[*] posted on 23-1-2014 at 15:28


If I mix Cl- and Cu2+, the tetrachlorocuprate complex ion is formed. Am I producing tetrachlorocupric acid when I mix HCl and CuCl2, or is it just a mixture? I'm guessing it depends on the complexation constant for the ion.

Similarly, are there isolable salts of ABCx, where A is a alkali/alkaline earth metal, B is a first-row transition metal and C is a halide? (a hypothetical example being potassium tetrachloronickelate)

Continuing the nitric acid questions, does orthonitric acid (H3NO4) exist?




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[*] posted on 23-1-2014 at 16:40


Quote: Originally posted by Brain&Force  
If I mix Cl- and Cu2+, the tetrachlorocuprate complex ion is formed. Am I producing tetrachlorocupric acid when I mix HCl and CuCl2, or is it just a mixture? I'm guessing it depends on the complexation constant for the ion.

Yes. It is an aqueous mixture of hydronium ions, and ions such as tetrachlorocuprate, so it's referred to as tetrachlorocupric acid.
Quote:
Similarly, are there isolable salts of ABCx, where A is a alkali/alkaline earth metal, B is a first-row transition metal and C is a halide? (a hypothetical example being potassium tetrachloronickelate)

Yes- I've made K3FeF6, and I've seen preps for KCuCl3 ( http://infohost.nmt.edu/~jaltig/CuCmpds.pdf ). I've also made (NEt4)2NiCl4; the potassium salt would probably also be isolable, though not as stable.

Quote:
Continuing the nitric acid questions, does orthonitric acid (H3NO4) exist?


Mmm...don't think so.

[Edited on 24-1-2014 by DraconicAcid]




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[*] posted on 24-1-2014 at 11:14


Quote: Originally posted by DraconicAcid  
Yes- I've made K3FeF6, and I've seen preps for KCuCl3 ( http://infohost.nmt.edu/~jaltig/CuCmpds.pdf ).


I just tried this prep. I did not get "red needles" or "ruby-red crystals", as the compound is described as. I got a deep green solution, and a lighter green precipitate. Bah.




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[*] posted on 24-1-2014 at 14:49


I have tried to make nitrocellulose many times, but it has failed every time. I used this method, but substituted sodium nitrate instead of the potassium nitrate. I correctly scaled down stoichiometrically. Every time I have tries this the cellulose gets attacked by the sulfuric acid and becomes a mush. Any pieces I could salvage were not at all flammable.
Can someone please help?




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[*] posted on 24-1-2014 at 16:23


Does anyone know the products of paracetamol and sodium hydroxide other than 4 aminophenol? If I write the reaction out it is missing only sodium atoms in the products. I think it might be a salt of a carboxylic acid or possibly sodium nitrate.



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[*] posted on 24-1-2014 at 17:00


Quote: Originally posted by thebean  
Does anyone know the products of paracetamol and sodium hydroxide other than 4 aminophenol? If I write the reaction out it is missing only sodium atoms in the products. I think it might be a salt of a carboxylic acid or possibly sodium nitrate.

4-aminophenol and sodium acetate.

HOC6H4NHC(O)CH3 + NaOH -> HOC6H4NH2 + NaO2CCH3

[Edited on 25-1-2014 by DraconicAcid]




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[*] posted on 24-1-2014 at 17:44


Can a more detailed writeup of this equation be posted? What solvent should be used?



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[*] posted on 24-1-2014 at 19:19


Quote: Originally posted by TheChemiKid  
Can a more detailed writeup of this equation be posted? What solvent should be used?


For hydrolysis of paracetamol? Use HCl instead. The reaction mixture turns dark from oxidized crap from the free aniline and deprotonated phenol.

If it's anything like acetanilide, it needs very little heating to split the amide group in ~20% HCl. Bring it up to reflux and hold for maybe 10 minutes. There should be no solids by the time you reach reflux.

Cool, and neutralize with base to precipitate p-aminophenol It can probably be recrystallized easily from hot, distilled water.




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[*] posted on 24-1-2014 at 20:57


The names he gave you before the equation is the more detailed way to describe an organic molecule as they are too complex to be accurately described in a simple linear equation. First, in case you don't have much knowledge in o-chem, (Something)-R is a shortcut to write organic molecules, the R is any carbon chain. I'll try to explain to you what happened. First, take a look at the molecule's structure http://commons.wikimedia.org/wiki/File:Paracetamol-skeletal.... . According to Draconic, NaOH will attack the bond between the amine (R-NH-R) and the Carbon that does a double bond with the Oxygen. I have not seen amide reactions yet in my o-chem classes, but according to the current knowledge I have, I should be able to describe what happened :

The carbon double bonded with the oxygen have a partial positive charge as the oxygen is very electronegative and attracts the electrons much stronger to itself. A partial positive charge is a perfect weak spot for the negatives OH- ions from NaOH to attack.

The negative charge from OH- forms a bond with the partial positive carbon, and the bond between N and the carbon breaks and the electron goes to the N. In simple, OH takes the place of R-NH, it is a substitution reaction. At this point, you have HOC6H4NH with a negative charge on N (extremely basic but stabilised by resonance with the cycle), you have Na + ions in solution and you have CH3COOH aka acetic acid http://commons.wikimedia.org/wiki/File:Acetic-acid-2D-skelet... . The N- from HOC6H4NH being extremely basic, it will steal the H from the OH on the acetic acid (simple acid-base neutralisation). You get a now neutral HOC6H4NH2, the acetic acid lost a proton and has become CH3COO- and you still have the Na+ ions in solution so of course you get the sodium acetate salt http://commons.wikimedia.org/wiki/File:Sodium-acetate-2D-ske... .

For the solvant, paracetamol is a bit soluble in water, its solubility gets much better at high temp and of course NaOH is very soluble. It should be a good solvant that does not produce undesired side reactions. I can't think of any other solvant. The use of other solvants could cause not wanted side reactions because of the negative R-NH created during the process that attacks pretty much everything : double bonds, triple bonds, alcools, partial positive spots created by links with halogens and ketones.... It also reacts with water, but it does not change anything as it will create OH- that steal the hydrogen from the acetic acid anyways.

That was a good revision of my o-chem class :p I hope it helped.

Edit: Chaos, the formation of a sodium salt with the "phenol part" should not be a problem as if this happen, it means that there will be acetic acid left (as long as stoechiometric amounts are used) that will protonate the basic salt back in "phenol".

[Edited on 25-1-2014 by alexleyenda]
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[*] posted on 25-1-2014 at 09:53


Its good that you're trying to apply your knowledge Alexleyenda, but you'll need an excess of sodium hydroxide as one equivalent will deprotonate the phenol first; a second equivalent is needed (though it would be best to use an excess, maybe 5 eq. in total) for the amide hydrolysis. Phenoxide anions tend to be sensitive to oxidation, hence the dark tarry crap formed. For paracetamol at least, hydrochloric acid is an easier alternative.
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[*] posted on 25-1-2014 at 11:18


@DJF90
Right, I did not even take time to think about this, in my head I decided for no reason that the hydrolysis would occure before the deprotonation of the acidic phenol, that was quite stupid! However, I don't understand how the phenoxide would oxidize, could you explain it?

At least I guess I correctly understood the mechanism as you did not say anything about it :)

[Edited on 25-1-2014 by alexleyenda]
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[*] posted on 26-1-2014 at 07:20


Your description of the mechanism was so long I didn't bother to read it. In hindsight I should have because it is wrong.

What you describe is Sn2 displacement of the R-NH(-) species. Due to stereoelectronic effects (essentially overlap of the reacting orbitals) Sn2 cannot occur at an sp2 center (e.g. amide carbonyl carbon, as we are discussing here). What happens is a stepwise mechanism, first attack of the nucleophile at the carbonyl carbon and breaking of the C=O double bond to form a C-O(-) structure, called a "tetrahedral intermediate". The negative charge on the oxygen can then close down to reform the C=O double bond, and the RNH(-) group is displaced.

I beleive this is not quite accurate though, as it doesn't account for the energetic favourability for the displacement of hydroxide vs the amine anion (technically an "amide" but lets not go there...) as difference in pKa and leaving group ability between OH(-) and RNH(-) is significantly large. It is more likely that the tetrahedral intermediate is deprotonated also to form a double anion (both residing on the oxygens) and then elimination of the amine anion occurs, leaving the carboxylate salt. This mechanism would provide more of a driving force for elimination of the RNH(-) vs the OH(-).


[Edited on 26-1-2014 by DJF90]
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[*] posted on 26-1-2014 at 12:18


Does Aluminum amide exist ? Al(NH2)3 ?
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[*] posted on 26-1-2014 at 13:14


Just to clarify, would adding HCl to potassium hydrogen phthalate produce the free acid and KCl?



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