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Author: Subject: Can strong acids react in non polar solvents?
mycotheologist
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[*] posted on 9-12-2012 at 13:00
Can strong acids react in non polar solvents?


I know that acids can only dissociate in polar solvents but I was wondering if really strong acids like methanesulfonic acid or fluoroantimonic acid can protonate compounds on collision (as opposed to dissociating first) even in non polar solvents. Obviously that depends on the stability of their conjugate base in the NP solvent so I wonder if organic strong acids like trifluoroacetic acid would have a more NP stable conjugate base.

Side question: Is 98% H2SO4 less corrosive than slightly more dilute solutions? I'd prefer not to test out my hypothesis but I suspect that if I spilled a bit of 98% H2SO4 on my skin, it would burn less than say 80% because there is less water for dissociation to occur.

[Edited on 9-12-2012 by mycotheologist]
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[*] posted on 9-12-2012 at 13:27


I dunno about the first question, but 80% sulfuric acid would definitely be more corrosive than 98%. 98% can be stored in steel drums, whereas anything much less than that cant.



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[*] posted on 9-12-2012 at 13:27


Yes acids definitely can. An example could be p-Toluenesulphonic acid being used in fischer esterifications in non-polar solvents and azeotropically distilled during the reaction. To shift the equlibrium towards the product by removing water.

edit - I guess another example could be in a biphasic mixture. Such as the synthesis of toluenesulfonic acid itself. Concentrated sulfuric acid refluxed and stirred with toluene(2 layers), will over the course of a short period of time sulfonate toluene.

Another example would be to say dissolve an organic acid such as citric acid or similar to a dry solvent such as acetone. Adding this to a non-polar solvent(say toluene) containing an amine such as say aniline will have the amine salt fall out of the solution(so long as aniline citrate is not soluble which it likely wouldn't be).

There are also examples of heterogenous solid acid catalysts such as silica sulfuric acid. The nature of solid state chemistry is a bit of a mystery to me still but I think it works on collision theory, or kinetics, as you speculate.

As far as the H2SO4 I wouldn't test the hypothesis, your skin might be passivated for a bit temporarily but with time acid burns are definitely a reality at any concentration. Conc. H2SO4 will eat/char through paper towels in seconds, granted skin is a bit more resistant then cellulose(I think).

[Edited on 9-12-2012 by smaerd]

[Edited on 9-12-2012 by smaerd]




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[*] posted on 9-12-2012 at 14:00


98% H2SO4 is still significantly more corrosive, because if it doesn't have water, it finds some. Namely, from your skin and underlying body. So, in addition to a chemical burn, you get a physical burn from the acid heating up with the water from your skin, and local dehydration due to loss of water.



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[*] posted on 9-12-2012 at 14:17


Yes. A solution of 5-nitrotetrazole in ethyl acetate will react with ammonia gas precipitating ammonium nitrotetrazolate hemihydrate.
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[*] posted on 10-12-2012 at 18:19


Thanks for the informative replies, that answers my questions and more. I didn't know about the synthesis of toluenesulfonic acid, this is something I was thinking about aswell, I suppose that could be explained as the toluene being protonated at the interface between the 2 layers though. The first example seems like a definite example of a non ionic acid protonating a compound though. Toluenesulfonic acid seems like it would have a conjugate base that'd be relatively stable in a non polar environment since it has that benzene ring to delocalise the charge across the whole molecule.

I put a drop of conc. hydrochloric acid on my hand once to observe how fast it started to burn. Started off as a mild tingling sensation. It was a good 30 seconds before the tingling started to become pain, at which point I washed the acid off. I got about a mL of conc. H2SO4 on my lab coat one day and although it didn't eat through the lab coat (not until I washed it that is), it burned a hole in my cotton t-shirt underneath.

Quote: Originally posted by elementcollector1  
98% H2SO4 is still significantly more corrosive, because if it doesn't have water, it finds some. Namely, from your skin and underlying body. So, in addition to a chemical burn, you get a physical burn from the acid heating up with the water from your skin, and local dehydration due to loss of water.

I don't think thats correct. KOH is extremely hygroscopic but I'd prefer to handle pure KOH than a solution of it. The H2SO4 will find water but theres only so much water it can find in a given space of time. A more dilute solution already has its water so it can begin protonating the skin instantly.

[Edited on 11-12-2012 by mycotheologist]
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[*] posted on 10-12-2012 at 18:37


H2SO4, despite being "Oil of Vitriol", is still fairly ionic. I forget the dissociation constant, unfortunately, but it's something like:

2 H2SO4 <---> H3SO4(+) + HSO4(-)

Where H3SO4 could be written: O=S(OH)3

Concerning biological acid interactions, my personal experience has been similar: I still have a few cotton shirts with holes around stomach level (bench-level splashing), and cotton-poly blends with conspicuously thinned, white spots (obviously, the cotton, which burned away, had absorbed all the dye, leaving perfectly white polyester, and a much thinner web of fabric, in the spot!). I've gotten acid on myself before (HCl more often than H2SO4), but it only hurts me where the skin is thin -- if I've been picking at my cuticles or something, it can hurt like a m(#$&(!^)#er. Most of the skin on my hands, particularly the fingertips, is thick enough that nothing really bothers me.

Tim




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