deadpool
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nitrosylsulfuric acid help again
I'm sure many of the gurus chemist will probably roll there eyes at this post, but I've having difficulty understanding nitrosylsulfuric acid as a
substance a bit. According to Wikipedia it can be made with sodium nitrite and sulfuric acid in an ice bath. It then shows this equation below :
HNO2 + H2SO4 → NOHSO4 +H2O
This doesn't show any sodium reaction at all, just how nitrous acid and sulfuric acid may behave? I'm assuming that this equation here would be in an
equilibrium as well. I more curious of the actual reaction of the sodium. The byproduct be sodium sulfate? I seem to remember reading about not using
concentrated sulfuric acid but a dilute solution. Can any one help clear up my fuzzyness? Any help is greatly appreciated.
[Edited on 14-3-2014 by deadpool]
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woelen
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This reaction occurs in concentrated sulphuric acid.
If you add solid sodium nitrite to ice cold concentrated sulphuric acid then the following happens:
NaNO2 + H2SO4 ---> HNO2 + Na(+) + HSO4(-)
So, you get nitrous acid in concentrated sulphuric acid. This nitrous acid then in turns reacts to form NOHSO4.
In reality, however, I doubt that free HNO2 will be present as species. It is a method of describing the reaction, but I can imagine that in reality
the sodium nitrite dossolves and that the nitrite ion immediately reacts with sulphuric acid:
NaNO2 + 2H2SO4 --> Na(+) + NOHSO4 + HSO4(-) + H2O
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deadpool
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Thank you for clearing this up a little bit. For curiosity I wanted to see what would happen if the reaction sat out for some time and decomposed. I
mixed the two chemicals in an ice bath and let the temperature slowly rise. Eventually as it approached room temperature the mixture turned greyish
color and slowly bubbled. The reason for my curiosity is because I see sodium nitrite added to several organic chemistry reactions, and I've always
was concerned that the free sodium ion would reacted in an unexpected way or cause a lower yield. Has anyone ran into an issue like this? is their an
effective method of obtaining clean nitrosylsulfuric acid (in h2so4 solution) without particulate or contaminates?
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DJF90
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Brauer has a method where sulfur dioxide is bubbled into fuming nitric acid, and the resultant solid is filtered from the acidic mother liquors
(unchanged nitric acid).
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woelen
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A salt
like sodium nitrite does not contain free sodium, such a salt contains sodium ions. And sodium ions really like to stay like that and so are very
unreactive. You really have to put a lot of energy in them to get them reacting with something. So, no need to worry about reactions of free sodium in
reactions where sodium salts are used.
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deadpool
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unfortunately I don't have access to a fume hood so sulfur dioxide and fuming nitric acid are out. I'm aware the sodium will never be in a "free"
state just the ion will linger around in solution. Would it eventually form sodium sulfate? just wondering what will actually happen to it. If it did
form a sulfate, I would imaging it would suck up any water in the solution:
NaN02 + 2H2S04 -> NOHS04 + NaSO4 + H20 + H2
Probably incorrect, but I may try some experimenting on my own to see if I can identify good molar ratio and achieve a clean product. Any thoughts,
ideas or comments Please! 
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deadpool
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Thank you guys for help, figured I would post additional thoughts
Hello everyone again, I want to thank anyone here bothering to read my silly posts. I'm just updating what I think is happening for this reaction,
please correct me if I'm wrong. The easiest and most common method I found for producing nitrosylsulfuric acid is by adding sodium nitrite to sulfuric
acid as mentioned before. I figured I would show my entire balanced equation to see if anyone had issues with it.
2NaNO2 + H2SO4 ->
Na2SO4 + 2HNO2 + {2H2SO4} <-> 2NOHSO4 + 2H20
I know the nitrosylsulfuric acid is in equilibrium and will exist if excess sulfuric acid is used (and can even form crystals in concentrated H2S04
under some conditions). I was wondering anyone knows of a good method for removing the sodium sulfate from mixed acids? (if my equations even are even
correct). I was really wary about filtering such strong acids on the frit. I've noticed once this reaction warms the mixed soup will turn blackish,
anyone know if this is normal or a common side reaction that taking place that should be avoided? Last but not least once a concentrated
nitrosylsulfuric acid mixture is obtained does it degrade under cool storage? I've seen conflicting documentation about this. Thank you again for any
help, I'm not asking for hand holding just clearing up little details that are hard to find.
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AvBaeyer
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While looking for something else this evening, I ran across this:
Preparation of nitrosylsulfuric acid.
Concentrated sulfuric acid (98%, 80 ml) was taken in a 250 ml flask and cooled to 0°C. Sodium nitrite (6.9 g, 0.1 mole) was added slowly into it
under stirring maintaining temperature below 10°C. After completion of the addition, stirring was
continued further for 15 minutes. The reaction mixture was then gently heated to about 70°C and stirred at this temperature until all residual
nitrite dissolved. The clear solution was then cooled to room temperature and used for diazotization.
Ref: ARKIVOC 2005 (xiii) 141-149 (Free)
Hope this is useful.
AvB
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Dan Vizine
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deadpool,Re. your questions:
I know the nitrosylsulfuric acid is in equilibrium and will exist if excess sulfuric acid is used (and can even form crystals in concentrated H2S04
under some conditions). I was wondering anyone knows of a good method for removing the sodium sulfate from mixed acids? (if my equations even are even
correct).
I don't know of a method other than to isolate the nitrosylsulfuric acid.
I was really wary about filtering such strong acids on the frit.
Not a problem. Glass frits are unaffected. Same for the ceramic fiber filters. You just shouldn't use paper.
I've noticed once this reaction warms the mixed soup will turn blackish, anyone know if this is normal or a common side reaction that taking place
that should be avoided?
Never experienced this when I made it. But I isolated the "pure" material, not a solution in sulfuric acid.
Last but not least once a concentrated nitrosylsulfuric acid mixture is obtained does it degrade under cool storage? I've seen conflicting
documentation about this.
Aldrich sells a 40% soln in sulfuric acid, so it seems it must have fair stability. However, I bought the "pure" acid from
them once. A pale yellow solid which didn't work in my intended reaction. It evolved almost no heat upon hitting water, so I knew it was garbage. I
tried to convince Aldrich that it was faulty but they cited their IR characterization and refused to make good on it. I made my own, which looked
similar to theirs, but dissolved very exothermically in water and worked in my reaction. So, there are also reasons to have have some concerns about
stability. A well-sealed bottle is most important in my view.
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