chornedsnorkack
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Do selenonic acids explode?
Nitric acid is a strong oxidant. Nitro compounds and nitrates are renowned explosives.
Sulphuric acid and sulphur trioxide are feeble oxidants.
Selenic acid is a strong oxidant compared to sulphuric acid - it even dissolves gold, which nitric acid does not. Even selenous acid is easier to
reduce than sulphurous acid.
Are selenonic acids and selenates explosive?
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woelen
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No, they are not explosive. I have done quite a few experiments with selenic acid and with selenous acid. Selenous acid is fairly easily reduced to
selenium, but this reaction is not violent. Selenic acid is a stronger oxidizer, but it is not energetic like nitric acid. A strong oxidizer may be
strong thermodynamically (i.e. high oxidation potential), but me be slow kinetically. An example is peroxodisulfate ion. It is one of the strongest
oxidizers available (redox potential just over 2 volts, much higher than that of permanganate or chlorate), but it also is sluggish. A similar thing
(to a lesser extent) is the case for selenic acid.
Btw, selenic acid can dissolve gold, but only VERY slowly and only under specific circumstances. For practical purposes, it hardly dissolves gold. A
mix of nitric acid and hydrochloric acid is much more effective.
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Bedlasky
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Selenic acid is also quite strong acid (comparable with sulfuric acid). It behaves similary like sulfuric acid - you can make "selenic oleum" by
dissolving SeO3 in H2SeO4. You get mixture of polyselenic acids (mainly mono-, di-, tri- and tetraselenic acids) and free SeO3. You can also make
mixed S-Se oleum, by dissolving SO3 in H2SeO4 to form mixed acid H2SSeO7.
More info in this document, it's free.
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chornedsnorkack
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And does mention explosions. Page 1646,
| Quote: |
RESULTS AND DISCUSSION (A) Cryoscopic Study of the SeO3-H2SeO4 System.- The progressive addition of
SeO3 to 100% H2SeO4 causes depression in the freezing point of pure selenic acid.1 When the
mol ratio SeO3 : H2SeO4 reaches unity the freezing point of the system has a maximum in the freezing
point-composition diagram. Mixtures with such high SeO3 content are very hygroscopic and become explosive in the presence
of some organic solutes, particularly amines and some ketones.4 |
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woelen
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What you describe here is not normal selenic acid, but the selenium variation of oleum. This is MUCH more agressive than normal selenic acid. It is
just as with sulfuric acid and oleum. Oleum also is MUCH more agressive than concentrated sulfuric acid (have you ever seen the effect of adding oleum
to water or adding oleum to sugar?).
Normal selenic acid does not explode with generic oxidizable stuff like sugars, wood or reducing metal salts like ferrous salts, copper(I) salts or
chromium(II) salts. Of course, it may explode when mixed with LiAlH4 or other extremely reducing compounds, but such compounds may cause fire or even
explosion with any acid and any somewhat oxidizing agent.
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ChemTalk
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Thanks everyone, this thread is turning out to be very informative!
- ChemTalk
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Bedlasky
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But this explosion occurs because of formation of gaseous products from violent oxidation of amine/ketone. It isn't explosive on it's own. Btw. this
behavior is observed with selenoleum which concentration of 5,8% SeO3 in pure H2SeO4 - this isn't pure selenic acid.
On the other hand - that freezing maximum 18,5°C is weird. Pure selenic acid have freezing point 62°C (source).
[Edited on 31-1-2021 by Bedlasky]
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chornedsnorkack
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So the melting points for pure SO3/H2O and pure SeO3/H2O systems:
H2SO4 - 10,4 C
H2S2O7 - 35 C
SO3 - sublimes at 62 C without melting
H2SeO4 - 62 C
H2Se2O7 - 18,5 C
SeO3 - 118,5 C
Does H2SSeO7 exist?
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Bedlasky
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Look at document in my first post, there is mention about H2SSeO7. Here is another source.
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chornedsnorkack
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Quote: Originally posted by Bedlasky  | But this explosion occurs because of formation of gaseous products from violent oxidation of amine/ketone. It isn't explosive on it's own. Btw. this
behavior is observed with selenoleum which concentration of 5,8% SeO3 in pure H2SeO4 - this isn't pure selenic acid.
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Does the amine oxidize directly or does selenoleum first undergo a quiet, non-redox reaction to form e. g. a selenamide, which later undergoes an
explosive internal redox reaction whether left in selenoleum or separated?
The sources that discuss H2SSeO7 discuss H2SO4 with a small admixture of SeO3. What would be
interesting is the behaviour in the region of 40 % H2S2O7 / 60 % H2Se2O7. Does it
have a melting point maximum with a distinct crystal structure?
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Bedlasky
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| Quote: Originally posted by chornedsnorkack | | Quote: Originally posted by Bedlasky | But this explosion occurs because of formation of gaseous products from violent oxidation of amine/ketone. It isn't explosive on it's own. Btw. this
behavior is observed with selenoleum which concentration of 5,8% SeO3 in pure H2SeO4 - this isn't pure selenic acid.
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Does the amine oxidize directly or does selenoleum first undergo a quiet, non-redox reaction to form e. g. a selenamide, which later undergoes an
explosive internal redox reaction whether left in selenoleum or separated?
The sources that discuss H2SSeO7 discuss H2SO4 with a small admixture of SeO3. What would be
interesting is the behaviour in the region of 40 % H2S2O7 / 60 % H2Se2O7. Does it
have a melting point maximum with a distinct crystal structure? |
I don't know mechanism of reaction between selenoleum and amines. This is just single mention in that document without further explanation.
It should have freezing point maximum - these condensed molecules or adducts (like hydrates etc.) can be well determined by measuring of freezing
point maximum.
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