Rhodanide
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Trouble with synthesizing HClO4
Hi everyone,
I have tried twice to synthesize Perchloric acid by way of distilling a mixture of a Perchlorate salt and semi-diluted Sulfuric acid. My source of
Perchlorate is in the form of anhydrous Magnesium Perchlorate. I bought the Mg salt because not only was it a good deal, but the Sodium salt isn't
available for purchase here, it seems (NE U.S.). Neither distillation worked as far as I can tell. The first and second ones only gave a clear,
semi-acidic, clear & colorless liquid with no oxidizing properties as far as I can tell. What's more is that the second distillation began
belching out Cl2 when the temperature hit 200C. Should've seen that coming? I Guess? Anyways, the only other legitimate option would be to react the
Magnesium Perchlorate with conc. HCl, right? I tried that on a small scale thinking that the MgCl2 would precipitate but instead I got a clear
solution and no MgCl2. Is it really THAT soluble in 31% HCl? If it is then I don't really know where to go from here. I could possibly combine
solutions of Sodium Carbonate and Mg Perchlorate to precipitate out MgCO3 and leave NaClO4 in solution, but that'd be a huge pain. What am I doing
wrong here?
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Fery
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most skilled member in HClO4 synthesis in this forum is woelen, he posted few methods, but the starting compounds were Na or NH4 perchlorates
search the forum for his posts
perhaps you can convert Mg salt into NH4 salt by ammonia and then the second step is to destroy the ammonia by HCl+HNO3 or by N oxides like NO2 etc
or the method you mentioned to obtain Na salt and react with HCl and precipitate NaCl
very likely the problem is that MgCl2 does not crystallize anhydrous but as hexahydrate - solubility of hexahydrate in water is 235 g / 100 ml at 20 C
which is very soluble salt
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clearly_not_atara
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Assuming you still have magnesium perchlorate, you could try adding oxalic acid and filtering.
But keep in mind that dilute perchloric acid is not oxidizing. A better test for perchlorate is to add a little bit of the solution to a concentrated
solution of KCl, which should give a precipitate of KClO4.
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unionised
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I suspect the equilibrium constant for that is .... it's not going to work.
If you want the sodium salt you can react MgClO4 with Na2CO3 then filter off MgCO3
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Metacelsus
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A few years ago I made perchloric acid by vacuum distillation of a mixture of NaClO4 solution and sulfuric acid, to obtain the azeotrope (72.5%). This
method should also work for magnesium perchlorate.
I used vacuum distillation but regular distillation may also be an option. The azeotrope boiling point is 203 °C at atmospheric pressure.
If you do this, make sure to carefully calculate the amount of water to add, so your acid doesn't become too concentrated.
[Edited on 2020-3-22 by Metacelsus]
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AJKOER
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Some of my prior research results on preparing perchlorate:
Per the supplied paper by Icelake, "Perchlorate Formation by Ozone Oxidation of Aqueous Chlorine Oxy-Chlorine Species - Role of ClxOy Radicals", a few
observations/comments.
First, one role of O3 is as a source O2 and O (atomic oxygen). However, the latter (as I once noted on SM with references) can also be obtained via
reactions involving singlet oxygen. The latter is much more easily prepared, and I suspect, less toxic than ozone, albeit, it has a half-time of
around 45 minutes per my recollection.
Second, I also recollect more mentions of perchlorate creation per photolysis routes in the literature (while only a few mentioned in the cited work
and many of the remaining references appear dated, in my opinion).
Lastly, the focus of cited work is to account for how small amounts of perchlorate can be created in the upper atmosphere (which is under intense UV
radiation working with primarily O2,...). This work is not concerned with potential larger scale and more general lab preparation paths.
-------------------------------------------
An interesting seemingly simple path (but likely very difficult to implement safely) is via photolysis of ClO2 (which normally explodes in light, so
here the ClO2 is likely dissolved in a diluent, a liquid, CCl4, or gas, CO2, with concentration under 15%) resulting in unstable chlorine
perchlorate (although, I suspect, low temperatures are required to avert decomposition/explosion of ClO2 and ClOClO3 along with dilution in nitrogen,
see https://pubs.acs.org/doi/abs/10.1021/j100221a001, and avoiding organics, which will also result in a detonation). To quote from Wikipedia on
chlorine_perchlorate ( https://en.wikipedia.org/wiki/Chlorine_perchlorate ):
"Chlorine perchlorate is the chemical compound with the formula Cl2O4. This chlorine oxide is an asymmetric oxide, with one chlorine atom in oxidation
state +1 and the other +7, with proper formula ClOClO3. It is produced by the photolysis of chlorine dioxide at room temperature with 436 nm
ultraviolet light:[2][3]
2 ClO2 → ClOClO3
......
Chlorine perchlorate is a pale greenish liquid which decomposes at room temperature.
Properties
It is less stable than ClO2 and decomposes to O2, Cl2 and Cl2O6 at room temperature.
2 ClOClO3 → O2 + Cl2 + Cl2O6
Chlorine perchlorate reacts with metal chlorides forming anhydrous perchlorates:
CrO2Cl2 + 2 ClOClO3 → 2 Cl2 + CrO2(ClO4)2
TiCl4 + 4 ClOClO3 → 4 Cl2 + Ti(ClO4)4 "
Note, ClOClO3 decomposition product is Cl2O6, which is apparently more stable and also a mixed source of chlorate and perchlorate salts! Per Wikipedia
(https://en.wikipedia.org/wiki/Dichlorine_hexoxide ) to quote:
"Dichlorine hexoxide is the chemical compound with the molecular formula Cl2O6, which is correct for its gaseous state. However, in liquid or solid
form, this chlorine oxide ionizes into the dark red ionic compound chloryl perchlorate [ClO2]+[ClO4]−, which may be thought of as the mixed
anhydride of chloric and perchloric acids.
It is produced by reaction between chlorine dioxide and excess ozone:
2 ClO2 + 2 O3 → 2 ClO3 + 2 O2 → Cl2O6 + 2 O2"
So upon addition of water, I would presume the creation of HClO3 and HClO4 (which is, apparently, correct per this fully available paper, Equation
(13) at https://www.academia.edu/1557546/Chlorine_oxoacids_and_struc... which also mentions the products on the action of sunlight on ClO2), which
suggests a path to mix of chlorate and perchlorate salts.
Interesting speculation would be to flood an aqueous chlorate and hypochlorite with the hydroxyl radical:
•OH + ClO3- = OH- + •ClO3
•OH + ClO- = OH- + •ClO
•ClO + •ClO3 = ClOClO3
------------------------------------------------------------
Also, speculation, with nascent hydrogen, e- + H+ = •H, the very powerful hydrogen atom reducing radical, which will attack NO3- and create OH- and
•NO2, also •H + ClO3- = OH- + •ClO2,..., but however, with more •H, even further reduction is possible.
---------------------------------------------------------------------
Prepare Singlet Oxygen (see http://www.sciencemadness.org/talk/viewthread.php?tid=31729#... ) which with oxygen may make some very strong (but transient) oxidizing atomic
oxygen ......
Source on atomic oxygen: See Eq 4 at http://olab.physics.sjtu.edu.cn/papers/2017/29.Huan%20Yue_PC... , where apparently, O(3P) is created from severe collision quenching of O(1D) atom
with air or oxygen and acts as the major oxidant in the work by Huan Yue and colleagues ‘Exploring the working mechanism of graphene patterning by
magnetic-assisted UV ozonation’. Note, O(3P) is also known as highly reactive ground-state 3P oxygen and a form of atomic oxygen.
Photolysis may also be a path to perchlorates. To quote a source (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... ):
"[20] A role for water ice as a reaction surface for adsorbed species may be a possible path to perchlorate chemistry. ClO radicals are readily
produced by atmospheric oxidation of chlorine volatiles, and ClO can interact on ice to produce OClO when the ice sublimates [McKeachie et al., 2004].
Chlorine dioxide (the OClO molecule is not to be confused with Cl‐O‐O, which is the chlorine peroxy radical, unfortunately also sometimes called
“chlorine dioxide”) is a possible source of perchlorate because it can react with O3 or O to make chlorine trioxide [Wayne et al., 1995]:"
Some research notes that the whole sublimation of •ClO + ice under UV is likely a bridge too far as a path to •OClO radical. However, per another
source (https://www.researchgate.net/publication/222104943_Observati... ):
"The ClO + BrO reaction is presently believed to be the only source of OClO in the stratosphere, although several studies show this reaction system to
severely underestimate OClO production in this atmospheric subsystem"
Is a more likely path to the OClO radical, albeit slow, per the following reaction forming BrO- from added Br- and with radicals, •BrO :
OCl- + Br- = Cl- + BrO- (see http://old.sustainability.gatech.edu/publications/Ozone_Brom... )
just add hydroxyl radicals (from say the UV photolysis of aqueous N2O or the action of HOCl on Fe(ll) , or the action of microwaves on activated
carbon, ...) to the system together with atomic oxygen. Speculation? Perhaps or not (see https://www.researchgate.net/publication/250142618_Bromate_c... and https://awwa.onlinelibrary.wiley.com/doi/full/10.5942/jawwa.... ).
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clearly_not_atara
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unionised: Solubility product of MgC2O4 is 1.14 * 10^(-5). From Wiki, we have a solubility of 0.38 g/L and since it is a simple salt
we can just take (0.38 / 112)^2 to get the Ksp.
Assuming [Mg] = 1/2 [ClO4] = 1 M, we obtain:
1.25 + 4.14 = 5.39 = log[H2C2O4] - log[HC2O4-] + pH + log[HC2O4-] - log[C2O4(2-)] + pH = log[H2C2O4] - log[C2O4(2-)] + 2 pH
1.25 = log[H2C2O4] - log[HC2O4-] + pH
4.14 = log[HC2O4-] - log[C2O4(2-)] + pH
where
pH = -log([HCO4-] - 2 [C2O4(2-)])
Letting x, y, z = [H2C2O4], [HC2O4-], [C2O4(2-)] respectively, we obtain:
10^1.25 = 17.8 = x/(y^2 + 2zy)
10^4.14 = 13800 = y/(zy + 2z^2)
thus
356y^2 + 356zy - 10x = 0
13800yz + 27600z^2 - y = 0
Now we can add in the maximum solubility of oxalic acid ~= 1 M (convenient) so x + y + z = 1. WolframAlpha solves the system with some floating point
errors:
https://www.wolframalpha.com/input/?i=178y%5E2+%2B+356zy+-+1...
The solution we want is definitely the middle one with x = 0.7894, y = 0.2105, z = 0.00007241 = 7.241 * 10^(-5). That this is a solution can be easily
checked by plugging in the numbers.
Finally, we arrive at the minimum solubility of Mg2+ in saturated oxalic acid solution with no added base: [Mg][C2O4(2-)] = 1.14 * 10^-5, [C2O4(2-)] =
7.241 * 10^(-5) so [Mg2+] 1.14 / 7.241 = about 0.15M.
Conclusion: oxalic acid can be used to recover perchloric acid from 1M magnesium perchlorate with 85% efficiency ignoring multiple ion effects. We
slide in just under the wire w.r.t. the solubility; remember, no ClO4- ever gets protonated, only H2O gets protonated.
But of course the chemistry perspective on this question is just to notice that sulfuric acid was successfully obtained from magnesium
sulfate this way, so why not perchloric acid? Both are strong acids, and all strong acids act roughly the same below 1M in water.
[Edited on 22-3-2020 by clearly_not_atara]
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Tsjerk
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I like the above calculations.
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clearly_not_atara
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In distilling an aqueous mixture of oxalic acid and perchloric acid, one should take care to avoid inhaling carbon monoxide. A carbon monoxide
detector is strongly recommended.
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Rhodanide
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Yeah, I've got about +/-450g or roughly one pound of Mg(ClO4)2. Got it for about 20-something USD. What I want to know is why I got a ton of Cl2 the
second distillation.
I also just thought that the MgCl2 would be relatively insoluble because of how some other salts tend to behave in 31.45% HCl.
So from what I'm seeing, the double displacement route is the best way to go, yes?
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clearly_not_atara
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I would say yes, just make sure to be careful of possible carbon monoxide evolution during the distillation.
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woelen
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I would use Na2CO3 to precipitate all Mg as MgCO3. Use a little excess Na2CO3. Filter and keep the clear liquid. It should be slightly basic, if that
is the case it will be nearly free from Mg(2+) ions.
Next, boil down the solution and then mix the solution with concentrated HCl. A slight excess of Na2CO3 is destroyed and NaCl precipitates. The final
product will be fairly pure HClO4 once you have driven off the HCl by boiling until temperature reaches around 150 C. Getting it really free from
Na(+) ions requires distillation, but for most purposes, your acid will be fine.
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