nezza
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Chlorate from hypochlorite
I recently bough some sodium hypochlorite bleach for a project and have some left over so I thought I might make some chlorate from it. All of the
textbooks say hypochlorite is unstable and disproportionates into chlorate and chloride on heating :-
3OCl- -> ClO3- + 2Cl-
So I tried boiling an aliquot of it for a few minutes. The green colour is still there and it appears not to have done anything. (no precipitate with
K+ ions and still releases chlorine with acid).
Any suggestions ?.
If you're not part of the solution, you're part of the precipitate.
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HeYBrO
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Slow reaction rate and probably low conc bleach... Keep boiling!
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XeonTheMGPony
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need to boil it till you see sodium chloride crystals crash out
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S.C. Wack
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Might as well boil until all the salt has precipitated then, if one is going to go that far.
Time is more of a requirement than boiling heat.
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Texium
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Thread Moved
4-9-2016 at 09:30 |
AJKOER
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Try heating (around 50 to 70 C ) aqueous Mg(ClO)2 and some NaHCO3 with a touch of ascorbic acid in a cast iron vessel (my recollection is that this
was employed in an old commercial patent) or, perhaps (given my understanding of the chemistry) a copper retort, or with some support from the
literature on AOPs (advanced oxidation process), a glass beaker with pieces of both Fe and Cu. Passing air/O2 (with, for example, a fish tank air
pump in lieu of rapid boiling which can reduce yield) through the heated mix should improve yield even at temperatures significantly below boiling
(see links to references).
Logic: Magnesium hypochlorite is apparently more sensitive to air contact with the resulting formation of reactive oxygen species (ROS) (which could
include the likes of superoxide radical anion, hydroxyl radical, .HCO3, .CO3-, ClO,..) acting on hypochlorite to contribute to the final chlorate
yield. The bicarbonate will result in the formation of some HOCl also (which to a limited extent decomposes to O2 and HCl, the latter lowering pH)
and insoluble white MgCO3 on heating. The presence of bicarbonate has been cited to improve yield in at least one patent. Warming a hypochlorite in
open iron retorts (or better, I suspect, in neutral to alkaline conditions, with Copper/O2) could provide a Fenton (or Fenton-type) assisted path to
ROS and then chlorate. An alternate view is that the process is a direct speciation reaction referred to as ferrous (or cuprous) metal ion
auto-oxidation with dioxygen (see Urbañski reference below).
More chemistry specifics, see, my comments and references on my some of my prior threads including http://www.sciencemadness.org/talk/viewthread.php?tid=27013#... , http://www.sciencemadness.org/talk/viewthread.php?tid=34429#... and http://www.sciencemadness.org/talk/viewthread.php?tid=31003#... .
Note: I have prepared Magnesium hypochlorite by adding MgSO4 to aqueous NaOCl and freezing out the Na2SO4.10H2O. Do not use filter paper (will
decompose the hypochlorite), just carefully pour out the aqueous Mg(ClO)2 or use an inert filter agent like crushed glass.
A reference on the use of a mixture of Iron and Copper in AOPs, see "Generation of .OH initiated by interaction of Fe2+ and Cu+ with dioxygen;
comparison with the Fenton chemistry" by Norbert K. Urbañski and Andrzej Berêsewicz, available at https://www.google.com/url?q=http://www.actabp.pl/pdf/4_2000...
In my opinion, the reason that boiling sodium hypochlorite is ever cited as a path to chlorate is due to ignorance of the low yield and the associated
issues of boiling dilute NaOCl (problematic), or an intentional misdirection to limit successful chlorate production. Ironically, my suggested
embodiment employing Mg(ClO)2, a transition metal retort (I do have a suspicion that this could cause chlorate to decompose via a REDOX if acidic
conditions develop, so you may wish to omit this refinement), moderate temperature and aeration, may actually transform this route into a much better
procedure.
As a disclosure, I have yet to personally test this route given my good results with my provided link above, which also outlines my solar light
assisted methodology.
[Edited on 5-9-2016 by AJKOER]
[Edited on 5-9-2016 by AJKOER]
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S.C. Wack
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That sounds like a lot of dicking around unless you're starting from Cl and Mg hydroxide like it was suggested a century ago. Did everyone that was
using Ca hydroxide then go to that method or not. Bleaching powder with KCl is only a really convenient simple fast and inexpensive procedure that
works, for as long as it's cheap and not banned.
[Edited on 5-9-2016 by S.C. Wack]
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metalresearcher
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Electrolyzing NaCl solution yields ClO- which will be oxidized to ClO3- by the electric current. Goes a lot faster, there are plenty of topics on this
forum or websites on this.
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AJKOER
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Quote: Originally posted by metalresearcher  | | Electrolyzing NaCl solution yields ClO- which will be oxidized to ClO3- by the electric current. Goes a lot faster, there are plenty of topics on this
forum or websites on this. |
No, actually measuring the number of moles produced with time, electrolysis is slow!
This is related to a unit of charge known as a faraday. Per Wikipedia, "The magnitude of the electrical charge of one mole of elementary charges
(approximately 6.022×E23, or Avogadro's number) is known as a faraday unit of charge". Also, Coulomb (link: https://en.m.wikipedia.org/wiki/Coulomb ), which is the charge transported by a constant current of one ampere in one second, which is equivalent
to the charge of approximately 6.242×E18 electrons.
This is perhaps a good thing because if one was producing H2 and O2 from water rapidly via electrolysis, then 50 moles of water (around 900 grams,
less than 1 liter of water) would produce over 1,100 liters of hydrogen and half as much oxygen.
The latter is probably more than enough to cause an entire house to explode by turning on a light switch!
------------------------------------------
With respect to electrolysis of aqueous KCl, recall reading that potassium dichromate (carcinogenic, appropriate safety protection required having
been described as
'acutely and chronically harmful to health' per Wikipedia) is a recommended catalyst.
But why such a catalyst if the procedure is so good?
Then, there is the underlying chemistry, which is still dependent on radical pathways, many of which are not entirely understood. My suggested paths
at least affords some degree of control over the magnitude and selectivity as to which particular radicals, required for chlorate formation, are
generated.
Also, not finding it easy to acquire larger cheaper KCl amounts without using a credit card. Obviously purchases are being monitored.
Sometimes the non-popular routes are just better on many levels.
[Edited on 6-9-2016 by AJKOER]
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