Sciencemadness Discussion Board - Oxydising iodides

Oxydising iodides

bismuthate - 16-11-2013 at 04:21

As we know H2O2 can oxidise iodides to iodine, so could this happen with stronger oxidisers in nonaqueous conditions? For example would KI realse iodine when mixed with Mn2O7?
Sorry if it's a stupid question.

[Edited on 16-11-2013 by bismuthate]

deltaH - 16-11-2013 at 05:38

Oxone (persulfuric acid salt) quickly produces the free halogen from salt solution. I once had the misfortune of mixing a solution containing sodium chloride with an oxone solution and promptly formed copious amounts of chlorine gas

, luckily I was working in a fume cupboard, so no harm, no foul!

Sorry, this is not Mn2O7, just wanted to tell you about one other strong oxidiser than can easily do this.

PHILOU Zrealone - 17-11-2013 at 13:08

It may form I2 but also an explosion because Mn2O7 is hell sensitive explosive!

The wel known reaction related reaction (Mn2O7 and KMnO4 have both Mn in a VII oxydation state)
HCl + KMnO4 --> Cl2 + Mn(2+)
Work also with HI. In place of KMnO4, MnO2 might also be used!

It is better to get I2 to bubble Cl2 into KI solution.

eidolonicaurum - 5-1-2014 at 01:23

Yes it almost certainly would. I have used Mn2O7 a fair bit (on a small scale) and its never exploded for me. Im not sure it is explosive, as long as you keep flammables away from it.

blogfast25 - 5-1-2014 at 13:37

Mn2O7 is seriously dangerous. Only prepare the smallest amounts and in the absence of anything remotely oxidisable.

Oxidation of iodides with permanganate in acid conditions has been discussed on this forum several times and seems to work just fine, with some advantages over H2O2, it would seem.

Search and ye shall find!

bismuthate - 5-1-2014 at 13:59

I do not want to produce I2 I am meerly speculating about a possible reaction. I am also not looking at the reaction of permanganates with iodides although it is related and interesting.

chornedsnorkack - 6-1-2014 at 00:04

Oxidizing chloride takes permanganate in acid conditions, where the result is chlorine. Oxidizing iodide should be easier... what are the options? How basic can permanganate be and still oxidize iodide?

And what is the maximum pH where iodine or triioodide are stable? Hypoiodite, unlike hypochlorite, is an ephemeral species that quickly dismutes even in cold. So what is the pH above which a strong oxidant will oxidize iodide to iodate rather than iodine?

Can permanganate oxidize iodide to iodate?

blogfast25 - 6-1-2014 at 06:17

Quote: Originally posted by chornedsnorkack

Oxidizing chloride takes permanganate in acid conditions, where the result is chlorine. Oxidizing iodide should be easier... what are the options? How basic can permanganate be and still oxidize iodide?

And what is the maximum pH where iodine or triioodide are stable? Hypoiodite, unlike hypochlorite, is an ephemeral species that quickly dismutes even in cold. So what is the pH above which a strong oxidant will oxidize iodide to iodate rather than iodine?

Can permanganate oxidize iodide to iodate?

In alkaline conditions permanganate is reduced to MnO2, not Mn(II) (with a suitable reducing agent present, of course!) You can see the potential for a mess: solid I2 and solid MnO2!

The last two questions can speculatively be answered using the reduction potentials of the half reactions.

Certainly in alkaline conditions I2 tends to form iodide and hypoiodate and then iodate. I've no idea whether permanganate could help this along. As I said, work out the cell potentials for the relevant reactions from the half reactions' reduction potentials.

This sounds like something someone else here might have already tried. UTSF!

[Edited on 6-1-2014 by blogfast25]

chornedsnorkack - 6-1-2014 at 11:17

Quote: Originally posted by blogfast25

Quote: Originally posted by chornedsnorkack

In alkaline conditions permanganate is reduced to MnO2, not Mn(II) (with a suitable reducing agent present, of course!)

Searching for Pourbaix diagram confirms the memory that MnO2 is stable to dismutation at any pH.
http://www.wou.edu/las/physci/ch462/redox.htm

Quote: Originally posted by blogfast25

You can see the potential for a mess: solid I2 and solid MnO2!

Permanganates are strong enough oxidizers in acid conditions that they should be able to oxidize iodine to iodic acid at least. See the iodine Pourbaix diagram:
http://sti.srs.gov/fulltext/tr9900270/tr9900270.html

Quote: Originally posted by blogfast25

The last two questions can speculatively be answered using the reduction potentials of the half reactions.

Certainly in alkaline conditions I2 tends to form iodide and hypoiodate and then iodate. I've no idea whether permanganate could help this along. As I said, work out the cell potentials for the relevant reactions from the half reactions' reduction potentials.

These Pourbaix diagrams are slightly inconvenient to make exact measurements. But it seems to me that at least in alkaline conditions where permanganate is reduced to manganate not MnO2, it might be able to oxidize iodate to periodate.

blogfast25 - 6-1-2014 at 13:35

Quote: Originally posted by chornedsnorkack

As anyone who's worked with manganate solutions will tell you, it doesn't live very long. Pourbaix or not, MnO2 is what you'll get most likely. There's a lot of practical information on manganate/MnO2 on the sticky permanganates thread, worth reading IMHO.

[Edited on 6-1-2014 by blogfast25]

vmelkon - 7-1-2014 at 14:30

Quote: Originally posted by PHILOU Zrealone

It is better to get I2 to bubble Cl2 into KI solution.

That would produce some iodine monochloride along with iodine.
http://en.wikipedia.org/wiki/Iodine_monochloride

chornedsnorkack - 8-1-2014 at 14:15

Quote: Originally posted by vmelkon

Quote: Originally posted by PHILOU Zrealone

It is better to get I2 to bubble Cl2 into KI solution.

That would produce some iodine monochloride along with iodine.
http://en.wikipedia.org/wiki/Iodine_monochloride

In aqueous solution, iodine chlorides should promptly hydrolyze.