Many of you probably know that periodates (e.g. KIO4 or Na2H3IO6) can be prepared by treating a hot alkaline solution of an iodate with hypochlorite
or chlorine gas. This indeed is an easy prep of periodate, but it requires iodate.
In an old book of Vanino I found a synthesis of Na2H3IO6 (NaIO4.NaOH.H2O) based on iodine. I was thinking, cannot such a prep be done just with iodide
as a precursor? Iodides can be obtained easily in most countries and although not really cheap, they are quite affordable.
I tried an experiment with sodium iodide and sodium hydroxide and it works quite well. If you can get potassium iodide, then it is best to also use
potassium hydroxide, but even if you only can get potassium iodide and sodium hydroxide, then you can make something which is pure in the sense of
that it is periodate only (no iodide or chloride), but a mix of a potassium and a sodium salt.
I performed a synth, requiring besides the sodium iodide only OTC chemicals (hardware store, swimming pool chemicals) and only simple glassware like
beakers and erlenmeyers and a simple $5 alcohol burner.
I think that with this synthesis the really interesting class of periodate compounds becomes available for a large group of home chemists.
The yield most likely can be improved (suggestions are welcome) but even if not, then this still is quite interesting for small scale experiments with
periodates (redox reactions, cleaving of C-C bonds in adjacent diol structures, little pyro experiments with purple smoke and formation of interesting
complexes).The_Davster - 20-6-2009 at 15:56
Nifty! I do enjoy high oxidation state compounds.
As for the synthesis of iodates, I seem to remember doing a reaction with iodine and sodium carbonate to get sodium iodate. I am sure this would work
with potassium carbonate as well.
It was a simple synthesis, adding I2 to a boiling solution of sodium carbonate till the iodine dissolved. Nice thing is any extra iodine can be
removed by heating at elevated temperaturechemrox - 20-6-2009 at 18:48
Nice Cl2 generatorswatson.fawkes - 21-6-2009 at 07:56
The yield most likely can be improved (suggestions are welcome)
The most immediate thing that occurred to
me is that if you put your hot solution with precipitate under reflux for a while, you'd convert the fine powder precipitates to larger crystals,
which would lower your filtration losses.
A question: is the bent tubing you're using in the apparatus flint glass or borosilicate?zed - 21-6-2009 at 14:54
The following improvised filtration system, shows a very low percentage of loss.
Take a match head sized ball of cotton (or glass wool), affix it to the end of a hypodermic needle, an eyedropper, or a piece of glass tubing with a
finely drawn end. Then, isolate your solid product by drawing off your solution, via syringe, eyedropper, or vacuum source.
Now, since the your waste solution contains salts of Iodine, it would be nice to recover that Iodine. Preferably as I2 Crystals. Here in the United
State, I2 is hard to come by, and recycling is wise.
An experiment that produces Periodate as the main product, then subsequently produces I2 crystals from the recycled waste......That would be quite an
experiment.
Considering the Mix of Iodine Salts present in the filtrate, how do you suppose the I2 might best be recovered?
DJF90 - 21-6-2009 at 17:27
Considering there should be iodide and iodate in there, I would expect acidification to liberate at least some of the iodine. Follow up with hydrogen
peroxide and more acid and I suspect you'll recover the most of it.woelen - 22-6-2009 at 13:14
No, acidification does not yield any iodine. I tried this with the liquid I had left over, because I also wanted to know whether all iodide was
converted or not. When a non-reducible acid like H2SO4 or HNO3 is added to the waste liquid, then the liquid remains colorless. If you really want to
regain the iodine in this, then you first could add sodium sulfite to the acdified solution to reduce all to iodide (add just enough to make the
solution light yellow) and then add slight excess of hydrogen peroxide to convert all iodide to iodine, without any iodate or periodate being formed.
If slight excess of H2O2 is used, then hardly any iodine is lost, because it is virtually insoluble in water.
I have done such a synthesis of iodine some years ago and it works fairly well. You can rinse the iodine precipitate with water and then filter it and
then heat it in order to obtain the vapor (put a petri dish on a beaker with the wet iodine to which some concentrated H2SO4 is added, which is heated
from below). Iodine vapor is produced and the H2SO4 holds most of the water. Crystals form on the cold petri dish. You can scrape off the crystals and
repeat this action with a second batch of conc. H2SO4. This yields pure and dry iodine.
Right now, this is not worth the effort for me. I only lost 3 grams or so of NaI and given the ease with which I can buy iodine it is not interesting
at all. Periodates are much harder/much more expensive to obtain for me and that is why I tried the synth of this chemical, without paying much
attention to the regaining of iodine.Jor - 22-6-2009 at 14:02
I also tried exactly the same when doing iodine synthesis (I have planty of it, but i was for the fun of it) a few weeks ago. I also used H2SO4. I
first performed the experiment in a test-tube and it is remarkable to see that when you cover the iodine with a few mL of H2SO4 and you heat, you will
see the iodine melting! Cooling it down will produce a single large piece of iodine.
You can also see iodine melt when you heat over a small flame, but it is VERY hard to see, due to the very strongly colorred vapour. Liquid iodine is
nice to see, it resembles bromine, it is a very mobile liquid. It's just blackl/purple
Woelen, I might give the synthesis of KIO4 a try. I don't have NaI, but I have 200g of KI. I also have 50g KIO3 and 250g KH(IO3)2, but these are much
more valuable, so I prefer to use KI.
I will have to buy some TCCA however, until now I always avoided this as I had a few tablets of TCCA.
I am always impressed by your apparatus. Where do you buy those glass tubes (are these PTFE coated?) ?
Can you tell me how to bend the tubes like that? I have no experience at melting and working glass at all, and I am not sure how to fit these glass
tubes in stoppers.
zed - 22-6-2009 at 20:46
Remarkably, the suppliers I have checked, sell KI more cheaply than NaI. Much more cheaply. Go figure.
For heating and bending glass tubing, either a propane torch, or a Bunsen burner using natural gas...works nicely.
Just cut your tubing to length, by scoring it with the edge of a sharp file, and then, with a double thumb contact, pointing away from
yourself.....snap the tubing in two, as you would a string bean.
Fire polish the ends of the tubing in your Bunsen burner flame. Allow it to cool. Then, apply a little glycerine to the end of your tubing and
carefully work it through the hole in your neoprene stopper. Protect your hands!
Most likely, you will burn yourself at some point, likewise your will probably cut yourself a little. If you are very careful, theses injuries will
be minor. If you aren't very careful, you may require stitches.
As for bending glass tubing.....you will quickly get the hang of it.
Naturally, instructions aided by pictures will help you more than just instructions, and many beginning level Chemistry Lab Manuals contain
illustrated instructions.woelen - 22-6-2009 at 22:55
The tubes I have are ordinary glass, not borosilicate. This glass easily can be melted. I obtained these tubes as long rods of 90 cm length. What I do
is scratching these tubes around in a thin line (using a glass cutter) and then breaking it at the scratch. This can be somewhat tricky and the cut is
sharp and can be somewhat irregular. With a hot roaring flame of a propane torch these ragged and sharp ends can easily be smoothed.
Bending the tubes is the easy part. Just heat them in a roaring flame and very carefully apply force to bend them. What I did is applying weak force
while it is still cold and at a certain point you feel that it starts bending. The bending has to be done VERY slowly, otherwise it may crack, or the
glass is folded inside such that the tube gets closed.
it is not difficult at all to bend such glass tubes. You can buy all kinds of glass tube from eBay, I have tens of tubes ranging from a few mm
diameter to 30 mm diameter from different German eBay sellers.
[Edited on 23-6-09 by woelen]woelen - 29-6-2009 at 11:31
I have done some more testing on this reaction and I have found out how to improve the yield to much higher values (75% or so, measured from the
amount of used NaI).
You need to add more sodium hydroxide. In the experiment I took 5 grams of NaI and 15 grams of NaOH. This amount of NaOH is just 25% more than is
needed by the stoichiometry of the reaction in which Na2H3IO6 is formed.
Quite a lot of the chlorine, however, does not contribute to formation of Na2H3IO6, but just to formation of chlorate and chloride.
I think that the two following competing reactions occur:
Better results are obtained if 25 grams of NaOH are used and the volume of the solution is increased to 125 ... 150 ml. Two to three times as much of
chlorine must be bubbled through solution. When you do that, then you get a much better yield. So, in terms of used sodium hydroxide and chlorine,
this reaction is not very efficient, but in terms of the (expensive) iodide, its yield can be improved a lot.
I also modified the webpage, adding my new findings. Having this better yield makes the reaction even more interesting.
[Edited on 29-6-09 by woelen]ammonium isocyanate - 14-7-2009 at 18:12
Very interesting synthesis... I have some extra KI and KOH, so I'll have to try it some time.
By the way, if one only needs a small amount of periodate, or if high purity product is required, www.hometrainingtools.com sells KIO3 in 5g bottles for $5 each. It's pricey, but if you only need a few grams, it sure is easier.woelen - 15-7-2009 at 13:07
You are confusing iodates with periodates. In my experiment I made a compound, based on the periodate ion IO4(-). You are talking about iodate,
IO3(-). Periodate has iodine in oxidation state +7 while iodate has iodine in oxidation state +5.
Periodate exists in meta-form (based on the acid HIO4) and in ortho-form (based on the acid H5IO6). With potassium ion as counter ion you can best
make the meta-form, KIO4. With sodium ion as the counter ion you can best make an ortho-form, Na2H3IO6.
Iodate on the other hand only exists in a meta-form, IO3(-) and there is a so-called double form, HI2O6(-). Salts of both ions exist, KIO3 and KHI2O6,
the latter often written as KIO3.HIO3 or KH(IO3)2. chemoleo - 15-7-2009 at 16:19
One thing you could do with it is to convert i.e. any H2N-CH(CH2OH)-R or HO-CH(CH2OH)-R to the aldehyde CHO-R, all it requires is incubating said
sugar or amino sugar (or even amino acid such as Ser or Thr) with a molar excess of NaIO4. It basically cleaves C-C bonds having primary or secondary
hydroxyls or amines on each carbon.
The aldehyde can be easily tested for, for instance with hydrazines (dinitrophenylhydrazine) or hydroxylamines.... just in case you want to play with
the periodate.DJF90 - 16-7-2009 at 07:19
Slightly off topic but keeping with the theme of chemoleo's post; a-amino acids, i.e. H2N-CH(R)-CO2H, treated with sodium hypochlorite leads to the
aldehyde R-CHO. The mechanism involves N-chlorination, followed by decarboxylation to funish imines, which are then hydrolysed. With b-amino acids,
the methyl ketone R-C(O)-Me is formed.
