Sciencemadness Discussion Board

Making Sodium Iodide with Iodine + Sodium Thiosulfate - Problems?

LuckyWinner - 15-11-2020 at 12:00

I tried this reaction by adding iodine into an aqueous solution of sodium thiosulfate.
sodium thiosulfate was added till the solution was clear and was mag stirred for several minutes.

the solution turned a tiny bit yellowish and smelled a like sulfur.
ethanol 99% was added to this solution to precipitate out any formed
Sodium tetrathionate.

it precipitated at the bottom of the flask, but the solution was still very cloudy.

filtrate was cloudy and had a tiny yellowish tint and sulfur smell.

this solution was setup for distillation to remove the ethanol and water.
the distillate that came over had a yellow tint including the receiving liquid.

the main flask had some white/greyish discoloured precipitate.
hotplate reached 170C max to dry this out.

there must be some sulfur contamination.

the proper way to get clean sodium iodide crystals is to dissolve this in water
then filter it, (sulfur is insoluable in water)
reduce water amount to minimum ,
then place in a fridge to recyrstallize the NaI crystals.

will this be the proper way?


how do I get my ethanol free of sulfur?

*** was this sulfur generated by H202 or HCL residues from my Iodine?
this was precipitated from KI...
Quote: Originally posted by LuckyWinner  
quote wikipedia
https://en.wikipedia.org/wiki/Sodium_tetrathionate

Quote:

Sodium tetrathionate is formed by the oxidation of sodium thiosulfate (Na2S2O3), e.g. by the action of iodine:.[2]

2 Na2S2O3 + I2 → Na2S4O6 + 2 NaI

The reaction is signaled by the decoloration of iodine. This reaction is the basis of iodometric titrations.



https://pubchem.ncbi.nlm.nih.gov/compound/203055#section=Dep...






i found this patent
https://www.freepatentsonline.com/2439720.html
Quote:

Sodium tetrathionate dihydrate (Na2S4O6.2H20) which is the ordinary crystalline form of this salt, is commonly prepared-by the- interaction of-sodium thiosulfate and iodine in concentrated aqueous solution, the tetrathionate being -precipitated from the reaction mixture by the addition-of alcohol. Inasmuch as-sodiumriodide -(which is formed as a by-product during the reaction) is among the impurities known to interfere with the stability of dry sodium tetrathionate, it is obvious that the salt as first obtained must be further purified. It has been found impossible to obtain satisfactory purification by simple washing with ordinary 95 per cent ethyl alcohol even though sodium iodide is very soluble in this solvent, probably because the crystals of sodium tetrathionate as obtained are quite dense and frequently relatively large in size, making it impossible for the alcohol to leach out the impurity occluded within the crystals. According to the teaching of the prior art, this purification of the salt is best carried out by dissolving the crystals in water and recrystallizing upon the addition of alcohol. Such a purification results in a large loss of yield, particularly if it must be repeated a second time....



A quantity of sodium tetrathionate dihydrate is prepared in any convenient fashion, such as by the interaction of 410 grams of sodium thiosulfate dissolved in 180 cubic centimeters of water with 200 grams of iodine suspended in 30 cubic centimeters of water and 100 grams of ice, taking care that there is at all times an excess of iodine throughout the reaction mixture, and then precipitating the crystalline dihydrate salt by two liters of alcohol. After cooling and settling, the crystals are filtered and sucked reasonably dry.


[Edited on 15-11-2020 by LuckyWinner]

LuckyWinner - 15-11-2020 at 12:50

In short

add iodine into an aqueous solution of sodium thiosulfate.
minimal amount of water should be used.

once colour changes to white, all iodine is converted into NaI.

Add a solvent that NaI is soluble in and Sodium tetrathionate is not.
this is ethanol or would acetone also work?

by adding the solvent you push out the NaI from the water layer and
move it into the solvent.

this will cause the Sodium tetrathionate to crystallize out.

this precipitate can be filtered.

NaI is inside the solvent/water filtrate with some sulfur contamination.

this solvent/water mix needs to be boiled off.
once NaI+ Sulfur is dry, add water till NaI is dissolved, filter out sulfur.
(sulfur is insoluable in water)

redissolve NaI in water and recrystallize, filter.

any improvements to this?

Maurice VD 37 - 15-11-2020 at 13:43

You should check the pH of your solution. If sulfur is produced, this means that the solution was a little acidic, because Na2S2O3 is decomposed in the presence of even a small amount of acid : S2O3^2- + 2 H+ --> S + H2SO3.

Maurice VD 37 - 15-11-2020 at 13:43

You should check the pH of your solution. If sulfur is produced, this means that the solution was a little acidic, because Na2S2O3 is decomposed in the presence of even a small amount of acid : S2O3^2- + 2 H+ --> S + H2SO3.

LuckyWinner - 16-11-2020 at 01:57

Quote: Originally posted by Maurice VD 37  
You should check the pH of your solution. If sulfur is produced, this means that the solution was a little acidic, because Na2S2O3 is decomposed in the presence of even a small amount of acid : S2O3^2- + 2 H+ --> S + H2SO3.


thats probably it.

with what should I basify the iodine.
sodium carbonate water wash the iodine before I add the Thiosulfate?


to separate the sulfur , simply boil down the NaI solution till dryness,
then dissolve in water, filter out the sulfur and evaporate.

then recrystallize in hot water.

correct?

[Edited on 16-11-2020 by LuckyWinner]

LuckyWinner - 16-11-2020 at 03:13

whenever the ethanol sulfur mix is simple distilled,
the sulfur always comes over with the ethanol.
even after filtration.


how can the sulfur be separated from the ethanol?

is this caused by my hotplate being to hot?
sulfur becomes volatile at 200C?

that means by keeping the hotplate temperature low,
idealy a water bath, this should keep the ethanol free of sulfur vapors?

[Edited on 16-11-2020 by LuckyWinner]