Sciencemadness Discussion Board - Synthesis of potassium metaperiodate by persulfate method

Synthesis of potassium metaperiodate by persulfate method

Bedlasky - 1-9-2020 at 13:58

Hi.

I tried to make some KIO4 by persulfate method few days ago. It went better than I expected. Here is the original synthesis. Author have yield 12,5g, my yield is 13,8g (amounts of starting chemicals are the same).

I write article about it in czech and in english.

[Edited on 1-9-2020 by Bedlasky]

symboom - 1-9-2020 at 20:56

Nice potassium iodate can be made from electrolysis from the iodide there are two salts that use the name Persulfate but I see the formula you use the higher peroxydisufate type I was thinking if oxone could work peroxymonosufate it can oxidize potassium iodide to iodine and sodium chloride to chlorine but I'm not sure if it is possible it is much more obtainable.

woelen - 1-9-2020 at 23:24

Interesting synthesis. It would be even more interesting if you could use KI as startting material. The Cl2-method, which I used, also works with KI as starting material. I can imagine that the persulfate method also does, but you need 4 times as much K2S2O8 (iodine has to go from oxidation state -1 to +7 instead of from +5 to +7). Probably it works, but isolation and workup may be more difficult. It is worth a try though.

On the other hand, KIO3 can be made fairly easily from KI by means of electrolysis, so having your method of making KIO4 at hand is a nice achievement for amateur chemistry and it makes one more interesting more accessible for the home chemist.

Another nice change would indeed be to use CH3COOH instead of HNO3 for the final step of precipitating the KIO4. You do not need glacial acetic acid. The 80% acid also can be used. That acid is easier to obtain in many countries and acetic acid has no regulatory resitrictions as there are for HNO3 in many countries. Dou you have personal experience with the use of CH3COOH instead of HNO3?

Bedlasky - 2-9-2020 at 03:51

Quote: Originally posted by symboom

Nice potassium iodate can be made from electrolysis from the iodide there are two salts that use the name Persulfate but I see the formula you use the higher peroxydisufate type I was thinking if oxone could work peroxymonosufate it can oxidize potassium iodide to iodine and sodium chloride to chlorine but I'm not sure if it is possible it is much more obtainable.

I think it should work. But for me is much easier to obtain peroxodisulfate instead of peroxomonosulfate. Na2S2O8 is used for etching copper and is easy to obtain in my country. I have K2S2O8 thanks to my friend which help my to obtain some useful chemicals, but it can be make from Na2S2O8 by fractional crystallization or by electrolysis of KHSO4.

Quote: Originally posted by woelen

Interesting synthesis. It would be even more interesting if you could use KI as startting material. The Cl2-method, which I used, also works with KI as starting material. I can imagine that the persulfate method also does, but you need 4 times as much K2S2O8 (iodine has to go from oxidation state -1 to +7 instead of from +5 to +7). Probably it works, but isolation and workup may be more difficult. It is worth a try though.

On the other hand, KIO3 can be made fairly easily from KI by means of electrolysis, so having your method of making KIO4 at hand is a nice achievement for amateur chemistry and it makes one more interesting more accessible for the home chemist.

Another nice change would indeed be to use CH3COOH instead of HNO3 for the final step of precipitating the KIO4. You do not need glacial acetic acid. The 80% acid also can be used. That acid is easier to obtain in many countries and acetic acid has no regulatory resitrictions as there are for HNO3 in many countries. Dou you have personal experience with the use of CH3COOH instead of HNO3?

I already have KIO3, so I use it for this synthesis because I want better yield. But I want to buy some Na2S2O8, make some NaI from KI, tartaric acid and NaHCO3 and try this method for NaIO4, this time starting from iodide. Na2S2O8 and Na2SO4 are more soluble than their K analogs, so there shouldn't be problem keep them in solution. But I can try also KI as a starting material instead of KIO3.

In my country is acetic acid available as a vinegar or glacial acetic acid, nothing between them

. I mentioned it as an alternative because lots of people can't get HNO3. Yes, you can make it if you have distillation setup, but someone want this acid for other uses or has little money right know for buying setup so he/she rather use some alternative. Potassium acetate have a good solubility, so using 1+1 acetic acid for acidification is good alternative. I didn't try it so I don't have experience with it.

I like your chlorine method, I consider that I try it, but then I find this persulfate method. It's good for someone how lives in housing development like me

. I can do something like this only on small balcony and if something goes wrong entire neighborhood would smell chlorine gas. And my PET bottle/plastic goose method isn't really ideal for making chlorine gas in large quantities

. Working without chlorine is also more comfortable for me. And it is one pot reaction. Disadvantage is low solubility of K2SO4 and K2S2O8.

Fery - 2-9-2020 at 04:55

Bedlasky, beautiful, thx for sharing.
woelen - maybe using acetic acid would require another indicator than methylorange for HNO3 as they used in prepchem.com link... or maybe just adding some excess of acetic acid would be fine?
routes for KIO3 other than electrolysis of KI:
Boffis recently researched a reaction of I2 + ClO3- here: https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
Did someone produce KIO3 by reacting KI + 2 KMnO4 + H2O -> KIO3 + 2 MnO2 + 2 KOH ?
Relatively little of KIO3 can be also produced by reacting KOH + I2 where most of the product is KI and only little of KIO3 (this route is more suitable for someone who does not have KI but have I2, KIO3 could be obtained here as a byproduct)

[Edited on 2-9-2020 by Fery]

Bedlasky - 2-9-2020 at 05:34

Fery: Thanks. It doesn't matter which acid you use. Conversion of orthoperiodate in to metaperiodate occurs at certain pH. Nitric acid or acetic acid are good choices because they don't react with periodate and have potassium salts with great solubility. Another possibility would be phosphoric acid. Sulfuric acid is bad option because you already have bunch of potassium sulfate in solution. Hydrochloric acid reacts with periodate to form I2Cl6 (which stay in solution as [ICl4]- anion). So from the most common acids you have three choices for acidification.

I want to try make some KIO3 from KI and KMnO4 and also NaIO3 from NaClO3 and NaI. I will report the results in future.

[Edited on 2-9-2020 by Bedlasky]

Bedlasky - 29-12-2020 at 09:48

Hi.

I tried small scale synthesis of sodium orthoperiodate. This time is starting material iodide, not iodate. Starting from iodide is however inefficient. You need 77,5 g of sodium persulfate for 21,35 g Na2H3IO6 in theory (and practical yield is just 10,4 g, which corresponds to 48,72% yield). For small scale synthesis this is fine, but for large scale you need to start from iodate.

I plan to make NaIO3/KIO3 and try large scale synthesis of Na2H3IO6/KIO4. From these two I'll make other periodates.

Here is writeup in czech/english.

Btw. I tried to use phenolphtalein as indicator during acidification, but phenolphtalein was easily oxidized by periodate even in alkaline solution, so it didn't last much long. So pH papers are better option than indicator.

[Edited on 29-12-2020 by Bedlasky]

Fery - 29-12-2020 at 10:08

Hi Bedlasky, nice preparation!
I remember that decades ago I did an acidobasic titration without any indicator, using only thermometer to detect the neutralization point - the solution was added from burette at 1,0 ml portions and a graf was made where on X axis was the volume from burette and on Y axis the temperature. The titration flask was thermally insulated. I have also pH meter at home but I'm not sure whether it will give correct pH in such a concentrated solutions and strong oxidising environment.

Bedlasky - 29-12-2020 at 10:16

Fery: I din't know that equivalence point in acidobasic titration can be determiend from temperature change. This is quite interesting.

Fery - 30-12-2020 at 03:50

Hi Bedlasky, I'm currently out, I have the paper in my house, I'll try to dig it out. I remember that the point was determined from graph, on X axis there were ml of solution added from burette in 1,0 ml steps and on Y axis there was temperature recorded. Neutralization is quite exothermic reaction so the curve wraps at some point, it is necessary to prolongate the 2 linear parts of the curve (the first linear part where exothermic neutralization and the second one when everything already neutralized) and where they meet is the point of neutralization. It is necessary to add solution from burette even after the neutralization point to obtain the second linear part (when the T does not increase due to neutralization, it can slightly increase due to diluting the solution from burette). So you don't obtain neutral solution in the titration flask, but you can then mix both solutions at the ratio you obtained from the titration. It is not so comfortable as using indicator but avoiding indicator could have also some advantages as is in your case.