Sciencemadness Discussion Board - Sodium thiosulphate from NaOH and S

Sodium thiosulphate from NaOH and S

Oscilllator - 31-7-2013 at 20:39

In a 500ml beaker was placed 30g of NaOH, which was then dissolved in a minimum of water. 50g of sulfur was then added and stirred with a glass rod. This was then placed on a hotplate and brought to a boil:

After boiling for about a minute, a vigorous reaction was observed in which most of the sulfur disolved and the remainder of the liquid had a blood-red colour:

This mixture was then cooled in a water bath, then filtered to obtain a blood-red liquid (a small sample is shown in the picture)

A small portion of this liquid was diluted with water, and a small amount of 30% HCl added. An immediate precipitate of sulfur formed, indicating the presence of thiosulphate.
The reaction (according to wikipedia) is meant to proceed like this:

6NaOH + 12S = 2Na2S5 + Na2S2O3 + 3H2O

I made sure to add an excess of sulfur, so that all of the NaOH would react, however the product still tests as strongly basic.
I assume that this red stuff in solution is some kind of sulfur polymer manifested from the Na2S5, and the problem is that I cant seem to remove it. Does anyone have an idea how I could get it to precipitate and so filter it off?

j_sum1 - 23-3-2016 at 03:09

Hey. That's pretty cool.
I think it might be easier to buy sodium thiosulfate, but it is an interesting synth. I might have to try it.

If nothing else, it is good to know that a useful reducing agent like thiosulfate can be made from otc items. And even where NaOH is banned, it is not impossible to make it.

I concur on the red colour. Some polymeric sulfur thing seems likely. And such things are awkward.

gsd - 23-3-2016 at 06:27

It is a mixture of thiosulfate and polysulfide. The red colour is due to latter.
https://en.wikipedia.org/wiki/Sodium_polysulfide

gsd

Daffodile - 23-3-2016 at 08:24

In Robert Bruce Thompson's illustrated guide for the home chemist, apparently your procedure produces only polysulfide, and the precipitate from the addition of acid occurs with polysulfide as well as thiosulfate.

chemrox - 23-3-2016 at 19:46

Quote: Originally posted by j_sum1

.. even where NaOH is banned, it is not impossible to make it.

NaOH "banned?" Stupidity of regulators and lawyers never ceases to amaze me. Where is lye illegal? Well in my state it's considered a 'precursor' which is one of the reasons I got a license.Cool pictures. This reminds me of a college course; Chem 1b, qualitative analysis.

[Edited on 24-3-2016 by chemrox]

Daffodile - 23-3-2016 at 20:42

Quote: Originally posted by chemrox

Quote: Originally posted by j_sum1

.. even where NaOH is banned, it is not impossible to make it.

I don't think its really banned in most places, but more commonly made scarce in its pure form. It gets harder to find in large, pure amounts, a pure 10lb jug I got awhile ago looks like a dream compared to what is available now, the blue and purple pellets filled with dyes and odd crap, in 200g or less packages.

j_sum1 - 23-3-2016 at 21:13

Well it(NaOH) is not banned round here. But I understand that there are many places where it is not otc.
Much the same as sulfuric acid cannot be purchased easily where I live, but in the US they just pour it down the drain.

Oscilllator - 24-3-2016 at 14:39

Yay, somebody brought back my thread!
One thing I have thought about is adding a solvent - is it possible that adding a non-miscible solvent might somehow be able to extract the polymer? or perhaps drying it out and roasting it might somehow break it up, allowing it to be re-diluted and filtered off.

Zandins - 12-8-2016 at 10:16

According to wikipedia, sodium sulfite is oxidised by air to form sodium thiosulfate. Perhaps simply bubbling air through the mixture would work?

MrHomeScientist - 12-8-2016 at 11:29

Sodium sulfite and sodium sulfide are very different compounds.