Synthesizing sulfur(II) chloride, attempt 2

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In this note I’ll describe my second failed attempt the synthesis of sulfur dichloride.

Glassware and equipment

Chlorine generator

  • 29/32 500ml Büchner flask
  • 29/32 polypropylene stopper
  • D=6mm L=500mm PVC hose
  • magnetic stirrer

Reactor

  • 29/32 250ml round-bottom flask
  • 19/26-29/32 hose adapter
  • 24mm rubber stopper with d=5mm hole
  • 200mm D=5mm glass tube
  • magnetic stirrer with heating mantle
  • D=6mm L=500mm PVC hose
  • gas washing bottle

Chemicals

  • manganese(IV) oxide
  • 38% hydrochloric acid
  • sulfur
  • sodium hydrocarbonate
  • hexane
  • carbon dioxide
  • aqueous ammonia

Apparatus

The idea for the apparatus was that hexane would dissolve chlorine, and a stir bar would agitate the whole mixture, exposing as much of the sulfur’s surface area to chlorine as possible.

Overview

See previous note.

In the reaction were used:

  • 32 g of sulfur
  • 116 g of manganese(IV) oxide
  • 60 ml of hexane

Before filling the chlorine generator with acid, the apparatus was purged with $\ce{CO_2}$ to make sure that the hexane vapors cannot ignite.

After starting the chlorine generator, a squirt bottle was used to flush various parts of the apparatus with ammonia vapor and detect leaks.

Results

Regarding improvements from the previous attempt:

  • PVC hoses are, indeed, resistant to chlorine. They do not get brittle or appreciably permeated by chlorine, at least compared to silicone hoses. They appear to be usable in this application.
  • Instead of chlorine-resistant grease, all leaking joints were covered with Parafilm. This decreases the rate of leakage enough that it is not detectable with ammonia.
  • A magnetic stirrer was not able to agitate sulfur in the reactor, probably because the chosen stir bar was too small or had the wrong shape.

Overall results:

  • Hexane changed color to become slightly orange, which indicates dissolved $\ce{S2Cl2}$ and/or $\ce{SCl2}$.
  • Many bubbles of gas were evolved from within the sulfur powder, which can only mean hydrolysis of the forming sulfur chlorides by the water in the chlorine stream.
  • Reaction speed was very low. The amount of sulfur did not visibly decrease over around a hour the reaction was conducted.

To conclude, this was a failure, but the apparatus is a significant improvement over the previous one. It almost doesn’t leak, and is overall simpler.

Observations

  • The glass tube was submerged underneath the surface of hexane. As a result, when removing the stopper from the Büchner flask, hexane vapors would push hexane towards the chlorine generator. This has the potential to siphon the entire mixture (above the tube’s opening) into the generator.
  • The polypropylene stopper requires a significant force to achieve a gas-tight seal, and even then it is not trivial.

Improvements

  • Chlorine must be dessicated. It is not clear what is the best option for doing so.
  • Siphoning, both from the gas washing bottle, and from the reactor, must be prevented. In case of the reactor, it might be enough to raise the chlorine inlet tube, but in case of the gas washing bottle it’s not clear.
  • A larger stir bar should be used. A test should be conducted to make sure that the stir bar is capable of agitating the mixture before starting the generator.
  • No polypropylene stoppers. A pity, since they seem so convenient.

Acknowledgements

  • @peroxycarbonate for suggesting the use of hexane as a nontoxic alternative to chlorinated solvents.

Want to discuss this note? Drop me a letter.