- Introduction
HO-CH2-CH2-OH =H2SO4=> HO-CH2-CH2-OSO3H =H2SO4=> HO3SO-CH2-CH2-OSO3H
The mono- and disulphonated dioxanes thereby obtained react with excess of free dioxane to form an ether, for example:
HO-CH2-CH2-OSO3H + HO-CH2-CH2-OH ==> HO-CH2-CH2-O-CH2-CH2-OH
Formed di- ethylene glycol ether can be sulphonated further. When one of the ends gets sulphonated, the other end (free alcohol) substitutes the sulphone group to give a cyclic ether - dioxane. This last step (cyclisation) is fast since it's intramolecular.
Although dioxane is the favored product, note that there's a possibility that reaction also forms larger cyclic and linear poly-ethers. The former type of compounds are known as crown ethers, which are not healthy to have around...
Materials to prepare dioxane are easy to get. As ethylene glycol I've used a brand of antifreeze that told to be an aqueous solution of ethylene glycol (also had some blue dye), glycol was dried prior to use, by heating slowly to 198oC.
- Procedure
| Materials: |
| Ethylene glycol ((CH2OH)2) (dry) |
| Sulfuric acid (H2SO4) 96% |
| Potassium carbonate (K2CO3) |
| Potassium hydroxide (KOH) (can be substituted by NaOH) |
| Sodium (Na) (optional, to give more compleate drying) |
Whole procedure is done outside!
Place 30 ml dry ethylene glycol and 2,9 ml 96% H2SO4 into 100 ml roundbottomed flask equipped with a Vigreux column with a thermometer and a downward distiller. Reaction flask is placed on a gauze and carefully heated with a gas burner to a boil (I heated it on a hotplate with no problems). Product starts to distil after a while (if not, both Vigroux column and reaction flask are isolated by glasswool). Temperature will remain at 84-90*C in the beginning, and raise to 102*C in the end.
Distilation is ceased when reaction mixture becomes black, starts to foam alot and evolve SO2.
With increased temperature and concentration of H2SO4, rates of some byreactions will increase: first, dehydration of ethylene glycole to form acetaldehyde and second, oxidation-reduction reactions which leads to charring of reaction mixture and evolution of SO2.
Next, product is salted out: powdered potassium carbonate is added to the colorless distillate until solution separates in two layers. Upper dioxane layer is separated and dried first by dry potassium carbonate and then by potassium hydroxide. On addition of potassium hydroxide, solution becomes orange-brown because acetaldehyde (a byproduct) polymerises in basic conditions. First pieces of KOH dissolves on stirring (an additional layer separates), while following pieces remains unchanged.
Dried product is transfered to another flask, a peasize piace of metallic sodium is added and dioxane is destilled collecting a fraction of 100-103oC. Yield is 12 g (51% from theoretical).
Adding sodium is optional, this is basically an additional drying step. Instead of sodium one can add couple of KOH pieces simply to be sure that no peroxide accumulates during the distilation (well, just to be on the safer side).
Dioxane is a colorless liquid, mixes with water, ethanole and diethyl ether. mp = 11,7oC; bp = 101,3oC; dencity at 20oC = 1,03375.
On storage dioxane forms explosive peroxides (as many other ethers).
- References