Al Koholic
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Diol + Base = ?
5ml of ethylene glycol was placed in a test tube and a small amount of NaOH was added. This mixture was heated upon which some boiling occured with
the dissolution of the NaOH. The solution became a light tan color at this point.
In another test tube with 5ml of EG, a small lump of sulfur was placed and this was heated. The sulfur dissolved but did not react with the EG. Only
a small pool of sulfur was formed at the bottom of the tube and the solution remained clear.
I returned to the first tube which had NaOH in EG. I added a small lump of sulfur to this and heated it again to boiling. The sulfur melted and
dissolved in the solution with a color change to dark red. When this cooled, there was some sulfur liquid collecting at the bottom of the tube so
some more NaOH was added and the tube was reheated. Now all the sulfur reacted and when cool, the mix is homogenous and a clear deep orange color.
When a drop of the orange solution is added to HCl(aq), there is a distinct smell of H2S and some bubbling. The evolution of gas is slow at first due
to the solutions not being entirely miscible.
When heated to drive off some of the EG, the vapors take on a slightly sulfurous odor after some of the EG disappears. When cooled, the remaining
solution deposits a fine white precipitate.
Upon standing, the original batch of orange solution slowly thickens over time and I am beginning to see the appearance of small crystals
precipitating out of the liquid.
I was thinking of these experiments to see if I could form sodium sulfides or hydrosulfides under EG solvent. EG was selected because of it's high
boiling temp and to protect the sulfur from oxidation by atmospheric O2.
What has happened here though? I have searched my text books and googled a bunch but have found no clear explainations for either the reaction of EG
(or any other diol) with NaOH, and certainly not for the reaction of this solution with sulfur.
[Edited on 31-10-2006 by Al Koholic]
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Nicodem
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NaOH dissolves well in ethylene glycol.
NaOH reacts with sulphur yielding sodium polysulfides, Na2SO3 and possibly other disproportionation products.
Ethylene glycol, being an alcohol, is susceptible to atmospheric oxidation in the presence of hydroxides. Possibly the deprotonated ethylene glycol is
also susceptible to oxidation from sulfur.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Al Koholic
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The white solid obtained after driving off the ethylene glycol was isolated and tested. First the thick syrupy solution was treated with isopropanol
to thin it. The solid did not dissolve appreciably and the liquid was decanted from the mix. The solid was then shaken with 3 portions of
isopropanol.
Addition of distilled H2O caused immediate dissolution of the solid. Addition of HCl caused fuming in the test tube and the presence of H2S was
rapidly noted.
The solid could certainly be misc. poly/hydo/sulfides of sodium.
If this proves to be true, this could be a useful method for making these compounds without using high temp carbon reductions of sulfates.
I'd like to test the solid for it's ability to reduce aromatic nitro compounds. I also think it would be worthwhile to test the solution obtained
from EG+NaOH+S directly for the same purpose as were this the desired use, further purification could be unnecessary.
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not_important
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I thinjk Nicodem has it. You formed sodium sulfides and other reaction products. When you really heated the mix to vapourise the glycol you got
reactions that are effecitively oxidation of glycol by sulfur. Given the boiling point of ethylene glycohol you were getting that solution pretty hot
for a mixture of sulfur or polysulfides and organics, certainly pushing the edge of regions where reactions are expected especially give the presence
of strong base.
Also, if the reaction mix was not sealed away from the air oxygen will slowly dissolve in it to react with the polysulfides, and possibly the glycol
as well under the influence of strong base.
One other thing that can happen with hydroxides and glycohols when heated. There will be an equalibrium ROH + NaOH <=> RONa + H2O. As you heat
the mix, assuming that oxygen is kept away, you drive off the water and shift the equalibrium to the right. At some point the sodium alkoxide will
start to precipitate out. This assumes that you haven't added sulfur as well.
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Al Koholic
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The equilibrium is something I believe I observed in my experiment. I heated the EG to coax the NaOH to dissolve quicker. This caused an evolution
of gas which, due to the high temp of the EG solvent, could easily have been H2O. The evolution of this gas stopped after a minute or so of heating
so this seems likely.
Plus there was a color change in the EG/NaOH solution.
It was at this point that I added the sulfur.
I have cooled the initial stock of orange solution in the freezer after dilution with isopropanol. It has precipitated a large quantity of white
crystals. These are morphologically different from the crystals obtained from the solution after driving off EG.
I'll do some tests on these later.
Seems like a viable method for sulfide production. Avoids a lot of the inconveniences with high temp reductions.
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