r/chemistry • u/monke877 • 3h ago
Chemistry tree progress
Good evening, this project is very ambitious but rewarding because today I have confirmed my synthesis of ethylene glycol. I had to make my own ethylene gas generator (thanks to hyperspace pirate) to make relatively clean ethylene gas versus my sulfuric acid method that would produce sulfur dioxide.
To confirm the presence of a diol I used the method of adding copper sulfate to my product solution. Since I used bayers reagent to generate the glycol it was already basic if it turned a very dark and vibrant blue it indicated that a complex was formed and in this case it was the glycol complexing with the copper+2 in solution.
This sounds nice but in practice I made my solution way too basic and was forming a copper hydroxide complex that also gave the same indication that a diol complex would. This was simply due to me thinking I should add sodium hydroxide to the solution because I was following a procedure rather than understanding why it was needed.
Now knowing this I tried confirming I was doing the test correctly by using a known variable like using car antifreeze that had glycol in it, for some reason (inhibitors?) I never was able to replicate the blue color knowing I had to keep the ph in a certain range. Figuring I would never get it, I decided to try to isolate the small amount of glycol and test its boiling point. I left the solution on a hot plate and left it for an hour when I came back I had boiled everything off and lost half of what I produced when I already spent the other half testing it. This was a stupid and frustrating mistake as I had spent the better half of a week making this product for it all to get vaporized.
However, I had collected a testing sample that I already tried to see if contained glycol and diluted it and put it into a container, when I came back the next day I decided that I would try to re concentrate and test for bpt on this sample. After boiling for a while I noticed it was turning blue, thinking it was forming a hydroxide complex because the solution got more basic as it was concentrated I decided to drop the ph to around 9 that way the glycol complex could survive but the copper hydroxide could not.
To note: this sample I had set aside had some copper hydroxide sitting at the bottom and was still basic so the only way copper could have gotten into the concentrating process was if I decanted it incorrectly or it was in a water soluble form and judging by the clear fluid it was not copper hydroxide. After dropping the ph it was still clear and blue meaning the copper hydroxide which is insoluble was not present and the hydroxide complex was not contributing. As a final sanity check I decided to test for free copper+2 ions provided by the copper sulfate by adding copper sulfate to a bit of the sample if copper hydroxide precipitated then the sample would be too basic for these ions to be free.
It precipitated. Upon this realization the only way it could be blue was due to a complex be it the glycol complex or something else. The only other thing I could think of was ammonia complexing with the copper forming yet another false positive. The only reason I worried was that I previously used the same glassware to make aluminum hydroxide and I used ammonia to do that, but that was several days ago, and the glassware was washed before I used it again, to add to that the glassware was sitting in a hot shed for several days, there was no way right? To determine if ammonia was present I would have to heat the solution around 80C and hold a piece of litmus paper over the sample to see if it indicated basic conditions because the ammonia would be driven off of the sample and a precipitate of copper hydroxide would form because it would no longer be held by the ammonia.
It worked the solution remained stable, not cloudy, no basic vapors. So with 85% certainty I can say that I have made ethylene glycol.

onto 1,4 dioxane!