Unknown yellow substance from mixing ascorbic acid, baking soda, and rubbing alcohol, then boiling So lately I've been using ascorbic acid (very very tiny amounts) to neutralize the chlorine and chloramine in my tap water (temporary solution to improve flavor in lieu of a proper filter).

Just for fun, I decided to react a solution of ascorbic acid with some sodium bicarbonate in an attempt to make a sodium ascorbate solution. Then I got to thinking, how can I get the ascorbate out of the solution?

I figured boiling would do the trick, but for some reason, I thought that adding isopropyl alcohol to the solution might do something, maybe precipitate the crystals out? That probably sounds completely stupid, but forgive me, it's been years since I studied any kind of chemistry (and I wasn't planning on ingesting the solution, so I figured it couldn't hurt to try).

Anyway, the alcohol did nothing visible, so I figured I'd go ahead and book off the solution (figuring the alcohol would dissipate quickly with its low boiling temp).

All went well for some minutes, the alcohol seemed to have boiled off (the smell was gone), and the liquid level was going down so I expected to see some white precipitate forming after a while. Instead what happened surprised me, the solution started turning yellow, then darker as more water boiled off. I did eventually start seeing some cloudiness at the bottom which I assume was the sodium ascorbate, but I didn't boil all of the water off because the color intrigued me.

Here's what it looked like after boiling about 2/3 of the water off:


Any ideas what this could be? My first thought was some contamination, but the pan I used was washed and rinsed very thoroughly.

Some more details on the solution:


about 1/2 teaspoon ascorbic acid
about 1/4 teaspoon sodium bicarbonate
mixed in roughly 2oz water and added a bit more sodium bicarbonate until everything stopped bubbling
when the solution was completely clear and not bubbling, added about 1oz isopropyl alcohol (maybe less)
boiled off about 2/3 of the solution


I eyeballed a lot of this and added stuff as I went (wasn't sure exactly how much ascorbic acid would dissolve) so those amounts may be quite a bit off, but the solution was crystal clear and not bubbling at all after I was done adding everything.

Hope someone with more knowledge than I can offer some insight!
That's sort of the colour that vitamin-C tablets go if they are kept long beyond their expiry date. I'd go with it being oxidation of some sort but chemistry.oregonstate.edu/courses/ch130/old/VITCTEXT.htm indicated that the simple oxidation of ascorbic acid is colourless... so what you've got is a more complex mix of oxidation products.

Instead of boiling off in an open pan, boiling off in a stable atmosphere might work better. You'd probably need some distillation glassware and a source of non-oxidising gas to flush out the oxygen dissolved in the water / keep an oxygen free atmosphere. You could probably get away with any arc welding gas or even use carbonated water as a source of CO2 gas to flush the air out of your equipment. Or of course you could go the whole chemistry-department route and boil the water off in a low pressure system without adding much heat.