Sciencemadness Discussion Board

Mystery substance

Baphomet - 26-9-2008 at 06:02

I have a substance that was inadverntently made but I have no idea what it is.

A vitamin C solution was produced by dissolving 1 tablespoon of L-Ascorbic Acid in 100mL of tap water. This was then placed in a plastic bottle.

After a couple of days the spray smells distinctly of pine tar. It is still a clear solution however. Some questions:

- Maybe it is dehydroascorbic acid? Though I thought I had made it previously and it didn't smell like that

- Has the acid somehow reacted with the plastic bottle? I don't know what kind of plastic since there is no recycling designation. It is only an aqueous solution so I'm scratching my head

Also I'm 99% certain there was nothing in the bottle beforehand

ScienceSquirrel - 26-9-2008 at 06:40

It could be down to some trace contamination of the bottle, a little goes a long way when it comes to smells.

Baphomet - 26-9-2008 at 06:51

Could be.. maybe some kind of resin left from manufacture? I'll try again and see if the same thing happens

chemrox - 26-9-2008 at 12:05

ascorbic acid is pretty stable... it's used as a preservative. where's the bottle from?

Nicodem - 29-9-2008 at 00:32

Aqueous solutions of ascorbic acid slowly oxidize on air.

PS: I'm moving this to Beginnings section.

Ramiel - 29-9-2008 at 02:31

When you mentioned the smell of pine tar, it immediately occurred that you might have somehow got terpenoids. I'm going out on a limb here to justify the smell as a terpene not due to the bottle itself.

As you know, ascorbic acid is a C6, and monoterpenes are C5. Can we assume that the water in the bottle had most of it's oxygen gobbled up by oxidation of ascorbic acid? If so, is it possible that uv could have liberated CO<sub>2</sub> and resulted in a monoterpene alcohol? picture related (don't look too closely at the electron pushing, he he)

Was the bottle left in the sun perhaps?
Were there any bubbles or effervescence when you opened the bottle?
can you tell us exactly what kind of plastic bottle you've got? I'd be interested if there was any catalytic activity... how strong was the smell of pine?

fancy.gif - 7kB

12AX7 - 29-9-2008 at 16:17

You show an enol as the final step, it should be a ketone,
HO-CH2-C(=O)-C(CH2-OH)2 or 3-(hydroxymethyl)-1,4-diol-2-butone. And the third step doesn't make any sense? Five bonded carbon anyone? :o

If you simply remove the -O-(C-)=O section, which is, I suppose, the most likely to leave (even though it's an ester, which isn't likely to leave, it's got *two* reasonably strong bonds), you could get the extra bond looping around, but that would be a three-membered ring, which sucks, so the other end could loop around (losing a proton in the process I suppose), forming a six-membered ring with an ether link (etherol, I guess you could say, to be specific). That takes care of one bond; the other might be filled with that stray proton. Another option is the solvent, if any, or an intermolecular reaction, could come in and, say it's water, could add H + OH to it wherever. But like I said, ester isn't likely to leave all its own. I don't know how stable this stuff is to UV, but it seems to me it will need some hearty radiation to do anything...

Dehydroascorbic acid (the oxidized form) might be a more interesting target. With loads of carbonyls there might be something more willing to leave.

Tim

Baphomet - 30-9-2008 at 06:18

Thanks Ramiel. That's an interesting theory. Did you do the diagrams yourself? Because they look good!

A terpene is a probability. But most of the things that smell like pine tar are aromatic (ring) compounds, right? Not sure if the ring got opened...

No idea what plastic the bottle is made out of. That was the first thing I checked.

The smell of pine tar is quite strong. When I'm not so busy I will try again and see if the same thing happens.

BTW I'm sure there has been some kind of transformation. The pine tar smell appeared gradually over the course of a week!

Pomzazed - 30-9-2008 at 07:12

If you can reproduce the smell, please specify the kind of bottles and/or storage condition too.

Might be something interesting going on.

Nicodem - 30-9-2008 at 07:39

The end product of ascorbic and dehydroascorbic acid oxidation with air is threonic acid. The oxidation in aqueous solution would require several days, but if there are trace amounts of Cu(II) or similar ions the oxidation is fairly rapid. I have no idea what smell threonic acid has, but I doubt it has much of any smell as it does not appear as volatile enough.
I do agree that an aqueous solution of ascorbic acid gains some smell if left standing overnight, but in my experience the smell is so faint that it is barely detectable. However, the taste changes a lot.
There has been a lot of studies done on the oxidation of ascorbic acid in water solutions - due to its importance in food, etc. I suggest searching a bit the literature before rediscovering any "mystery substance".

Baphomet - 30-9-2008 at 19:19

Thanks for the suggestion. However I always research before posting, and a look at the literature revealed nothing.

The bottle was in a cool place, away from direct sunlight. The solution has turned to a light yellow colour over the last few days. Also when I opened it this morning to smell, most of the pine tar scent was gone! Only the usual medicine-like smell of L-Asc remained.

Baphomet - 12-10-2008 at 20:22

Follow-up to the previous: the smell is still there but is only obvious when the solution is atomised, whereupon it is easily identified. Solution has reached a more deep yellow colour. The experiment was reproduceable in a glass container.

Here is some relevant literature for any who may be interested.

http://www.springerlink.com/content/m44244403621k37r/
Volatile degradation products were isolated from a solution ofl-dehydroascorbic acid in phosphate buffers solution of pH 2, 4, 6 and 8 heated under reflux for 3 h or left at 25° C for 200 h. The products were identified by comparison of their gas chromatographic retention data, infra-red and mass spectra with those of authentic compounds. Fifteen products were identified, among which 12 had not yet been reported as degradation products ofl-dehydroascorbic acid. Concentrations of 5 main degradation products, i.e. 3-hydroxy-2-pyrone, 2-furancarboxylic acid, 2-furaldehyde, acetic acid and 2-acetylfuran depended on the pH value and temperature; the presence of oxygen had no pronounced effect.

I find it rather amusing that this thread was moved to 'beginnings' since no-one was able to even remotely identify the substance apart from Ramiel, who gave it a good shot :D

Nicodem - 13-10-2008 at 00:09

I guess I should have explained it earlier that this thread was moved to the Beginnings section because you opened it in beginner way: you did no literature search before posting and provided no references. I already told you that a lot of research on ascorbic acid degradation was already done and all that was needed to be done was to check the literature. I'm glad you finally did that and that this thread finally grew to be informative.

PS: According to that paper both me and Ramiel were completely off. The compounds that give the specific smell to aqueous solution of ascorbic acid have nothing to do with oxidation or photolysis to polyols (which have no smell anyway).

stoichiometric_steve - 13-10-2008 at 23:26

Quote:
Originally posted by Ramiel monoterpenes are C5


Just to be a BIT anal - monoterpenes are C10. C5s are isoprenoids ;)