Storage of acetals (eg MDA) in water

[aced126]

A lot of people say that amphetamines can be stored in water for extended periods of time (I agree), but can this logic be applied to said compounds?

Wouldn't storage of cyclic acetals like MDA over a long period of time result in an equilibrium mixture with some MDA hydrolysing into alpha-methyldopamine and formaldehyde? Especially as water is the solvent itself which should push the equilibrium more and more to the formaldehyde side? Storage in a relatively warm place is gonna push it that way even more.

 

[adder]

MDA is not a regular acetal that you can hydrolyse in acidic media, you can't prepare it as you normally prepare acetals either. If you count pi electrons and electrons from free electron pairs of oxygen atoms in the 1,3-benzodioxole moiety, you'll see that they meet Huckel's rule. MDA & MDMA as salts are stable in aqueous solutions.

 

[aced126]

So 1,3-benzodioxole system is aromatic? Wouldn't the sp3 carbon break aromaticity?

 

[adder]

Honestly speaking, I don't know if the second ring is aromatic by definition, I guess it's treated as a special case in some way, but unfortunately, I can't find any sources how it is called. Anyway, the extraordinary stability of the methylenedioxy bridge in 1,3-benzodioxole is likely due to additional interaction between lone electron pairs of oxygen atoms and the pi system of the other ring. I was sure 1,3-benzodioxole was a flat molecule, but I've just found an article in which it is stated that the non-planar conformation is actually more stable, I can't get deeper into it though as it's hard physical chemistry for me which I pretty much don't like. I would love to know more about 1,3-benzodioxole too, perhaps someone more experienced can chime in and explain it in more detail, if not, I can ask someone more knowledgeable tomorrow. Anyway, the methylenedioxy bridge in 1,3-benzodioxole won't be hydrolysed.

 

[aced126]

If it was aromatic then what would orbital would the middle carbon have?

 

[belligerent drunk]

Perhaps the hydrolysis is much slower because the "phenolic" oxygens are significantly less basic than aliphatic ones, so the first step of acidic hydrolysis, protonation of the oxygen, is hindered.

 

[belligerent drunk]

If it was aromatic then what would orbital would the middle carbon have?

I don't think it can be aromatic in the traditional sense, because it doesn't have any pi electrons.

 

[aced126]

That's just rate of reaction though? If left for long enough (years even) surely eventually it will reach equilibrium?

 

[belligerent drunk]

After enough time has passed, yes. There are 2 kinds of stabilities: thermodynamic and kinetic. Some things, while thermodynamically unstable, can persist in their unstable state for years due to kinetic hindrances. I'm too tired to think which one's the case here (maybe both), but it doesn't really matter, does it? Even if it's only kinetically stable, but the reaction is so slow that it won't reach equilibrium in years, it's still as good.

Adder, can you link the article in which the conformation of the molecule is discussed? I'd be interested to know why it isn't planar.

 

[Bagseed]

if you're talking about the CH2 group in between the oxygens, it has to be sp3 hybridized. no pi-electrones, as belligerent drunk said, just sigma bonds.

 

[adder]

After enough time has passed, yes. There are 2 kinds of stabilities: thermodynamic and kinetic. Some things, while thermodynamically unstable, can persist in their unstable state for years due to kinetic hindrances. I'm too tired to think which one's the case here (maybe both), but it doesn't really matter, does it? Even if it's only kinetically stable, but the reaction is so slow that it won't reach equilibrium in years, it's still as good.

Adder, can you link the article in which the conformation of the molecule is discussed? I'd be interested to know why it isn't planar.

Re-examination of the rotationally resolved spectra of the electronic origin and several vibronic bands of 1,3-benzodioxole

 

[belligerent drunk]

Re-examination of the rotationally resolved spectra of the electronic origin and several vibronic bands of 1,3-benzodioxole

Interesting, although sadly I don't really understand why exactly, this kind of physical chemistry is still sometimes too complicated for me. I originally thought it was in something like the "puckering mode" with oxygens still on the same plane as the benzene ring, didn't expect it to "flap" to a considerable degree.