Should sodium lipoate react with ascorbic acid?

[bassamnfs]

Hi,
I've bought R-Alpha lipoic acid powder (not sure about its purity). So I mixed 500mg of ALA with 250mg sodium bicarbonate to get sodium lipoate, 30 minutes later (when the reaction is over) I added some 250mg of pure ascorbic acid to the final mixture and some small amount of insoluble sulfuric color goo formed. my question: Is this an impurity in ALA ? In other words: should Sodium lipoate react with ascorbic acid in anyway? if it reacts what are the reaction's products?

Thanks in advance

 

[Comeback City]

I'm not sure what exactly the reactants would be, but the sulfuric color goo is likely sulfur itself or a sulfur compound, since Sodium Lipoate contains sulfur.
Also, just to clarify, would this be your reaction...
C₆H₈O₆ + NaC₈H₁₃O₂S₂
?

 

[bassamnfs]

Thanks for your replay.
Yes exactly, what would C6H8O6 + NaC8H13O2S2 ----> ?

 

[Comeback City]

Thanks for your replay.
Yes exactly, what would C6H8O6 + NaC8H13O2S2 ----> ?

I can't tell you off the top of my head. Unless anyone else knows, maybe you could try to figure it out intuitively. Was there any bubbling in the reaction to indicate a gas? Or any other visible products besides the sulfur (or sulfur compound)?

 

[bassamnfs]

There is a reaction after adding ascorbic acid because it produces the yellow insurable substance I mentioned earlier

 

[Comeback City]

There is a reaction after adding ascorbic acid because it produces the yellow insurable substance I mentioned earlier

Yeah I saw that part, but could you tell if their was any bubbling at the surface? That would indicate that a gas (such as CO₂ or H₂) was produced as another product.

 

[bassamnfs]

No, there was no gas or any indication of a reaction

 

[Comeback City]

No, there was no gas or any indication of a reaction

Then the best advice I personally can give you is that you can perform tests on the other products and attempt to match their properties with properties of potential products that could be produced (i.e. Density, freezing point). This might take a while but I can't think of any other way. Even so, it might not work if the products are in a mixture. Worth a try though if you have some spare time!

 

[TeethWhitener]

Could you be re-protonating the lipoate with the ascorbic acid and precipitating out the fatty acid? I don't know the pKa's of the species involved, but organic acids tend not to be water soluble when they're not dissociated.

 

[bassamnfs]

Thanks for the reply.
I retried the reaction again to find out that the gooey substance will be produced from the very first reaction ( ALA + Sodium bicarbonate), means without even adding ascorbic acid later. I get the same results ( waiting time for the reaction to complete 30 minutes, before not exactly 30 minutes ).
I took this gooey substance and put it on the stove, it melted to a brownish liquid then started to smoke, by smell it's similar to sulfur but not sure... anyway, I think this powder of alpha-lipoic acid is impure...

 

[Ygggdrasil]

It could be the lipoic acid polymerizing: http://pubs.acs.org/doi/abs/10.1021/ja01604a053

 

[bassamnfs]

Ygggdrasil, appreciate your help. thanks