Ques for chemists - Ascorbic acid and Sodium Benzoate?

[Eos of the Eons]

What is the chemical reaction of C6H8O6 + C6H5CO2Na?

Nader is calling for a ban of soft drinks that contain vitamin C and sodium or potassium benzoate. Some folks figure this causes benzene to be formed in the soft drinks.

http://www.msnbc.msn.com/id/12127641

Is that possible looking at the chemical formulas and soft drink can "environments"?

It's been so long since I was in my organic chemistry classes.

 

[casebro]

Benzene is carcinogenic. What study links soda to cancer? Or is this some more junk science- it could happen, it does in rats when we give them the quivalent of 2090 gallons of soda per day...

 

[Eos of the Eons]

I haven't found the study, and can't work out the chemical reaction above to see if it is even plausible.

Help!

Benzene is C6H6

 

[pgwenthold]

I haven't found the study, and can't work out the chemical reaction above to see if it is even plausible.

Help!

Benzene is C6H6

There's no direct reaction here that leads to benzene, although benzene is such a stable product that to claim it isn't formed at all would be a mistake. Thermochemically, it happens. For example, one pathway to benzene would be oxidation of the benzoate, which would then decarboxylate to give phenyl radical, which could H atom abstract to give benzene. However, it is awfully tough to oxidize benzoate, but it could happen to give something like parts per trillion of benzene.

Of course, it's silly to raise an alarm about such a thing. As I said above, benzene is a real thermodynamic sink, and so it is formed fairly regularly naturally. There is likely a higher concentration of benzene in regular carrots than there is a soft drink (actually, I wouldn't think that would be even close).

 

[Eos of the Eons]

Thanks! I would think thermochemical reactions would be rare in soft drinks?

 

[Eos of the Eons]

Okay, some more "stuff" on this that doesn't make much sense to my layperson outlook.

study showed that ascorbic acid initially reacted with metals, such as iron or copper, found in the water to create 'free radical' particles known
as hydroxyl radicals. [hydroxyl radicals then react with benzoic acid to
produce benzene]

His study showed that ascorbic acid initially reacted with metals, such as iron or copper, found in the water to create ‘free radical' particles known as hydroxyl radicals.

Sodium benzoate, meanwhile, breaks down into benzoic acid when placed in acidic conditions, such as in a soft drink.

The hydroxyl radical attacks the benzoic acid, removing the carbon dioxide from it and leaving benzene in its wake. Lawrence's study said this reaction could take place “under conditions prevalent in many foods and beverages”.

http://www.nutraingredients-usa.com/news/ng.asp?n=65840-soft-drinks-fda-benzene

Now it's just the vitamin c and iron or copper plus sodium benzoate and acid.

C6H8O6 + Fe or Cu = -OH and what?

C6H5CO2Na + Acid = C7H6O2 (benzoic acid) and what?


Then Hydroxyl -OH + benzoic acid C7H6O2= C6H6 and what?

Is this true?

What if the soft drink contains potassium benzoate instead of sodium benzoate? How likely is it that copper and/or iron is in the water used in making soft drinks?

 

[Shrinker]

Sorry, I know little about the subject but this minor story broke a few days ago in the UK... http://news.bbc.co.uk/1/hi/health/4864226.stm

Worrying levels of the cancer-causing chemical benzene have been found in four soft-drinks available in the UK, the Food Standards Agency says.

Benzene, which can cause certain cancers, is thought to be formed when two commonly used soft-drink ingredients - the preservative sodium benzoate and ascorbic acid - interact.

but...

"The levels of benzene reported in this survey will only make a negligible impact on people's overall exposure to benzene and so any additional risk to health is therefore likely to be minimal."

 

[DrDave]

May be of some use:

http://www.bfr.bund.de/cm/245/indic...ion_of_benzene_from_benzoic_acid_in_foods.pdf


Dave

 

[pgwenthold]

Thanks! I would think thermochemical reactions would be rare in soft drinks?

All reactions are thermochemical

When I used thermochemical in the above, I was just using it in the sense that benzene is a thermochemically favored product, and, in fact, is pretty highly favored thermochemically (or thermodynamically, if you prefer). Therefore, it is likely going to happen to some extent, although it might not even be detectable.

 

[pgwenthold]

Okay, some more "stuff" on this that doesn't make much sense to my layperson outlook.


http://www.nutraingredients-usa.com/news/ng.asp?n=65840-soft-drinks-fda-benzene

Now it's just the vitamin c and iron or copper plus sodium benzoate and acid.

C6H8O6 + Fe or Cu = -OH and what?

organometallic complex

C6H5CO2Na + Acid = C7H6O2 (benzoic acid) and what?

sodium salt of the acid

Then Hydroxyl -OH + benzoic acid C7H6O2= C6H6 and what?

CO2 and water

Is this true?

Nominally, yeah. It's pretty much what I said above, although I didn't see the use of the metals to get the thing going.

What if the soft drink contains potassium benzoate instead of sodium benzoate? How likely is it that copper and/or iron is in the water used in making soft drinks?

No difference on the potassium benzoate.

The real question is to what extent is there cu or fe in the mix. More importantly, what oxidation state does it need to be in? There are a lot of different states of metals, and in this reaction, only a select state or two is going to be active. Fortunately, these states are generally not the states present in most aqueous solution. Sure, there is iron in water, but that's in the most stable oxidation state, and sure isn't going anywhere.

As I said any extent of this reaction is going to be way too small to be worth worrying about. If Nader can find that the concentration of benzene in soft drinks is higher than that in, say, a carrot, then I would only worry about how much you ingest, not that you ingest it.

 

[Oldpossum]

Hello all.

I've done a little reading, and talking to other Organic chemists here at work, and I've established that the following reaction sequence is occuring.

1) Ascorbic acid is reducing Copper ions in solution, from Cu(II) to Cu(I), and in return being oxidized itself.

2) Cu(I) ion + Benzoate ion, react to give Cu(II) ion + CO2 + Benzene.
Effectivly the Cu(I) is reducing the benzoate ion, and itself being oxidized back up to Cu(II).
This reaction is heat sensitive, and so proceeds more rapidly at higher temperatures.

3) Rinse and repeat, untill you either consume all avaliable Ascorbic acid, or all avaliable benzoate, or product is consumed!
(Note as there is usually only trace ammounts of free copper ions in solution, it's going to take a long time to make even ppm ammounts of Benzene.)

Strongly acidic conditions promote the formation of Benzoic acid, in solution, instead of benzoate ions, and so this reaction will probably not occur.
As the benzoic acid is not suseptable to being reduced by this method.
ie Reduciton of benzoic acid to benzene, and CO2, requires the intermediate formation of a benzoate ion.

Other chemicals in solution may also bind the copper, thus making it unavaliable. For example Orthophosphoric acid, can react with copper ions, to make the water insoluble, Cupric Phosphate, salt.

Exactly how UV light, promotes the formation of Benzene, I have yet to work out.

 

[Art Vandelay]

All reactions are thermochemical

No, gravatational reactions, for instance, are not.