Salicylic acid synthesis by hydrolysis of asprin

[DONMAN]

I am attempting to perform hydrolysis on Acetylsalicylic Acid (asprin) to create salicylic acid. I am wondering if 31.45% (by mass) HCl is strong enough to dissociate Acetylsalicylic Acid into Acetic acid and salicylic acid. I have also heard that Acetylsalicylic Acid can also undergo autocatalytic degradation to Salicylic acid in the presence of H2O. Can any one give me some insight into the situation....

[Alexires]

I would think that HCl would be a strong enough acid to hydrolyse ASA into Salicylic acid and Acetic Acid.

I've found a few interesting journal articles (none of which I can read all of) that mention accelerating the hydrolysis of ASA by using a hydrocarbon/H2O mixture. I'm trying to find a copy for you.

Hmmm, no luck.

As I understand it, ASA will by hydrolysed by water, but I would imagine as the acidity of the solution rises (from the acetic acid), the solution would approach equilibrium. I'd just hit it with some HCl, or you can try water and use NaOH to raise the pH.

[Hinckleyforpresident]

I achieved a >80% yield simply refluxing tap water with ASA for 8 or 9 hours. As the ASA breaks down the pH drops due to AcOH formed, this in turn catalyzes more breakdown in a self feeding process.

At the end of the reaction you will have a flask filled with SA crystals. I recommend recrystallizing from boiling acetone.

[kurtz]

And the solubility in strong acid is?
Using base works great from pills.

[Hinckleyforpresident]

And the solubility in strong acid is?
Using base works great from pills.

To my knowledge, the solubility of SA in water isn't good no matter what the pH.

[FUTI]

Hm, and what was the SA needed for? I was shocked to find out that some of the reaction of SA actually work better if you use ASA instead (e.g. less oxidation or aromatic substitution). It is more expensive for the industrial purposes as it would mean 1 more synthetic step (acetylation of SA), but for hobby type chemist availability of the compound means a lot;-). HTH

[Hinckleyforpresident]

I used my salicylic acid to make methyl salicylate. My house hasn't stopped smelling since!

[JouMasep]

For esters, the rate for base hydrolysis is much better than for acid hydrolysis. It is the preferred route in this case.

So I would propose use of a 10N solution of KOH (or NaOH).

You add one equimolar amount to neutralize the (very) acidic hydroxyl radical and then an equal amount –plus a wee bit of excess- to quantitatively hydrolyse the methyl ester.

The reaction is carried out at room temperature. At first the reaction goes very fast (may even get slightly warm I reckon); but in order to go fully to completion, it needs to stand for a few days.
Then acidify with dilute sulphuric acid to pH around 1 and re-crystallise from a suitable solvent (mixture) Acetone or isopropyl alcohol and the like.

This is not a truly catalyzed hydrolysis as the hydroxyl ions get consumed in the reaction. When half-decently carried out, the yields should be quite better than for acid-hydrolysis

[kurtz]

To my knowledge, the solubility of SA in water isn't good no matter what the pH.

I thought that it was obvious that I was talking about the subject of the thread, acetylsalicylic acid and conc. acid, which is a practical consideration. Of course both SA and ASA are perfectly soluble in equivalent bicarbonate (foam and spray) or hydroxide solution, etc. if acetylsalicylic acid remains that way for any length of time in the presence of base that is. The solubility of SA in boiling water is high enough for it to be my preferred purification method.

[Alexires]

JouMasep - Perhaps I have missed something, but wouldn't attempting hydrolysis with a base lead to a salt being formed instead of the desired product? I see that you acidify with H2SO4 but would it not just be easier to use an acid in the first place, or merely refluxing with water as Hinckley suggests? Or reflux with acid?

[JouMasep]

The first equimolar amount of base will indeed neutralize the proton on the (very) acidic hydroxyl group. (It will not really form “a salt” as all is in solution -but I get your drift and you are thinking right here.)
The second (again equimolar) amount of base will hydrolize, split or saponify the methyl ester group. The rate for saponifications of esters is way better than acid hydrolyses.

I see that you acidify with H2SO4 but would it not just be easier to use an acid in the first place, or merely refluxing with water as Hinckley suggests? Or reflux with acid?.
Well, if easy is the objective, chucking a load of aspirin tablets into boiling water would be the ticket.

But if optimal (close to quantitative) yield would be one’s goal, then base hydrolisis would be best.

And besides, I feel that a lack of need for boiling, refluxing for many hours counts for something too.

It is not a big deal: add base, stirr, walk a way. Come back in two days and acidify. Easy as well methinks.

[Nitrato]

Long time ago I made my SA doing the basic hydrolisis then adjusting with H2SO4, exactly like JouMasep have said in this thread and IMHO is better than refluxing (I hate reflux!) ASA with water or HCl, although acidic hydrolisis isn't seem to be really slow (I have not tried direct acidic hydrolisis, but here http://www.crscientific.com/article-aspirin.html is claimed that at 60-85°C you need at least one hour of reflux).

But since I discovered a place where methyl salicylate is real cheap and OTC, I discontinued to hydrolise ASA to get SA.

[FUTI]

Nitrato I would appreciate if you send me a private message with source for that OTC methyl salicylate since forum practice is not to publish it where three letter agencies can see it.

[Barnacles]

Nitrato I would appreciate if you send me a private message with source for that OTC methyl salicylate since forum practice is not to publish it where three letter agencies can see it.

You have private messages off. so pm me and I will give you a source...

[Skean Dhu]

Methyl salicylate AKA Oil of Wintergreen is available as a topical pain releif rub for sore muscles in many pharmacies as well as places that sell essentail oils for flavoring.
Should you be located in a particularly draconian area it is found naturally in Eastern Teaberry(Gaultheria procumbens) and Sweet Birch(Betula lenta) plants.

[megalomania]

The concentration of methyl salicylate in oil of wintergreen is very low. It would be very expensive, as well as time consuming, to extract a useful quantity.

[FUTI]

I can confirm Mega's word as the products contain methyl salicylate in my part of the globe up to 3-10%, although net info about percent in some USA products is up to 50%.

[tapira1]

Another good source of SA is the natural one. Salix trees. They grow here all over the land, specially near water. A decoction of it can yield several grams without too much effort.

Regarding hydrolysis of ASA, it will hydrolize even with water, but the best method is to use dilute (not 10 N, buy 0.01 N) NaOH; solubility os low enough to allow extraction from the acidified medium.

[Hinckleyforpresident]

If you use a base to hydrolyze acetylsalicylic acid, you will wind up with a salt of salicylic acid.

[tapira1]

That is correct, however, 0.01 NaOH is easily neutralizable (HCl, H2SO4); then, you get your SA from an acidic medium. Overall, the process is les time and energy consuming.