Sciencemadness Discussion Board - Esterfication Question

Esterfication Question

Steam - 17-7-2014 at 13:40

So I am trying to make an ester with Salicylic acid and 1-Octanol. Is it possible to combine the two together with a few drops of sulfuric acid to produce Octal Salicyliate?

mnick12 - 17-7-2014 at 13:55

Probably, but you are going to need to reflux it for a while. I would suggest a dean-stark apparatus or possible refluxing in the presence of some sieves. Normally with a fischer esterification you want a large excess of either the alcohol or acid, but considering you substrates that could make work-up difficult.

Crowfjord - 17-7-2014 at 14:01

In short, yes. This is how folks have been making the analogous methyl salicylate. Purification may prove difficult, though. You will probably have to vacuum distill residual octanol from the product (I'm assuming octyl acetate has a higher boiling point than octanol).

Steam - 17-7-2014 at 15:23

I am working with fairly small quantities (0.05 moles). How long would a reflux take at this scale? I am not too concerned about separating it from the octanol since the ester will be reacted with a Cu or Fe slalt to from a organometalic complex after.

Ascaridole - 17-7-2014 at 19:04

Use an organic acid like pTsOH or strongly acidic cation exchange resin as your catalyst. Octanol as you know is a fatty alcohol so thats why I suggest an organic acid as sulfuric may or may not be sufficiently miscible to allow a good reaction rate. Also if you use ion exchange resin easy removal of acid (just filter it off) and maybe one wash with bicarbonate to remove any "loose" acid. Any aqueous workup may produce an emulsion so the less water you need to use the better.

TheChemiKid - 18-7-2014 at 04:33

Quote: Originally posted by Crowfjord

(I'm assuming octyl acetate has a higher boiling point than octanol).

Do you mean Octyl Salicylate?

Steam - 18-7-2014 at 07:05

No not octyl. I mean strait chain octan-1-ol.

Metacelsus - 18-7-2014 at 07:28

Quote: Originally posted by Ascaridole

Use an organic acid like pTsOH or strongly acidic cation exchange resin as your catalyst.

I recommend the resin because it's easy to remove; just filter it out.

blogfast25 - 18-7-2014 at 08:18

Quote: Originally posted by Steam

No not octyl. I mean strait chain octan-1-ol.

With octan-1-ol you get octYL salicylate (not octAL salicylate, as you wrote high up).

Once you're above the MP of salicylic acid (159 C) and both reactants are liquid, this should proceed fairly fast. Separating the product from unreacted reagents will be a bit more of a challenge than for usual esterifications.

[Edited on 18-7-2014 by blogfast25]

Steam - 18-7-2014 at 08:30

If I have an unknown " charged" resin which has a ph less than 1.7 on ph test paper. It has the appearence of the acidic cadionic exchange resin on wikipedia. Is this an appropiate resin to use?

Crowfjord - 18-7-2014 at 12:15

@thechemikid: Whoops, yes, that was a typo. I did mean octyl salicylate. I must have been tired when I posted that.

[Edited on 18-7-2014 by Crowfjord]

Ascaridole - 18-7-2014 at 12:42

Steam, what do you mean by charged?
Charged as in exhausted, all H+ replaced by a metal cation or charged as in regenerated with acid to kick out all of the metal cations and put the resin back into all H+'s...

Also its very difficult determine what type of resin you have. There are hundreds of resins out there that all look alike but have very different properties. Best idea is to do a small scale test to see if the resin will do what you expect of it before sacrificing a large quantity of reagents.

Steam - 18-7-2014 at 16:52

Got it, Thank you very much. I did do a small test with the resin and the solution turned golden brown upon heating to reflux. The resin began to turn dark brown. I have never worked with resin before so I don't know if this is normal. I plan to try to restore the color with a bit of activated carbon tomorrow. I don't know if it was spent or not! It was not labeled.

Also I am a bit confused about the octyl vs octal. Isnt octyl salicylate come from 2-ethylhexanol (according to Wikipedia)?

Steam - 18-7-2014 at 16:56

Quote: Originally posted by Ascaridole

Any aqueous workup may produce an emulsion so the less water you need to use the better.

Also you were right about the emulsion Ascaridole. The solution began to turn milky after the bicarbonate wash.

Ascaridole - 18-7-2014 at 16:57

Ahhh your reflux temperature may be exceeding the thermal limit of your resin. Perhaps the high temp will not allow the use of a resin after all. Hrmmm... I'll check acs for a fatty ester synth and see what they used.

UnintentionalChaos - 18-7-2014 at 17:23

Quote: Originally posted by Ascaridole

Ahhh your reflux temperature may be exceeding the thermal limit of your resin. Perhaps the high temp will not allow the use of a resin after all. Hrmmm... I'll check acs for a fatty ester synth and see what they used.

How about using octanol and a small excess of salicylic acid with toluene in a dean stark (sulfonate resin or pTsOH catalyst). Refluxing octanol is excessively hot for an esterification and at those temperatures, you will have competing thermal decarboxylation of the salicylic acid to phenol.

Excess salicylic will be easier to remove than excess octanol. Take up the product in some DCM and wash with saturated NaHCO3.

Edit: You could also give acid-catalyzed transesterification a shot. Combine equimolar methyl salicylate and n-octanol with a small amount of p-TsOH as catalyst and heat. Methanol should distill well below the boiling point of the mixture. Perhaps a 100C oil bath and a slow current of inert gas or at least dry air to remove the methanol vapor. The phenol makes base-catalysis (which is much faster) impractical.

[Edited on 7-19-14 by UnintentionalChaos]

Steam - 18-7-2014 at 17:32

That sounds easy enough! I will try that tomorrow!

Ascaridole - 18-7-2014 at 17:41

Quote: Originally posted by UnintentionalChaos

Quote: Originally posted by Ascaridole

And this is why UC is a much better synthetic chemist than I, didn't even think about decarboxylation..

UnintentionalChaos - 18-7-2014 at 17:47

Quote: Originally posted by Ascaridole

And this is why UC is a much better synthetic chemist than I, didn't even think about decarboxylation..

It helps that I have a prepub writeup on phenol prep from thermal decarboxylation of salicylic acid. Decarboxylation happens, albeit quite slowly at the boiling point of phenol (181C). n-octanol boils at 195C.

Steam - 18-7-2014 at 18:32

Quote: Originally posted by UnintentionalChaos

Excess salicylic will be easier to remove than excess octanol. Take up the product in some DCM and wash with saturated NaHCO3.
[Edited on 7-19-14 by UnintentionalChaos]

Would I filter the salicylic out then take it up in DCM or would the Salicylic remain in the ester and be removed by the DCM/Na+?

Is Salicylic acid soluble in DCM?

Magpie - 18-7-2014 at 19:24

I think using a lower boiling solvent, like toluene, is a good idea. Especially since you can then remove water as the reaction at reflux progresses. Toluene forms an azeotrope with water and this mix can be distilled off periodically. The water can be allowed to separate and discarded. The toluene is then returned to the refluxing reactants. This is what a Dean Stark trap does continuously and automatically. But if you don't happen to have one you can do this manually, as stated.

I generally follow a tried and true published procedure. But when you are doing something new like this you have to do quite a bit of research to determine what solvent would be best, and what the various solubilities and azeotropes will be. It helps that the Fischer esterification is a widely used and well understood process. A yield maximum of 67% can be expected without using some scheme to remove the product(s) during the reflux. Normally a large excess of the cheaper reactant is also used. See Le Chatelier's principle.

UnintentionalChaos - 20-7-2014 at 21:26

Quote: Originally posted by Steam

Quote: Originally posted by UnintentionalChaos

Excess salicylic will be easier to remove than excess octanol. Take up the product in some DCM and wash with saturated NaHCO3.
[Edited on 7-19-14 by UnintentionalChaos]

Would I filter the salicylic out then take it up in DCM or would the Salicylic remain in the ester and be removed by the DCM/Na+?

Is Salicylic acid soluble in DCM?

Residual salicylic acid will be dissolved in the ester. Sodium salicylate will extract into the aqueous phase readily. That is what the bicarbonate wash is for. You'll want to use a solvent like DCM because it's 1) mostly nonreactive, 2) reduces mechanical loss by diluting the product 3) lowers viscosity (if that turns out to be an issue) 4) is trivial to remove because of it's low boiling point.

@Magpie: which is why I suggested toluene with a dean stark to drive the equilibrium. A large excess of the cheaper reagent is appropriate when the excess is trivial to remove (acetic acid, methanol, ethanol, etc.). This obviates the need for the Dean Stark apparatus. Since the molar mass and melting point of salicylic acid are both rather high, a huge excess is extremely inconvenient. Octanol, with minimal unique reactivity relative to octyl salicylate's phenol group and a fairly high boiling point (and fairly similar polarity), would be difficult to remove in huge excess.

Fortunately, salicylic acid's carboxylate makes it easy to remove with a weak base like bicarbonate that will not interact with the phenol of the desired product. A slight excess of this, and the Dean Stark should ensure nearly quantitative conversion of the octanol to ester so that it need not be removed from the product.

@Steam

May I inquire what sort of synthesis the product is destined for? 2-ethylhexyl salicylate is commercially available and used on a massive scale as a sunscreen ingredient. If the octyl chain is to impart lipophilicity, the (probably dirt cheap) commercial product should be acceptable, no?

EDIT: not sure why I suggested DCM. You're already dissolved in toluene. Good enough. wash that with bicarbonate. strip the toluene under a mild vacuum.

[Edited on 7-21-14 by UnintentionalChaos]

Magpie - 21-7-2014 at 09:11

Quote: Originally posted by UnintentionalChaos

@Magpie: which is why I suggested toluene with a dean stark to drive the equilibrium. A large excess of the cheaper reagent is appropriate when the excess is trivial to remove (acetic acid, methanol, ethanol, etc.). This obviates the need for the Dean Stark apparatus. Since the molar mass and melting point of salicylic acid are both rather high, a huge excess is extremely inconvenient. Octanol, with minimal unique reactivity relative to octyl salicylate's phenol group and a fairly high boiling point (and fairly similar polarity), would be difficult to remove in huge excess.

I agree. I was just stating some general limitations/approaches to The Fischer esterification. Each case must be evaluated separately for the best approach.

In Steam's case water removal to drive the reaction so that removal of the octanol would not be required would indeed be a good approach, as you say. It will also improve yield considerably. Being able to do this is dependent on what he has for equipment. If he has no Dean-Stark trap the manual removal by repeated azeotropic distillations would suffice I think.

Also, he has <7g each of starting acid and alcohol. This may be a limiting factor, depending on the glassware he has available.

Steam - 21-7-2014 at 18:06

I am trying to make an nonmetallic complex more soluble. I plan to try to form a complex with it with copper (II). My goal is to form a complex similar to copper (II) acetylsalicylate, except with one of the groups replaced with this fatty ester.

Progress report. After Refluxing in toluene for 36 hours, I preformed a bicarbonate wash followed by a DCM extraction. The result was an oily liquid which had subtle hits of citrus and octanol.
I am a bit unsure if this will even complex with copper... if at all! I might try octyl salicylate later on if I feel that the reason I got no complex was due to problems with the quality of the ester.

DraconicAcid - 21-7-2014 at 18:21

Quote: Originally posted by Steam

I am trying to make an nonmetallic complex more soluble. I plan to try to form a complex with it with copper (II). My goal is to form a complex similar to copper (II) acetylsalicylate, except with one of the groups replaced with this fatty ester.

An ester of salicylic acid, in my opinion, is unlikely to form a complex with copper(II). To get something analogous to the acetylsalicylate, you'd need to put the new organic group on the phenolic oxygen, not the carboxylic acid oxygen.

Steam - 21-7-2014 at 20:24

Yeah, I am hoping that a protonated Phenolic oxygen in conjunction with the electronegative region on the =O in the ester bond would be enough to couple. As a future experiment I will have to change were the chain is added.

I'll update this tomorrow.

DraconicAcid - 22-7-2014 at 08:13

Well, methyl salicylate is readily available. See what that will do with copper(II), if anything.