Sciencemadness Discussion Board - α-pinene to α-terpineol acetate

α-pinene to α-terpineol acetate

blogfast25 - 6-12-2015 at 07:38

The Wilki entry on α-pinene claims that (unspecified) treatment of the latter with glacial acetic acid yields α-terpineol acetate.

If true that would be an addition/rearrangement with no leaving group or by-product(s). Below is NOT an attempt at explaining the reaction mechanism but rather the diagram shows where the various bits and pieces of the reagents end up (assuming there is such a reaction at all):

alpha pinene to terpineol acetate.gif - 4kB

The acidic H would end up on the atom labelled 1, the bond between 1 and 2 would open up and the acetate group bonded to 2. Atom 3 then ensures the cyclohexene ring remains closed.

But I'm far from understanding electron movements here. I suspect auto-protonation of the GAA may play a part but can't see how.

What's more, I can't find references to this process, re. reagent quantities, temperatures and (presumed?) reflux times and work-up procedures.

Any insights would be most welcome.

[Edited on 6-12-2015 by blogfast25]

Crowfjord - 6-12-2015 at 09:06

Here is a paper that might lend a little bit of insight. It's not much, but maybe it will help.

Attachment: Hydration and acetoxylation of monoterpenes catalyzed by heteropoly acid.pdf (103kB)
This file has been downloaded 991 times

Magpie - 6-12-2015 at 09:30

Is that product terpenyl vs terpinol? I don't see an alcohol group. The paper from Crowfjord shows terpenyl.

[Edited on 6-12-2015 by Magpie]

[Edited on 6-12-2015 by Magpie]

blogfast25 - 6-12-2015 at 09:37

Quote: Originally posted by Magpie

Is that product terpenyl vs terpinol? I don't see an alcohol group. The paper from Crowfjord shows terpenyl.

The reaction product in my diagram is α-terpinol acetate. There's no alcohol group because the alcohol has been esterified.

In the paper they call the alcohol α-terpineol and the acetate α-terpenyl acetate. Not sure why...

Thanks, Crowfjord.

[Edited on 6-12-2015 by blogfast25]

Magpie - 6-12-2015 at 09:42

Is this not the same compound:

https://pubchem.ncbi.nlm.nih.gov/compound/alpha-terpinyl_ace...

edit: I see in the synonyms it can be called terpineol.

[Edited on 6-12-2015 by Magpie]

blogfast25 - 6-12-2015 at 09:46

Quote: Originally posted by Magpie

Is this not the same compound:

https://pubchem.ncbi.nlm.nih.gov/compound/alpha-terpinyl_ace...

edit: I see in the synonyms it can be called terpineol.

[Edited on 6-12-2015 by Magpie]

Yes, they appear to be synonymous. Trivial names, eh?

[Edited on 6-12-2015 by blogfast25]

deltaH - 6-12-2015 at 10:28

Quote: Originally posted by blogfast25

Below is NOT an attempt at explaining the reaction mechanism...

What a pretty reaction!

Here's my attempt at a possible mechanism:

I would think you'd need a much stronger acid to catalyse this, acetic acid is probably too weak to protonate the alkene and get the ball rolling...

[Edited on 6-12-2015 by deltaH]

blogfast25 - 6-12-2015 at 10:51

Quote: Originally posted by deltaH

Quote: Originally posted by blogfast25

Below is NOT an attempt at explaining the reaction mechanism...

What pretty reaction! This is what I think the mechanism MIGHT be...

What a pretty reaction mechanism!

But is it based on anything?

I'll grant you this: the acidic H seems likely to play a part in it. Which makes me wonder aloud whether conc. H2SO4 might be a catalyst to consider here?

deltaH - 6-12-2015 at 10:53

Hey I just edited my post to exactly that, yes I think one needs a very strong acid here to generate the carbocations at a good rate.

So then the acetic acid doesn't actually do the protonation in the mechanism, but rather the strong acid catalyst.

Heteropolyacids would work well.

I take it you're wanting to try this one? I just want to know what the product smells like, should be pretty intense

[Edited on 6-12-2015 by deltaH]

deltaH - 6-12-2015 at 11:13

Quote: Originally posted by blogfast25

But is it based on anything?

Based on 100% brain fart. It's just me practicing electron pushing, no doubt poorly.

Here's mechanism V2.0 assuming this needs a strong acid catalyst to proceed.

That mechanism reminds me of something...

[Edited on 6-12-2015 by deltaH]

blogfast25 - 6-12-2015 at 11:25

Quote: Originally posted by deltaH

Heteropolyacids would work well.

H3PW12O40 is the acid recommended in Crowfjord's paper.

deltaH - 6-12-2015 at 11:45

Quote: Originally posted by blogfast25

Quote: Originally posted by deltaH

Heteropolyacids would work well.

H3PW12O40 is the acid recommended in Crowfjord's paper.

Hmm... yes, it would help if I read through the thread before posting, sorry, my bad :mad:

blogfast25 - 6-12-2015 at 12:28

Interesting bit from that "Hydration and acetoxylation of monoterpenes catalyzed by heteropoly acid" paper here:

Quote:

The molar catalytic activities of PW in acetoxylation/hydration
of limonene, -pinene and -pinene are
approximately 80 times higher than those of H2SO4,
as found from the initial reaction rates. For limonene,
the initial rates with HPA and H2SO4 were found
to be 0.156 and 0.0020 mol l−1 h−1, respectively, at
40◦C, [catalyst] = 0.0060 mol l−1, [limonene] =
0.30 mol l−1 and HOAc/H2O = 90/10. For -pinene,
they were 0.270 and 0.0040 mol l−1 h−1 at 25◦C and
for -pinene 0.358 and 0.0050 mol l−1 h−1 at 15◦C
and otherwise the same conditions. This is in accordance
with the relative acid strengths of PW and
H2SO4 in acetic acid (pK1 4.8 and 7.0, respectively
[29]).

Didn't realise just how strong these poly acids were...

deltaH - 6-12-2015 at 12:38

Yes, I knew that

, I even prepared one a VERY long time ago, it was one of the molybdenum, vanadium, phosphate ones that's used for organic oxidations with O2. I forget what it was called, it had a catchy acronym for a name and I think it was an ammonium salt. Anyway, not relevant to this thread and I don't remember much more about it than that unfortunately. :mad:

EDIT: Ah found it, it was called NPMoV... not really that catchy of an acronym now that I see it again. I also found the paper I was working from and the application I was using it for, top of page 22, FYI. It was cool chemistry.

Attachment: NPMoV.pdf (325kB)
This file has been downloaded 598 times

[Edited on 6-12-2015 by deltaH]

AvBaeyer - 6-12-2015 at 19:26

There is a fair amount of information on the conversion of a-pinene to a-terpineol acetate if you do the search in Google scholar. Bottom line is that, as already pointed out above, a strong acid catalyst is required to carry out the reaction. A quick search gave the attached paper as an example.

AvB

Attachment: Conversion of a-pinene to terpinyl acetate over zeolitespdf.pdf (361kB)
This file has been downloaded 590 times

deltaH - 6-12-2015 at 20:57

Looks like sulfuric acid is used to prepare the terpenol in a two-step process, followed by esterification with acetic anhydride, so I'm guessing sulfuric acid + acetic in a one-step reaction doesn't work well/is messy. Guess you need either a heteropoly acid or zeolite catalyst then.

Heteropolyacids are very easy to prepare if you have the reagents. Also a useful catalyst to have in the 'toolbox'.

UC235 - 6-12-2015 at 22:16

Here are my relevant papers on production of alpha-terpineol. I also recall a prep using trichloroacetic acid in place of the trifluoroacetic.

Attachment: terpineol via F3CCOOH and limonene.pdf (33kB)
This file has been downloaded 448 times

Attachment: Hydration of turpentine to terpineol.pdf (60kB)
This file has been downloaded 480 times

deltaH - 6-12-2015 at 23:53

Nice! I wonder if the local dentist is willing to part with a little, they use it to etch teeth prior to applying filling epoxies AFAIK

blogfast25 - 7-12-2015 at 08:52

Thank you UC235 and AvBaeyer.

I'm still inclined to go with the GAA+poly phosphotungstic acid after reading your papers, although other opinions will be considered.

Poly phosphotungstic acid is expensive to buy but relatively easy to prepare, although I've yet to find a free (non-paywalled) preparation procedure for it. As deltaH mentioned, it's a real good thing to have in the larder too.

Years ago I attempted to prepare α-terpineol from natural turpentine, H2SO4 and acetone and all I got (at RT) was an ever darkening mass over a few days, going basically black over a week. Frustrating...

[Edited on 7-12-2015 by blogfast25]

Crowfjord - 7-12-2015 at 10:27

Quote: Originally posted by blogfast25

I'm still inclined to go with the GAA+poly phosphotungstic acid after reading your papers, although other opinions will be considered.

Poly phosphotungstic acid is expensive to buy but relatively easy to prepare, although I've yet to find a free (non-paywalled) preparation procedure for it. As deltaH mentioned, it's a real good thing to have in the larder too.

[Edited on 7-12-2015 by blogfast25]

Do you have the reference information for these preparations, blogfast? There are plenty of us here willing to help with access to such things.

aga - 7-12-2015 at 11:14

Searching for terpinyl acetate brought up Shitao Yu as one of the cited researchers on a paid-for site.

Searching "Shitao Yu terpinyl acetate" found a free version.

It wasn't a pdf file extension, so here is the renamed file :

Attachment: terpinylacetate.pdf (609kB)
This file has been downloaded 780 times

[Edited on 7-12-2015 by aga]

blogfast25 - 7-12-2015 at 11:34

Quote: Originally posted by Crowfjord

[

Do you have the reference information for these preparations, blogfast? There are plenty of us here willing to help with access to such things.

I've found some old preps in Brauer's book in the SM library, pages 1720 (sodium salt) and 1700 (Dreschel's method to obtain the free acid). But I'm looking for something more modern like:

http://onlinelibrary.wiley.com/doi/10.1002/jctb.5000690906/a...

blogfast25 - 7-12-2015 at 11:36

Quote: Originally posted by aga

Searching for terpinyl acetate brought up Shitao Yu as one of the cited researchers on a paid-for site.

Searching "Shitao Yu terpinyl acetate" found a free version.

It wasn't a pdf file extension, so here is the renamed file :

[Edited on 7-12-2015 by aga]

I'll have to it take to the 'Canton Dragon', around the corner...

I'll get some chow mein to go as well.

[Edited on 7-12-2015 by blogfast25]

Crowfjord - 7-12-2015 at 12:05

Quote: Originally posted by blogfast25

But I'm looking for something more modern like:

http://onlinelibrary.wiley.com/doi/10.1002/jctb.5000690906/a...

I don't have access to the full article, but luckily CA/Scifinder gives an abbreviated preparation:

Quote:

Na phosphotungstate (I) is prepd. by adding 200 cc. concd. HCl to a boiling soln. of 250 g. Na tungstate (II) and 37.5 g. Na2HPO4 in 300 cc. H2O. After chilling, the ppt. is filtered and dried. The air-dried crude product (180 g.) is recrystd. from H2O (80 cc.), yield 135 g. of a product having a variable amt. of water of crystn. The mother liquor from the recrystn. can be reused. All mother liquors in the process can be treated with BaCl2 crystals to obtain Ba phosphotungstate (III). III is prepd. by adding 250 g. BaCl2.2H2O in 800 cc. boiling H2O 330 g. Na tungstate in 1 l. boiling H2O. After cooling, the ppt. is filtered, washed with hot H2O and dried at 90°, yield 398 g. of Ba tungstate (IV), sparingly sol. in H2O. 3.5 cc. of 86° H3PO4 is added to 160 g. IV suspended in 250 cc. boiling H2O. Concd. HCl (100 cc.) is added and the mixt. boiled for 2 hrs. Completion of the reaction can be detd. microscopically since the cryst. form of the suspension changes. The yield of filtered, washed, and air-dried III is 120 g. To prep. III from I, a soln. of I (130 g.) in boiling water (300 cc.) is added to a soln. of BaCl2.2H2O (40 g.) in boiling water. Upon concn. to 350 cc. and cooling, III crystallizes out. The yield of washed and air-dried product is 127 g. To prep. phosphotungstic (V) acid from IV, 240 g. IV is suspended in 200 cc. boiling water and treated with 5 cc. 86% H3PO4, then with a mixt. of 33.5 cc. concd. H2SO4 and 100 cc. water with agitation and boiling. After 2 hrs. the BaSO4 is filtered off while hot. The filtrate is concd. to dryness under reduced pressure. The yield of V is 160 g. It can be purified with charcoal. The soly. in water at 20° is approx. 5 g. per cc. To prepare V from III, 200 g. of the Ba salt is suspended in a l. of boiling water and a mixt. of concd. 5.4 cc. H2SO4 and 50 cc. water is slowly added with agitation and boiling. The boiling is continued for 1 hr., charcoal is added, the BaSO4 is filtered off, and the filtrate evapd. to dryness at reduced pressure. The yield is 180 g.

A similar preparation from Zhurnal Obshchei Khimii (1955), Volume25 Pages 2388-91:

Quote:

To prep. H7P(W2O7)6], mix 1.3 g. BaWO4 (prepd. by pptg. Na2WO4 with BaCl2) with 2.031 l. of boiling H2O, add 28 ml. H3PO4 (87.9%) to the suspension, boil for 15 min., add 812.5 ml. of concd. HCl, and stir for ∼2 hrs. Dissolve the Ba3H8[P(W2O7)6]2 in boiling H2O (1 kg.:5 l.) add 27 ml. of concd. H2SO4, boil with stirring for 1 hr., and filter off the BaSO4. Evap. the filtrate to dryness in vacuo. The yield is 76%.
To prep. H7P(W2O7)6], mix 1.3 g. BaWO4 (prepd. by pptg. Na2WO4 with BaCl2) with 2.031 l. of boiling H2O, add 28 ml. H3PO4 (87.9%) to the suspension, boil for 15 min., add 812.5 ml. of concd. HCl, and stir for ∼2 hrs. Dissolve the Ba3H8[P(W2O7)6]2 in boiling H2O (1 kg.:5 l.) add 27 ml. of concd. H2SO4, boil with stirring for 1 hr., and filter off the BaSO4. Evap. the filtrate to dryness in vacuo. The yield is 76%

aga - 7-12-2015 at 12:19

Quote: Originally posted by blogfast25

I'll have to it take to the 'Canton Dragon', around the corner...

I'll get some chow mein to go as well.

Once you have menu item numbers 16, 23, 47 and of course 54 (two portions) safely back home, scroll down past the Chinese 1st page to get to the synthesis in English.

It is short, so you'll be wanting more to eat by the time you finish reading it.

Edit:

Astonishing that there are still a handful of people who still cannot read Canton Chinese ...

[Edited on 7-12-2015 by aga]

blogfast25 - 7-12-2015 at 13:13

@Crowfjord:

Thanks a bunch, that settles that bit, as far as I'm concerned. Saved.

Next, some questions on work-up from a poly acid catalysed conversion of α-pinene to α-terpineol acetate in GAA.

Crowfjord - 7-12-2015 at 15:01

If I were to try, I think I would crash out the phosphotungstic acid with hexane or something similar. After filtering or decanting, add water to separate the nonpolars. Wash the nonpolar with bicarbonate, water, then brine. Dry and remove solvent, then distillation should separate the desired ester and alcohol, as they have fairly higher boiling points than the starting compound and side products.

blogfast25 - 7-12-2015 at 16:07

Quote: Originally posted by Crowfjord

If I were to try, I think I would crash out the phosphotungstic acid with hexane or something similar. After filtering or decanting, add water to separate the nonpolars. Wash the nonpolar with bicarbonate, water, then brine. Dry and remove solvent, then distillation should separate the desired ester and alcohol, as they have fairly higher boiling points than the starting compound and side products.

Quote:

The homogeneous reactions were performed by
adding monoterpene (0.3 mol l−1) to a 0.003–0.012
mol l−1 H3PW12O40 solution in acetic acid or an
HOAc/H2O mixture pre-thermostatted at 15–60◦C.
At appropriate time intervals, aliquots were taken,
diluted with hexane (1/10 v/v) to precipitate the heteropoly
acid and then analyzed by GC.

The catalyst is suspended on silica (Aerosil 20), so it seems more logical to filter off the silica/acid first, at least to me.

What worries me a bit is that there's such a lot of GAA to get rid off: only 0.3 M of α-pinene to start with... Probably have to distil most of the GAA off, then wash several times with water to remove the last bits of GAA. Final rinse with NaHCO3 suspension maybe...

[Edited on 8-12-2015 by blogfast25]

Crowfjord - 8-12-2015 at 10:40

That's right. I was assuming use of the homogeneous version, without the silica support. You're probably right about the acetic acid, too. It may be simpler to just distill it off, considering the large amount.