Sciencemadness Discussion Board

Converting limonene to terpin hydrate

alchemizt - 16-12-2025 at 20:28

I hear that reacting limonene with water and dilute acid at cold temperatures will produce terpin hydrate. What would be the exact reaction conditions? Would mixing with 1% phosphoric acid for a few hours ar 5 to 10 degrees Celsius be a good reaction environment?

Fery - 16-12-2025 at 21:13

You can get it also from alfa pinene from turpentine - hydratation catalyzed by diluted H2SO4. Because they are not much miscible, p-toluene sulfonic acid is added to speed up the reaction.

https://patents.google.com/patent/US2481845A/en
Quote:
Terpin hydrate is commonly produced by reacting pinene with dilute acid, usually 25% sulfuric acid, at temperatures of about 30 to 40 C. 10 to 15% of toluene sulfonic acid is used to promote the rate of reaction. The reaction which, as commonly carried out requires substantial time, for example, 30 to 40 hours


here someone used cheap technical turpentine without purification to alfa pinene
https://www.youtube.com/watch?v=s9s241fjnBg

alchemizt - 17-12-2025 at 18:37

Yes, turpentine is one route. I'm interested in limonene though.

semiconductive - 22-12-2025 at 09:27

I don't have the expertise to advise you. But I do have a bottle of limonene separated from goo-bee gone cleaner. I would be willing to check a few conditions if you could explain how I could test if the product really is (in-deed), terpinol.

The reactions I've read about (several years ago) of limonene to terpinol were often done around room temperate, just as suggested by the video conditions from α-pinine.

I think you can even convert terpinol back into α-pinene by a distillation procedure.
https://www.scribd.com/document/559627569/Elimination-Experi...

The reaction, is therefore, partially reversible.

The wikipedia page on limonene suggests that it limonene is structural isomer of α-pinene; I don't have time to check if that's correct or not (and I'm not sure it is); but if it is, then the conditions to convert it to turpinol ought to be very close to the same as for α-pinene.

I tried (and failed) to convert turpentine to turpinol using only water and sulfuric acid a few years ago after letting it sit for a week; which leads me to suspect that miscibility problems could severely limit conversion and that original anecdotes about the reaction do not record the conditions accurately.

I see quite a few write ups from a quick search that use cream of tartar as an ingredient, which I didn't use.

Let me know what you find out from your own research.
You might check the Sciencemadness Library, on essential oils.

https://library.sciencemadness.org/library/books/the_chemist...
https://library.sciencemadness.org/library/books/the_chemist...


[Edited on 22-12-2025 by semiconductive]

alchemizt - 25-12-2025 at 06:35

I'm learning all this myself, but terpineol is very easy to tell apart from limonene by it's smell. It's a piny smell, as opposed to a lemony smell. I did an experiment yesterday:

20ml limonen
25ml water (coreactant)
1ml phosphoric acid (acid catalyst)
60ml glacial acetic acid (helps the two phases mix, supposedly increases yield greatly)
2.5g oxalic acid

And stirred at 70C for 7 hours

Im still working it up, but it's obviously converted a good percentage of the limonene to terpineol type molecules because the oil now smells like citrusy pine oil. Unmistakably different to limonene. Some side products like terpinolene have pine like smell so it's not necessarily alpha terpineol. I need to do a TLC to get an idea of how many products formed.

[Edited on 25-12-2025 by alchemizt]

semiconductive - 26-12-2025 at 02:12

That sounds fun!
I'd like to try and replicate your experiment in a few weeks.

I have ammonium phosphate, which gives up ammonia when heated.
I also have Glacial acetic acid and powdered oxalic acid on hand.

( My hands shake too much to do accurate measurements, but perhaps I can automate the TLC part of the process. )

I ordered an Epson™ DS 70 portable scanner that can roll through driver's licenses and paper, and reach 1200 DPI resolution along with a pack of 80 silica gel TLC slides.

If I can make the Epson work with a Raspberry PI™, and Linux SANE™ scanner software, I'll write a script to process these commercial 25mm by 75mm TLC slides and make highly accurate spot diffusion measurements.

What solvents are you using for TLC?

I'm not really fond of hexane's effect on nerves, although I see it is used a lot for TLC. I've got relatively safe solvents like acetone, MTBE (methyl-tert-butyl-ether), di-propyl ether and ethanol. I'll have to figure out what can be substituted to get about the same polarity as what you end up using.

For stains:
I have bromo-succianate and anise-aldehyde on my desk.

If those don't work out, I might even consider replacing the Blue light emitting diode in the scanner with an ultraviolet diode to capture fluorescence :) I'm better at electronics than I am at chemistry.



alchemizt - 30-12-2025 at 17:34

Very interesting what you say about Rasberry PI for TLC. I need to get into this. I'm a programmer, so really should get into applying it to chemistry.