Gary1234
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Extraction of terpenes from eucalyptus and conversion to p-cymene
Hi,
Having been inspired by an article on the synthesis of p-cymene (4-isopropyltoluene) via 1,8 cineole extracted from eucalyptus leaves, I want to give
it a try myself.
Firstly, I need to extract the volatile organics from the leaves. Some of these organics are rather delicate molecules and undergo thermal
decomposition or oxidation with ease.
I have decided that the best method for extracting these organics from the cellulosic matter and chlorophyl in the leaves would be to boil the crushed
leaves in water under reflux, followed by steam distillation.
I pose a question to the more experienced organic chemists amongst us: should I distil under reduced pressure to prevent thermal decomposition of the
delicate organic molecules, or use an inert atmosphere to avoid oxidation of the organics by atmospheric oxygen?
In the paper, the authors use Pd-doped alumina to catalytically transform 1,8-cineole into p-cymene (4-isopropyltoluene). Alumina is easy to obtain,
so their procedure should not be too much of a problem to replicate. Pd is difficult, but not impossible, to obtain.
I just need to work out to dope the alumina. One possible method is to use the sol-gel route. However, this would require the use of aluminium
alkoxides, which are not easily obtained (how I wish chemical acquisition was simply a matter of ordering from Sigma Alrich or Fischer!  ). How easy is it to sythnesise aluminium propoxide or ethoxide? These are very
water-sensitive compounds, which hydrolyse easily in moist air.
Considering that I do not live in Australia, you might be wondering how I am able to obtain eucalyptus leaves. Although I live in the UK, it is not
that difficult to come across hardy eucalyptus species, which are commonly grown for ornamental purposes.
If I could synthesise p-cymene with ease from a readily available feedstock (eucalyptus), then this would be a good source of a benzene backbone for
various aromatic syntheses. Benzene can be synthesised rather easily, but given its reputation of being a strong carcinogen  , I would'nt touch it with a barge pole!
http://pubs.acs.org/doi/abs/10.1021/ie201092h
http://pubs.rsc.org/en/content/articlelanding/2010/gc/b91646...
[Edited on 29-11-2011 by Gary1234]
[Edited on 29-11-2011 by Gary1234]
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Magpie
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Gary this looks like a fun experiment. Even if it didn't work just think of the wonderful smell you would have in your lab when distilling the
eucalyptus oil. During my stay in southern California I noticed that some roads were lined with eucalyptus trees. But it should be readily available
anywhere in flower shops.
I have some Pt supported on alumina wool from a catalytic propane heater. I wonder if that would suffice if stuffed in a quartz tube and placed in a
tube furnace.
http://www.catalyticheaters.us/catalyst.htm
I would be tempted to try this if I didn't have so many other experiments planned (or still hanging).
[Edited on 30-11-2011 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Chemistry Alchemist
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Could you just use Eucalyptus oil from the shops or would it be better to use it fresh from the leaves? Where i live (Australia) there are some bush
areas that are filled with Eucalyptus trees
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unionised
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I wouldn't worry too much about the degradation of the chemicals here.
Most of the degradation products will still have the same carbon skeleton and will give p Cymene under those conditions.
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starman
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Yes p-Cymene is often close to the end of the line for many terpenes in many plants. See for instance various monoterpenes involved in cannabinoid
biosynthesis.
Chemistry- The journey from the end of physics to the beginning of life.(starman)
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Panache
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Quote: Originally posted by Magpie  | Gary this looks like a fun experiment. Even if it didn't work just think of the wonderful smell you would have in your lab when distilling the
eucalyptus oil. During my stay in southern California I noticed that some roads were lined with eucalyptus trees. But it should be readily available
anywhere in flower shops.
I have some Pt supported on alumina wool from a catalytic propane heater. I wonder if that would suffice if stuffed in a quartz tube and placed in a
tube furnace.
http://www.catalyticheaters.us/catalyst.htm
I would be tempted to try this if I didn't have so many other experiments planned
(or still hanging).
[Edited on 30-11-2011 by Magpie] |
Omg magpie i didn't know of these heaters, flameless propane, approved for use with toluene, mek and acetone. Have you used one? I've gotta find an
australia supplier, i imagine they are pricey, when the catalyst nears it end life do the heaters start spewing out flammables?
And mr alchemist you are crowned the king of understatement.
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Magpie
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| Quote: Originally posted by Panache |
Omg magpie i didn't know of these heaters, flameless propane, approved for use with toluene, mek and acetone. Have you used one?
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These catalytic heaters have been around for decades. My dad had one for heating his boat while fishing on cold winter days.
I don't have much personal experience. I just picked one up at a garage sale for $1 and thought I would experiment with the media sometime.
Here's one that looks something like what I bought. I had fired it up once or twice last summer (with difficulty) and was outside showing my wife how
it worked when the damn thing began leaking propane and caught fire. I quickly turned off the gas then sprayed it down with a water hose. For a few
seconds I was envisioning a disasterous explosion/fire with my wife and I being terribly burned. Also I was thinking of the irony of not having a
fire in my lab for the last 9 years then going down in flames over a $1 piece of junk. Of course the fire department would then thoroughly
investigate and blame my chemistry lab. The newspaper would grab this angle and sensationalize it, etc, etc. You know the rest.
http://compare.ebay.com/like/120823175929?var=lrgimg&sor...
[Edited on 6-12-2011 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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benzylchloride1
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I love terpenes! Sounds like a good experiment, I would buy some eucalyptus oil, since the amount obtained from steam distillation will probably be
extremely small, but would still be worth doing. Once you obtain some of your final product which you expect to be p-cymene, I would do a structural
degradation to prove what you have buy refluxing your compound with a large excess of potassium permanganate to produce terephthalic acid which could
easily be identified by its high melting point. One could also synthesize p-cymene, here is a procedure from Weygand and Hilgetag's Preparative
Organic chemistry, this book is available in the library. Cumene: Benzene (50g) is heated with isopropyl alcohol (19 g) and 80% sulfuric acid
(400 ml) for 3-4 h at 65°. The usual working up then gives a 65% yield of cumene.
Toluene, xylenes, phenols, cresols, resorcinol, 0-nitrotoluene, chlorobenzene and naphthalene
have been condensed in the same way with isopropyl alcohol, sec-butyl alcohol, isobutyl
alcohol, and cyclohexanol.
p-Cymene can be obtained from toluene and isopropyl alcohol in the presence
of phosphoric acid, the yield then being 80%. 658
658 I. P. Tsukervanik and V. Tambovtseva, Zh. Obshch. Khim., 15, 699, 820 (1945);
Chem. Abstr., 40, 5707 (1946); 41, 732 (1947).
One should be able to cleave the cyclic ether linkage in 1,8-cineole with azeotropic hydrobromic acid and probably dehydrate to p-cymene, this is pure
postulation though off the top of my head.
Attachment: 1,8-Cineole cleavage.rtfd.zip (27kB)
This file has been downloaded 353 times
[Edited on 9-12-2011 by benzylchloride1]
[Edited on 9-12-2011 by benzylchloride1]
Amateur NMR spectroscopist
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