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                     Isomerization of Eugenol to Isoeugenol
                                 by Psychokitty
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500 g of clove oil (undistilled; about 98% eugenol) was put in a 1000 mL
erlenmeyer flask along with a 3" stir bar. Added 150 g of KOH (calculations
required 200 grams but only had 150 grams available) and 25 grams of PTC
(hexa-decyl-tributylphosphonium bromide).

Started to heat the reaction using a hotplate/magnetic stirrer. Used a standard
thermometor to measure the increase in temperature. Did not make use of a reflux
condenser nor did I apply reduced pressure to effect this reaction.

Tried to stir mess while the temp was rising. Even with a stong magnetic
stirrer, this was virtually impossible (the solution was full of KOH which after
a while made the surrounding solution look opaque brownish-black).

Temp finally rose to about 100 deg C or so and then WHOOOOSH!!!! An exothermic
reaction suddenly kicked in making the temp rise quickly to 125 degrees C. And
before I knew what was going on, the KOH was being absorbed with the occurance
of a simultaneous deposition of potassium eugenolate (brown color).

As the temp rose to about 135 deg C, the potassium eugenolate began to melt and
by 140-145 or so degress C, it was completely melted making the potassium
eugenolate mixture homogenous (black opaque solution). The smell of eugenol was
very powerful (but not terribly unpleasant) so to keep it from evaporating
easily, a damp paper towel was crumpled up and fitted loosely into the mouth of
the flask. This application worked very well.

About 30 seconds later, the stirrer began working and when the temp reached
about 150 deg C, the solution started to boil. YES, IT STARTED TO BOIL. Stirring
and heat were maintained for fifteen minutes at which point a somewhat
unpleasant (but tolerable) smell filled the air, which promted me to remove the
flask from the stirrer/hotplate to cool (used a fan).

As the temp reduced to about 135 deg C, the solution began to crystallize and by
125 deg C or so, solid potassium eugenolate was everywhere in the flask
(brownish tinge). It was so solid that I had trouble removing the thermometer.

The solution was heated up to 150 deg C again slowly just to see where the
potassium eugenolate first began to melt and then boil. There was no exothermic
reaction at 100 deg C this time for obvious reasons. Thus, I'm convinced that
the above figures indicating the m.p. and b.p. of the potassium eugenolate are
pretty accurate.

Water was added to the flask to try and dissolve the potassium eugenolate. This
was the first step taken towards recovering the suspected isoeugenol. And it
worked only moderately. Dilute HCl and then concentrated HCl were added; this
too worked only moderately. Next,10% H2SO4 was added, working ideally as it
neutralized all of the base and potassium eugenolate quicly and easily. The
whole mixture was then transferred to a large one-gallon empty and clean mayo
jar and diluted with distilled water. The suspected isoeugenol floated to the
top (it was opaque and dark brownish-black). It was extracted with
trichloroethane (OTC) and worked up using standard techniques. Vacuum
distillation of the oil provided isoeugenol as the sole product which through
distillation comparisons, has a b.p about eight to ten degrees higher than
eugenol.

Catalyst was salvaged as a dirty oil which presumably can be used again. Meager
attempts to recrystallize it using petroleum ether failed. This reaction is best
repeated with the infinitely cheaper and more readily available PTC catalyst
Aliquat 336 (or whatever it's called). Also, it is my belief that magnetic
stirring is not a requirement as the boiling phase provides, in my opinion, the
amount of agitation required to complete the isomerization. A simple reflux
set-up with slow heating up to the boiling poing of the solution (with no temp
measurement) for fifteen or so minutes should work ideally. Increasing the
reaction time could allow for a reduction in both KOH and PTC catalyst.

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Okay, here goes. I search CA all the way from the beginning to about 1962 or
something. Basically, I stopped looking when the index indicated that eugenol
would from then on be listed as 1-allyl-3-methoxy-4-hyroxybenzene. I didn't look
under "isoeugenol" so there might have been a few isomerization abstracts that I
might have missed. The ones I'm about to list were located by searching under
"eugenol" in the index.

In no particular order:

CA 2485 (1941)

Conversion of eugenol and its ethers into the corresponding propenyl compounds.
T.F. West. J. Soc. Chem. Ind. 59, 275-6(1940).

Eugenol (1000g) (I) is mixed in an iron still with 1 L of aqueous solution
containing 450g of KOH. H2O is removed at 80-100 deg C @ 20-50 mm of pressure,
300g of diethylene glycol (II) and 100g of triethanolamine (III) are added and
the mixture is heated until a thermometer indicates the reaction has occurred
(absorption of heat). About 3 minutes at 160 deg C is required. The melt is run
into H2O, neutralized with dilute H2SO4 and extracted with benzene. The
isoeugenol (largely the trans isomer) is distilled at 1-3 mm yielding 900g of
isoeugenol.

The original article is printed in english. For more information, I suggest that
somebee go to the library, retrieve the article, and then later on, post the
highlights.

CA 1995 (1924)

Conversion of eugenol to isoeugenol. S.K. Gokhale, J.J. Sudborough
and H.E. Watson. J. of Indian. Inst. Sci. 6, 241-55 (1924).

Kind of a crappy method. Complete conversion of eugenol into isoeugenol can be
brought about by fusing with eleven equivalents of KOH for 5 minutes at 220 deg
C or with 8 equivalents for 40 minutes at 220 deg C. Fusion with NaOH at 200-10
deg C produces little or no conversion. The addition of parrafin as a diluent
does not effect conversion. In effect, you need either 1100 or 800 grams of KOH
to convert 100 grams of eugenol into isoeugenol. Too much base but fast though.

The next one is really weird.

CA 2671 (1926)

Catalytic reactions. II. Induced reaction. 1. Isomerization of eugenol.
Ricki Horiuchi. J. Chem. Soc. Japan 45, 209-29 (1925); c.f CA 19, 1081.

I quote:

Most examples given for induced reactions in the literature are those of induced
reaction. According to Nagai's method (C.A. 14, 2839), isomerization of safrole
can be easily accomplished by boiling 70% safrole with 20% KOH at 180-200 deg C
for 5-6 hours. If eugenol is treated by the same method, practically no
isoeugenol is found. If, however, safrole and eugenol were treated together by
N's method, both safrole and eugenol were completely isomerized. When safrole
was boiled with 15% KOH at 160-170 deg C for 3 hours even safrole is not
isomerized at all, yet by addition of and equal amount of eugenol to the
safrole, not only isoeugenol is produced, but also the safrole is now completely
isomerized. When eugenol alone is used with alkali the mixture becomes very
viscous and is difficult to stir but the presence of safrole makes the mixture
more fluid. In order to see if the change in viscosity alone might account for
the isomerization of eugenol in the presence of safrole, H. dissolved eugenol in
benzyl ether (bp 297-8), PhCH2CH2OH (bp 218-20) and isosafrole (bp 253-3) and
tested for isomerization. The results show that with PHCH2CH2OH, 65% isoeugenol
was obtained, but none of the other two, showing that viscosity alone is not
responsible. The reasons why this isomerization is due to mutual induced
reactions are given in detail.

CA 1597 (1928)

Vanillin. R.H Bots and Soc. Anon. Produits Chimiques Coverlin. Brit. 271,819,
May 25, 1926. The allyl side chain of compounds belonging to the allyl-phenol
group is transformed into the propenyl chain, e.g. eugenol is converted into
isoeugenol by heating with KOH in the presence of an amino compound such as
PhNH2, o-toluidine or o-anisidine. The proceedure may be applied to oil of
cloves as an intermediate step in production of vanillin. Cf. CA 21, 3908


CA 2127e Vol. 53

Synthesis of some isomeric methoxyallyldiethylaminoethoxybenzenes. M. Pal'gi
(State Univ., Tartu, Estonian, S.S.R.) Zur. Obshchei Khim. 28, 2239-42 (1958).

Edited version:

Heating eugenol with 1:1 aqueous KOH for 3.5 hours at 170 deg C under nitrogen
gave 85% isoeugenol, bp @ 8 torr 128-130 deg C.

Here are two more references that use Pd metal and Raney Nickel to effect the
isomerization that didn't make my top ten list (too expensive and elaborate):

CA 1002 sec 6 (1937) & CA 927i vol. 46.

So it would seem that to isomerize eugenol to isoeugenol, it's going to take a
little more than simple refluxing in alcoholic KOH like the way one does to go
from safrole to isosafrole.

Hope this helps somebee out besides me. Hell, why not just purchase pure
isoeugenol? After all, it's still perfectly legal.

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