Improvements in the Manufacture or Preparation of Isoeugenol and Derivatives thereof.
Year: 1897

page_text: Date of Application, 16th June, 1897-Accepted, 24th July, 1897
COMPLETE SPECIFICATION.
Improvements in the Manufacture or Preparation of Isoeugenol and
Derivatives thereof.
I, BENJAMIN WILLCOX, of 47 Lincolns Inn Fields, in the County of London,
Patent Agent, do hereby declare the nature of this invention (which has been
communicated to me from abroad by C. F. Boehringer & Soehne, of Waldhof near
Mannheim, in the Empire of Germany) and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
According to the methods of preparing isoeugenol known at the present time, it
is not easy to convert eugenol into isoeugenol, since the concentrated alkali and high
temperatures required to bring about the molecular rearrangement of eugenol
(compare German Patents 57808, Class 53, and 76982, Class 12) induce partial
resinification, polymerisation, and oxidation of the eugenol and isoeugenol.
There is obtained by this method isoeugenol which cannot be applied directly to
the preparation of vanillin, it being necessary to protect the free phenolic groups
present in the substance by the introduction of acid or alcohol radicles.
The isoeugenol derivatives hitherto obtained in this manner are all insoluble in
water, and consequently do not readily undergo oxidation to derivatives of vanillin.
My foreign correspondents have found that the production of isoeugenol from
eugenol may be carried out quantitatively by means of phosphoric acid derivatives
of eugenol, the product consisting of an isoeugenol derivative which is particularly
applicable to the preparation of vanillin.
The neutral eugenol and isoeugenol phosphoric ethers, described by the communica-
tion in the Berichte der Deutschen Chemische Gesellschaft, 272,456, are insolublein
water, and do not lend themselves to the foregoing process; it is necessary to employ
as the initial material the acid phosphoric ether of eugenol.
The chloride of the hitherto unknown eugenol phosphoric acid is readily obtained
by the action of phosphorus oxychloride on eugenol in accordance with the
equation

page_text: rearranged into the propenylic group,-CH=CH-CH,, with direct production of
isoeugenol phosphoric acid.
Ow
CH CH
_CH=CH-CH₂
-OCH,
OCH₁.
If, however, eugenol phosphoric acid be heated with alcoholic alkali, not only does
molecular rearrangement into isoeugenol phosphoric acid take place, but saponifica-
tion of the intermediate product isoeugenol phosphoric acid occurs simultaneously,
giving rise to phosphoric acid and isoeugenol; the exclusive end-product therefore is
isoeugenol:
ZOLD
AL
CALL
C3H,
>C% Hg. O. PO-
CHO
UFL
OK
=
315
CH.O
CH. OH + KPO,
1 part of eugenol is mixed with 2 parts of phosphorus oxychloride, and boiled in
a reflux apparatus for from 6 to 7 hours. The clear, pale brown liquid is evaporated
in a vacuum to remove phosphorus oxychloride, and the bright reddish brown,
viscous residue taken up with from 3 to 4 volumes of ether, and agitated with con-
centrated, aqueous potassium carbonate solution so long as liberation of carbon
dioxide is perceptible.
By saturating the alkaline solution with dilute sulphuric acid, eugenol phosphoric
acid is set free and isolated by extraction with ether. After distilling off the ether,
eugenol phosphoric acid remains as a clear, brownish-yellow syrup, which on standing
in the air, solidifies to a hard, striated crystalline cake.
Eugenol phosphoric acid is obtained quite pure by crystallisation from benzene or
dry ether.
The acid obtained in this way consists of concentric aggregates of small slender
needles, which still contain water, and melt at 46°-50% Centigrade; after long
exposure to a vacuum over concentrated sulphuric acid, the acid passes into the
anhydrous compound melting at 105° Centigrade which crystallises without water
from dry benzene in blunt, short prisms, and deliquesces and takes up water from
the air.
The acid is readily soluble in water, alcohol, ether, and acetone.
Eugenol phosphoric acid is a powerful dibasic acid, decomposing carbonates with
readiness, and forming alkali salts which dissolve readily in water.
The acid alkali
salts are sparingly soluble in alcohol and can, together with the acid salts of aromatic
bases, be employed for recognising the acid.
The acid aniline salt, for example, crystallises from solution in not too dilute
alcohol, in concentric groups of small needles, and melts at 147° Centigrade.

page_text: In order to prepare isoeugenol phosphoric acid it is not necessary to make use of
pure, well-crystallised eugenol phosphoric acid; it being sufficient to heat the syrupy
acid with from 7 to 8 parts of a 10 per cent. solution of caustic potash with gentle
ebullition for 30 hours, to bring about complete molecular rearrangement into
isoeugenol phosphoric acid.
The latter is set free from the cold, alkaline solution by treatment with dilute
sulphuric acid, and is then taken up with ether.
The syrupy residue from evaporation of the ether soon becomes crystalline, and
the acid is purified by crystallisation from ether.
Isoeugenol phosphoric acid crystallises with one molecular proportion of water like
eugenol phosphoric acid, and melts at 105°-106° Centigrade, the anhydrous
substance melts at 133° Centigrade.
When it contains water, the acid is stable in air, and crystallises from a con-
centrated, aqueous solution in concentric, or lustrous, scaly aggregates of small
needles.
The acid dissolves readily in water, alcohol, ether, acetone, and hot benzene; it is
a powerful, dibasic acid, decomposing carbonates with readiness, and forming easily
soluble alkali salts.
The acid alkali salts dissolve with difficulty in alcohol; the acid aniline salt melts
at 1880-189° Centigrade, and crystallises from alcohol in slender, flat, nacreous
prisms. This substance may be employed in clearly distinguishing between
isoeugenol phosphoric acid and eugenol phosphoric acid.
If eugenol phosphoric acid be used as the initial material in the preparation of
isoeugenol, one part thereof is boiled in a reflux apparatus for from 15 to 20 hours
with 24 parts of powdered caustic potash and 5 parts of alcohol and is then diluted
with water. The alcohol is distilled off, and isoeugenol separated from the alkaline
solution by dilute sulphuric acid.
Isoeugenol obtained in this way is pure after one distillation, and boils at 258°—
262° Centigrade; it yields the characteristic acetyl and benzoyl derivatives.
To prepare isoeugenol from isoeugenol phosphoric acid, the well dried acid sodium
or acid potassium salt of isoeugenol phosphoric acid is heated at 160°-170° Centi-
grade for from 1 to 2 hours; under this treatment the mass liquefies owing to the
production of isoeugenol, and the metaphosphoric salt separates from the liquid as a
jelly.
The greater part of the isoeugenol can be separated from the inorganic salt by
decantation, whilst the remainder may be obtained by dissolving the metaphosphoric
salt with water, and extracting the liquid with ether.
Isoeugenol obtained in this way is completely pure, and exhibits the proper
boiling point.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
a
1. Converting eugenol into isoeugenol in such a way that the free hydroxyl group
of the eugenol is protected by the introduction of the phosphoric acid radicle. .
2. A modification of the process claimed by the preceding claiming clause

page_text: consisting in transforming eugenol by the action of phosphorus oxychloride into
eugenol phosphoric acid, and then heating the latter with alcoholic alkali.
3. A modification of the process claimed by the first claiming clause consisting
in heating eugenol phosphoric acid with aqueous alkali, whereby it is converted into
isoeugenol phosphoric acid, and transforming the latter into isoeugenol by the action 5
of heat on the acid alkali salts.
D
1007