Physical properties:
Empirical
formula: C10H10O2
Molecular weight:
162,18
Optic rotation:
nD20 1,5383
Density:
1,096 g/ml at 20ºC
Flash point:
97ºC
Melting point:
11,2ºC
Boiling points:
Chemical class: aromatic bicyclic phenol ether
Solubility: insoluble in water, very soluble in ethanol,
chloroform, diethyl ether; solidifies into monoclinic prisms.
Habit: colourness or a reddish yellow liquid at room temperature
Isolation Methods
Camphor oil is produced by the steam distillation of wood, rootstamps and branches of the type of Cinnamonum Camphora which grows in Japan; the oil is fractionally distilled under vacuum and yields 50% of crude camphor and 50% of a camphor oil that contains light terpenes, cineole, safrole, terpineol, sesquiterpenes and sesquiterpene alcohols. These are separated into various fractions; one of them is Brown Camphor oil (20-22% of the decamphorised oil) whose main constituent is safrole. This fraction is most interesting from the perfumer's point of view since safrole isolated from the oil is used as a starting material for heliotropin, vanillin and other perfume materials.
The oil derived from steam distillation of foliage of Juniper Virgiana gave 11% of safrole and 6,7% of cis-safrole, when eluted from a DB-5 gas chromatography column.
The root bark of sassafras albidum can be extracted at room temperature with hexane and chloroform as solvent. The isolated essential oils yield, when analyzed with GC and GC/MS, as major compounds, safrole (85%), camphor (3,25%) and methyleugenol (1,10%). There are numerous members of sassafras family; a guide to the safrole content oil is it's congealing point (accuracy is " 2%):
% Safrole Congealing
point (ºC)
To purify safrole
from nutmeg, is tricky process, but not impossible. The shot must be Soxhlet
extract from a few kilos of nutmegs to obtain the oil; this may need to be filtered
at room temperatures to remove the nutmeg fats (myristic acid and glycerides).
Then the oil is fractionally distilled at reduced pressure to obtain the correct
fraction (it's boiling temperature can be calculated fro the Clapeyron equation).
Double distilling is almost certain necessary to remove the last of the impurities.
Refinement methods from the
oil:
These are several ways of extracting safrole from the oil:
1)
cooling the oil or the safrole containing
fraction of the oil, to at least -12ºC; safrole will crystallize.
2)
using fractional distillation, followed by cooling and crystallization.
3) when safrole is contaminated
by oily constituents in an essential oil as in red camphor oil, the method of
Ikeda and Takeda may be employed. The purification of safrole from essential
oils can be done using another mercury salt, mercuric acetate. This procedure
seems to be an attractive way to get high purity safrole without careful and/or
repeated distillation, and the mercuric acetate can be used over and over again.
Synthesis of safrole
Safrole can be produced
by simple methylenation of 4-allylcatechol with methylene chloride, under inert
atmosphere of nitrogen. The 4-allyl product can be obtained in the reaction
of catechol with allylbromide to form a monoallyl ether that undergoes Claisen
rearrangement distilled to isolate the 4-allylpyrocatechol. The misture can
be fractionally distilled to isolate the 4-allyl product and then methylated
to safrole.
(esquema)
A better method by far for producing 4-allylcatechol is to remove a methyl group from eugenol. Eugenol is found in essential oils in a higth percentage.
A Grinard reaction
of RMgBr ( R = 3,4-methylenedioxybenzene) with allylbromide (CH2=CHCH2Br) yields
87% of isosafrole. The reagents in Grinard reactions must be absolutely dry
and THF can be used as a solvent (which is dried by distillation with sodium
metal under an atmosphere of dry nitrogen).
Syntheses of safrole by the Friedel-Crafts reaction of R and 3-cloro-allylcloride
(CH2ClCH=CHCl2) is also possible; the chloride compound formed must be reduced
with sodium to safrole.
There are many other synthesis of safrole from other compounds described.
The isomerization of safrole
The reaction, which
is general for the conversion of nearly all allylbenzenes (like safrole, apiole,
diapiole and elemicin) to their corresponding propenylbenzene isomer, is usually
carried out by heating the allylbenzene together with an inorganic catalyst
misture under reflux, with or without the use of a solvent. After the reaction
is finished, the catalyst is removed by filtration, any solvent removed under
vacuum, and the residue is distilled to purify the propenylbenzene from unreact
allylbenzene and polymerized material.
The isomerization always gives a misture of both cis- and trans-isomers of the propenylbenzene; the ultimate is thermodynamically more stable, so with longer reaction times, the ratio of the trans-isomer is increased in respect to the cis.
More about safrole in lab
http://www.rhodium.ws/chemistry/mercury.html
http://www.rhodium.ws/chemistry/tcboe/chapter5.html
http://rhodium.ws/chemistry/isomerizafrole.html
http://www.rhodium.ws/chemistry/safrole.html
http://www.rhodium.ws/chemistry/safrolefaq.txt
http://www.herbmed.org/Herbs/Herb66.htm#Category30Herb66
http://www.rhodium.ws/chemistry/extration.faq