III. EXTRACTION WITH VOLATILE SOLVENTS
This method was first applied to flowers in 1835
by Robiquet.31 Somewhat later Buchner,32 and Favrot33
experimenting independently, processed flowers with diethyl ether. Around 1856,
Millon34 in Algeria extracted flowers with various solvents; Hirzel35
in 1874 suggested petroleum ether as the most suitable solvent and obtained patents
for his apparatus in several countries of Europe. Gradually the new method attracted
the attention of the manufacturers in Southern France (Grasse and Cannes) and large-scale
experiments were conducted independently by several industrial workers such as Piver,
Vincent, Roure, Naudin, Massignon, Chiris, Charabot, and Garnier.36 The
latter obtained a patent for a novel type of rotatory extractor and extended his
activities from Southern France to Bulgaria, Syria, Egypt and Reunion Island. Finally
all the flower oil manufacturers in Grasse were forced to adopt the volatile solvent
process, and constructed special extraction plants in addition to their
existing enfleurage buildings.
The principle of extraction with volatile solvents
is simple: fresh flowers are charged into specially constructed extractors and extracted
systematically at room temperature, with a carefully purified solvent, usually petroleum
ether. The solvent penetrates the flowers and dissolves the natural flower perfume
together with some waxes and albuminous and coloring matter. The solution is subsequently
pumped into an evaporator and concentrated at a low temperature. After the
solvent is completely driven off in vacua, the concentrated flower oil is obtained.
Thus the temperature applied during the entire process is kept at a minimum; live
steam, as in the case of distillation, does not exert its action upon the delicate
constituents of the flower oils. Compared with distilled oils the extracted flower
oils, therefore, more truly represent the natural perfume as originally present
in the flowers.
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31 J. Pharm.
21 (1835), 335. Buchner's Repert. f. d. Pharm. 54 (1835), 249. Pharm. ZentraM. (1835),
553.
82 Buchner's
Repert. f. d. Pharm. 56 (1836), 382.
83 J. Chem.
med. (1838), 221. Pharm. Zentralbl. (1838), 442.
84 J. Pharm.
chim. [3] 30 (1856), 407. Compt. rend. 43 (1856), 197.
35 "Toiletten-Chemie,"
3d Ed., Leipzig (1874), 77.
86 For details see Perfumery
Essential Oil Record 12 (1921), 197-222.
Despite this obvious advantage the volatile solvent
process cannot entirely replace steam distillation, which remains the principal
method of isolating essential oils. Steam distillation, in most cases, is a simpler
process: by employing portable direct fire stills, distillation can be carried out
even in remote and primitive parts of the world, whereas solvent extraction necessitates
complicated and expensive apparatus, and a crew of welltrained workers. Running
expenses arc comparatively high; a mistake in operation can be costly; the unavoidable
loss of solvent, of which large quantities are employed during the process, is an
important factor in the price calculation of natural flower oils. Extraction with
solvents can, therefore, be applied advantageously only to the higher priced materials,
particularly the flowers. A loss of 10 liters of solvent per 100 kg. of flower charge
remains rather insignificant in the calculation of absolute of jasmine which is
normally valued at several hundred dollars per pound;37 but with low-priced
oils such as rosemary or eucalyptus, ranging normally below $1.00 per pound, the
loss of a few liters of solvent would make extraction prohibitive.
All extracted flower oils are of more or less
dark color because they contain much of the natural plant pigments which are not
volatile. Steam distilled oils, on the other hand, are in most cases of light
color. Furthermore, they usually are soluble even in dilute alcohol, while
extracted oils require 95 per cent alcohol for complete solution.
Despite these drawbacks, the products of extraction
possess one supreme advantage, i.e., their true-to-nature odor. In addition,
certain types of flowers e.g., jasmine, tuberose, jonquil, hyacinth, acacia, mimosa
and violet do not yield their volatile oil on steam distillation, and must, therefore,
be extracted with solvents.
c. The Evaluation of Natural Flower Oils and Resinoids
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37
Up to $2,000.00 per Ib. in 1946.
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