334 THE CHEMISTEY OF ESSENTIAL OILS
This final quantity gives the amount of benzoyl eugenol, from which
the amount of eugenol is easily calculated, eugenol having the formula
164a;
C 10 H 12 O 2 , and benzoyl eugenol C 17 H 16 O 3 , so that ^QO~ X 100 = *ne per-
centage of eugenol, if x equals the weight of benzoyl eugenol obtained,
and y the weight of oil used in the estimation. Under these circum-
stances the eugenol-content should not fall below 75 per cent., or if
estimated by absorption with potash not below 82 per cent., usually
from 85 to 90 per cent.
Thorn has recognised the inaccuracy of the foregoing, and now
recommends the following process. It consists in heating 5 grms. of
the oil in a water-bath with 20 c.c. of a 15 per cent, soda solution for
thirty minutes. After allowing the hydrocarbons to separate, the
eugenol soda solution is run off, and the hydrocarbons washed with
dilute soda solution twice, the washings being added to the original
soda solution. The reaction is now effected at water-bath temperature
with 6 grms. of benzoyl chloride. The whole is allowed to cool, and
the crystalline mass transferred to a beaker with 55 c.c. of water. It
is heated in order to melt the crystals, and well agitated with the
water to wash the benzoyl eugenol. This washing is repeated twice.
The crystalline mass is then transferred to a beaker with 25 c.c. of 90
per cent, alcohol, and warmed till complete solution takes place. The
solution is allowed to stand till the bulk of the crystals have separated
out, and is cooled to 17° and filtered through a paper 9 cm. in diameter,
previously dried and tared. The filtrate measures about 20 c.c. and
the crystals are washed with more alcohol until it measures 25 c.c.
The paper and crystals are then dried in a weighing-glass and weighed,
the temperature of drying being not more than 101° C. The solubility
allowance for 25 c.c. of alcohol is 0 * 55 grm. The total eugenol is cal-
culated from the formula^vhere P is the percentage, a the weight of benzoyl eugenol obtained*
and b is the weight of clove oil used.
Verley and Bolsing propose the following method. It depends on the
fact that acetic and other anhydrides react with phenols in excess of
pyridine. Eugenol reacts readily, forming eugenyl acetate and acetic
acid, the latter combining with pyridine to form pyridine acetate.
This compound reacts towards indicators such as phenolphthalein in
the same way as acetic acid and therefore a titration is possible. Ver-
ley and Bolsing use from 1 to 2 grms. of the oil, which is placed in a 200
c.c. flask, and 25 c.c. of a mixture of acetic anhydride (15 parts) and
pyridine (100 parts). The mixture is heated for thirty minutes on a
water-bath, the liquid cooled, and 25 c.c. of water added. The mixture
is well shaken and titrated with normal potash, using phenolphthalein
as indicator. A blank experiment is carried out without the eugenol,
and the difference between the titration figures in c.c. of normal alkali,
multiplied by 0
- 582, gives the amount of eugenol in the sample taken.
As the boiling-points of eugenol and caryophyllene are both high,
no appreciable portion of the oil should distil below 245°, or even a few
degrees higher. These tests will ensure the presence of a due propor-
tion of eugenol, a point very necessary to take into account, because of