4. THE DETECTION OF TERPINYL ACETATE
It has been pointed out in the
"Determination of Esters" that certain esters are not completely saponified
under the standard analytical conditions if the time of reflux is limited to 1 hr.
Terpinyl acetate is such an ester.
Additions of esters of this type to readily
saponifiable esters (such as linalyl acetate) will be revealed by a difference
in the ester numbers obtained by saponification for periods of 1 and 2 hr., respectively.
Under standard conditions linalyl acetate is completely saponified in a period of
30 min.; terpinyl acetate requires about 2 hr. Hence, an appreciable difference
between the ester numbers determined after heating for 30 min. and for 1 hr. (or
2 hr.) indicates the presence of certain foreign esters, such as terpinyl
acetate, in oils containing only readily saponifiable esters (e.g., bergamot oil
and lavender oil). If only small amounts of terpinyl acetate have been added, the
difference will be too small to draw any definite conclusions. However, by modifying
the experimental conditions, such small differences may be greatly magnified. The
method outlined below is the classical method developed by the chemists of Schimmcl
and Company190 for the detection of terpinyl acetate as an adulterant
in bergamot oils; it is also applicable to lavender oils and to synthetic linalyl
acetate. With further modification, it can be used for the detection of
terpinyl acetate and terpineol in numerous oils; such applications, however, should
be made with discretion.
Procedure: Pipette 2 cc. of the oil into each of three
tared saponification flasks and weigh accurately. To flask I add 10 cc. of 0.5 N
alcoholic sodium hydroxide solution and 25 cc. of alcohol. To flask II add 20 cc.
of the alkali solution, but no alcohol. To flask III add 10 cc. of the alkali solution
and 5 cc. of alcohol. (The alkali solution should be measured accurately from a
burette or pipette.) The contents of flask I and flask III are refluxed on a steam
bath for a period of 1 hr.; the contents of flask II, for 2 hr. Calculate the ester
numbers for the three determinations.
In the case of pure bergamot oils, the difference
between ester number I and ester number II will not be greater than 5; the
usual value lies below 3. In the case of an oil adulterated with 4 per cent terpinyl
acetate, the difference amounts to about 10.0; with 10 per cent terpinyl
acetate, about 19. 0.m Furthermore, in the case of pure oils, ester number III will
be approximately the arithmetical mean of ester number I and ester number II.
For oils containing larger amounts of ester, the
size of the sample must be reduced; 1 cc. will often prove sufficient. In the case
of synthetic linalyl acetate, a 1 cc. sample should be used and the quantities of
alkali should be doubled.
Fractional saponification may also be used to
detect the presence of terpineol by carrying out the determination on an acetylized
oil; great discretion must be used, however, since terpineol and certain difficultly
saponifiable esters may be present as natural constituents, or the process of
acetylation may result in the formation of such esters. Recourse to fractionation
of the oil or of the acetylized oil with subsequent fractional saponification
of the proper fraction may frequently prove of value. Table 4.19 gives the boiling
points of terpineol and terpinyl acetate at various pressures:
-----------------------------------
190 Schimmel & Co., October
(1911), 115.
191 Schimmel & Co., October
(1911), 115.
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