5. DETECTION OF TURPENTINE OIL
The addition of turpentine oil as an adulterant
generally reduces the specific gravity and affects the solubility and optical rotation
of most essential oils. Its presence may be proved in oils which contain no pinene
as a natural constituent by the separation and identification of a-pinene, the main
constituent of turpentine oils.
Highly purified d-α-pinene has the following properties:
Boiling Point = 155-156
Specific Gravity at 15o = 0.864
Refractive Index at 20o = 1.4656
Specific Rotation = + 48o24'
Solubility at 20 4 vol. of 90% alcohol and more.
The boiling point of α-pinene lies below that
of most of the terpenes and oxygenated constituents found in essential oils. Consequently,
in testing for the presence of pinene it is customary to fractionate the oil, collecting
the first 10 per cent, or better the distillate coming over below 160 at atmospheric
pressure.
Procedure:192 Distill a 50 cc. sample of the
oil from a three bulb, 125 cc. Ladenburg flask, collecting only the first 5 cc.
Mix this distillate with 5 cc. of glacial acetic acid and cool to 0o
in a freezing bath. Add 10 cc. of amyl nitrite and then add dropwise, with
constant stirring, 2 cc. of dilute hydrochloric acid (2:1). Permit the mixture to
stand in the freezing bath for 15 min. arid collect the crystals which form on a
Biichner funnel. Wash thoroughly with alcohol. Permit the crystals to dry at room
temperature and dissolve in a small amount of chloroform. Add methyl alcohol to
the chloroform solution dropwise until the nitrosochlorides precipitate out. Separate
the crystals by filtration and dry at room temperature. Mount in a fixed oil (olive
oil) and examine microscopically. Pinene nitrosochloridc193 crystals
have irregular pyramidal ends (melting point, 103o).
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192 The procedure as given is
essentially the official method of the Association of Official Agricultural Chemists,
6th Ed., 374, for the detection of pinene in orange and lemon oils.
193 Limonene nitrosochloride*,
which may also be present, crystallizes in needles.
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