DETECTION OF TURPENTINE OIL

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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