TEST FOR FURFURAL (The Essential Oils)

7. TEST FOR FURFURAL

To detect the presence of furfural in an oil, the following procedure proves satisfactory. It is based on the water solubility of furfural and on the wellknown color reaction of furfural with aniline in the presence of glacial acetic acid.

Procedure: Shake thoroughly 100 cc. of the oil with 25 cc. of distilled water in a separatory funnel. Permit the mixture to stand until a good separation is obtained. Filter the aqueous layer through wetted paper to give a clear solution. Add 1 cc. of the filtered aqueous layer to 5 cc. of a 2% solution of freshly distilled aniline in glacial acetic acid. The presence of small amounts of furfural will result in an inytdfise deep red color within 5 min. If a negative test results, extract thfc filtered aqueous layer with 25 cc. of ether. Cautiously evaporate the ether on a steam bath. Add 1 cc. of distilled water and then 5 cc. of the acetic acid aniline solution. The appearance of an intense deep red color within 5 min. indicates the presence of traces of furfural.

If a red color is obtained, the furfural may be separated from a fresh sample of the oil (following the above procedure), and identified by the formation of a suitable derivative.

If only a small sample of the oil is available, the test may be carried out directly on the oil itself. Garratt¹⁴⁶ has suggested the following method for the determination of furfural.

Procedure: To 0.1 cc. of the oil in a test tube add from a burette 5 cc. of a 2% solution of freshly distilled aniline in glacial acetic acid. Protect from bright light, and allow to stand for 10 min. Examine in a Lovibond tintometer, and measure the "red value."

According to this authority, the test may have value for the detection of adulteration, if the adulterant has a relatively much higher furfural content than the oil to which it has been added, and if the adulterant has not been treated to remove the furfural. Garratt tentatively suggests its use for the detection of light camphor oil in rosemary oils; of clove oil in bay or pimenta berry oils; of Japanese mint oil in American peppermint oil.¹⁴⁷ It may also have value for the detection of added synthetic methyl salicylate to wintergreen and sweet birch oils. 148

The "ten minute red values" obtained by Garratt149 for reputedly genuine samples of these oils are given in Table 4.15.

TABLE 4.15. LOVIBOND TINTOMETER VALUES FOR FURFURAL-CONTAINING OILS

The reader is referred to the original literature for further details; a list of "ten minute red values" is given for more than 50 different oils by Garratt.¹⁶⁰

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145 Wallach and Gildemeister, Liebigs Ann. 246 (1888), 282.

146 Analyst 60 (1935), 369, 371.

147 This is the basis of the color reaction for the detection of oil of Mentha arvensis (Japanese mint), in oil of Mentha piperita L. (peppermint oil) ; this test is official in "The United States Pharmacopoeia," Thirteenth Rev., 390. It has been the experience of the laboratories of Fritzsche Brothers, Inc., that this test is far from being satisfactory and that the test which was official in "The United States Pharmacopoeia," Eleventh Revision, is to be preferred. (See also "Detection of Mentha arvensis Oil," p. 343.)

148 LaWall (Am. J. Pharm. 92 (1920), 891) reports the presence of furfural in wintergreen and sweet birch oils, and -its absence in synthetic methyl salicylate.), 595.