An Artifact in a Synthetic Pine Oil

RESEARCH NOTE J. Ess. Oil Res., 3, 41-42 (Jan/Feb 1991)

Duane F. Zinkel USDA Forest Service, Forest Products Laboratory* One Gifford Pinchot Drive Madison, WI 53705-2398

ABSTRACT: The isopropyl ether of a-terpineol was identified as an artifact in the synthetic pine oil produced when isopropyl alcohol was used as the emulsifier.

KEY WORD INDEX: Synthetic pine oil, a-terpineol isopropyl ether, terpinen-4-ol isopropyl ether, turpentine.

INTRODUCTION: The manufacture of synthetic pine oil is the primary use for turpentine. The synthesis involves the acid-catalyzed hydration of a-pinene at the in terface ofan emulsion of pinene/mineral acid (1). Various emulsifiers have been used, one of which is isopropyl alcohol. Our gas chromatographic examination of a commercial distilled pine oil, produced using the isopropyl alcohol emulsifier, revealed the presence of 4-5% of a higher boiling component product not present originally in the turpentine.

EXPERIMENTAL: NMR spectra were obtained at 310 K with a Bruker WM250 (250 MHz proton and 62.9 MHz carbon) FT spectrometer controlled by an Aspect 2000A minicomputer; DEPT spectra were obtained with a standard Bruker program. Gas chromatography was done with a Hewlett Packard 5880 gas chromatograph (FID) and fused-silica columns: a DB-1 (a methyl silicone) column from J & W Scientific (Folsom, CA), 15m x 0.25mmi.d. witha 0.1-µmfilmoperatedat60°Cand a Carbowaxcolumn,30m x 0.25mm with a 0.25-µm film temperature programmed from 60°C to 225°C at 8°C/min.

isopropyl etherwas isolated by liquid chromatography. The commercial pine oil was chromatographed on neutral alumina (III) with pentane as solvent to obtain a fraction enriched to about 20% of thae isopropyl ether. Rechromatography provided l material of99+% purity. H NMR(CDCl3): 5.45 (lH, brd), 3.81 (1H, m), 1.64 (3H C 7 Me, br s), 1.099 and 1.1033 (6H isopropyl ether Me, pair d,J = 6.2 Hz), 1.078 and 1.108

* The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and subject to U.S. copyright. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement by the United States Department of Agriculture. 41 42 JOURNAL OF ESSENTIAL OIL RESEARCH

(6H C-9 and C-10 Me, 2s) [the data for the methyl protons from 1.0 to 1.2 were obtained with a Bruker AM500 spectrometer because this region was only partially resolved at 250 13 MHz]; (C6D6): 5.38, 3.58, 1.64, 1.073, and 1.062 (6H,prd,J = 6.1 Hz),0.99 (6H,2s). C-

NMR(CDCl3): 134.0 (C-1), 121.0 (C-2), 77.0 (C-8), 62.8 (C-2 of isopropyl ether), 43.1

(C-4), 31.2, 27.2, and 24.0 (CH2, C-3,5,6), 25.2, 25.0, 23.7, 23.4, and 22.8 (CH3, C-7,9,10 and C-1,3 of isopropyl ether).

RESULTS AND DISCUSSION: The higher-boiling artifact (retention relative to terpineol was 2.474, DB-1) was isolated by chromatography on alumina. The retention of Carbowax (about two-thirds of a-terpineol indicated the artifact did not have an -OH group. From the GC retention characteristics and the components of the simple hydration system, a compound derived from and isopropyl alcohol was expected. How ever, initial inspection of the 13C spectrum showed peaks for only 12 carbon atoms. The EI mass spectrum provided little information in that the largest ion was m/z 136 and was similar to the spectrum for but the ammonia-CI spectrum contained a weak

M + 1 peak at 197. Reexamination of the 13C spectrum in C6D6 revealed the thirteenth peak, a quaternary carbon that was obscured by the middle peak of the CDCl3 peaks in that solvent. The 13C- and 1H-NMR characteristics suggested that the artifact was, indeed, the expected isopropyl ether of a-terpineol. GC and spectral comparison with synthesized material (reaction of chloride with zinc oxide in isopropyl alcohol (2) and subsequent comparison with authentic material obtained from Gurudutt confirmed the identity.

Several preparations of the described isopropyl ether were synthesized from distilled fractions of chloride. One terpinyl chloride fraction contained an impurity that resulted in a contaminant in the crude a-terpinolisopropyl ether. The GC retention of the contaminant on DB1 was 75% of that for the isopropyl ether of A small amount 1 of this contaminant was isolated by chromatography on SiO2. The H-NMR spectrum 0.902 (2 Me d, J = 6.9 Hz), 1.071 and 1.115 (2 Me, pair of d, J = 6.1 Hz), 1.643 (1 Me br s), 3.80 (1H, m), and 5.27 (1H, br d)] is consistent with that expected for the ispropyl ether of terpinen-4-ol.

ACKNOWLEDGMENT: The author is grateful to Dr. K. N. Gurudutt of the Central Food Technological Research Institute, Mysore, India, for a generous sample of a-terpinol isopropyl ether, and to Dr. J. Ralph, U. S. Dairy Forage Research Center, Madison, Wisconsin, for the 500 MHz proton spectrum.

REFERENCES

1. M. J. Kelly and A. E. Rohl, Pine Oil and Miscellaneous Uses. In: Naval Stores-Pro duction, Chemistry, and Utilization. Eds. D. F. Zinkel and J. Russell, pp. 560-572, Pulp Chemicals Association, New York (1989). 2. K. N. Gurudutt, B. Ravindranath and P. Srinivas, Solvolytic Displacement of Alkyl Halides by Metal Salts. Tetrahedron, 38, 1843-1846 (1982).

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