Acknowledgment
J. H. Norman developed the analytical procedures used with the mass spectrometer. literature Cited (1) Adams, R. M., "Boron, Metalloboron Compounds and Boranes," pp. 655-7, Interscience: New York, 1964. (2) Cueilleron, J., Guillot, P., Bull. SOC. Chim. Franc., No. 333,
(3) Dunstan, I., Blay, N. J., Williams, R. L., J . Chem. SOC. 1960, p. 5006. (4) Zbid., p. 5012. (5) Zbid., p. 5016. (6) Gallaghan, J., Siegel, B., J . A m . Chem. SOC.81, 504 (1959). (7) Garrett, A. B., Weilmuenster, E. A., Harris, S. W., Altwicker, E. R. (to Olin Mathieson Chemical Corp.), U. S. Patent 2,999,117 (Sept. 5, 1961). RECEIVED for review March 23, 1965 ACCEPTED October 8, 1965
2044 (1960).
HYDROFORMYLATION OF TERPENES W I L L I A M
H. CLEMENT AND M I L T O N ORCHIN
Department of Chemistry, University of Cincinnati, Cincinnati, Ohio
Four representative terpenes-a-pinene, dipentene, a-terpinene, and myrcene-were hydroformylated, each in three solvent systems-hexane, methanol, and 6% aqueous acetone-at 150" under identical oxo conditions. Dipentene and a-pinene show similar reactivities and yield similar products in methanol and aqueous acetone. Myrcene and a-terpinene react at much slower rates. All reactions lead to complex, highly saturated mixtures of monofunctional products, with little or no difunctional products resulting. Surprisingly, a-pinene and dipentene yield an identical, unsaturated ether in methanol. In aqueous acetone a-pinene, dipentene, and a-terpinene form an identical saturated alcohol, believed to be of a neopentyl type, in addition to yielding large amounls of p-cymene. Implications from the experimental data are discussed and reaction schemes are presented.
literature contains many references to the hydroformylation of terpenes ( 2 ) ,but no single study exists in which various terpenes have been treated in the oxo synthesis under comparable conditions, although such studies have been carried out with simple olefins (8). The present work was therefore undertaken in a n efyort to provide rate and product distribution data for a series of terpenes and to determine whether by simple solvent modifications, the quantities of difunctional compounds such as dialdehydes and diols could be increased. Dipentene, a-pinene, a-terpinene, and myrcene were chosen as representative terpenes and were each hydroformylated under comparable oxo conditions using several solvent systems. HE
A Dipentene, d/-p-mentha-l,8diene
a-Pinene, 2-pinene
r'A
However, data obtained from gas absorptions provide relative reactivity relationships. Product Distribution. The crude oxo reaction products and their yields are shown in Table 11. All materials remaining after removal of the monofunctional compounds (aldehydes, alcohols, ethers, acetals, and esters) are combined under the heading high boilers. T h e monofunctional compounds were further investigated and the following information was obtained. DIPENTENE. I n hexane, this terpene yields a mixture of aldehydes and alcohols (more than four each). I n methanol, a complex mixture of more than four saturated and unsaturated alcohols is formed in addition to acetals, aldehydes, and esters plus a n unsaturated ether. T h e functional groups are attached to various positions of the ring nucleus and the mixture is 46y0 olefinic. T h e chief product (33%) from the reaction is a n unsaturated ether; its structure, I is believed to be:
a-Terpinene, Myrcene, p-mentha-1,3- 7-methyl-3diene methylene-l6-octadiene
I Results
Rates. T h e reactivities of the various terpenes in the hydroformylation reaction, determined a t 150" in hexane, in methanol, and in 6y0 aqueous acetone, are summarized in Table I. The method of Krabacher, Kirch, and Orchin (5) was employed in establishing reaction rates, and the data are reported as rates relative to a-pinene in hexane, whose rate was assigned a value of 1.0. Because of the multiplicity of reaction paths, true rate constants could not be established.
Table I.
Relative Rates of Terpene H y d r o f ~ r m y l a t i o n ~
6% Aqueous Acetone a-Pinene 1. o 4.8 Dipentene 5.6 4.8 4.2 a-Terpinene 0.3 0.5 0.3 Myrcene 1.1 2.3 0.3 All reactions carried out at 150" under identical conditions. Hexane
a
VOL. 4
NO. 4
Methanol 5.0
DECEMBER 1965
283
I n 6% aqueous acetone, dipentene gives a mixture of aldehydes and alcohols plus a small amount of acid; the product mixture is 33% olefinic. Approximately one third of the reaction product appears to have the skeletal structure, 11.
I1 The recovered hydrocarbon is nearly 507, p-cymene.
-
C H , ~ C H / 'CH, c H s
CY-PINEXE. I n methanol this terpene forms a similar but even more complex mixture of products than that found with dipentene; the mixture is 287c olefinic. The component present in the largest amount (15%) is identical with the unsaturated ether, I , obtained in the dipentene study. Hydroformylation in 6% aqueous acetone gives a mixture of aldehydes and alcohols plus a small quantity of a carboxylic acid. The mixture is 17% olefinic. Essentially one third of the product consists of compound 11, identical with that generated from dipentene. The recovered hydrocarbon fraction is again 507, p-cymene as with dipentene. a-TERPINENE. I n methanol this terpene forms a complex mixture of saturated alcohols, aldehydes, esters, and acetals. In 67Gaqueous acetone, compound 11, identical with that isolated from dipentene and a-pinene reaction products, constitutes approximately two thirds of the product. However, all reaction products are saturated. The hydrocarbon fraction is practically pure p-cymene. MYRCESE yields a complex mixture of saturated products in methanol; the bulk of the material is of high molecular weight. In 6% aqueous acetone the reaction is extremely slow and most of the product is again high-boiling. The structure of the ether, I , was established in the following manner: Refluxing in either acidic or basic media left I unaffected, but it did react with concentrated HBr to form a bromide. A sample of this compound, isolated by preparative gas-liquid chromatography (g.l.c.), \vas examined by infrared spectroscopy. Its spectrum showed the following groupings : >C=CC=C
