Organic Syntheses Procedure

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Org. Synth. 1973, 53, 63

DOI: 10.15227/orgsyn.053.0063

HOMOGENEOUS CATALYTIC HYDROGENATION: DIHYDROCARVONE

[2-Cyclohexen-1-one, 2-methyl-5-(1-methylethyl)-]

Submitted by Robert E. Ireland¹ and P. Bey².

Checked by N. Haga and W. Nagata.

1. Procedure

Caution! Benzene has been identified as a carcinogen; OSHA has issued emergency standards on its use. All procedures involving benzene should be carried out in a well-ventilated hood, and glove protection is required.

A 500-ml., two-necked, creased flask, containing a magnetic stirring bar and connected to an atmospheric pressure hydrogenation apparatus equipped with a graduated burette to measure the uptake of hydrogen, is charged with 0.9 g. (0.9 × 10⁻³ mole) of freshly prepared tris(triphenylphosphine)rhodium chloride (Note 1) and 160 ml. of benzene (Note 2). One neck is stoppered with a serum cap, and the mixture is stirred magnetically (Note 3) until the solution is homogeneous. The system is then evacuated and filled with hydrogen. Using a syringe, 10 g. (0.066 mole) of carvone (Note 4) is introduced into the hydrogenation flask. The syringe is rinsed with two, 10-ml. portions of benzene, and stirring is resumed. Hydrogen uptake starts immediately (Note 5) and stops 3.5 hours later when the theoretical amount of hydrogen has been absorbed. The solution is filtered through a dry column (4 cm. diameter) of 120 g. of Florisil (60–100 mesh). The column is washed with 300 ml. of diethyl ether, and the combined solvent fractions are concentrated under reduced pressure. Vacuum distillation of the yellow residue through an 11-cm. Vigreux column (Note 6) affords 9.1–9.5 g. (90–94%) of dihydrocarvone; b.p. 100–102° (14 mm.), n²⁴D 1.479 (Note 7) and (Note 8).

2. Notes

1. The tris(triphenylphosphine)rhodium chloride catalyst was prepared according to the procedure of G. Wilkinson and co-workers.³

2. The benzene was distilled from calcium hydride.

3. Efficient stirring is necessary to assure good surface contact during hydrogenation.

4. The carvone was distilled before use; b.p. 105–106° (14 mm.). The checkers used l-carvone obtained from Shiono Koryo K.K. (Japan).

5. With old catalyst, very erratic results with respect to the initiation time and the rate of hydrogen uptake have been observed.

6. When the hydrogenation is carried out on a smaller scale, purification can be affected by evaporative distillation in a bulb to bulb apparatus.

7. GC analysis shows contamination by less than 3% of carvone. The checkers used a 1 m. by 4 mm. glass column packed with 5% PEG 6000 on Chromosorb W (60/80 mesh). The retention times were 3.7 minutes and 2.75 minutes for carvone and dihydrocarvone, respectively, at 100° with a nitrogen flow rate of 90 ml. per minute.

8. The product shows the following spectral properties: IR (neat) 1678 cm.⁻¹

; UV (C₂H₅OH) λ_max 237 nm (ε = 9150); ¹H NMR (CDCl₃), δ 0.88 [d, J = 6 Hz., 6H, CH(CH₃)₂], 1.71 (d, J = 1.5 Hz., 3H, CH₃C=CH), 6.70 (m, 1H, CH=C).

3. Discussion

⁴

This procedure is an example of the use of a soluble transition metal complex for the catalytic transfer of hydrogen to an olefin. First developed by Wilkinson and co-workers,³ subsequent extensive investigation in those laboratories and others⁵ has shown that the hydrogenation is sensitive to steric congestion; only unhindered double bonds are reduced. As a result, the rhodium complex has been found useful for the selective saturation of unhindered double bonds in polyolefinic substances, such as carvone.⁶ Unhindered double bonds may be reduced even in the presence of functions such as keto,⁷^,⁶ nitro,⁶^,⁸ and sulfide⁶ groups. The mechanism³ and stereochemistry⁹ of the catalysis have been investigated, and cis-addition of hydrogen is the general rule. The catalyst is effective for deuterium addition to unhindered olefins¹⁰ without the extensive hydrogen–deuterium exchange observed with palladium and platinum heterogeneous catalysis. The rhodium complex causes the decarbonylation of aldehydes and acid halides; the hydrogenation of such unsaturated systems is complicated by the loss of these functional groups.³, Isomerization of nonreduced olefinic bonds is also an observed side reaction.¹¹

References and Notes

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91109.
Department of Chemistry, Research Laboratories, Richardson-Merrell, Inc., Strasbourg, France.
J. A. Osborn, F. H. Jardine, J. F. Young, and G. Wilkinson, J. Chem. Soc. (A), 1711 (1966).
For further discussion and bibliography, H. O. House, "Modern Synthetic Reactions," 2nd ed., W. A. Benjamin, New York, 1972, p. 28.
For reviews, J. Tsuji, Adv. Org. Chem., 6, 109 (1969); J. A. Osborn, Endeavour, 26, 144 (1967); R. Cramer, Acc. Chem. Res., 1, 186 (1968); R. F. Heck, Acc. Chem. Res., 2, 10 (1969).
A. J. Birch and K. A. M. Walker, J. Chem. Soc. (C), 1894 (1966).
M. Brown and L. W. Piszkiewicz, J. Org. Chem., 32, 2013 (1967);
R. E. Harmon, J. L. Parsons, D. W. Cooke, S. K. Gupta, and J. Schoolenberg, J. Org. Chem., 34, 3684 (1969).
F. H. Jardine, J. A. Osborn, and G. Wilkinson, J. Chem. Soc. (A), 1574 (1967).
J. R. Morandi and H. B. Jensen, J. Org. Chem., 34, 1889 (1969).
J. J. Sims, V. K. Howard, and L. H. Selman, Tetrahedron Lett., 87 (1969).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Benzene (71-43-2)

diethyl ether (60-29-7)

hydrogen (1333-74-0)

nitrogen (7727-37-9)

platinum (7440-06-4)

palladium (7440-05-3)

calcium hydride (7789-78-8)

rhodium (7440-16-6)

deuterium (7782-39-0)

Dihydrocarvone

2-Cyclohexen-1-one, 2-methyl-5-(1-methylethyl)- (43205-82-9)

tris(triphenylphosphine)rhodium chloride

carvone,
l-carvone

Notes

References/EndNotes

Article Compounds

Authors