Tet. Lett., vol. 28, No. 12, 1321-1322 (1987)
Selective C=C bond hydrogenation in unsaturated nitro compounds in the precense of the RhCl3-Aliquat 336 catalyst system.
We wish to report that the RhCl3-Aliquat 336 ion pair, [(C8H17)3NCH3]+[RhCl4(H2O)n]-, which has already been shown to be a most efficient and selective olefin and arene hydrogenation catalyst, does not only catalyze the preferential reduction of olefinic bonds in unsaturated nitro compound, but promotes, to some extent, also hydrogenation of nitrobenzenes to nitrocyclohexenes.
When e.g., a solution of 1 mmol of an unsaturated nitro compound in 0.5 ml of an organic solvent was hydrogenated in the precense of the ion pair generated from10 mg of RhCl3*3H2O in 0.5 ml triple distilled water and 22 mg of commercial Aliquat 336 in the apparatus described previously[1], the sole product was a saturated nitro compound.
Beta-nitrostyrene with DCM as solvent gave after 22 hours reaction time (at atmospheric pressure) 2-nitro-1-phenylethane, with a 17% conversion yield and no byproducts.
Only after complete reduction of the double bond was the nitro group affected. Thus, e.g., in the hydrogenation of beta-nitrostyrene, 2-phenethylamine started to accumulate only after 72 hours when all the starting compound had dissapeared. The conversion of the nitroalkane into the aminoalkane was then accomplished during 12 hours.
[1]This is just a atmospheric pressure hydrogenation, so the kind of apparatus they use is of no great concern. As usual the only important thing is the agitation so the hydrogen is effectively transported to the catalyst.
