(Hive Addict)
01-16-03 14:42
No 398684
(Rated as: excellent)
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.
Catalytic hydrogenation freak
(Hive Bee)
01-16-03 22:44
No 398817
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.
Am I missing something... 17% yield? Rhodium compounds along with an exotic PTC such as Aliquat 336, not exactly cheaply obtainable reagents... They mention the nitro group begins to get reduced after complete reduction of the double bond at 72 hours. Do they mention anything about getting fuller conversion after more time?
-SpicyBrown
(Stoni's sexual toy)
01-17-03 15:43
No 399038
> They mention the nitro group begins to get reduced after
> complete reduction of the double bond at 72 hours.
100% conversion not good enough for you?
> Do they mention anything about getting fuller conversion
> after more time?
It's damn hard to get better than 98% yields...
I'm not fat just horizontally disproportionate.
(Hive Bee)
01-17-03 18:40
No 399084
100% conversion not good enough for you?
Yea, 100% sounds good. I completely missed this and thought the article was stating 17% overall yields. My ignorance hath been exorcised.
-SpicyBrown
(Hive Addict)
01-19-03 16:42
No 399702
J. Chem. Soc. Perkin. Trans., 2509-2512 (1973)
Homogenous hydrogenolysis af organic halides and hydrogenation of the carbonyl, epoxy- and nitro-groups.
The catalyst formed from trichlorotris(pyridine)rhodium with sodium borohydride in DMF is shown to be effective for the homogeneous hydrogenation of, blah blah blah, styrene oxide gives 2-phenylethanol. In the case of 2-nitro-1-phenylpropene and 1-(3,4-dimethoxyphenyl)-2-nitroethene only the olefinic bond could be hydrogenated, as has been observed for similar hydrogenations catalyzed by RhCl(PPh3)3.
The catalyst was prepared from recrystallized RhCl3py3(trichlorotris(pyridine)rhodium and sodium borohydride, which was recrstallized from diethylene glycol dimethyl ether.
1-(3,4-Dimethoxyphenyl)-2-nitroethene (392 mg) with the catalyst (68 mg) absorbed 43 ml hydrogen in 30 minutes to give a liquid product, which with LAH in ether gave 2-amino-1-(3,4-dimethoxyphenyl)-ethane identical with an authentic sample (NMR comparison). no yield was given
2-Nitro-1-phenylpropene gave 2-nitro-1-phenylpropane. no yield was given
Catalytic hydrogenation freak and the sluttiest slut of all sluts