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zed
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I've had access to Parr type hydrogenators. Always preferred Brown's method. Quiet, unobtrusive, very effective. At least, very effective for what
I wanted to do.
http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/1962/84/i14/...
A very clean, low-tech way to produce a lot of product with minimal equipment. Uses a fair amount of Sodium Borohydride, if you are using NaBH4 as
your only hydrogen source. But, you can just use Borohydride to generate your catalyst, then use H2 from a different source to run your
hydrogenation.
[Edited on 18-9-2008 by zed]
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solo
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| Quote: | Originally posted by zed
I've had access to Parr type hydrogenators. Always preferred Brown's method. Quiet, unobtrusive, very effective. At least, very effective for what
I wanted to do. |
..........may I ask what's Brown's method?.......solo
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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zed
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I just added a link to the original post.
Another good point about Brown, you can calculate the amount of hydrogen used, by observing the amount of Borohydride solution that has been consumed.
To produce a really large quantity of product, because the vessel is stationary and accessible.....If you construct it with a few extra inlet and
outlet tubes, you can siphon-filter-out reduced product, and inject more material for reduction, while retaining your hydrogen atmosphere and
catalyst. So, multiple runs can be made....Until, of course, your catalyst becomes poisoned.
[Edited on 18-9-2008 by zed]
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Barium
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| Quote: | Originally posted by gsd
For reduction of C = O to C- H.
2) U-Ni-A : Was nearly as good, could be recycled 10 times but T/P conditons were higher as compared to Pd/C
3) Raney Ni: Could complete the reduction at all. Inspite of using drastic T/P conditions , the reduction proceeded only upto C - OH
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What temperatures, pressures and mixing conditions were you using? How much catalyst was used? How was the U-Ni-A activated? Acetic acid or
hydrochloric acid and for how long time? Was there any other functional groups pressent in the substrate? Details please!
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chemrox
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Back to Solo's dilemma; I've also been wondering how to calculate how much H2 is used in the Parr. The gauges are fine for observing when no more
gas is taken up but getting from there to a precise calculation of moles used didn't seem practical. However I don't know how I missed the
standardization procedures. I have Parr manuals too thanks to Sauron. Maybe the one posted by Wizard is more up to date. Anway the procedure claims
a 0.1 mole sensitivity at least and I'm not after more than that as precision. Solo's article was interesting too in that it's a lot like the
original Ogata method but sort of a one pot approach in the hydrogenator if I got it right. In Resolution of Ephedrine, Ogata reacted p2p with Meam
over Hg amalgam and then put the product in the hydrogenator. Brown's method is very interesting but would it work on benzillic hydroxyls which can
be reduced under medium pressure with Pd/C?
[Edited on 20-9-2008 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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zed
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Depends which Parr you are using. If you are using the High Pressure Reactor, you might just be able to calculate the unfilled volume of the
reactor...Fill it with enough high pressure H2 to accomplish your reduction, then control the rate of reduction by controlling the solutions
temperature and speed of agitation.
As for Brown's method. It supposedly produces an unusually active catalyst; the more active your catalyst, the less pressure your hydrogenation will
require. I don't know what pressures you are working at, but If you have to use significant pressure for your reduction, then the glass apparatus
that Brown uses, isn't the way to go. Still, there is no reason that Brown's method, or a modification of it, can't be used in a metal vessel.
Another interesting hydrogenation catalyst, that might work under moderate conditions, depending on your substrate, is Tungsten Carbide. It likes
acidic conditions, and it may require less heat and pressure than Raney Nickel. It likes to work at 5 to 10 Atmospheres, and the more pressure you
give it, the less heat it requires. Quite active, once you get it going. Reported to resist poisoning.
I would imagine that a Parr shaker with a metal bottle (rather than glass), should be able to easily utilize Tungsten Carbide as a hydrogenation
Catalyst.
Now that prices for Platinum and even Palladium, have skyrocketed, maybe Carbide deserves a look. Not much literature on it, or at least I haven't
seen much.
I don't know what reactivity it has with Benzylic Alcohols, might be useless. But, it isn't impossible that it would be effective at reducing
Nitrostyrenes to amines. Keep the pressure up, the acidity high, and temperature down....and it has a good chance of working.
US Patent. 5,646,085 Catalyst for Preparation of aromatic Nitro compounds.
The key passage being on page 5, paragraph 7.
"When work is performed in a liquid medium that is acidic and reactive (said medium being homogeneous or heterogeneous and having an acid titre
equalling at least 0.1N and preferably1N), IT IS NOT NECESSARY TO INCREASE THE PRESSURE MUCH ABOVE 2 ATMOSPHERES IN ORDER TO REACH THE (ACTIVATION)
THRESHOLD, AND THIS CAN BE DONE AT RELATIVELY LOW TEMPERATURE (ABOUT 50 DEGREES C.).
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sec...
[Edited on 21-9-2008 by zed]
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Klute
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Hum, aromatic nitro compounds are much more easily reduced than aliphatic, or nitrostyrenes under cat hydrogeantion conditions... I don't think that
statement can be applied to nitrostyrenes, which require very high catalyst loadings. There have been a few sparse claims about atm hydrogeantion to
the amine, but it wasn't backed up with any hard info or details... Aliphatic nitro compouds could be more inclined to be reduced under tese
condiitons, considering that they behave pretty well under cTH conditions, the CTH donors could be swapped for atmospheric H2.
Two other interesting catalyst would be Cu/SiO2 and Ni/C IMHO.
Cu/SiO2 is very easily made (I have made a few grams a few months ago), and is apparently very good at reducing the double bond in a,b-unsaturated
ketones. Maybe by analogy itcould be used to reduced nitrostyrenes to aliphatic nitroalkanes? It can also be used to deoxygenate aromatic keto,nes to
alkanes, as a Clemmensen or Wolf-kisher but in much smoother condiitons (atm H2, toluene, 90°C 1/1-5/1 w/w sub/cat)... A very promising path,there
is a series of papers avaible the ref forum on this catalyst.
Ni/C is said to be also pretty easy to prepare, and surprisingly doesn't require excessive pressures and temps to get working (although the authors
sued to it for various coupling, and dehalogeantion of aryl chlorides). The cheapness of the catalyst could make it a viable alternative to the common
palaldium and Pt.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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transformer
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| Quote: | Originally posted by Barium
If you can make a really active Raney nickel you should be able to use it at such low pressures for the reduction of a imine. |
Do you have the details for making a really active Raney nickel?
And does this differ a lot from the average fresh commercial Raney nickel?
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Klute
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Preparation of the very active W-6 Raney Nickel from OrgSyn:
Raney Nickel, W-6
I think this the most active Raney nickel commonly used. Maybe more active catalyst can be prepared with additives or special conditions..
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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chemrox
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I think for nitrostyrenes you're going to use LAH. I don't see a way to use the medium pressure Parr. Maybe high pressure (?) I don't know .. can't
go there with my gear.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Nicodem
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Chemrox, what are you talking about? Where did high pressure come from?
beta-Nitrostyrenes can be hydrogenated at 1 atm or more to either alpha-phenylacetaldoximes or beta-phenylethylamines depending on conditions and
catalyst loading/type. No high pressure is needed and even Pd-C works even though it sucks in regard of oxime reductions (which means only
beta-unsubstituted bet-nitrostyrenes can be reduced all the way to the amine since ketoximes are generally unreducible with Pd-C).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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chemrox
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I didn't bring it up ..I don't know anything about using high pressure H2.. someone mentioned it ala Parr. No idea why.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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