08-12-01 13:28
No 203809
Hey bees! Swic has been contemplating using a catalytic hydrogenation to reduce good old 2,5 DMNS. He read a great patent on Rhodium's site using Pd/BaSO4 as a catalyst, but was wondering if any bees see a problem with using straight PtO2 as the catalyst. Also, instead of GAA as the solvent, he seems to remember KrZ stating that an ethyl acetate/GAA mix would help increase solubility of the nitrostyrene, anybody care to agree/disagree?
As an on the side question, swic wanted to know if anyone could help him understand something he read. He was reading into some 'modified catalyts' and came across the Lindlar catalyt. As he continued to read he saw that this catalyt is configured to only perform a sort of partial hydrogenation (The example is for the synthesis of cis alkenes). From what he has understood Pd/C and PtO2 are used for complete saturation, and not a partial saturation, correct? Thanks.
(Hive Addict)
08-12-01 15:11
No 203853
lindlar's is what's known as a poisoned catalyst- beleive that it is BaSO4 that's been washed with a lead acetate solution and then add the metal catalyst to that. a quick search will turn up the prep. if you use the metal/BaSO4 without the lead actate, you'll be fine.
(Hive Bee)
08-12-01 16:04
No 203897
You need presure (at least 2-3 bar) and PtO2 to reduce the 2,5-DMNS. The modifiet modified catalyts are just catalyst with is not ad efektive as PtO2 (with will bee reduced to werye fine Pt metal. The solvent is not that important. GAA and EtOAc works just fine.
(Hive Bee)
08-12-01 19:16
No 203948
Thanks for your help guys. Obituary, swic's book says that Lindlar's catalyst is Pd on CaCO3 poisoned with lead acetate and quinoline(don't know what quinoline is). This bee doesn't like dealing with barium salts anyways. Hest, swic was planning on using about 60 psi of pressure for the reaction, or roughly 4 atm, little more than 4 bar if he did his calculations correctly. He will also have to add a little sulphuric acid to the mix, according to the patent. What role does the acid play? Thanks again.
(Chief Bee)
08-12-01 19:19
No 203949
The acid protonates the amine, making it less prone to michael addition to the electron-deficient nitroalkene, forming a dimer.
(Hive Bee)
08-12-01 19:31
No 203955
OH! That makes SOOOO much sense! Don't really know what the michael addition is, but I will in about an hour of reading. Understand how the acid protects the amine though. Thanks.
(Stoni's sexual toy)
08-13-01 06:56
No 204080
Most nitrostyrene/propene hydrogenations I´ve seen so far used a strong inorganic acid together with acetic acid, e.g. H2SO4, HCl etc.
I also remember having seen a reference once where aqueous HCl and Pd/C were used to hydrogenate nitroalkenes in pretty good yields, but I can´t find it anymore. I´m not sure if alcohols were used as cosolvents, and the pressures used were a bit higher than usual too, but I´d like to see that literature reference again. Has anybody come across that one?
(Hallucinogenius)
08-20-01 06:22
No 205995
The reference which I read concerning HCl was in the Canadian Journal of Medicinal Chemistry. They used aq. 31.45% HCl, and EtOH saturated with HCl. However, both times they yielded the amino-alcohol and not the amine. I would stick with a good excess of H2SO4 to be safe, best not to stray too far from the documentation. Remember, you cannot gauge completeness of this reaction by hydrogen uptake as reduction of the GAA is occuring simultaneously. BTW if you are looking for that article, it was about producing DOB, not 2CH/2CB.
(Stoni's sexual toy)
08-20-01 09:37
No 206013
No, it was another ref, not CJC. And they used pressures in excess of 10bars (which might explain the reduction of the benzyl alcohol). But thanks anyway.