(Chief Bee)
01-21-03 05:43
No 400079
(Rated as: excellent)
Palladium-catalyzed transfer hydrogenation in alkaline aqueous medium
Tetrahedron Letters 41, 7847-7849 (2000)
Catalytic transfer hydrogenation can be an effective method for reducing a variety of organic substrates, which avoids some of the technical and safety concerns associated with using compressed hydrogen gas. The heterogeneous mixture of Pd-C and ammonium formate in alcohol solvent has proven to be a particularly effective reagent in organic synthesis. Replacing organic solvents with water offers economic advantages, improves safety, reduces the environmental impact of the waste stream, and in combination with the development of catalytic processes offers great opportunities for 'green chemistry'. We have studied transfer hydrogenation in alkaline aqueous conditions as part of a broad investigation of noble metal-catalyzed reactions of organic substrates in water. Herein, we report a convenient, effective method for reducing unsaturated carboxylic acids using the non-pyrophoric catalyst palladium(II)chloride, formic acid, and sodium hydroxide base in water.
The reduction of cinnamic acid 1 was carried out using 10 mol% PdCl2 and 4 equivalents of hydrogen donor, in 2.5 M aqueous NaOH solution, heated to 65°C for 16 h. A series of potential hydrogen donors was investigated, from which formic acid was the most effective (yield of hydrocinnamic acid 98%), followed in decreasing order of effectiveness by: glyoxylic acid (80%), gluconic acid (35%), N-(2-hydroxyethyl)ethylenediaminetriacet
In summary, PdCl2 is an effective catalyst for transfer hydrogenations using formic acid in alkaline aqueous media. This procedure is advantageous because no organic solvent is required, the reagents are inexpensive, and the catalyst is non-pyrophoric. These reaction conditions should be suitable for the reduction of a wide variety of organic substrates, and offers an economical, safe, and environmentally benign alternative to available procedures.
Typical procedure:
To a stirred solution of cinnamic acid (50 mg, 0.33 mmol) in 2.5 M aqueous NaOH (4 mL) was added PdCl2 (6.0 mg, 0.025 mmol). Formic acid (50 uL, 1.3 mmol) was added dropwise, then heated to 65°C for 16 h. The reaction mixture was neutralized with 2 M HCl, extracted with diethyl ether (2x5 mL), washed with H2O (10 mL), and dried (Na2SO4). The product was then purified by a short column of silica gel eluted with 25% ethyl acetate in hexanes. Removal of solvent in vacuo gave hydrocinnamic acid (50 mg, 98% yield).
(Master Searcher)
01-22-03 01:58
No 400307
I found this one today.
Patent US3793354
dehydrogenation of alcohols to ketones and hydrogenation of nitro compounds to amines.
How about nitromethane to methylamine?
http://www.geocities.com/dritte123/PSPF.
The hardest thing to explain is the obvious
(Hive Bee)
01-23-03 22:56
No 400930
maybe it would work for Sunlight's CTH of ketone with ammonium formate, or am I way off? If it did work it would be much better since Pd/C is so hard to get because it isn't accepted by any major shipping companies. And it don't look good getting truck shipping to a house.
The working man is a sucker
(Stranger)
02-20-03 00:25
No 409893
an acid and a ketone are quite different
Who knows though, maybe there is a CTH out there from ketone to amine using PdCl2 solution instead of Pd/C. Maybe it hasn't even been discovered yet. Maybe it will be someone here to do it 
(Pioneer Researcher)
02-21-03 17:11
No 410446
I suppose that they are actually using Pd(OH)2 as the catalyst. Perhaps it works the same with the CTH reductive amination, but the problem is the recovery of the catalyst without a support.
(Hive Bee)
02-21-03 18:56
No 410472
swim would be willing to try it at a 3 gram scale in the summer, if he is spoonfed suggested molar ratios, rxn times, etc.
Catalyst recovery is really no problem for swim if it works, because this is a damn simple synth.
The working man is a sucker
(Pioneer Researcher)
02-21-03 22:06
No 410527
Check my post about the procedure. In recent runs I've got a 82 % yield using the same proportions but a 20 % of 10 % Pd/C respect to the ketone, so a minimum of 2 % of Pd metal content will be necessary. BTW, I think I'll make a micro test in the very next future.
(Pioneer Researcher)
02-24-03 02:14
No 411256
I was wrong, the catalyst is Pd metal. I'm almost sure that I read in a patent given by PoliethyleneSam that NaOH precipitated Pd hydroxide, the fact is that adding a bit of PdCl2 to a NaOH solution, it get dissolved, and adding NaOH to a acidic PdCl2 solution to a strong basic pH it is dissolved as well, I'm surprised, may be it forms something like Na2PdCl2 that is easily soluble.
Respect to the reaction, if formic acid is added to a solution of NaOH and PdCl2, Pd metal precipites, and the same happens if PdCl2 is added to a solution containing Ammonium formate. The black precipitate is not soluble in concentrated HCl, but adding a few drops of 30 % H2O2 it goes easily in solution, so it is Pd metal.
I'm making a 2 grams test of the CTH reductive amination with 200 mg of PdCl2, and it seems to work, I hope the catalyst won't die before complete the reaction. Recover the catalyst will be recover the Pd metal and convert it again to PdCl2, so though we must use an irrational amount of PdCl2, it can be recovered with a small mechanical lost, it can be very useful.
(Pioneer Researcher)
02-27-03 01:09
No 412083
The rxn, 2 gr of ketone in 33 ml of 9:1 methanol : water with 6.8 gr of am formate dissolved, 200 mg of PdCl2 were added and in the course of a minutes was converted in Pd metal, with extensive generation of bubbles, it presented a good activity, but after two or three hours the activity decreased dramatically. 24 hours later TLC has not good aspect, there was not ketone and there was the amine and the byproduct, but the appearance is that there is little amine. Making the workup, in the acid wash there was a lot of acid insoluble product, yield < 50 %, even much less, went to the drain.
It is the same problem that occurs with my homemade catalysts, and I'm thinking now that may be the problem is not in the carbon support but in the PdCl2 itself, that is not reagent grade but from a photographic supplier that may have impurities that poissons the catalyst. May be it works with PdCl2 reagent grade, but then may be better to buy commercial an active Pd/C ... it's another choice.