Sciencemadness Discussion Board

Cu/SiO2 a cheap versatil hydrogenation catalyst?

Klute - 22-6-2008 at 08:20

While seaching information on the selective 1,4-hydrogenation of unsaturated ketones ("Raspberry ketone" thread), I stumbled on the use of 8% Cu/SiO2 catalyst as a selective, easily made hydrogenation catalyst. Further enquiry showed that by changing reaction conditions, preparation conditions, etc, this catalyst could be usefull for reduction of ketone to alcohols, deoxygenation of aromatic ketone to methylen compounds (so long dirty Clemmesen and Wolf-Kishner!), and of course selective 1,4- hydrogenation of unsaturated ketones, without producing the corresponding alcohol or other side products...

The catalyst is easily prepared, by adding silica to a solution of Cu(NH3)4 2+ (made by adding conc. ammonia to Cu(NO3)2.3H2O solution, and diluting the slurry to hydrolyse the complex and deposit a finely dispersed precipitate of Cu(OH)2. Filtration, washing and drying prior to calcination at 350°C and reduction by H2 at 270°C under atm pressure afford a finely dispersed Cu/SiO2, non pyrophoric or pyrogenic catalyst.

This catalyst is commonly used in the industry, and can be recycled several times. I'm sure it can be usefull for other applications than those cited previously, possibly dehalogeantion, reduction of nitro compounds, etc. By modifying the loading and the preparation, it's selectivity can be changed.

This could turn out to be a versatil, easily made catalyst for the home-chemist, opening doors to reactions that otherwise require expensive and/or pyrophoric catalyst such as 10% Pd/C, raney nickel, etc.

I decided on trying out this catalyst on the 1,4-hydrogenation of an unsaturated ketone, to compare the selectivity and efficienty to Pd/C, and then try other applications. Different grades of silica will be tried.

Preparation of 8% Cu/SiO2

Preparation of the unreduced catalyst

Cu(NO3)2.3H2O solution was prepared by adding fine 3.5g (55.12 mmol) Cu pellets (Panreac) (washed with acetone and dH2O prior to addition) to 13mL (143.27 mmol) 53% w/w HNO3 (technical) (excess Cu). there was vigorous evolution of NO2, and significant heating up as the solution quickly turned blue. the erlenmeyer was then heated to 50°C for 12H, and left to rest at RT for another 24H.
This resulted in a slightly viscous cyan blue solution, with a little amount of unreacted copper. The solution was decanted of the metal, and completed with a little dH2O to 10mL (~12g/10mL : 1200g/L solution).

Concentrated solution (1200g/L):

Diluted solution (160g/L):

3.3mL of this solution were diluted to 25mL with dH2O (160g/L solution). 30% NH4OH (Panreac) was then added until the Cu(OH)2 precipitate that initially formed redissolved. pH was >9, and a very dark blue solution was obtained.

30% NH4OH:

Cu(OH)2 precipitate:

Cu(NH3)4 2+ solution:

10g of chromatographical grade silica gel (60-200mesh, Acros) were then added in portions, with slow magnetic stirring. there was significant warming up of the solution. The dark blue slurry was stirred for 30min at RT.

Silica gel:


The slurry was then transfered to a 1L beaker placed in a ice bath, and slowly diluted to 1L with strong magnetic stirring. The blue color cleared up to a dark cyan blue colour. After 10min stirring, the blue solid was left to decant, leaving a very slightly blue supernatant. Half of the solution was filtered off, and the remaining supernatant diluted to 1l with stirring. After decantation, the now colorless supernatant was filtered off, leaving the solid in the beaker, and the first filtrate added, and diluted to 1L with stirring. The solid was then vacuum filtered, thoroughly washed with 200mL, and dried by suction for 5min.

First dilution:

Decanted solid:

Filtered solid:

The solid was then transfered to a pyrex dish, and heated on the hotplate to ~100°C. The caked solid quickly dried back to a very fluid powder, as dried silica gel, and was left at 100°C overnight. There were a few light white particules, which was considered to be talc from the latex gloves..

Wet solid:

Dried solid:

In the morning, the solid still was cyan blue. It was transfered to a 250mL beaker, heating increased to 150°C for 1H, the solid turning slightly darker, then placed on a heating mantle and slowly heated to 350°C. The solid gradually turned dark green, and was kept at that temperature for 4H.

After 12H drying:


The catalyst will be reduced prior to the reaction, by atmospheric H2 at 270°C. The formed water will be removed either by vacuum distn, or by refluxing toluene with a Dean Stark (the reaction will be performed in toluene at 90°C)

References: (Available in the Ref's forum)

Thank very much to Nicodem, who very kindly recovered most of the articles.

Cu/SiO2: an improved catalyst for the chemoselective hydrogenation of a,b-unsaturated ketones
Nicoletta Ravasio, Marisa Antenori, Michele Gargano and Piero Mastrorilli
Tetrahedron Letters 37(20), 3529-3532 (1996)

Selective hydrogenation of 4-(6-methoxy-2-naphtyl)-3-buten-2-one to Nabumetone®
Nicoletta Ravasio, Federica Zaccheria, Pietro Allegrini and Mauro Ercoli
Catalysis Today, Volume 121, Issues 1-2, 15 March 2007, Pages 2-5

Heterogeneous selective catalytic hydrogenation of aryl ketones to alcohols without additives
Federica Zaccherianext , Nicoletta Ravasiob, Rinaldo Psarob and Achille Fusi
Tetrahedron Letters 46(21); 3695-3697 (2005)

Cu/SiO2-catalyzed hydrogenation of cyclohexanones under very mild conditions
Ravasio, N.; Psaro, R.; Zaccheria, F.
Tetrahedron Letters 43(21); 3943–3945 (2002)

Heterogeneous Cu-catalysts for the reductive deoxygenation of aromatic ketones without additives
Federica Zaccheriaa, Nicoletta Ravasiob, Mauro Ercolic and Pietro Allegrini
Tetrahedron Letters 46(45), 7743-7745 (2005)

Dr.3vil - 22-6-2008 at 13:35

Nice work! I am looking forward to seeing the writeup for the reduction of the catalyst by H2. So far this seems like a great way to open up hydrogenation to the home chemist.

Klute - 23-6-2008 at 09:11

Thank you! I hope this catalyst can be used for lots of different reactions involving hydrogen, giving a very cheap and safe substitute to Raney Nickel, Pd/C, copper chromite, etc

The final weight was 10.5g, so it seems not all the copper was absorbed, and that the catalyst hasn't got an 8% loading. Thsi could be du to thet fact that I added a little too much ammonia, and the the volume of water required for complete hdrolysis was superior to what I added. In one of the articles, they dilute the complex's solution to 3L!

Next time i will add the ammonia dropwise, or maybe use excess Cu salt to compensate.

The silica was initially dry (I can through it in the oven for 30min at 150°C to be sure of the weight), so I would assume at most 0.1g silica loss, giving 0.6g of absorbed CuO (7.5 mmol) giving just under 0.5g Cu when reduced, so a 5% loading.

I will moniter H2 uptake during activation of the catalyst (after flushing the setup with argon, then H2 to compensate for the volume of the setup), to compare results. I will use a little more catalyst during reductions to obtain the same substarte/cu ratio as the ones used in the articles.

Klute - 28-9-2008 at 06:27

Attempted reduction of dehydrozingerone by Cu/SiO2-catalyzed hydrogenation

The catalyst prepared above was used in the atm hydrogenation of 4-(4'-hydroxy-3-methoxyphenyl)but-3-en-2-one ("dehydrozingerone") according to Ravasio et al. (see ref above).

The catalyst was easily reduced by atm hydrogen at >250°C, and the substrate as a toluene/AcOEt solution under argon was introduced. reduction was performed at 90°C with atm hydrogen for 24h.

Reduction of the catalyst

A 100mL 3-neck 14/19 flask was equipped with the following: a simple distn setup with no vacuum inlet (receiver directly attached to the condenser), a claisen adaptator fitted with: a gas inlet connected to a hydrogen generator (pressure equalized addition funnel on 4-neck 250mL RBF), a gas admission tube connected to an inverted 250mL cylinder immersed in a beaker of water; a septum.

0.90g (Ratio substrate/catalyst ~5% mol/mol) of the previously prepared catalyst were weighed and introduced in the flask, with a stir bar.


The whole system was purged with argon 3 times, then the H2SO4 was drippe donto the Zn slurry, and the system purged with H2 two times. The cylinder was filled with H2, and the flask was heated with a mantle to 250-300°C, stirring and shaking the fluid catalyst, which gradaully darkened over 15min. H2 absorption started very quickly, and stopped after ~15min. Heating and stirring was continued for another 15min. A few small water droplets had deposited in the top of the necks.

Under a stream of argon, the distn setup was removed, and the condenser fitted between the flask and the claisen. The setup was purged with H2 3 times.

Reduction of the unsaturated ketone

The unsaturated ketone was introduced in a schlenk, and 30mL distilled toluene were added. Not all the ketone dissolved, so ~5mL AcOEt were added to acheive complete dissolution. The very light yellow solution was degassed 3 times, and transfered to the reduced catalyst by canula. The system was briefly purged with H2, and the cylinder refilled.

The flask was heated to 90°C in an oil bath, and vigorously stirred under H2 atmospher for 24h, withdrawing samples with a a syringe evry 6h. After 24H, the mixture had taken a green colour.

Unfortuanly, TLC revealed that no reduction had taken, not the slightest little spot wher ehte saturated ketone should ahve been... No alcohol, unsaturated alcohol, just a tiny un-eluted spot from condensation products I guess.....

I'm not sure about the reason for this complete inactivity of the catalyst. I can only suppose the kind of silica is truely determinating... Most of the articles mention "fumed silica", I never thought it would have such different properties from chromatographic silica... IIRC, chromatographic silica is prepared by acidification of sodium silicate, or hydrolsyis of Si(OCH3)4, while pyrogenic silica is prepared by combustion/hydrolysis of SiCl4. Which properties one has that the other one hasn't is behond me, but I thinkit has something to do with the stabilisation of copper hydride species.
I have written to Mrs. Ravasio asking her if she has encoutered similar problems with different grades of silica...

Until then, I will start looking elsewhere, NiB catalyst to be precise. These could be easily made from Ni salts and NaBH4,a nd are said to be very active, non-pyrophoric selective catalyst. An improved caatlyst can even be prepared from used NiMH batteries! the variosu lanthanes, Cobalt, Mn species present exhalte the reducting properties.. Until then, back to paperwork...


Hydrogenation catalysts from used nickel metal hydride batteries
Mark R. St J. Foreman, Christian Ekberg and Arvid Ödegaard Jensen
Green Chem. 2008, 10, 825 - 826,

A synthesis of a safe and effective hydrogenation catalyst has been developed with used nickel metal hydride electrical cells as the starting material.

availble at the ref forum.

Barium - 28-9-2008 at 07:50

Nice work Klute!

Even if you didn't get the result you were hoping for you still got some valuable experience and that is priceless.
I haven't had any success with any of the "cheap n' easy" versions of the classic catalysts. The Raney type (RaNi, RaCo, RaFe, RaCu) and the precious metal
catalysts are, so far, the ony ones which have behaved as supposed. Urushibara nickel, nickel boride, cobalt boride, you name it. I've tried them all
and all have failed. But I might just be a world class bum when it comes to prepare them. Who knows?

[Edited on 28-9-2008 by Barium]

Klute - 28-9-2008 at 08:39

Thank you Barium, I am very honored.

Would you care elaborating on your experience with metal borides? Did you prepare the collodial catalyst? or supported/polymer-protected? in water, or EtOH?

I am going to purchase some NiSO4.7H2O for preparing nickel complexes anyway, so might just aswell give it a try. The PEG-protected and Mg(OH)2-supported catalyst looked very promising, but so did the Cu/SiO2... i know that the Cu/SiO2 when correctly prepared works well, some colleagues have used commercial 30% for dehydrogenations with great results. I guess it's the quality of silica that counts, and pyrogenic silica is expensive and cancerigen, so it ruins the point of getting easily made, cheap and safe catalyst somewhat..

Here are some related refs:
Colloidal nickel boride on rare earth oxides for hydrogenation of olefins
Yu-Lin Jiang 1, Xue-Yun Wei, Shou-Ping Tang and Liu-Bin Yuan
Catalysis Letters; 34 (1995) 19-22
available at the ref froum

An extremely active and colloidal nickel boride was prepared by using rare earth oxide as a
support in the presence of polyethylene glycol (PEG) at room temperature which could act as
a catalyst in the hydrogenation of olefinic compounds, such as 4-(41-hydroxyphenyl)-3-buten-

Preparation and catalytic activity of colloidal nickel boride dispersed in ethanol
Yukimichi Nakao and Shoei Fujishige
Chemistry Letters; (8)8, 995-996 (1979)

Colloidal nickel borides in ethanol were prepared by the reaction of nickel(II) chloride with sodium borohydride in the presence of a polymer like poly(vinylpyrrolidone). The colloid was effective for the hydrogenation of acrylamide at 30°C under an atmospheric hydrogen pressure.

A highly active supported catalyst for olefin hydrogenation from collodialNickel Boride
Yukimichi Nakao
Chemistry Letters; (7)11 , 997-998 (1982)

Supported catalysts, which were prepared from colloidal nickel boride by immobilizing on inorganic substances such as Mg(OH)2, exhibited higher activity for olefin hydrogenation than a sol-type catalyst of colloidal nickel boride protected by polyvinylpyrrolidone.

Looks very promising, especialyl if NiMH batteries can be used as starting material!

[Edited on 28-9-2008 by Klute]

smuv - 28-9-2008 at 18:41

Before giving up it might be worth following the procedures outlined in literature more closely...especially catalyst loading, this seems to be important for even common hydrogenation catalysts.

Although, I am a little suspicious of this catalyst based upon the fact that this research seems to be done by a small group of individuals; all the papers you referenced contain at least 1 common researcher.

Nice writeup.

[Edited on 9-28-2008 by smuv]

DJF90 - 28-9-2008 at 23:18

I'm slightly confused, so I just want to check something... You are hydrogenating your substrate yes? But you say

some colleagues have used commercial 30% for dehydrogenations with great results

Is that right? Because I think it's either a typo ( incrediably likely compared to the other option I'm about to propose:P) or you're using a DEhydrogenation catalyst for hydrogenation?

Klute - 29-9-2008 at 02:27

Cu/SiO2 is pretty commonly used in the industry, so I have no doubt it works.
It can be used as a hydrogenation AND dehydrogenation catalyst depending on the conditions (just like palladium for example): it can also be used as a CTH catalyst (with IPA, dehydrogeantion of IPA to acetone, and hydrogeantion of an substrate, or hydrogenation of acetone and dehydrogenation of a substarte for example).

I have contacted to the author, N. Ravasio, which replied to me very quickly. She confirmed that pyrogenic silica is not required to have an active catalyst, but her guess is that the phenol interfers with the freshly reduced, reactive copper metal. I wil try using an alkyl ether, or using straight benzalacetone (which they have succesfully reduced)

The catalyst loading used was that of the procedure in the article, the only difference was that soem AcOEt was added to acheive complete dissolution of the substrate. Mrs Ravasio thinks AcOEt can slow the reduction. She has been helpfull, and I must say I am rather impressed as most of the authors I have already contacted when failing their procedures simply never answered or didn't care about my results, blaming bad lab technic.

I will use the remaining prepared catalyst with other substrates, but wil also start working with NiB catalysts.

News to come

[Edited on 29-9-2008 by Klute]

Barium - 13-10-2008 at 19:56


I have prepared both P1 and P2 nickel boride in different ways. P1 was prepared in the usual way by adding 1M aqueous sodium borohydride with powerful stirring to 0.5M aqueous nickel(II)chloride. I tried it immediately in both a stirred hydrogenation vessel at about 8 bar pressure and in a CTH reaction at STP using potassium formate as the hydrogen donor.

The P2 nickel boride was prepared trying EtOH, diglyme and (if I remember correctly) N,N-dimethylacetamide as solvents. The P2 catalyst made in these solvents was tried in the same reactions as the P1.

If I remember correctly the substrates in the hydrogenations was 1-(2,4-dimethoxyphenyl)-2-nitroethane and 1-(5-methoxy-1H-indol-3-yl)-2-nitroethane.
In all cases the result was crap, nada, null! As a result of this I never tried nickel boride with any other substrate.

Klute - 14-10-2008 at 09:49

Ah, but I don't recall any mention of nitro grousp being reduced by NiB... Did you read anything ont he subject, or did you just assume that it would work seeing that NiB catalyst are often compared to Pd/C or Raney Nickel?

I'm going to try the Cu/SiO2 reduction on methyalted phenylbutenones, and am still waiting for my nickel chloride has Acros were out of stock lately.

I will keep you informed when I get things started. Didn't you trt reducing the nitroalkenes to nitroalkanes?

Barium - 14-10-2008 at 15:39

D. E. Nichols, Synthesis of alpha-Alkyltryptamines, J. Org. Chem., 51, 4294-4295 (1986)

stoichiometric_steve - 15-10-2008 at 00:39

Originally posted by Barium
In all cases the result was crap, nada, null!

Same for me. I much prefer using NaBH4 and CTH in sequence.

Barium - 15-10-2008 at 08:14

Steve, which substrate have you tried nickel boride on?

Klute - 15-10-2008 at 10:03

Ok, I've finally bought some NiSO4.6H2O as the chloride was taking too long to getin stock, I will start some hydrogenations next week. I will start with phenolic phenylbutenones, and then maybe try out some alcenes, and might give a try with unsaturated nitro compounds, but from you guys experiences, I'm not expecting much out of it. I will surely prepare the NiB supported on CaCO3, and eventually polymer-protected. This eems to have quite an influence on the absorption rate.

kmno4 - 20-10-2008 at 07:54

Cu/SiO2 sounds nice....
But I see your reduced catalyst and I do not see any metallic Cu in it. I saw reduction powdered CuO by H2 and black material turn into bright-red one. I think your catalyst should behave similary

Zn/H2SO4 is not good solution, because of traces H2S in H2 stream. I would use Al/NaOH (currently I am building electrolyzer for H2 generation, pure and wasteless way for hydrogen).

reduced Cu on SiO2 should be deep violet color, not bright Cu as I though.

[Edited on 21-10-2008 by kmno4]

stoichiometric_steve - 20-10-2008 at 09:31

Originally posted by Barium
Steve, which substrate have you tried nickel boride on?

Not allowed to say ;) I'd much rather use Zn/H+ any day...

starman - 20-10-2008 at 17:05

Originally posted by stoichiometric_steve
Originally posted by Barium
Steve, which substrate have you tried nickel boride on?

Not allowed to say ;) I'd much rather use Zn/H+ any day...

could you post some details over on the zinc thread?

stoichiometric_steve - 20-10-2008 at 23:17


If you were truly interested in the matter you would have made use of the search engine of the forum.

I have long ago laid out the conditions for a real one-pot reduction of nitroalkenes using NaBH4 and Zn/H+ in sequence (work based on Bandils posts at the Hive).

FrankRizzo - 21-10-2008 at 00:35


Fumed silica can be found commercially as product called Cab-O-Sil. Taxidermy supply houses usually carry it.

Barium - 21-10-2008 at 03:34

Originally posted by stoichiometric_steve
Originally posted by Barium
Steve, which substrate have you tried nickel boride on?

Not allowed to say ;) I'd much rather use Zn/H+ any day...

Can you say if it was a phenyl-2-nitroethene, phenyl-2-nitroethane, phenyl-2-nitropropene or phenyl-2-nitropropane? I dont care about any substitution patterns on the ring.

stoichiometric_steve - 21-10-2008 at 09:31

Ba: the latter.

Klute - 23-10-2008 at 03:05

Thank you for the comment KMnO4. I too was pretty surprised byt he color, but I just considered thatt he low catalyst loading gave that color. I am pretty sur ethe copper has been reduced, as there was the theorical amount of H2 absorbed, no more, no less, and it was very rapid. I will try out new variations, using non-phenolic substartes pretty soon.

Communications with the author revealed that fumed silica is not at all mandatory, and that excellent results where obtained with chromatographic silica, although the catalyst has a stronger acidity which can cause some condensations etc with delicate substrates (cyclisation of b-ionone). but lower catalyst loadings still give perfect results with most substrates.

bfesser - 3-12-2008 at 12:34

I'm curious. Did you use acidic, neutral, or basic silica gel? Also, do you think it would be possible that your technical grade nitric acid contained metal ions that could have poisoned the catalyst?

[Edited on 12/3/08 by bfesser]

Klute - 3-12-2008 at 13:57

I used neutral chromatographical silica gel, well it has a certain acidity. The nitric acid has never posed any problems before, and even if there would be some metals, it would only be very small traces...

I have contacted the main author of the series of publication, and she recons the problems comes from the phenolic substrate: the very fine Cu metal is very reactive, requiring absence of water, so changes are it's the phenol function poisoining the catalyst.. I was going to alkylate the substrate and try the reduction again, aswell as trying out the reduction of benzylidenacetone, a reaction N. Ravasio et al have done, to compare the results with the same substrate, and see if the preparation of the catalyst (type of silica, dilution, etc) has a major influence on the selectivity and yields, but I cannot work on this anymore. Feel free to try it out! It would be very interesting to see how this goes

Jor - 3-12-2008 at 14:02

Klute, when will your lab be up running again? You already working on your hood? ;)

bfesser - 3-12-2008 at 15:08

I've been wondering if it would be possible to use L-ascorbic acid to reduce the copper instead of hydrogen (skipping the calcining step altogether) and then to dry the catalyst in vacuo. Of course, the L-ascorbic acid would have to be eluted from the silica prior to drying. Do you think this would work?

Klute - 4-12-2008 at 00:18

@Jor: Unfortunaly, not in any close futur, my lab is packed in boxes, 1000km from where I now live (14m2), so no more personal lab work until easily 6-12month.. Sigh..

It's a pity, I had started to collect some nice elements for the hood, including a large 180x110cm large window pane, some porcelain panes for the bench, a N2 trap and dewar, etc

But I'm going to be more than busy at work, I will be working in two seperate teams that have been waiting for another member since at least 2 years! So plenty of things to do...

@Bfesser: Well, even if I guess some metalli copper will be obtained, I think it will be no where as active. Indeed, the catalyst is very active because it can form copper hydride in a stabilized form, that will exist long enough to be able to reduce the substrate. Using ascorbic acid will surely give a less finely divided metal surface, and perhaps not as organised (apparently the Cu is formed as largish (at a microscopic scale) cristallites that are necessary to complete the adsorption-reduction-desorbtion cycle. Also, chances are copper hydride will react with the ascorbic acid function, etc There is a very complete article on the preparation of coppe rhydride on various supports, which has some very valuable info concerning the first steps in the reduction, with lots of complete data. I will try to find the ref, I thinkI left the printed paper at my old town.

ANyway, It wouldn't be possible to elute the ascorbic acid from the catalyst, as after reduction the catalyst needs to be protected form traces of oxygen, so unless you directly transfert the catalyst to a degassed column via schlenk technics, and elute with degassed solvents, the catalyst will be ruined or at least partially desactivated IMHO, no worth the effort.

A good alternative would be using IPA a a H2 donor in CTH condiitons, surely other donors can be used too! But H2 is still needed to reduce the catalyst, and I"m pretty sure calcination is required to obtain an active catalyst. I'm not familiar enough with the theory surround this, but I have seen that in nearly all metal SiO2- or Al2O3- supported catalyst preparation, there is a calcination, I guess to produce metal silicates and have more than just an adsorbed metal, that will leach off gradually, but a truely bonded metal. Even the reduction requires miniam temps to give an active catalyst, most of the time above 300°C...

So Ni borides do look a more practical alternative, provided they work, and with which substrats..

Barium - 4-12-2008 at 07:46


If I ever find my silica gel I'll try to make the same copper catalyst using sodium borohydride in MeOH instead of dihydrogen at elevated temperature for the last step.

Outer - 4-12-2008 at 09:58

Is it possible to prepare the same catalist by adding water solution of CuSO4 to solution of Na2SiO3 ???

Klute - 4-12-2008 at 10:31

@ Barium: that might indeed be worth a try. But I think you will obtain Cu boride, which could be a perfectly suitable hydrogenation catalyst. there isn't much in the litt on this compound...

@Outer: I don't think there would be any advantage in forming the silica in presence of a copper salt, as most will stay in solution, and you would need to add lots of NH3 and then dilute to a huge volume before you can precipitate the hydroxide/oxide.. It would be more reasonable to just form the silica, wash and filter it, then add the copper complex.
In any case, i think adding the Cu 2+ salt to a solution of Na silicate will form insoluble Cu silicates, isn't there a demonstration where various transition metal salts are added to a silicate solution and it forms colorfull trailings?

Outer - 4-12-2008 at 10:55

Somewhere I read about using of sodium hypophosphite (NaH2PO2) to reduce Cu(2+) salts to metal copper. May be, it can be used instead of H2 or NaBH4.

About insoluble copper silicates. As I know, CuSiO3*x H20 that forms in this reaction, is a mixture of Cu(OH)2 gel and aqueus Silica gel. May be, after reducing, it may be useful as a catalist?

[Edited on 4-12-2008 by Outer]

Klute - 4-12-2008 at 12:00

Well, it could be worth a try. I am a little sceptical I must admit, although copper metal will surely be formed, it might not have the catalytic properties the calcined, H2-reduced catalyst has. I don't think you can reduce it in aqueous conditions and still expect copper hydride to form.

The silicate method could work, but you will have to add more silica to obtain a suitable loading. Also, the fact that the copper salt will immediatly precipitate will surely not give a good dispersion on the surface of the silica, but large agregates. It could be possible to gradually add a dilute sodium silicate solution to a suspension of fine silica gel in a dilute copper salt solution, gradually precipitating the hydroxide/silicate on the surface of the silica...

Nicodem - 5-12-2008 at 01:23

Originally posted by Klute
Well, it could be worth a try. I am a little sceptical I must admit, although copper metal will surely be formed, it might not have the catalytic properties the calcined, H2-reduced catalyst has. I don't think you can reduce it in aqueous conditions and still expect copper hydride to form.

There is a paper where the NaBH4/CuSO4 system is used in H2O/EtOH solvent (if I remember correctly). A brown precipitate immediately forms after adding CuSO4 to NaBH4. This combination is claimed to reduce a some functional groups that NaBH4 alone can't (like the nitro group, for example). I would imagine some highly active catalytic copper or copper hydride could be responsible for this change in borohydride chemoselectivity since borane formation is ruled out due to protic solvent conditions. I don't have the reference here, but I guess you can find it (it is quite possible the paper was already uploaded somewhere around this forum).
Of course, loading this active copper species on SiO2 for use in hydrogenations could prove quite possible and is certainly worth trying.

Klute - 5-12-2008 at 01:46

yes, I remeber some discussion on this, I think it was Isomeric Fred that tried out the reaction with some nitro compound and got satisfying results after a little optimization. It would be nice to compare the selectivity between Cu boride/hydride and Ni boride.

stoichiometric_steve - 5-12-2008 at 01:58

Originally posted by Klute I think it was Isomeric Fred that (...) got satisfying results after a little optimization.

Nope, he didnt. I was also pretty interested in that but as of late, i came to the conclusion that all M+/BH4- combinations that claim reductions which NaBH4 alone won't do on its own are either very picky or unreliable.

Klute - 5-12-2008 at 02:37

Ok, thanks for clearing that out. A pity, though..

Barium - 5-12-2008 at 05:56

In Tet. Lett. 1986, vol. 27, No. 10, pp 1205-1208 they compare a Cu2+/borohydride-system with the more well known Co2+ and Ni2+-systems. They also claim the active species to be a copper boride, which I personally doubt.
In Synth. Comm., 1989, 19(17), 3047-3050 a Cu(I)Cl/KBH4-system is evaluated for the reduction of aromatic nitro groups and found to be superior to Ni2+ and Co+2/NaBH4-systems. Nothing is mentioned about the active copper species though.

[Edited on 5-12-2008 by Barium]

[Edited on 5-12-2008 by Barium]

solo - 5-12-2008 at 07:27

Reference Information

Cu2+/BH−4 reduction system: Synthetic utility and mode of action
J. A. Cowan
Tetrahedron LettersVolume 27, Issue 10, Pages 1205-1208, (1986)

Cu2+/BH−4 offers a mild, method of reduction for aromatic and aliphatic tertiary nitro groups. Its mode of action has been studied, in comparison with related reagents, by deuterium isotope experiments.

Attachment: Cu2+:BH−4 reduction system- Synthetic utility and mode of action.pdf (175kB)
This file has been downloaded 1322 times

NICOLERAV - 7-10-2010 at 00:34

I would like to note that we carried out a couple of tests on the selective hydrogenation of 4-(4'-hydroxy-3-methoxyphenyl)but-3-ene-2-one to Zingerone and 4-(4'-hydroxyphenyl)but-3-en-2-one to Rheosmin by using Cu/SiO2 as already described for other -unsaturated ketones[1].
The reaction carried out by klute probably failed due to the use of AcOEt as solvent. Actually we have some evidences that these kind of esters lead to a poisoning of the metal centres, thus inhibiting the hydrogenation activity. In order to use solvents suitable for the substrates, but compatible with the catalysts we employed a mixture of toluene and 2-propanol with 4-(4'-hydroxy-3-methoxyphenyl)but-3-ene-2-one and pure 2-propanol with 4-(4'-hydroxyphenyl)but-3-en-2-one.
We used the same catalyst over silica prepared by klute according to the procedure described in Tetrahedron Letters [2], under 1 atm of H2 at 80°C observing in both cases complete conversion of the substrate after 1.5 h and high selectivity in the corresponding saturated ketone. The reaction mixtures were separated from the catalyst by simple filtration and raw reaction mixtures characterised by 1HNMR, comparing the spectra with those recodered for the references sent by klute.

Hydrogenation of hydrogenation of 4-(4'-hydroxy-3-methoxyphenyl)but-3-ene-2-one in toluene/2-propanol gave after 1.5 h 94% zingerone. Spectrum of raw reaction mixture available.

Experimental conditions:
Catalyst prereduction- The catalyst was activated before use by treatment at 270°C in air for 20 min, under reduced pressure at the same temperature and then under H2 at the same temperature by removing the water formed by the reduction under reduced pressure. Reaction conditions: 100 mg cat (8% Cu), 100 mg substrate, 1 atm H2, 90°C, magnetic stirring-

*In the GC-MS analysis the saturated ketone is the only product. The 1HNMR of the raw reaction mixture shows some impurities but seems to be better respect to the reference sent by Vincent .

Nicoletta Ravasio

[1] N. Ravasio, F. Zaccheria, M. Guidotti, R. Psaro, Topics in Catal. 27, 2004, 1-4;
N. Ravasio, F. Zaccheria, P. Allegrini, M. Ercoli, Catalysis Today121, 2007, 2-5
[2] N. Ravasio, M. Antenori, A. Gargano, P. Mastrorilli, Tetrahedron Lett. 37, 1996, 3529-3532

Nicodem - 7-10-2010 at 07:14

Thanks for reporting your findings and taking the time to check your reduction system on this substrate. Klute has not been around in the last few months, but I'm sure he would appreciate.
Your catalyst seems very useful for certain reductions, but preparing it just to test if it is able to perform a desired reduction is a bit annoying. Are there any chances of it becoming commercially available? I don't know how much interest there would be in general, but I'm sure I would order some if it was made available trough the common chemical companies. Perhaps you should check if there is any company willing to manufacture it? Is the prereduced, ready for use, catalyst stable for storage and still maintains its activity?

kmno4 - 14-10-2010 at 13:57

There is very similar catalyst being in use in chemical industry.
It is CuO promoted with Fe/Cr (packed in steel drums). Fresh catalyst is reduced in stream of H2 to Cu.
Unfortunately, in reduced state it is very sensitive to air.
Recently we have reached more than 700 C during deactivation (with air) of used up catalyst.