Sciencemadness Discussion Board

Electrochemical hydrogenation with Ni and Fe electrodes

ziqquratu - 25-8-2008 at 02:00

Scanning for new pracs to implement in some classes I teach, I stumbled across this article which looks like it might be quite useful to the home chemist.

Catalytic Hydrogenation of Organic Compounds without H2 Supply: An Electrochemical System
Daniela Maria do Amaral Ferraz Navarro and Marcelo Navarro
J. Chem. Educ. 2004 81 1350

Basically, they take a (sacrificial) nickel anode and an iron cathode (both of which are reusable multiple times) in an undivided cell. The cell is run at around 180mA/dm2, in an electrolyte of MeOH/aqueous NH4Cl with magnetic stirring.

With this (simple!) setup, they obtain a 92% yield of ethylbenzene from styrene, 99% yield of benzyl alcohol from benzaldehyde and 95% yield of 1-phenylethanol from acetophenone, all with current efficiencies of about 30%.

The only significant downside I see is the concentration is small - 0.5mmol of substrate in 40mL of solvent. This could probably be tweaked if the reaction was required on a larger scale, though, and the solvents are cheap anyway!

I'd be very interested in hearing the results if anyone tries (or has tried!) this method out.

Attachment: Electrochem_hydrogenation_Ni_Fe_electrodes.pdf (136kB)
This file has been downloaded 3162 times

dapper - 25-8-2008 at 04:44

In the interest of keeping the number of threads down (and because this is related to electrochemistry)
I was wondering what people who used unglazed ceramic flowerpots for their cell divider did to fill the hole that invariably exists in every flower pot bottom I've ever seen. (though I'd scavenge dividers from new auto batteries)

Arrhenius - 26-8-2008 at 12:27

Ziqquratu: Interesting article. I greatly enjoy reading that journal, but haven't seen that article. I have very little experience with electrochemical cells, and they seem quite unpopular on a preparative scale. I presume the 'current density' is calculated based on the surface area of the working electrode? Would be a fun experiment to reproduce or play around with.

Dapper: no idea... maybe some epoxy resin or silicone would do the job, as they're both pretty inert/resiliant.

Klute - 31-8-2008 at 11:17

Nice!

Maybe a anode made of plated nickel could be used? A certain layer of Ni could be deposited on a carbon or lead electrode, and regenerated after each electrolysis? Thsi would avoid using Ni metal sheets or rod, and could help recycling the Ni deposited on the cathode?

But i am still a little sceptic, considering the micro-scale, even at 10-20 mmol problems could arise as the concentration is increased (to avoid using liters of electrolyte)..

brew - 12-3-2009 at 21:59

This post confuses me, and perhaps reflects my inexperience with chem. I though if a reduction takes place in an undividied cell, then the reduced specie would get oxidised at the anode. hence the need for a divided cell which prevents this from happening. I dare say the sacrificial anode is the part that prevents this, but I am unsure as to how. Any help in understanding how an undivided cell could maintain a reduced specie, without it being ozidixed would be appreciated.

Brew.

Sydenhams chorea - 21-8-2009 at 11:22

This type of electrocatalytic hydrogenation using a sacrificial Ni anode is not uncommon, I have seen procedures using other cathodes than iron. The sacrificial anode surpasses the need for a diaphragm, as the most favoured anode reaction becomes oxidation of the metal to the anion.

Cathode surfaces of Ni have, like Pd and Pt, a pretty low overvoltage so the dominant reaction is the generation of a layer of hydrogen atoms. These are absorbed on the surface of the metal akin to regular catalytic hydrogenation.

This opposed to "straight" electroreductions, which need high overvoltage cathodes and (in most cases) a suitable diaphragm.

Scaling up should not be problematic, as far as I see the nickel anode is the most limiting factor.

chloric1 - 21-8-2009 at 16:44

Quote: Originally posted by dapper  
In the interest of keeping the number of threads down (and because this is related to electrochemistry)
I was wondering what people who used unglazed ceramic flowerpots for their cell divider did to fill the hole that invariably exists in every flower pot bottom I've ever seen. (though I'd scavenge dividers from new auto batteries)


Believe it or not dapper, I have used plumbers putty to plug the hole. I am not even sure what the composition is but it is quite insoluble in polar liquids like water and electrolyte solutions.

If you are going the terracotta pot route, you need to partially close some of the pores to get an effective cell divider. You take your pot and soak it in a solution made of equal volumes of water glass(sodium silicate) and water. Rinse then immerse in a dilute sulfuric or hydrochloric acid solution. This deposits silicic acid in the pores creating a membrane. Another option is to get into ceramics and control porousity by firing temperature. Porcelain would be the best choice as far as clays go.

Sydenhams chorea - 25-8-2009 at 01:33

For a flower pot look for the decorative type. I've seen them in all sorts of forms, little clay shoes to hang on your wall etc but also the unglazed terracotta pot without a hole in the bottom. It is meant to put another plastic pot with holes in the bottom in there, so the whole becomes more aesthetically pleasing to the average retiring old lady.

I've used above described pots succesfully as a cell divider in an acidic medium, after soaking it for some hours in dilute H2SO4. The resistance is high though and lots of generated heat will have to be coped with.

Preliminary results using Tyvek enveloppes as a cell divider looked promising. Tyvek is very resistant to acid, base en polar solvents, and is unaffected up to 100°C. Read up on DuPonts technical sheet:
http://www2.dupont.com/Tyvek/en_US/products/product_properti...



[Edited on 25-8-2009 by Sydenhams chorea]

DerAlte - 25-8-2009 at 21:14

I use melted HDPE from old plastic bottles to plug the hole in terra cotta pots. It resists most chemicals...

Regards, Der Alte

starman - 19-4-2010 at 23:23

Quote: Originally posted by ziqquratu  
Scanning for new pracs to implement in some classes I teach, I stumbled across this article which looks like it might be quite useful to the home chemist.

Catalytic Hydrogenation of Organic Compounds without H2 Supply: An Electrochemical System
Daniela Maria do Amaral Ferraz Navarro and Marcelo Navarro
J. Chem. Educ. 2004 81 1350

Basically, they take a (sacrificial) nickel anode and an iron cathode (both of which are reusable multiple times) in an undivided cell. The cell is run at around 180mA/dm2, in an electrolyte of MeOH/aqueous NH4Cl with magnetic stirring.

With this (simple!) setup, they obtain a 92% yield of ethylbenzene from styrene, 99% yield of benzyl alcohol from benzaldehyde and 95% yield of 1-phenylethanol from acetophenone, all with current efficiencies of about 30%.

The only significant downside I see is the concentration is small - 0.5mmol of substrate in 40mL of solvent. This could probably be tweaked if the reaction was required on a larger scale, though, and the solvents are cheap anyway!

I'd be very interested in hearing the results if anyone tries (or has tried!) this method out.


Sorry to revive this old thread but if someone will indulge I have a question about the cell set up in the attached paper.
It talks about measuring potential without benefit of a reference electrode by simply attaching a multimeter to the feed lines.My knowledge of electrochemistry is very elementary.Is this correct?Even if it only approximates,it would still be very useful.

smaerd - 26-5-2011 at 19:53

Hate to bump a two year old thread, at least I didn't start a new one.

http://www.youtube.com/watch?v=AWlMVgBWBzw&NR=1
Someone has a video up of this going on you-tube, no clue what they're hydrogenating or their success/failure in doing so. I think this is a great idea to build upon for at home hydrogenations.

edit and an interesting patent mentioning catalysts for a similar system - http://www.freepatentsonline.com/4526661.html

[Edited on 27-5-2011 by smaerd]

White Yeti - 27-7-2011 at 17:55

Interesting..
I've been looking for ways to make ethylbenzene from styrene, and this might be the answer. Catalytic hydrogenation is a pain -.- and the Friedel-Crafts reaction is also a pain to perform.

Thanks for sharing! I'll look into this further and possibly try this.

Thor - 28-7-2011 at 05:12

If a metal like platinum was used with a membrane, would the activity be increased? And the electrode may not be sacrificed? Would be a much cleaner alternative to Pd/C.