ziqquratu
Hazard to Others
Posts: 385
Registered: 15-11-2002
Member Is Offline
Mood: No Mood
|
|
Electrochemical hydrogenation with Ni and Fe electrodes
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 3152 times
|
|
|
dapper
Hazard to Self
Posts: 66
Registered: 8-11-2006
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 282
Registered: 17-8-2008
Location: US & A
Member Is Offline
Mood: Stochastic
|
|
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
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
Member Is Offline
Mood: No Mood
|
|
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)..
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
|
|
|
brew
Hazard to Self
Posts: 96
Registered: 25-4-2008
Member Is Offline
Mood: enthralled
|
|
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
Harmless
Posts: 29
Registered: 16-8-2009
Member Is Offline
Mood: No Mood
|
|
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.
Il n'y a point de sots si incommodes que ceux qui ont de l'esprit.
François de La Rochefoucauld.
|
|
|
chloric1
International Hazard
Posts: 1142
Registered: 8-10-2003
Location: GroupVII of the periodic table
Member Is Offline
Mood: Stoichiometrically Balanced
|
|
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.
Fellow molecular manipulator
|
|
|
Sydenhams chorea
Harmless
Posts: 29
Registered: 16-8-2009
Member Is Offline
Mood: No Mood
|
|
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]
Il n'y a point de sots si incommodes que ceux qui ont de l'esprit.
François de La Rochefoucauld.
|
|
|
DerAlte
National Hazard
Posts: 779
Registered: 14-5-2007
Location: Erehwon
Member Is Offline
Mood: Disgusted
|
|
I use melted HDPE from old plastic bottles to plug the hole in terra cotta pots. It resists most chemicals...
Regards, Der Alte
|
|
|
starman
Hazard to Others
Posts: 318
Registered: 5-7-2008
Location: Western Australia
Member Is Offline
Mood: No Mood
|
|
| 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.
Chemistry- The journey from the end of physics to the beginning of life.(starman)
|
|
|
smaerd
International Hazard
Posts: 1262
Registered: 23-1-2010
Member Is Offline
Mood: hmm...
|
|
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
National Hazard
Posts: 816
Registered: 20-7-2011
Location: Asperger's spectrum
Member Is Offline
Mood: delocalized
|
|
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
Harmless
Posts: 19
Registered: 13-6-2011
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
