Sciencemadness Discussion Board

New possible efficient and clean electrolytic hydrogenation/reduction of aromatic compounds

Electra - 11-1-2014 at 13:21

As per request I will provide a bit of reference. I am posting this post off the known 2003 discovery that Toluene can be indirectly electrochemically oxidized through the use of molecular O2 being bubbled over the cathode in an electrolyte containing V5/V4 redox couple.

Link to study

Here is another article talking about the ionization of hydrogen in an electrochemical cell, albiet, the anodic oxidation of hydrogen to H+ via the Tafel-Volmer reaction.

http://link.springer.com/chapter/10.1007%2F978-1-84800-936-3...

Electrochemistry is an underexplored field and has a lot of potential for clean, efficient, and cheap reactions. In Electrochemical reactions an electricity source is used to provide current and voltage and as a result electrons will flow through the electrochemical system. This will facilitate various reactions to happen as the electrons flow through the circuit and the overall net electrical charge of the system attempts to balance itself out. The following idea will be focusing on the use of molecular H2 being bubbled over the cathode in a divided cell to produce Hydride anions, which can then react with organic substrates in the solution to reduce and hydrogenate them. The substrate can also be reduced at the cathode itself and then be hydrogenated. The reaction can be limited strictly to the reduction of H2 to 2H- by controlling the electrical overvoltage of the cell by adjusting the current density.

Most electrochemical reductions of aromatic compounds involves reducing the substrate in an acidic environment. The usual mechanism would involve the substrate being reduced at the cathode and then gaining hydrogen from the donation of the acid in the solution. Sulfuric Acid is commonly used in excess as it is an effective electrolyte as well as proton donor. The big downside to this is the huge excess required, and the messyness of cleanup. Excess of sulfuric acid must be used to account for protons donated, resultant bases that get converted into sulfate salts, and to maintain the electrolyte. The neutralization of sulfuric acid is not a fun one.

Theoretically in a divided cell with an unreactive electrolyte hydrogen gas can be bubbled over the cathode to form Hydride (H-) ions/Hydrogen Anions, this in the presence of the substrate. What results is a solution highly saturated in hydrogen, as well as hydride ions. The hydride ions should be able to reduce and hydrogenate the substrate as a side reaction, while the substrate can also be reduced at the cathode, and then react with molecule H2 in the solution. This is theoretically a very clean reduction & hydrogenation happening via 2 pathways. A redox couple may be able to be used to increase the speed, efficiency, and overall yield of the reaction.

The advantage of this is that no acid needs to be neutralized at the end and extraction can take place almost instantly. After extraction the electrolyte can be reused. By bubbling hydrogen gas over the cathode a very reductive atmosphere can be initiated, without hugely messy/exothermic reactions one might find with the use of metal-hydrides. Another obvious advantage is that molecule H2 is gas form is a very common industrial product and is readily attainable anywhere in the world.

Disadvantages include the required use of a fume hood as hydrogen gas is very flammable.

[Edited on 11-1-2014 by Electra]

[Edited on 11-1-2014 by Electra]

UnintentionalChaos - 11-1-2014 at 13:46

What the fuck are you talking about. I feel like I'm reading some sort of drivel posted by Anders Hoveland. You can run all the thought experiments you want, but sometimes the world just doesn't work like you think it does. Basically, provide references/experimental data or stop clogging up the forum with crap.

Electra - 11-1-2014 at 13:53

Is there a particular part of this that would not work?

This doesn't have to be complicated.

H2 molecules are electrolytically reduced to Hydride Anions. Hydride Anions can react with organic molecules to both reduce them and hydrogenate them. This reaction is basically a LAH or NaBH4 reduction without the transition metal to provide the hydride anion. Instead the Hydride anion is generated electrochemically. I'm not here to start trouble but this is not hard to understand.

Edit:

If you're looking for a reference I am basing this off the known ability to electrochemically oxidize in high yields toluene -> Benzaldehyde by bubbling molecular oxygen over the cathode in the presence of a V5/V4 redox couple. Here is the paper.

http://chemistry.mdma.ch/hiveboard/rhodium/pdf/toluene2ba.va...

There is a lot of electrochemistry that is very unexplored. The field in general is underexplored. There are a ton of industrial processes that could be done much more cheaply, cleanly, and efficiently if done electrochemically. The recent 2003 find of electrochemical oxidation of toluene -> Benzaldehyde backs this. The use of molecular gas in these reactions is very unexplored and has a lot of potential, has proven by the previous study.

While my post is only theory, there is no reason why it shouldn't work. The electrochemical reduction of H2 to 2H- is a very basic reaction, and I shouldn't need to spell that out.


[Edited on 11-1-2014 by Electra]

elementcollector1 - 11-1-2014 at 14:26

Do you have any idea what it takes to ionize hydrogen? At the required electrical power, your product would combust, your glassware would melt, and your whole apparatus would promptly shatter due to pressure buildup from hydrogen.
While your post is only theory, you seem to lack the understanding of why neon sign transformers exist, as well as common sense.

Electra - 11-1-2014 at 14:42

Quote: Originally posted by elementcollector1  
Do you have any idea what it takes to ionize hydrogen? At the required electrical power, your product would combust, your glassware would melt, and your whole apparatus would promptly shatter due to pressure buildup from hydrogen.
While your post is only theory, you seem to lack the understanding of why neon sign transformers exist, as well as common sense.


The electrochemical cell is not in an enclosed environment so no pressure would be built up. Hence the need for a fume hood. The energy required to break/separate the bond between molecular H2 is actually much less than the energy required to reduce the bond between, lets say for instance a R-NO2 molecule. The reduction of H2 would inevitably occur without much energy release, as energy is being added in the form of electrons from the power supply. The goal of this is not to build up large amounts of pressure, which could/would indeed combust, but to create a catholyte environment that is saturated in both molecular H2 and H- Anions.


On a side note I do intend to try this in a about a week or so when I get my small scale power supply. I will be experimenting with very small quantities 1-2g, and the reaction should take no more than 10 minutes.

Edit:

See the great thing about electrochemical cells is that you can directly control just how much energy is being dumped into the electrolyte by controlling the current density. By controlling the current density you can control which reactions occur in the solution and which don't, by having an understanding of the energy required for each reaction. The primary reactions are going to be occuring at the surface of the electrode, and this is also where the hydrogen will adhere to and become reduced.


Here is another article talking about the ionization of hydrogen in an electrochemical cell, albiet, the anodic oxidation of hydrogen to H+ via the Tafel-Volmer reaction

http://link.springer.com/chapter/10.1007%2F978-1-84800-936-3...




[Edited on 11-1-2014 by Electra]

Galinstan - 13-1-2014 at 06:01

Firstly you havn't given any evidence to support that hydrogen can be reduced to the hydride ion at the cathode at any voltage let alone the 4v you have suggested.
And secondly assuming the principle is sound which im fairly sure it is not, you can't just expect any old organic molecule to be reduced by this set up electrochemical cells are normally designed specifically for a certain reaction as a reaction at one voltage may not will not work for all similar reactions in different compounds.

Organikum - 13-1-2014 at 06:29

Quote: Originally posted by Electra  

......
This doesn't have to be complicated.
........

There is a lot of electrochemistry that is very unexplored. The field in general is underexplored.
.........


Organic electrochemistry is seen as underestimated by those who never tried it, those who tried it tend to see it the other way round.

Just think of the dreaded Kolbe reaction. Oh my.

That the field is unexplored is just utter bullshit, go to scribd.com and download books over books on the topic.
Not that they will make you any wiser.


/ORG

Templar - 20-8-2014 at 16:11

Shut down

Lol

Just post some refs, make a writeup, etc

Jus do it mayn

FireLion3 - 22-8-2014 at 12:53

Some of the people here are remarkably rude. Electra, your idea is not a new concept, and I am sorry to say you didn't invent it.

This kind of hydrogenation is common practice and certainly works with the right cathode material. Countering what elementcollector1 said above, hydrogen can be electroreduced to hydride if the right cathode material is present. Most transition metals can adsorb hydrogen allowing it to be easily reduced to hydride. Using special cathodes or plated cathodes of metals such as platinum, palladium, nickel, and several of the other transition metals in electrolysis is usually referred to as electrocatalysis. Almost all of the transition metals have "hydrogen storage" capabilities, and evidence of such can be found online.

Electra, bubbling hydrogen over the cathodes is pointless hazard. With the right cathode and water present in the system, water is be reduced and the hydrogen are then adsorbed to the cathode material, and get reduced to hydride. This is a very common hydrogenation technique in electrochemical studies and I am sorry to say that you did not come up with it :p.

aga - 22-8-2014 at 15:02

i've been on Noob holiday for a week in Scotland.
Something kept bugging me, and i think it started with (this) Electra's thread.

Chemistry all comes down to electron happiness and wellbeing right ?
(jump in now all well soothed naysayers)

Electron Disassociation in benzene has been fascinating to me for some time, then i find this: http://en.wikipedia.org/wiki/Aromatic_ring_current

Whilst being personally too ignorant to say whether Electra is right or wrong, i have to agree with the OP statement "Electrochemistry is an underexplored field".

Specifically, for me, the effects of large excess or absence of electrons, and how magnetic fields affect things is extremely interesting.

Perhaps lower energy routes from state1 to stateN can be found using things other than chemical catalysts and a bunsen burner.

Particularly Sodium Benzoate -> Benzene, CO2 and Elemental Sodium seems likely.

No, i don't know either, which is where random experiments must begin.

Before anyone inadvertently farts in triumphant excitement, vacuum and no solvent.

Metacelsus - 22-8-2014 at 15:15

Quote: Originally posted by aga  

Particularly Sodium Benzoate -> Benzene, CO2 and Elemental Sodium seems likely.

No, i don't know either, which is where random experiments must begin.

Before anyone inadvertently farts in triumphant excitement, vacuum and no solvent.


If you try to write out the equations, you will see why it shouldn't work.

aga - 23-8-2014 at 00:13

Quote: Originally posted by Cheddite Cheese  
If you try to write out the equations, you will see why it shouldn't work.

It almost certainly will not work at all, especially in my hands.

Certainly a fun prospect !

blogfast25 - 23-8-2014 at 04:59

Quote: Originally posted by aga  
It almost certainly will not work at all, especially in my hands.

Certainly a fun prospect !


What's your idea though? Electrolysis of sodium benzoate? I can see why you think this might yield sodium but I can assure you it won't, at least not in aqueous conditions.

And if this was a reasonable way of obtaining benzene for such an OTC chemical we'd all be doing it ('if it sounds too good to be true etc')

Trust me, electrochemistry is far from an underdeveloped subject, quite the opposite I'd say.

[Edited on 23-8-2014 by blogfast25]

aga - 23-8-2014 at 06:40

i was thinking more of an environment where a large number of electrons are whizzing about in vacuum, and in focused patterns, rather than a glass of saltwater and a battery.

blogfast25 - 23-8-2014 at 08:30

Quote: Originally posted by aga  
i was thinking more of an environment where a large number of electrons are whizzing about in vacuum, and in focused patterns, rather than a glass of saltwater and a battery.


If they're whizzing about in a vacuum, how could they affect a molecule? No molecules in a vacuum.

[Edited on 23-8-2014 by blogfast25]

aga - 23-8-2014 at 08:53

i knew there was a flaw in the plan somewhere ;)

Maybe slightly less vacumy then, with bits in it.

blogfast25 - 23-8-2014 at 09:16

Seriously though, the direct bombardment of organic molecules with electrons of sufficiently high kinetic energy would result in unpredictable changes in the electron configuration (bonding orbitals) of the target molecules. In all likelihood that would result in a witches' brew of compounds, some fragments, others polymeric/oligomeric in nature, mostly useless junk and with anything of value possibly difficult to extract from it.

[Edited on 23-8-2014 by blogfast25]

aga - 23-8-2014 at 13:04

Fully equipped with a vast expanse of ignorance, i see it like this:

Chemistry deals with electrons, so it's electron manipulation essentially.
This is an Observed phenomenon in a reaction between 2 or more chemicals.

Therefore (ignoring all sensible arguments) it should be possible to create altered electron states in matter in other ways.

Off the top of my head, electrons will probably be involved, and we can do those.
Magnetic fields we also have.

First thought with sodium benzoate would be to use magnetism to induce the ring current effect to 'skewer' the molecules, then a huge pulsed electrostatic field on one side to snap all the Na+ off in that direction.

Scanning virtual crystal matrix made from single-electron beams to trap the Na in a similar way to how it gets trapped naturally in a disassociated electron flow.

Stuff like that.

Electron Bombardment would be like hitting it with a rock.

We could just grind it up in a pestle with NaOH, shove a flame on it, then collect the juices.

Somehow that sounds a bit like the Rock option, despite the fact that it works.

FireLion3 - 23-8-2014 at 15:29

aga the reason shooting electrons at molecules would not have the same effect as using reducing agents is because as blogfast25 said the electrons will enter random orbitals and create a mess of compounds. With reducing reagents, the manner in which the electrons interact with the molecule to be reduced is not nearly as violent and direct as an electron beam or solvated electrons.

I have thought of this too as a replacement for electrolysis. How awesome would that be, to fire an electron beam at a compound to reduce it. For this to work the technology would have to be highly sophisticated with the aspects of the electrons being very precisely controlled, and the orientation of target molecules being very precisely oriented. The electron would need to hit the exactly correct position on the molecule with the exactly correct amount of force or any number of chaotic products would result.

[Edited on 23-8-2014 by FireLion3]

aga - 24-8-2014 at 00:04

Interesting point FireLion3.

It begs the question: by what mechanism do two randomly oriented molecules align with each other in order to precisely exchange even 1 electron to/from the correct orbital ?

That implies actual physical movement, which would take a finite amount of energy, and time.

blogfast25 - 24-8-2014 at 04:52

Quote: Originally posted by aga  
It begs the question: by what mechanism do two randomly oriented molecules align with each other in order to precisely exchange even 1 electron to/from the correct orbital ?



The answer lies in collision theory. In a reagent mix, say A + B, molecules of A and B constantly collide with each other. The vast majority of these collisions are simply purely elastic, like bumper cars hitting each other on a 'dodge'm' track or pool balls on a pool table.

Occasionally a collision will be of the right type: sufficiently energetic and correct alignment and electron configuration modification can then occur: A + B = C. It's a highly statistical process.

Note that actual electron transfer only occurs in redox reactions: other reactions involve the 'destruction' of existing molecular orbitals (bonding orbitals) and the formation of new ones.

But it's somewhat pointless to generalise too much: in each reaction the devil is in the detail.

[Edited on 24-8-2014 by blogfast25]