Sciencemadness Discussion Board

Silent discharge in preparative chemistry?

Jimmymajesty - 12-4-2015 at 14:06

Hi folks,

I am just wondering what useful chemicals could be made out of OTC chems with this method. As I understand you give energy to the molecule mainly without heating the rectants too much, it is like the socalled "microwave effect" I saw some papers on preparation of amino acids and hydrazine, but what else could be made with it?

It is completely doable with standard glassware so feel free to experiment and do not forget to post the results here!

aga - 12-4-2015 at 15:26

Please read what you typed and try again.

Your post makes almost no sense at all (maybe to you).

Bert - 12-4-2015 at 17:42

Please give a link to your source material?

I will put this thread into "beginnings", at least until you provide some background references/documentation-

Jimmymajesty - 13-4-2015 at 02:55


I do not have references, the question is what woluld be the outcome if you refluxed simple chems like ethyl acetate through silent discharge, would it decompose? Can you induce molecular rearrangements of any sort with it?

blogfast25 - 13-4-2015 at 05:05

Explain what you understand by 'silent discharge'.

If you don't have any references at all, then where did the idea come from?

Metacelsus - 13-4-2015 at 06:45

I think he means dielectric barrier discharge.

HgDinis25 - 13-4-2015 at 11:55

Dielectric Barrier Discharge is just a fancy name for Silent Discharge. There are a few papers out there, concerning the decomposition of certain gases by Silent Discharge, like the two:

I didn't understand your system, though. Are you talking about having a continuous discharge in a reflux apparatus, for gas-phase decomposition? That's not easy. If you were able to get it working, though, Ethyl Acetate would probably decompose into dozens of different chemicals.

Nicodem - 13-4-2015 at 12:05

There is very little on preparative chemistry using silent discharge reactors. It's nearly only application in academic and industrial setting is for the production of ozone. Otherwise, a similar technology found its use in the plasma reactors used for depositing materials or surface etching.
There was some research into use of (modified) silent discharge reactors for the partial oxidation of alkanes to alcohols mainly, or generation of hydrogen from hydrocarbons. There was also some interest for their use in the decontamination of trace amounts of volatile organic compounds in the exhaust gases. But there is almost nothing more complex or interesting.
The reason is probably in its limitation to vapour phase reactions and due to the limitations imposed by the reactivity and instability of cationic species formed from the compounds being ionized. Any complex substrate, like organic compounds, would tend to undergo complex fragmentation (or complete oxidation in the presence of oxygen).

violet sin - 13-4-2015 at 12:37

after reading the opening post I looked into the silent discharge research in hydrazine production. the paper I found was using reduced pressure oxidation of ammonia vapor. it stated that the hydrazine was produced exclusively in the positive column and was related to some of the other actions happening but also independent of some species entirely.
and this one has some interesting info as well,

" It has been found that sustained high yields of hydrazine may be obtained by passing a stream of ammonia through an extended glow discharge if the stream of gas is maintained under conditions of highly turbulent flow in its passage through the discharge and is eificiently cooled while it is in the discharge zone. "

interested in this one also,

" The term electrolysis is conventionally applied to chemical changes brought about by passing an electric current between conducting electrodes dipping into a liquid phase containing ions, where the changes can be satisfactorily explained by electron transfer between the ions and the electrodes. If, however, the liquid phase is itself made an electrode and an electrical glow-discharge is passed to it from a conductor located in the gas space above the surface, a completely different situation arises in which novel chemical reactions can be brought about in the liquid phase, and this process is referred to as glow-discharge electrolysis (GDE). "

looks like I might have some research and papers to request when I get time to look around more. I LOVE electrochem

Jimmymajesty - 15-4-2015 at 08:58

I finally had some time to try it out. I used 95% ethyl alcohol. Aluminum foil was wrapped around a column and a copper wire went all along in a zig-zag way inside the tube. I used a flyback transformer as a power source, switching it on without Et-OH it generated ozone as it should.

I set up the Et-OH for reflux, waited for 10 mins. Then switched on the H.V. source, the blue glow was apparent inside the tube but small to zero gas evolution could be observed (~2ml/min). I smelled inside the condenser but apart from the ozone-ish smell nothing special.

I do not really know how to do a better trial... The electric power trasferred to the Et-OH molecules was too little I think.

IMG_3658.JPG - 530kB

violet sin - 15-4-2015 at 10:49

Did you see the last link I provided? It said different effects take place when one electrode is below the surface. Could be more reactive and not too different that you would have to scrap the first setup entirely. At least worth a try I would wager

Jimmymajesty - 16-4-2015 at 12:12

Yup, I tried it out out today with Et-OH, but nothing really happened apart from after some time the ethanol started to boil. I really do not see how this could be used to make anything at all, at least with my stuff.

I did another experiment today inspired by the patent attached.

I mixed ozone and acetaldehyde gas then bubbled them into 20°C water. The gas flow was around 5ml/sec for each feed.
But again nothing really happened... I even prepared for an explosion but the ozone and the acetaldehyde did not even react. After 30mins I put some KI crystals into the water and it turned yellow, so there were some ozone dissolved but also there was a strong smell of acetaldehyde. Thought they are easily forming acetaldyde monoperacetate so I boiled the resulting liquid but not a single trace of acetic acid, just acetaldehyde, so it appears they not.

Attachment: acetaldehyde monoperacetate GB877662A.pdf (393kB)
This file has been downloaded 326 times

violet sin - 17-4-2015 at 02:28

well that sucks( scientific term lol) I had hoped to see some results of some kind.

good one with pic's and diagrams
" The effects of the third electrode on the discharge and ozone generation characteristics of a wire-plate type
nonthermal plasma reactor, with a slit dielectric barrier, have been investigated. When a third electrode is installed just
above the slit of the slit dielectric barrier, where an intense surface corona discharge occurred, it is found that a
significantly-increased ozone can be obtained, especially from a negative corona discharge. "

oxidative coupling of methane with AC and DC coronal discharge

plating in a coronal discharge
" It has been demonstrated that boron can be deposited on tungsten in a corona discharge. "

Jimmymajesty - 19-4-2015 at 06:58

violet sin, thanks for the papers.

I tried out couple of things in the last days mainly with acetaldehyde.

I mixed ozonized air with acetaldehyde and let the gases into a temp. controlled reactor.
Above 100°C a bleach like smell was indicating that something was happening still I could not really condense anything after the reactor, (after 1 hour 0,1ml of oily liquid that was flammable and strongly smelled of formaldehyde+bleach) this was at 120°C, then I went above the ignition temp. of acetaldehyde (to 220°C) but this time nothing condensed at all.

Also I tried to use ozone as a catalyst in water at 40°C. I let the acetaldehyde into the water together with ozonized air, the acetaldehyde escaped as it entered, the smell again was somewhat formadehyde-ish but I think my nose was tricked by the smell of ozone because its smell is way stronger than that of acetaldehyde.
Then I added 2 ml of saturated copper acetate into the sparger without any detectable effect. The time frame for each experiment was around 1 hr, so they either proceeded very slowly or I was doing something wrong.

It seems the thread does not deseve much attention afterall...

WGTR - 19-4-2015 at 13:58

I have experienced silent discharges in the lab before. Thankfully, I was positioned in front of the fume hood. I merely opened the sash a little wider, and no one was the wiser.

This was a topic that I found fascinating back when I was trying to synthesize liquid hydrocarbons from common materials. The silent discharge was a general area of research in the late 1800's to early 1900's, but as others have mentioned, the main application today is ozone generation.

The following reference contains several experiments and experimental conditions with the silent discharge. It seems that the procedure works better when the electrodes are as close as possible together, a few mm at most. Enjoy.