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Author: Subject: Cell for smallscale electroreduction of nitroalkenes
Vitus_Verdegast
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[*] posted on 12-7-2005 at 16:14
Cell for smallscale electroreduction of nitroalkenes


Introduction

Biologically active primary amines of considerable interest can be obtained by the reduction of a variety of aryl-2-nitroalkenes. These nitroalkenes can be conveniently prepared by the Henry reaction between arylaldehydes and nitroalkanes(1). Usually aryl-2-nitroalkenes are reduced to the corresponding primary amine using LAH(2), Red-Al (Vitride)(3), DIBAH(4), catalytic hydrogenation(5), or zinc or aluminium amalgams(6). These methods suffer from several drawbacks, such as the handling of hazardous reagentia, cost, availability, the acquisition of an expensive hydrogenation apparatus, use of mercury salts or the necessity of processing large amounts of metal salts. Alternative reductions are two-step methods that first reduce the double bond, commonly using borohydride(7) or 2-phenylbenzimidazoline(8), whereafter the respective nitroalkane can be reduced by a variety of metals in acidic environment(9). Obviously, next to it being more tedious, these methods carry at least one of the drawbacks previously stated.

The electroreduction of nitroalkenes is a well-known process, and the literature on this dates back to the beginning of the 20th century. Especially interesting is the procedure of Slotta and Szyszka, where 3,4,5-trimethoxynitrostyrene is electrochemically reduced in a divided cell to mescaline in 77% yield(10). The authors used porcelain as the cell-divider. A recent paper describes a millimole scale preparation using glass frit as the cell divider, obtaining primary amines in fair yields(11). More recently, encouraging results have been made using a PC power supply as the current source(12).

The following setup is presented as being perfectly suitable to reduce small amounts of said nitroalkenes to the primary amines in moderate to fair yield.



Preparation of the cell

An unglazed clay flowerpot with an upper diameter of 8 cm and height of 7 cm was scrubbed inside and outside with medium coarse sandpaper. It was washed well with water and allowed to stand a night in a dilute sulphuric acid solution.

From a clean HDPE bottle, having about the same diameter like the flowerpot, the bottom was cut off at about 7.5 cm height and at the top a small hole was cut. This will serve as container for the anolyte, and inside the flowerpot comes the catholyte.

This is basically the design: :)




Volume used inside the flowerpot is maximum 100 ml, to allow for some breathing room. The cell is usable for reducing small amounts of nitroalkenes, up to 10 grams. Connections are made directly from the copper wire to the electrodes. The copper wire is rigid and can carry high current without problems (mine is 2.5 mm diameter and can carry a maximum of 20 A). Care must be taken that the copper connection to the anode is outside the hole, as contact with the anolyte will dissolve the copper fast.

The cathode and anode are both rectangular sheets of lead of about 20 cm2 surface area (10 cm x 2 cm). They are first scrubbed and defatted with acetone, then cleaned electrolytically by putting them in the above divided cell, both compartments filled with dilute sulphuric acid, and putting a charge (12 V) through them forwards and backwards, about half an hour each time. The one covered with a brown layer of PbO2 will be used as the cathode.


Practical example of a nitroalkene reduction


https://synthetikal.com/synthforum/viewpost.php?p=8273

(EDIT: I replaced this part to synthetikal, as it discusses the preparation of a controlled substance.)


Judging from this email, cooling of the substrate seems to be the main problem, as considerable heat is evolved during the reduction. Good stirring of the catholyte is essential.

I'm sure that there could be many improvements made. Your input would be very appreciated.


References

1 & 2 For multiple examples of the Henry condensation of arylaldehydes and nitroalkanes, and the nitroalkene reduction using LAH, consult 'PiHKaL' (Alexander Th. Shulgin, Transform Press).
http://www.erowid.org/library/books_online/pihkal/pihkal.sht...

3 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/red-al.h...
https://www.synthetikal.com/Rhodiums_pdfs/chemistry/red-al.n...

4 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/phenethy...

5 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/ns.hydro...

6 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/znhg.alh...

7 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/nitrosty...

8 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/phenylbe...

9 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/nitro2am...

10 J. Prakt. Chem. 137, 339 (1933)
https://www.synthetikal.com/Rhodiums_pdfs/chemistry/electrom...

11 https://www.synthetikal.com/Rhodiums_pdfs/chemistry/electror...

12 https://www.synthetikal.com/synthforum/about774-.htmlall


[Edited on 13-7-2005 by Vitus_Verdegast]

[Edited on 13-7-2005 by Vitus_Verdegast]

[Edited on 13-7-2005 by Vitus_Verdegast]
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[*] posted on 29-3-2006 at 00:19


Hi Vitus, sorry to drag up such a (relatively) old thread. I am interested in what you've done above, and wondered if perhaps you could provide the experimental details that you removed from this board. I've attempted to find a copy of the post to synthetikal, but have been unsuccessful!

If you dont feel that it would be appropriate to post it to this board, I would be most appreciative if you culd PM it to me. Or, if you were so inclined, perhaps the details of the actual substance reduced/produced could be omitted?

Thank you in advance!
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[*] posted on 30-3-2006 at 09:57
flowerpot electroreduction apparatus


Dear ziqquratu,

I'm afraid I've lost the experimental details posted on synthetikal. If I would have known what I know now, I would not have posted it there in the first place. Of course I have not made any controlled substance myself without a proper license. The information was obtained from an anonymous e-mail I received and subsequently posted with the author's permission. Whether this author possessed the necessary license was not clear from his e-mail. The substrate he used was, if I remember correctly, 3,4-methylenedioxyphenyl-2-nitropropene.

However, you are welcome to ask any question you might have concerning the flowerpot electroreduction cell. I can assure you that the apparatus can be succesfully employed on a phletoria of nitroalkenes. Common substrates can be (but are not limited to) beta-nitrostyrene, 3-methoxy-4-ethoxyphenyl-2-nitropropene, 1-nitrocyclohexene etc...

It is important that you try small amounts of substrate first, a couple of grammes, to see how well your cooling system handles it. Strong magnetic stirring of the catholyte suspension is essential, as to maximize contact of the nitroalkene with the cathode surface.

The catholyte can be a solution of 4 parts acetic acid, 4 parts ethanol (or isopropanol) and 1 part conc. aq. HCl (parts are by volume). A 50% H2SO4 solution can substitute for the hydrochloric acid. For the anolyte dilute sulfuric acid is used, a 10% solution will do.

You will need to deliver 8 F per mole of nitroalkene. Best results are obtained with a current density of 200 - 400 mA/cm², although according to the literature it should be possible to go much lower, down to 50 mA/cm².

As mentioned in my first post, I must again stress the importance of pre-coating your cathode with a layer of PbO2. As this is reduced, a spongy layer of lead will form which is vital to obtain the required high overvoltage for this reduction. Small amounts of certain metal contaminants on the surface can lower the overvoltage potential of the lead cathode drastically. Using this method hardware-store "roofing-quality" lead sheet can succesfully be employed as cathode material. Also, note that your cathode can best be used only once. For each new reduction you will need to use a freshly prepared cathode.

After the 8 Faradays are passed through, you will have a colourless or slightly coloured solution from which the amine can be liberated after a standard acid/base workup.

The reduction capabilities of this apparatus are not only limited to nitroalkenes. Nitroalkanes, nitroarenes and oximes are also suitable substrates using the method described here.

I must add that I have abandoned the use of the flowerpot clay diaphragm with its high resistance in favor of semi-permeable polypropylene bags which are found inside a car battery. These bags pose a *much* lower resistance, and the electrodes can be placed closer to each other. After each use these bags can easily be cleaned using a tooth-brush. Naturally, in this case the anode is placed inside the bag and the cathode outside to allow for magnetic stirring :D.

Recommended further reading:

Electrolytic Reduction of Organic Compounds.
Frank D. Popp, Harry P. Schultz

Chem. Rev. 1962; 62(1); 19-40
http://rapidshare.de/files/16803179/cr60215a002.pdf.html

---------------------

Note to the moderator: Is it possible to change the links starting with "https://www.synthetikal.com/Rhodiums_pdfs/chemistry" into "https://www.erowid.org/archive/rhodium/chemistry" in the first post?

[Edited on 30-3-2006 by Vitus_Verdegast]
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[*] posted on 30-3-2006 at 11:51


For the entire thread, google: "electrochem reduction of 1-nitroalkenes to amine Success!" ("page 1 of 3" OR "page 2 of 3" OR "page 3 of 3") site:synthetikal.com and remember to click on the cached links. (and save it to you hard disk ;) )
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[*] posted on 30-3-2006 at 12:51


Here is a copy of the missing post from synthetikal on electro reduction mentioned by Vitus.......solo

Attachment: electrochem reduction of 1-nitroalkenes to amine Success! _).pdf (106kB)
This file has been downloaded 6277 times





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[*] posted on 31-3-2006 at 11:15
danke schön


Thank you solo and wa gwan! :cool:


Here is a nice picture of the inside of a car battery:
(from electrobattery.com)



1. Polytex Case - for superior protection against vibration and impact damage
2. Die-Cast terminals with stainless Steel Studs - for solid cable connections
3. Flame Arrestor to eliminate the chance of explosion due to external spark
4. Single Gas Outlet - to direct gases away from terminals
5. Anti-Spewing Baffle Design - to trap acid and return it to cells
6. Removable Battery Cap - for emergency access.
7. Enveloped Polyethylene Separators - for insurance against electrical shorts.
8. Waffle- Patterned Case bottom - for extra defense against perforations.
9. Through - The -Partition Connectors the most direct, efficient current path.
10. Molded-Into-Cover Terminal Design - for superior torque strength.
11. Offset Terminal Construction - to protect plates and guard against leakage.
12. Heat-Sealed Case and Cover - for tight, leak-proof bond.


You'll only need to open one battery to obtain a lifetime supply of diaphragms.

[Edited on 31-3-2006 by Vitus_Verdegast]
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[*] posted on 31-3-2006 at 15:31


My dear boy,

Those polyethene separators look just the job. I had been waiting to acquire a goretex jacket from the local hostelry, but perhaps I shall acquire a battery instead.




The reformative effect of punishment is a belief that dies hard, I think, because it is so satisfying to our sadistic impulses. - Bertrand Russell
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[*] posted on 31-3-2006 at 16:35


BTW, you'll get at least 24, each enclosing spongy Pb and next to PbO2, supported on Pb/Ca (OEM, maybe) Pb/Sb (replacement). If not a lifetime supply, enough to keep you busy, and make you think of lead salt uses.
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[*] posted on 2-4-2006 at 14:49


Hi all, just wanted to say a quick thank you for all your extremely helpful replies!

One more quick question, when taking those divders from the battery, would an old, worn out battery do the job (eg. from a wreckers), or do the films degrade too much over time to make that a feasible option?
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[*] posted on 2-4-2006 at 15:26


Used ones are structurally fine but need to be cleaned of Pb on the inside and fine PbSO4 crystals on the outside. I'd use a new one to take full advantage of the electrodes before they fall apart.
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[*] posted on 3-4-2006 at 06:01
It is maybe a detail, but:


Use a heat gun (for paint removal) or similar to soften the outer plastic case before attempting to cut it.

It is a lot easier and you reduce the change of damaging the separators or losing a finger.

[Edited on 3-4-2006 by Vitus_Verdegast]
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[*] posted on 19-5-2006 at 09:28


I just saw that the synthetikal thread solo posted seems to be incomplete.

I wonder if someone still has the complete one, including the information on voltage/current regulation using the LM338 5A adjustable regulator that bio posted there.

------------------------------EDIT--------------

I could recover only this from Google cache:

Quote:

This was emailed to me recently. I hope the sender doesn't mind me posting it here.


Quote:


# To: vitus@hotmail.com
# Subject: Electrochemical reduction
# From: georgewbush@aol.com
# Date: Thu, 15 May 2005 10:19:28 -0700
# Content-transfer-encoding: 7BIT
# Content-type: text/plain; format=flowed; charset=us-ascii

Dear Sir,


A couple of days ago I was informed by the Federal Bureau of Thought Investigation (FBTI) that you were pondering on the possibility of electrochemical reduction of nitroalkenes in a divided cell, using commonly available materials such as ceramics and a PC power supply. This concept intrigued me so I decided to perform a small experiment. The PC-AT power supply from daddy's old 80286 was used as the current source.


anolyte was 8% H2SO4
catholyte consisted of 30 ml IPA, 30 ml 80% AcOH, 10 ml 29% HCl and 10 ml conc. NH4OAc solution.

(The NH4OAc can probably be left out, it was added as an attempt to improve conductivity)

In the flowerpot was suspended 4 g of a substituted phenyl-2-nitropropene, and magnetic stirring was started. Using the 12 V line of the PC power supply the current delivered was 3.5 A (makes current density around 175 mA/cm2).

Temperature control was not easy, but the catholyte could be kept relatively stable around 40°C using the cooling spiral (made from plastic tubing). The cooling bath for the anolyte had to be refreshed with cold water from time to time. A running water bath should work much more efficiently.

1 F = 96500 coloumbs; 6 * 96500 = 579000 A.s = 160.84 A.h
For 0.02 mol 3.22 A.h are needed in theory.

With 3.5 A current passing through the reaction mixture, based on the article of Slotta and Szyska (10) one would need about 2.5-3 hours to reduce it completely to the amine.

At the 1 hour point all nitroalkene in suspension was gone and a light-yellow solution was obtained. An hour later the solution was clear. At this point the current had dropped to 1.5 A, and there was considerable corrosion noted at the anode. There was also an increase in hydrogen evolution noted.

At the 5 hour point the current had dropped to 1 A, and the process was terminated.

After standard A/B workup there was obtained 1.7g of amine.HCl, which corresponds to a yield of about 50%.

Now I know that the current drop was caused mainly by the excessive corrosion of the anode. I've read on a well-known internet bulletin board that addition of some gelatine to the anolyte helps minimize corrosion ( https://sciencemadness.org/talk/viewthread.php?tid=533 ). A small experiment using 1% gelatine added to the anolyte consisting of an 8% sulphuric acid solution showed that this helped considerably, and a constant current of 4-5 A could be maintained for several hours. Care must be taken that a lot of frothing occured in the anolyte this way.


I hope this was in any way helpful to you.

Jesus saves!

yours,

W."


[Edited on 19-5-2006 by Vitus_Verdegast]

[Edited on 19-5-2006 by Vitus_Verdegast]

[Edited on 19-5-2006 by Vitus_Verdegast]




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[*] posted on 19-5-2006 at 17:10


Hey, I've attached a zip file containing the pages I saved from google... They're in Internet Explorer .mht format (it was the only way I could think of to save them easily). If someone can tell me how to put them into .pdf files, I'm happy to do that if people would prefer.

Attachment: electrochem reduction of nitroalkenes.zip (226kB)
This file has been downloaded 1696 times

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[*] posted on 4-7-2006 at 01:30
Lead electrodes and overvoltage


Taken from "Die Wasserstofpolarisation in verdünnter Schwefelsäure an Blei" by Julius Tafel,
Z. Physik. Chem. 50, 641 (1905)


I. Rough electrodes

When one takes a freshly casted pure lead electrode and rubs the surface with cotton wool and wet sandpaper, a rough matt surface is obtained. We will refer to such treated electrodes as "rough" in the text that follows.

When such a rough electrode is polarised in a divided cell then, at least at higher current densities, in contrast to cadmium an immediate rise to a high value of cathode potential is obtained. This high cathode potential is attained at medium current densities around 10-20 minutes in most cases. With higher current densities (150-300 mA/cm2) this potential begins to decrease rapidly and in all cases of continuous polarisation the cathode potential will first more rapidly, then slower and more evenly decrease, so that no lower limit could be attained.

Cathode potentials of a rough cylindrical lead electrode were measured in a 2N acidic solution with a current density of 300 mA/cm2 (RT):

1.356V - 1 min.
1.304V - 5 min.
1.290V - 10 min.
1.272V - 20 min.
1.251V - 30 min.
1.202V - 60 min.

At lower temperatures (around 10°C) higher peak potentials are obtained, around 2.000V using a current density of 150mA/cm2.

There are clearly slight fluctuations in potential values between various seemingly identical shaped "rough" electrodes. In the author's opinion this can be ascribed to differences in density and its ability of the surface to desintegrate.


II. Pre-treated lead cathodes

When the lead cathode was pre-treated with a layer of PbO2 initially no hydrogen evolution is observed and the measured potential was very low. When 1/4 to 1/2 minute has passed hydrogen evolution starts and the potential rises sharply and one minute later a constant value is attained. This value was slightly lower than what was observed using the rough electrode.

Eg. for similarly shaped electrodes in a vertical apparatus using a current density of 125 mA/cm2, when one minute passed a value of 1.845V was obtained for the pre-treated electrode, while for the rough electrode this was 1.902V .

Also with the pre-treated electrode the potential drops more rapidly over time. When 10 minutes passed the potential dropped 0.047V for the pre-treated electrode vs. 0.015V for the rough one. One hour later, though, the potential of the pre-treated electrode only dropped 0.034V so we can conclude that in this case there also seems to be a stabilisation occuring.


III. Influence of acid concentration

Generally, like is observed with a mercury cathode, it is commonly agreed that the cathode potential rises ceteris paribus with the lowering of the acid concentration. In practice this difference is neglegible for lead cathodes.


IV. Potential depression

When using a divided cell (Pt anode, 125mA/cm2, 2N H2SO4, 12°C) and a rough lead cathode one observes the potential lower only slightly over 180 minutes (peaks first at 2.010V and lowers gradually to around 1.980V). The last 150 minutes the drop is only 0.005V .

When the cathode is then removed, rubbed with cotton wool and wet sandpaper, and replaced the observed peak is somewhat lower (around 1.950V) and the potential gradually declines to 1.850V at the 160th minute. Around the 180th minute there is a sudden drop observed to 1.350V . A similar depression is observed when cadmium is used as the cathode, but there the drop occurs much sooner than in the case of lead.

Lead also seems to have the characteristic ability -again contrary to cadmium- to relieve itself from this depression. In some cases the potential rises again with 0.200V half an hour after the depression point.

Pre-treated electrodes seem to be somewhat more labile in this aspect, as the occurence of a depression seems also to be influenced by other factors, such as the contamination with anolyte in case of long polarisation times.

As a rule will pre-treated electrodes, when the -by a sudden sharp rise in potential- characteristic reduction of PbO2 has ended, first of all even show depressed values, or at least values that are situated between depression and peak potential. What happens hereafter is in many cases very variable.

When anolyte can contaminate the catholyte the following situations can be observed:

1. The cathode will constantly attain a depression value (generally around 1.300-1.350V using above conditions, observed for 50 minutes)

This phenomenon occurs most frequently with those electrodes which during pre-treatment have been strongly oxidised for a long amount of time (20 mA/cm2 10-40 minutes).


2. The cathode reaches a low value, gradually recovers and reaches a high value, whereafter the potential decreases again to its depression value (observed over 120 minutes).

This phenomenon occurs most frequently when the electrode has been electrolytically oxidised for 40 minutes (or more).


3. The cathode reaches a low to medium value, then within minutes risis sharply to its peak value and more or less attains it (generally around 1.900V using above conditions, observed for 50 minutes). It is similar to what is observed with rough electrodes.

This phenomenon occurs most frequently when the electrode has been electrolytically oxidised for a very short time (3-15 minutes).


V. Potential elevation

When one re-polarises an depressed cathode -taking care that anolyte cannot contaminate- one can reach again a high potential value. Such method in practice requires more than just dilute H2SO4. Good results have been obtained using a caffeinated H2SO4 solution. In such a case the climbing to a peak potential goes together with the start of the reduction of caffeine.

Eg. A pre-treated cathode that has attained a depression value of 1.440V was placed in caffeinated 2N H2SO4. Using a current density of 125 mA/cm2 the reduction of the caffeine commenced and proceeded fast, after 14 minutes the optimum for a pre-treated lead cathode was reached. After this treatment the electrode had a peak potential in (pure) 2N H2SO4 of 1.910V

Although this procedure is quite sound, once the author experienced a failure, where after 40 minutes only an increase of 0.003V was recorded. No reduction of caffeine occured in that case.


VI. Maximum overvoltage

Considering the above it is not surprisable that for an evaluation of the heights of the elevation values at the lead electrodes, the attempts, which were implemented in an undivided cell, are just as useful as the ones in a divided cell, if only each time fresh electrolytes were implemented and only the behavior in the beginning of the attempt is drawn in consideration.

It can be concluded that there are no fixed limits on the 'specific overvoltage' of lead, even when considering the depression values. There are, however, several pointers which can be applied to specific conditions. The limits for peak potential values the author has in his extensive experimental work encountered are: (12°C)

10 mA/cm2 : between 1.760V and 1.868V
100 mA/cm2 : between 1.898V and 1.965V
125 mA/cm2 : between 1.902V and 2.037V

Values for pre-treated cathodes are slightly lower, and the bottom limits depend on duration of electrolytical oxidation.




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shocked.gif posted on 4-8-2006 at 13:37
Phenyl-2-Nitropropen to amine SUPPORT needed!


Hello everybody, SWIM hopes he is right in this forum.
This *will* yield in a functioning route, but help from skillful people is requiered.

Please read the total post, there are many informations and everyone is asked to help. thank you.

First of all: all reagents used are 99%+ pure used in the following description.

The aim in the experiment was to reduce P2NP by electrolysis to the corresponding amine.

description:
P2NP was prepared by refluxing Nitroethane+Benzaldehyd with n-Butylamin with Ethanol.
The amounts used were the regular amounts described in most papers.
It was refluxed for 6 hours at about 80-110°C with higher temperatures at the end of the process.
After freezing and recrystalizing with Ethanol the crystals were washed with tape water and then again with destilled water.
The crystals were recrystalized again and yielded a very high quality product, seemingly to be P2NP by mp temp.

Then different methods for reduction were used:

First: With a low power power supply 2 petri dishes with GAA,H2SO4,Ethanol and dH2O for catholyt and HCl and H2SO4 for anolyt were connected through a salt bridge of paper satured with KCl solution Agar Agar were connected. A Cu Kathode and graphit Anode was used.
The voltage could not be exactly measured due to the power supply model, but should be around 7V and 100-200mA.
After 30h the product from the cathode was filtered out and yielded an orange oil, which did not freeze in the fridge(-25°C). Smell was not of P2NP at all and an allergy test was performed, since SWIM is allergic to P2NP.
At room temp the oil was relativly mobile with a characteristic smell which is very difficult to describe. A series of reagent tests from the EZ Test family were *all* negative by color reaction. Dropped on lackmus paper and added water resulted in a low pH about 5-6. This could be due not perfect isolation from the catholyt solution, although not necessarily! Might posses property of H+ donor..
Further a test was performed on a mice with a dose of <20µL of the pure oily substance. The mice reacted by hyperactivity for about 15 Minutes and calmed down.


First question: Is this substance familiar to anyone or does anyone have an idea, what this substance could be?

Second preparation was exactly like the first, with a HighTech Precision Lab DC Supply was used and it was run at 30V and 0,8A. A pot was used for anode fluid.
Yield was very low, but substance had similar properties. Conc. of the catholyt solution was as described in "Amphetamin Synthesis". In other words H2SO4, Ethanol,GAA with *no* water

Third preparation: Using 12V @ 0,35A same catholyt as in Prep#2 yielded small amounts of a very sticky dark red oily substance

The smell of the substance from #2+#3 were both not very intense compared to #1.

Fourth preparation used the urushibara Nickel catalyst methode as compare and yielded an extremly sticky red substance which was not mobile at room temperature with extremely weak smell (like P2NP polymer). Allergy reaction was positive.
The animal test of the Urushibara sticky oil resulted in "normal" sedation of the animal for about 10 hours.

It seems, water is essential for good yield and good outcome of the electrolysis process.

All preparations were all negative in the specific primary amine tests (EZ Tests) and to the lackmus test except ONE from preparation #2 to the so called Robadope Test (look www.eztest.com)
saying: ROBADOPE'S : a noticeable color CHANGE to reddish/purple indicates the presence of a primary amine. (MDA, dex-Amphetamine, PMA, 2C-B, DOB or waste product from the production process.)

All preparations for precipitation of the substances with H2SO4 Solution in IPA (and Acetone both tested) were all negative.

Now the question: If this works, and SWIM believes it does, this would be a very intresting method. But at the moment it doesn't not work.

Does anyone more skilled and experienced have an idea what could the reason be for *all* failed reductions? Including the Nickel! SWIM is open for any suggestions and willing to do further trials for exploring this method.

SWIM was afraid something in the the P2NP synthesis might have gone wrong, but this is relativly unrealistic.

SWIM is waiting for your suggestions and ideas.

PS: Water seems essential for the electrolysis process. when using low conc. of H2SO4 the process *seems* always to yield an orange oil which is observable during the electrolysis going from a clear yellow P2NP to an orange solution.
Normal conversation seems not to make any problems , but adding H2SO4 after the solution is already orange seems to induce the "red color" effect.

So the primary question is: What is the orange, oily mobile substance that is produced as a final product of electrolysis experiments?

[Edited on 4-8-2006 by d0c]
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[*] posted on 4-8-2006 at 15:22


I have successfully made the methylenedioxy variant a few times from the associated PNP compound by electrolytic reduction in a porous cup ( flower pot ) ,
using a sheet lead cathode wrapped around a glass bottle standing inside the porous cup , cold water circulated through a two hole stopper in the bottle
for cooling the electrode . The porous cup contained
a catholyte of denatured alcohol , glacial acetic acid and HCl , in which the PNP was partially dissolved and the undissolved portion was kept in suspension by a small
nylon propellor blade as is used for model boats on
the end of a stainless steel rod about 2mm diameter
for a propellor shaft , which was sheathed in plastic tubing and the tip and joint at the little propellor were sealed with RTV clear silicone . This stirrer was chucked
into a highspeed overhead stirrer with the propellor as close to the bottom of the porous cup as possible and
pitched tangent to the inside wall so as to swirl the agitated catholyte around the cathode in a circular flow .
The porous cup was set in the center of a much larger
glass mixing bowl which contained the plain battery electrolyte anolyte and a sheet lead anode , and this
outer bowl was itself set in a slightly shallower pan
of cooling water . Everything was thus coaxially arranged with provision for cooling water entering
the glass bottle in the center of the catholyte compartment and conducted through a long tube in the twohole stopper downwards to near the bottom inside
the bottle , exiting through a short tube in the other hole in the stopper and carried through a flexible hose to
the outer cooling bath for the anolyte cooling , a level
maintained there by an overflow port at the desired depth , having a flexible hose for conducting the overflow back to the picnic cooler containing a block of ice and the circulating pump .

The power is provided to the cell by a variac and fullwave bridge rectifier and the current monitored by a good ammeter . Makeup alcohol will have to be added to the catholyte unless some sort of cover is provided for it with provision for reflux of the evaporating alcohol . A thermometer should also be suspended in the catholyte
so that the reaction temperature can be monitored and a logsheet should be kept concerning the times for which a certain number of ampere hours have passed .

The reaction product will be in the catholyte as the hydrochloride salt and perhaps as the acetate salt .
Unreacted PNP or resinous byproducts can be extracted
with chloroform and discarded , the aqueous phase filtered and freebased carefully with NaOH , the freebase
extracted with benzene or chloroform or toluene and
then vacuum distilled . The sulfate of the product is
a much less hygroscopic and much easier to isolate pure form of the product than is the hydrochloride . To obtain
the sulfate is very simple . Using accurate scales weigh the vacuum distillled free base , this is easiest done prepared for in advance by carefully measuring the tare weight of the empty receiving flask and its teflon stopper , and then weighing the flask and doing the arithmetic to see how much freebase you have .
You then measure out the necessary amount of electrolyte grade sulfuric acid to just be sufficient for
the formation of the sulfate , a few hundreths of a per cent less than the requirement for theory is about right , as you do not want any excess acid . Then you dilute the measured neutralization amount of acid with a large excess of denatured alcohol , and you dilute the freebase
with an equal amount of alcohol . For example if you
are expecting 100 grams of product you would want
about one and one half liters of alcohol solution of freebase , and about one and one half liters of alcohol
diluted electrolyte premeasured for the salt formation .
You then simply pour these two separate solutions
simultaneously together into a separate vessel large
enough to contain the total volume of the combined
solutions , a large crock or even a large plastic bowl
will do . Precipitation is instant when the solutions are mixed and stirred together manually for a minute or two .
The slurry of fine crystals is too thick for filtering , so
it is simply poured into a large shallow tray and the alcohol evaporated away , the dry material left is
exceptionally pure and nonhygroscopic .

Lead is attacked by the catholyte and a sludge will be found from the erosion of the cathode . The anode is not attacked at all , just has a chocolate brown protective oxide . The best way of making these
is to cut them from sheet lead in an " L " shape with
the long leg being bent into a cylindrical form electrode
and the short leg of the " L " providing a riser tab for
connection of an alligator clip and power cable .

I didn't do a lot of experimentation with this sort of thing because of unwanted interest of unsavory characters ,
but the direction which I intended to go next was using
a pool of mercury metal as a cathode , to see if it would perform better . IIRC the yields using the lead cathode
were something near 80% .

About the color , well it is very nearly colorless when pure ,
and the sulfate salts are snow white , I mean put on your sunglasses white , sparkling like newfallen snow in sunshine .

[Edited on 4-8-2006 by Rosco Bodine]
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[*] posted on 4-8-2006 at 15:44


Hello,

thank you very much for your post, it is very intresting.

SWIM has a few important questions:

SWIM is using Cu cathode and Graphit anode.
Is there a significant difference between using Cu and Pb?

What voltage did you use?
How many Amper was the electrolysis running at and
is it significant in chemical means if it runs on lets say 300mA or 5A? (except the duration and the heat ofcourse)

By your description it would mean that:
SWIM's yellow oily substance is just a waste product and ready for the bin.

In case of using anhydrous Ethanol and HCl acid (which contains H2O) what means that using anhydrous Ethanol is actually making the process more expensive..

SWIM would need to isolate with Trichlormethane the aqous solution, discard the "oily substance" and basify. Reextracting with TCM and precipitating with dil. H2SO4.

You did not mention using H2SO4 as electrolyt in your catholyte. Why exactly did you not use it, it is an exceptional electrolyt while HCl acid reacts with the electrodes forming H and Cl ? Did you have negative experiences using H2SO4?

What would also be intresting if you could SWIM more precisly the consistence of your catho/anolyte solutions in proportions. SWIM had very varying results when using more or less H2SO4, es described the solutions going DARK RED or staying orange. What do these color changes mean in context with the acid conc. ?

Thank you and others ahead for further support!

[Edited on 4-8-2006 by d0c]

[Edited on 4-8-2006 by d0c]
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[*] posted on 4-8-2006 at 16:15


As I recall the procedure was taken pretty much directly
from a major english language journal of something like fifty years ago , but the cell design was my own idea for expediency . The cell was run pretty warm even with the
water cooling , as I recall having to add alcohol every few minutes to maintain the level , and the process took maybe four to six hours . What was the current density I don't remember . The material for the electrode
most definitely does make a difference , as does the composition of the electrolyte ....and this is general for electrochemistry , although I am not certain exactly why , but there is more involved than just conducting current through a reaction mixture , some combinations work as intended and other combinations simply don't work well at all . There is a surface chemistry apparently involved with the atoms of the electrode material itself and some sort of " handoff " which must occur involving the nascent hydrogen on the cathode , to the material which will be reduced and there are factors like " wetability" or or solubility that come into play as well as electrical attractions and it is different the way reactions behave than in a plain chemical reaction . Electrochemistry is a science unto itself . Anyway I don't know about what all doesn't work and why not so I can't explain those aspects . I know what did work and I am not even sure about all the reasons that it did work except that it did .
Know that's a big help huh .

About the catholyte , PNP is not very soluble so the catholyte
is mostly alcohol with some glacial acetic acid and then a small amount of HCl to increase the conductivity which is still poor , and so the cell has a lot of resistance and requires higher voltage to push sufficient current , which generates a lot of heat compared with an inorganic electrolysis using highly conductive solutions . Here you are dealing with an organic being reduced which is more difficult to manage because of the poor solubility of the PNP in the electrolyte which must therefore be designed specifically for compatability with the PNP . Whatever was the amount of
HCl was sufficient for the formation of the salt of the amine produced plus some extra for maintaining the conductivity of the cell . In this regard it may be of benefit to start out with a little HCl and add more little by little as the reduction proceeds . Sulfuric acid might work but I have a feeling it may not have worked because of coating the cathode with sulfate .

[Edited on 5-8-2006 by Rosco Bodine]
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[*] posted on 4-8-2006 at 16:29


Check out the term "overvoltage". Mercury has a high overvoltage for both hydrogen and oxygen, platinum is very low for hydrogen. There are tables of overvoltage values, lead and zinc are fairly high.

Surface roughness also plays a role, perhaps as with catalytic metals - rough surface or a deposit of 'metal black' gives a more active surface.

Effects from the formation of thin layers of different chemistry around the electrodes can amso change the direction of an electrochemical operation. That's part of the reason for vigorous stirring for some reactions.
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[*] posted on 4-8-2006 at 16:32


Doc:

read: https://sciencemadness.org/talk/viewthread.php?tid=4145

Using a flowerpot as Rosco describes was also used succesfully by yours truly, but the high resistance makes the heat generated indeed hard to cope with.

A much better diaphragm, therefore, is the semi-permeable PP or PE bags that are found as electrode separators in car batteries.

Only lead, mercury and cadmium have a high enough overvoltage to reduce your substrate completely in a decent yield. Copper isn't good and nickel is only good for electrocatalytic hydrogenation, which is a completely different process.

The voltage used is not as relevant as the current applied, if you use no reference electrode to finely adjust the required potential (-1.1V) for complete reduction of nitro group and double bond with no or only little H2 gas being produced.

Judging from your experiments, next to the wrong electrode material, the current density you've applied was far too low.

Normally the reaction goes through the stadia P2NP -> oxime -> hydroxylamine -> amine. What your yellow-orange oily substance is I have no idea, could be impure oxime, but keep in mind at the end of the reduction your solution should be completely clear, sometimes slightly coloured.

Also, as Rosco pointed out in his description of his apparatus, good stirring of the catholyte suspenion is essential.

EDIT:

BTW, forget about the Urushibara reduction, it is horribly messy and I know of no people that actually obtained a final product using this route. Many tried however.



[Edited on 5-8-2006 by Vitus_Verdegast]




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[*] posted on 4-8-2006 at 16:44


Thank you all very very much for all of the important info.
SWIM will get a porous (hightech) porcelan electrolysis cell next week and it will be tested directly with it.
It will also be possible to use higher currents.
The DC Supply goes up to 6A, this should be enough, or?
About the -1.1V I have read the paper, but they talk of 1-Nitropropens.
You mean, SWIM should let it run with -1.1V @ about 4-5A with a lead cathode. Can be tried out.
What about the optimal Anode material, do you have a tip?
I will post results as soon as trials are done, for any further information that can be involved into further experiments I thank everybody ahead!
As soon as it is running and working reproducably a paper will appear with highly detailed informations so it is available for everyone to share the knowledge.

PS: Yes, Urushibara is extremely messy, dangerous wastes and sux totally. If it would work it would correlate with the mess but it doesn't.

[Edited on 5-8-2006 by d0c]
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[*] posted on 4-8-2006 at 16:52


The applied current density was established by visual observation early in the reduction using my cell , watching
for any excessive evolution of free hydrogen bubbles ,
and then backing off slightly on the voltage until the cell
seemed to be putting the hydrogen into the reduction instead of filling the room with free H2 :D

Anytime the cell started bubbling , I just backed off on the power and followed the course of the reaction the same way , as towards the end there is not much hydrogen being absorbed and the cell is just making bubbles of H2 after the reaction is complete .

Don't buy a porous porcelain cup , they are tiny and soft ,
and don't do the job like a flower pot . Flower pots rule :D
Also don't use an expensive DC supply for this stuff , just get a heavy variac and a bridge rectifier .
Sheet lead is likely the best anode material , and it may be the best cathode material , even with the erosion I mentioned .

[Edited on 5-8-2006 by Rosco Bodine]
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[*] posted on 4-8-2006 at 17:01


Instead of porcelain, I really recommend you to open up a car battery. I know it is messy but you will have diaphragms for the rest of your life. Lots of lead in there too. Using the car battery diaphram the reaction runs much smoother, a lot less heat being generated.

Using 6A, ideally a cathode surface area of 30cm2 should be applied (gives 200mA/cm2)

The paper actually used beta-nitrostyrene and P2NP as substrates. The -1.1V is measured vs. a standard hydrogen electrode. As you don't have this, follow Rosco Bodines advice above.

Anode material, use the same, lead.

Don't forget to pre-treat your cathode with a layer of PbO2 as described in the link I gave you.

BTW:
You were referring to the "EZ tests" in your first post. These are no more than the Marquis reagent, which you can easily prepare yourself. Simply mix 2 drops of 40% formaldehyde with 3ml of concentrated sulfuric acid.
http://en.wikipedia.org/wiki/Marquis_reagent

Good luck, and report your results.

[Edited on 5-8-2006 by Vitus_Verdegast]




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[*] posted on 4-8-2006 at 17:37


The answer about why to use HCl in the catholyte instead of H2SO4 is because the amine HCl salt
forming is so much more soluble so the product
remains in solution , as opposed to the sulfate salt of the amine which would precipitate and greatly complicate
things .
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[*] posted on 4-8-2006 at 18:01


In my experience when H2SO4 is used no sulfate precipitates, I don't think it would precipitate from a concentrated acetic acid/alcohol mixture.

When I used a mixture of 80% acetic acid, ethanol and conc. H2SO4, there was a more profound ethyl acetate smell than when 29% HCl was used, this might increase the solubility of the P2NP somewhat.

Although in practice this doesn't seem to matter much, and I also prefer to use HCl.




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