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Electrochemical Reduction of Nitrostyrenes

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We all heard about or use the modern reduction using LiAlH4, NaBH4 or ones using PdCl2.

Uemura comes up with this thread to bring again attention to procedures, 70ty years old and more, when the first pioneers attempted to reduce the nitro-styrenes to the corresponding amines. All the stuff used should be OTC.

The following is from the paper mentioned in uemuras thread oon 'routes to the 3,4,5trimethoxyphenylethylamine' from 'Journal fuer Praktische Chemie (Vol 137) from the year 1933. Authors K. H. Slotta and G. Szyszka'. Uemura felt free to take the translation (by Dwarfer) available at Rhod's page and corrected some missing thingies and typos. The diagram is now included which seems to be essential.

The authors said: The electrolytical reduction of the corresponding nitro-styrol can be performed in all these cases with high yields if the conditions are choosen properly. The reason that all the valuable <<sic!>> phenyl-ethyl-amines haven't been exclusivly produced via this most simple method is: the yield is highly sensitive to the technical performance of the experiment.

A) Equipment for electrolytic reduction

An anode cell (Z) - a porous cell of Haldenwanger porcellain - was placed in a filter assembly of 500 ccm (F) volume. The anode had measurements of 75mm x 160mm with a 70mm wide glazed edge that prevented the drawing-up and smearing of the liquid to be reduced.

To the anode cell was added a solution of 25ccm concentrated sulfuric acid in 175ccm water. The anode used was lead or carbon rod and was enclosed in a tightly wound, glass spiral cooler. The water in this was conducted to the outer container to help cool the inner tube. By regulating the cooling water it was possible to keep the whole reduction solutionfor the first six hours at 20 degrees Celsius. In the last hours the temperature was allowed to rise to 40 degrees Celsius, to get a nearly quantitative course of the reduction.

The outer container contained a cathode (K) - a lead sheet (200mm x 90mm x 2mm), which before each experiment was coated electrolytically using diluted sulfuric acid, with lead superoxide.

B) Reduction

A solution of 30g 3,4,5-trimethoxy-beta-nitrostyrene in 100ccm glacial acetic acid and 100ccm ethanol was mixed with 50ccm concentrated hydrochloric acid and added to the cathode container. The anode cell was filled with dilute sulfuric acid to the outer level of the cathode cell. Now a current of 5 to 6 amps was passed through the equipment for 12 hours, so that the current density was about 3 amps.

After the finished reduction, the contents of the cathode cell was filtered and dried under vacuum. The remainder was then dissolved in 300ccm water. Any remaining unchanged nitrostyrene was removed by twice shaking it out with ethyl acetate. The ester in the solution was then removed by shaking out once with diethyl ether.

The liquid thus obtained of chloride of mescaline was then put in a separating funnel which had ether added. The amine was freed with a cold concentrated solution of 100g technical sodium hydroxide. The solution obtained, after extracting four times with ether, was dried with calcium carbonate and the amine precipitated with dry hydrochloric acid gas.

After twice dissolving in absolute, dry, non-denatured alcohol, completely pure mescalin hydrochlorid*xH2O was obtained as white leafs with a melting point of 184 degrees Celsius and a yield of 24g (77.3%)

Now some points for discussion:

1) has any bee performed this electrolytical reduction in the described or in any similar form. Report on the experiences are welcome.
2) 'porous cell of Haldenwanger porcellain': what could be used for that, a pourous clay pot? (swim has such a pot which he fills with water and grows orchids on the outside of the pot)
3) Could the glas spiral cooler be replaced with a PVC-tubing cooler?
3) What the opinion of the electrochemical bee-expert. Why is nobody using the above procedure (there are almost nil post on the hive)

Let's start a discussion! The above procedure seems really bee simple!  Lets find the proper conditions where it works!

"I want to know Gods thoughts, the rest are details" A. Einstein

It is certainly a very appeling route, but the problem is the mebrane. There are membranes available, like nafion, which is ion-selective, but the question is if they're resistant to the HAc/H2SO4/EtOH mix. Modern membranes comes in sheetform also, making the apparatus design a bit more complicated aswell.
The cooling can probably be done with a PVC tube, but the problem is that PVC is very insulating compared to a glass tubing, but I doubt that is a problem...

That is a splendid approach, uemura. The big argument these days is whether the anode must bee pure platinum, as Strike urges, or silver! Mercury is used in one variant, but there is a quasi-religious backlash against this element. It's now pretty clear that lead, or graphite, will give yields comparable to the high-flung theoretical speculations with four-digit calculations of electrochemical overvoltages, oui? I'd like to try palladized graphite, myself, partly because it's what I have available. This approach calls for too much individual tinkering to be popular, because it hasn't been standardized into a formula. Strike made a great advancement in suggesting the sheep gut condom for the membrane, but clay flower pots with the drain hole sealed are the alternative. This particular publication gives the unique contribution of its externally-cooled anode; such fancy glass blowing is not stylish, but plastic tubing, of vinyl or LDPE, would serve as well. Good one.


but there is a quasi-religious backlash against this element. It's now pretty clear that lead, or graphite, will give yields comparable to the high-flung theoretical speculations with four-digit calculations of electrochemical overvoltages, oui?
--- End quote ---
Well spoken, halfapint. It really looks not many bees fly around using lead. At the beginning of last century up to the 40ties, many researches did the reduction to the amin with a similar apparatus as the one shown above.

Uemura thinks he will jump into this experiment when he gets the lead from the divers shop. 2kg for 15$. Gives lot of metal to melt and to make nice anodes/cathodes.

"I want to know God's thoughts, the rest are details" A. Einstein

Dear Uemura!
Yesterday as I was digging out my potato crop an idea occured to me that, I gather, may be of interest to you. It's about the membrane for your electrolytic reduction. Take some dry CaSO4 powder, mix it intimately with some (about 20-30 % by weight, i'd guess) fine Al powder (it is used as paint filler), add water and make a thin-walled glass of this mass. When CaSO4 solidifies put your membrane-to-be in conc. soln. of NaOH, Al will dissolve and create precisely those fine pores we're looking for. In case Al powder is unavailable, you can always use smth. like electrolytic iron/HCl or - well, i guess, there are many variants. In any case, CaSO4 is inert to anything. However, this is only a theoretical proposition and, most importantly, proportions of CaSO4/Al should be established experimentally for the best performance of the membrane.

Good luck, Uemura, I will join you by the end of February!


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