Sciencemadness Discussion Board - the hunt for the reducing agent

have been trying to find a suitable substitute ,so it would be very helpful if you could correct my ideas and also suggest some of your own

Hydrogenation over Pd-C at atmospheric pressure is obviously the most obvious choice and probably also the most amateur friendly. Anything else will require a tedious isolation.

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1.hypo(Na2S2O3).this is a little silly i admit but hypo also gets oxidised to elemental sulphur(remember the double iodine/hypo titrations),and since the mechanism for dithionate reduction is a free radicle S02 by auto-oxidation http://pubs.acs.org/doi/abs/10.1021/j100784a510

"Hypo"? Where did that come from?
Na₂S₂O₃ is sodium thiosulfate.
So, what is the reference for the reduction of nitroaromatics with thiosulfates? I don't remember ever seeing one, though I can imagine that under certain conditions it might reduce some nitroaromatics. Though, probably not sufficiently practical.

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if we could generate a free radicle S02 ,we could be well on the right path(something similar to generating a N02 free radicle in vapor phase nitration)

Sounds like pure nonsense. Firstly, you probably mean sulfur dioxide which is SO2. The chemical symbol for oxygen is "O" and not "0" (zero)! Secondly, SO₂ is not a radical. While NO₂ is formally a radical, SO₂ is not. Thirdly, the article about the mechanism of dithionite reduction of nitrophenol talks about the SO₂^- radical.

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note:but since its diaminophenol wont the OH be acidic due to both the nitro groups and would zinc also react with it to liberate H2 rather than from HCl

I can't see how could this affect the reduction.

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note:it is better to do the Zn/HCl reduction in ethanol/HCl mixture because the solubility of h2 in ethanol is 0.0072g/kg compared to 0.0016g/kg in water.

What relevance the solubility of hydrogen has on the reduction of your substrate? In this case, who cares what the solubility of a gaseous side product is?

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but if ethanol is used is there any chance of formation of ethyl chloride(as ZnCl2 will be formed which will act as a dehydrating agent

The conditions used for these reductions are not the same as those required for the nucleophilic chlorination of aliphatic primary alcohols. While traces of ethyl chloride can always form in ethanolic HCl, this has no relevance to the reduction itself.

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note:i came across a better reduction using Zn/NH4COOH from the hive http://chemistry.mdma.ch/hiveboard/chemistrydiscourse/000351...

What makes you believe that method is any better than using Zn/HCl?

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as anyone ever done this before?

Chemists generally tend to avoid applying obvious fiction in their work.

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3.by passing S02 gas -a wild idea, i agree

What is the reference for the reduction of nitroaromatics with SO₂? Perhaps you confused it with H₂S, which is occasionally used for reducing nitroaromatics.

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4.by hypophosphorous acid(H3P02).-since the H is attached to a weakly electronegative P it can act as a reducing agent,worth a try

Do you have a reference for a non-CTH or non-catalyzed reduction of nitroaromatics with H₃PO₂? I have only seen CTH reductions with this reagents. (again, the symbol for oxygen is "O")

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and please dont suggest buying sodium dithionite as it is not availaible.i repeat,buying it is completely out of the question

Interesting. Where on earth is sodium dithionite unavailable to the average consumer?

macckone - 23-9-2014 at 10:45

Quote: Originally posted by gdflp

Couldn't you just reduce sodium metabisulfite or bisulfite with zinc and filter off the Zn(OH)2 to yield a solution of sodium dithionite? You would have to evaporate it carefully, but it shouldn't be too difficult. Another option if you live near a Wal-Mart(or another store that carries it) is Rit Color Remover.

[Edited on 23-9-2014 by gdflp]

Is there a good work up for purification from Rit?
Sodium metabisulfite is available from any brew supply
And zinc can be easily obtained from us pennies if
No other source.

gdflp - 23-9-2014 at 10:56

Not sure about the work up preparation. The MSDS claims it to mainly be sodium dithionite and sodium carbonate, with a small amount of disodium EDTA, sodium silicate, geraniol and silica. My CRC claims sodium dithionite is slightly soluble in ethanol and sodium carbonate isn't, so dissolving in anhydrous ethanol might work.

Attachment: MSDS_RITColorRemover.pdf (128kB)
This file has been downloaded 1079 times

[Edited on 23-9-2014 by gdflp]

CuReUS - 24-9-2014 at 04:33

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it is better to do the Zn/HCl reduction in ethanol/HCl mixture because the solubility of h2 in ethanol is 0.0072g/kg compared to 0.0016g/kg in water.
What relevance the solubility of hydrogen has on the reduction of your substrate? In this case, who cares what the solubility of a gaseous side product is?

the more soluble the H₂ gas is in the solvent,the longer it would stay dissolved and more product would get reduced.whats the point if all the H₂ just bubbles out of the container.2,4 dinitrophenol isn't that soluble in water or acid until it is reduced to amino

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note:i came across a better reduction using Zn/NH4COOH from the hive http://chemistry.mdma.ch/hiveboard/chemistrydiscourse/000351...
What makes you believe that method is any better than using Zn/HCl?

because the normal Zn/HCl reduction( https://www.erowid.org/archive/rhodium/chemistry/leminger.ht...)takes >12 hours compared to 2-5 minutes in the Zn/NH₄COOH version

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3.by passing S02 gas -a wild idea, i agree
What is the reference for the reduction of nitroaromatics with SO₂? Perhaps you confused it with H₂S, which is occasionally used for reducing nitroaromatics.

i know about that reduction,but it is not applicable here because it will partially reduce only one nitro group to amino ,i want diamino

[Edited on 24-9-2014 by CuReUS]

Nicodem - 24-9-2014 at 07:01

Hydrogen does not reduce nitro groups in absence of a hydrogenation catalyst. It is the zinc that reduces the nitro group. The hydrogen is just a reaction side product.

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What makes you believe that method is any better than using Zn/HCl?

because the normal Zn/HCl reduction( https://www.erowid.org/archive/rhodium/chemistry/leminger.ht...)takes >12 hours compared to 2-5 minutes in the Zn/NH₄COOH version

More than 12 h for the reduction under classical conditions and 2-5 min under fictional conditions? Are those experimental or fictional values? The first does not fit to experience while the second is only realistic for the Indian laws of chemical kinetics.

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3.by passing S02 gas -a wild idea, i agreeWhat is the reference for the reduction of nitroaromatics with SO₂? Perhaps you confused it with H₂S, which is occasionally used for reducing nitroaromatics.

i know about that reduction,but it is not applicable here because it will partially reduce only one nitro group to amino ,i want diamino

Like I already mentioned, I would like to read your reference about the SO₂ based reduction, please.

chemrox - 24-9-2014 at 12:58

"The hydrogen is just a reaction side product." which hydrogen? In the Clemmenson you need the proton to break up the Zinc complex don't you?

Crowfjord - 24-9-2014 at 13:51

Elemental hydrogen (H₂) is a side product. A proton is indeed needed; but as I understand it, the proton is abstracted from an acid like HCl or water after the election transfer (reduction) step is completed.

CuReUS - 25-9-2014 at 00:54

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Hydrogen does not reduce nitro groups in absence of a hydrogenation catalyst. It is the zinc that reduces the nitro group. The hydrogen is just a reaction side product.

but i always thought that the nascent hydrogen formed did the reduction

,if the metal is doing the reduction,then why are Sn and Fe more commonly used than Zn(especially Sn) when Zn is way above them in the electrochemical series(and dont say that Fe/Sn are cheaper,Fe may be but Sn is certainly not

wont Zn do a better job at reducing whatever it is you want to reduce?

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actually the truth is that i havent been able to get a proper reference on Zn/HCl reduction .the 12 h reaction time(shocked me too) was mentioned in this https://www.erowid.org/archive/rhodium/chemistry/leminger.ht... .i would be very grateful if you could give the correct procedure for the Zn/HCl reduction.and why are you so reluctant about the indian reduction,do you have something against the hive and its references

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3.by passing S02 gas -a wild idea, i agreeWhat is the reference for the reduction of nitroaromatics with SO₂? Perhaps you confused it with H₂S, which is occasionally used for reducing nitroaromatics.

i know about that reduction,but it is not applicable here because it will partially reduce only one nitro group to amino ,i want diamino
Like I already mentioned, I would like to read your reference about the SO₂ based reduction, please

i think i clearly mentioned that the SO₂ gas was a wild idea

i just thought that since H₂SO₄ was a reducing agent,SO₂ might be too

and i didn't shoot down your H₂S idea,i just said that i have come across several reaction involving NH₄HS reduction(i think H₂S works similarly) in which only one nitro group gets reduced.after getting everyone's feedback about my ideas,i think the Zn/HCl or the H₂S is probably going to be my best bet

[Edited on 25-9-2014 by CuReUS]

Crowfjord - 25-9-2014 at 12:41

H₂SO₄ is an oxidant, rather, and usually only at high temperatures. Sulfur dioxide can be a reducing agent under some circumstances, I think, but I don't remember seeing any reference I it being used to reduce organic molecules.

I think sodium sulfide (Na₂S) would be a little safer than hydrogen sulfide, and just about as effective. I used it a few years ago to reduce a tetranitro-phthalocyanine to the tetraamino derivative. I'll see if I can find the reference.

[Edited on 25-9-2014 by Crowfjord]

For some reason, I can't get electronic access even though my school has this particular issue of this journal on the shelves, but the reference I used is:

Achar, B.N. (01/1987). "Synthesis and structural studies of metal(II) 4,9,16,23-phthalocyanine tetraamines". Polyhedron (0277-5387), 6 (6), p. 1463.
DOI: 10.1016/S0277-5387(00)80910-9

[Edited on 25-9-2014 by Crowfjord]

Rabodon - 25-9-2014 at 17:59

My fav to Reduce NO2-Groups is Zn/HCOOH in EtOH.
You can make a slurry of fine Zn powder (you can activate it using thinned aq. HCl is your powder is old) in EtOH and add 85% HCOOH in portions. Reaction is very smooth unlike Al/Hg in IPA or LAH/THF. Good mechanical stirring is necessary to keep Zn in suspension - a good overhead stirrer is necessary for reductions larger then 10-15g substrate, for small batches strong magnetic stirring can be sufficient. After addition of all HCOOH heat a little further for 1-2h while still stiring to complete reaction. Workup is a charm, simply filter unreacted Zn, boil it down until Zn-formiate starts to precipiate, let it cool slowly to room temperature giving very nice large white shiny flakes of Zn-formiate, filter, wash Zn-formiate crystals with more EtOH, boil filtrate down again (and filter again if necessary), add aq. NaOH and extract free amine with solvent of your choice.

This method is using simple, basic, and dirt cheap chemicals, it gives very high yields (90%+ for most substrates), it's non toxic, doesn't produce ugly exhaust fumes, and it's ultra clean and selective (doesn't deshalogenate and I guess also doesn't attack double bonds if the aren't very activated).

Zn/HCl does also work in EtOH but it produces more side products (dark goo), especially if it get's too warm, while the HCOOH- way usually stays completly colorless and clean. Yields with HCl are smaller aswell in ALL the cases I've tested and workup is less beautyful.

CuReUS - 26-9-2014 at 00:40

Rabodon,this method is fantastic ,i wish someone had given me the details of the prodecure before ,as i have already carried out the reduction using Zn/HCl .the chemical i had to reduce was 2,4-dinitrophenol and it is extremely sensitive to air oxidation once it has been converted to the diamino.but if the diamino is immediately put in dil HCl ,the salt is formed which is resistant to oxidation .so i thought that i would kill two birds with one stone-by putting the dinitro(1.5g) in acid solution(10ml conc HCl +10ml water)and adding Zn granules(3g).the dinitro would get reduced to the diamino that would simultaneously form the salt with HCl. in the beginning the dinitro wasnt that soluble in the acid solution but as the reaction proceeded ,the solubility increased until it completely dissolved confirming that the reduction had taken place.i had expected to see a color change from yellow(nitro) to colorless(amino) but that didnt happen and the color changed from light yellow to a tan color .but when i filtered the solution(it had unreacted Zn granules) the filterate was exactly the same as described in the literature(slightly pinkish)

i didnt remove the ZnCl₂ though

(actually in standard metal/HCl reductions such as Fe/HCl or Sn/HCl you can precipitate the Fe,Sn using Zn but to precipitate Zn you need a more electropositive metal such as Mg,and the procedure is cumbersome ,not as easy as your method of just boiling it till Zn-formiate starts to precipitate.)

will that effect further reactions(i divided the filterate into two parts and did acetylation using acetyl chloride/pyridine for one and added FeCl₃ to the other half)

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Zn/HCl does also work in EtOH but it produces more side products (dark goo), especially if it get's too warm

this is exactly what i was scared of

(nicodem please take note) .initially i foolishly assumed that the H₂ evolved does the reduction and wanted to use ethanol as H₂ was more soluble in alcohol than in the water acid mixture,but nicodem cleared that misconception so i didnt use any ethanol in my reduction(thank you god and thank you nicodem

) .but i have references that use isopropyl alcohol along with Zn/HCl

surprisingly the reaction did not become too warm at all(i could hold the beaker on my palm) and i didnt use any freezing mixture either so maybe i have done something wrong

(there were a lot of bubbles from the Zn granules though)

but why do you think HCl gives less yield,isn't it a stronger acid than formic acid,so wont that make it a better proton donor.

[Edited on 26-9-2014 by CuReUS]

bbartlog - 26-9-2014 at 06:40

HCl is acidic enough to cause miscellaneous side reactions in a way that acetic acid does not. Also the excess energy (Zn + HCl generates more heat than Zn + HCOOH) probably contributes to the production of crap. Stronger is not the same as more selective.

zed - 26-9-2014 at 16:54

"Hydrogenation over Pd-C at atmospheric pressure is obviously the most obvious choice and probably also the most amateur friendly. Anything else will require a tedious isolation."

Was this approach overlooked, because it wasn't the answer you were looking for?

This method is worthy of consideration. When Nicodem makes a suggestion, it is usually a useful suggestion.

UnintentionalChaos - 26-9-2014 at 17:50

What's wrong with stannous chloride or mossy tin in HCl?

Having worked briefly with 4-aminophenol (and 2,4-diaminophenol being even more sensitive), this stuff oxidizes like crazy. Even in acid solution. Fortunately, the acid slows it down by keeping the anilines mostly protonated.

Any alkaline media is going to result in a big vat of black polyaniline tar or I'd suggest thiourea dioxide in aq. ammonia (or NaOH) which I have used very successfully for luminol.

CuReUS - 27-9-2014 at 03:05

"Hydrogenation over Pd-C at atmospheric pressure is obviously the most obvious choice and probably also the most amateur friendly. Anything else will require a tedious isolation."

Was this approach overlooked, because it wasn't the answer you were looking for?

This method is worthy of consideration. When Nicodem makes a suggestion, it is usually a useful suggestion.

i would have loved to use Pd/C or even lithium aluminium hydride but the problem is that they are not OTC,extremely difficult to work with(LiAlH₄) and ordering Pd/C will surely put you on Big brother's watchlist

CuReUS - 27-9-2014 at 03:14

Quote: Originally posted by UnintentionalChaos

What's wrong with stannous chloride or mossy tin in HCl?

nothing,its just that i had Zn lying around,btw would SnCl₄ be colorless like ZnCl₂

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Having worked briefly with 4-aminophenol

did you synthesize it ,if so which route did you use? were you going to use it for making paracetamol?

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this stuff oxidises like crazy ,even in acid

depends on the strength of the acid,1M H₂SO₄ or 2M nitric acid will keep the solution clear for days

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in alkaline solution,you will get tar,polyaniline...

thinking about it now,i remember when i was acetylating it with acetyl chloride,the moment i put the pyridine(7 ml) into the diamino.HCl,the whole solution became purpulish and a greyish white ppt formed.at that time i thought that it was because of the ZnCl₂ and continued the acetylation by adding acetyl chloride(7.5 ml).after the exothermic reaction was over ,the ppt has dissappeared and the solution has become a wine red color.i heated the solution in a water bath for 5 minutes and kept it in freezer to crystallise(didnt have ice around)

now after reading your post on the effect of alkaline medium on diamino phenol ,i think i have just screwed up big time

[Edited on 27-9-2014 by CuReUS]

[Edited on 27-9-2014 by CuReUS]

Rabodon - 27-9-2014 at 05:25

Has anyone here had success using HCOOH + ammonium formiate or potassium formiate + Pd/C for any reduction?
There are some references claiming to get extremly high yields for NO2-Reductions.

My 10% Pd/C by Merck seems to be very overreactive with potassium formiate + HCOOH as hydrogen donor, producing only tar with the aromatic substrates I've tried - I guess it's so strong it reduces the aromatic system in my case.

[Edited on 27-9-2014 by Rabodon]

bbartlog - 27-9-2014 at 07:05

What procedure are you trying to execute? There are no reducing agents in the chemicals you list, only catalysts and hydrogen donors, and furthermore potassium formate seems like it would be needlessly alkaline, but without any mention of substrate, conditions etc. I can't tell whether you are omitting details or actually trying to do something senseless.

Rabodon - 27-9-2014 at 10:57

Quote: Originally posted by Rabodon

My fav to Reduce NO2-Groups is Zn/HCOOH in EtOH.
You can make a slurry of fine Zn powder (you can activate it using thinned aq. HCl is your powder is old) in EtOH and add 85% HCOOH in portions. Reaction is very smooth unlike Al/Hg in IPA or LAH/THF. Good mechanical stirring is necessary to keep Zn in suspension - a good overhead stirrer is necessary for reductions larger then 10-15g substrate, for small batches strong magnetic stirring can be sufficient. After addition of all HCOOH heat a little further for 1-2h while still stiring to complete reaction. Workup is a charm, simply filter unreacted Zn, boil it down until Zn-formiate starts to precipiate, let it cool slowly to room temperature giving very nice large white shiny flakes of Zn-formiate, filter, wash Zn-formiate crystals with more EtOH, boil filtrate down again (and filter again if necessary), add aq. NaOH and extract free amine with solvent of your choice.

This method is using simple, basic, and dirt cheap chemicals, it gives very high yields (90%+ for most substrates), it's non toxic, doesn't produce ugly exhaust fumes, and it's ultra clean and selective (doesn't deshalogenate and I guess also doesn't attack double bonds if the aren't very activated).

Zn/HCl does also work in EtOH but it produces more side products (dark goo), especially if it get's too warm, while the HCOOH- way usually stays completly colorless and clean. Yields with HCl are smaller aswell in ALL the cases I've tested and workup is less beautyful.

Little addition, I forgot to mention that after filtration, before I'm boiling down, I'm adding a tiny splash thinned aq. HCl to lower the pH a littler further, to inhibit amide formation and to recover amines from potentially already formed amides. Might be a placebo, as you're usually adding aq. NaOH afterwards anyway which should recover the amides, at least slowly. One I forgot to add some HCl and only got ~80% instead of my usual 90%+, but that might be a coincidence, as my educt was from a different purity. HCl excess might harm your product, you might end up with more goo, and my suggested workup wouldn't work anymore, so only add a splash.

Another side note: Usual 90-96% EtOH works very well but MEK could theoretically cause N-(2-butyl) derivates as impurity in product. You can reflux and destill EtOH over NaOH to remove the MEK prior use or add a little NaBH4 if you have before starting Zn and HCOOH addition (NaBH4 addition doesn't harm yield at all) if you care. I don't know if IPA or MeOH are working as perfectly well as EtOH for this procedure, but they could be worth to try them, as they are comming usually much purer when bought OTC and they are free of ketones.

but why do you think HCl gives less yield,isn't it a stronger acid than formic acid,so wont that make it a better proton donor.

[Edited on 26-9-2014 by CuReUS]

It's my empirical data.
HCl a stronger proton donor for sure but in my experience simply also causes more side products. Don't forget you're using the HCl in large excess, and heating/boiling chemicals in such a strong acidic solution is actually not what I would call very sensitive. Also other factors like EtCl formation, worse soloubility of reactants due the water from the aq. HCl, the reactivity of ZnCl2, impurities like chlorine in technical grade HCl and others might play a role.

For me HCOOH instead of HCl worked always better, yielding often perfectly clear and colorless amine straight after simple acid/base workup while the HCl way always caused slightly to much lower yields and products which always cotained more or less visible goo, for some reactions sometimes very much of it.
And workup by precipiating the beautyful Zn formiate crystals is such a charm for your eyes, it's worth to do it even without an substrate inside you reaction mixture

[Edited on 27-9-2014 by Rabodon]

Rabodon - 27-9-2014 at 11:11

Quote: Originally posted by bbartlog

What procedure are you trying to execute? There are no reducing agents in the chemicals you list, only catalysts and hydrogen donors, and furthermore potassium formate seems like it would be needlessly alkaline, but without any mention of substrate, conditions etc. I can't tell whether you are omitting details or actually trying to do something senseless.

I didn't ask for explicit help for my reductions, I've only asked if someone here had success with it.

PS: As potassium formiate is generally used with excess HCOOH I thought the alkaline character doesn't matter, or did I make a bad mistake here?

zed - 27-9-2014 at 16:54

Nope. Pd and Pt, are very easy to obtain. E-bay

CuReUS - 28-9-2014 at 03:31

zed

even if they are easy to obtain,they arent that easy to work with

as i take it ,you must make a pd catalyst bed ,pass H₂ over that,the stream of gas should be steady,it has to be purified(dust,foreign objects kill the catalyst),and having a H₂ cylinder or a generator is like sitting on a time bomb

taking a beaker,dumping in your nitro compound and HCOOH,and adding Zn in portions seems much easier,and it is as i have already done it ,but with Zn/HCl (may be not faster but wayyyyyyyy easier)

CuReUS - 28-9-2014 at 03:45

Quote: Originally posted by Rabodon

It's my empirical data.
HCl a stronger proton donor for sure but in my experience simply also causes more side products.worse soloubility of reactants due the water from the aq. HCl, the reactivity of ZnCl2, ....

i agree on the solubility factor.i had mixed 10ml HCl and 10ml water and put that into a beaker with the dinitro compound,i didn't put any alcohol or any other organic solvent at all,to prevent side reactions

as a result ,initially the solubility was very bad,but as more and more dinitro got converted to the diamino, and the diamino formed salt with the HCl ,the solubility increased until everthing had dissolved

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For me HCOOH instead of HCl worked always better, yielding often perfectly clear and colorless amine straight after simple acid/base workup while the HCl way always caused slightly to much lower yields and products which always cotained more or less visible goo, for some reactions sometimes very much of it.

i didnt get a colorless solution at all

my starting compound,2,4-dinitrophenol made the solution color yellow and after 45 minutes( after most of the dinitro had got reduced)the color was tan yellow like light tea

but when i filtered the solution,the filterate was exactly according to literature-slightly pink

zed - 30-9-2014 at 14:10

On the contrary, Pt and Pd are easy to work with. I prefer Pt, because I think Pd is now vastly overpriced.

I used to like to produce Pt catalysts by the action of NaBH4 on Chloroplatinic Acid, in Ethanol.

Makes a very active catalyst, and it requires very little NaBH4.

Chloroplatinic acid can be produced by the action of Aqua Regia on Platinum. But, it is also quite possible, that electrolysis of Platinum in Hydrochloric acid will do the trick.

Catalyst bed? Not usually. Usually just a sealed flask, with Pt, H2, solvent and a stir bar.

Oh well, to each their own.

CuReUS - 1-10-2014 at 03:57

But, it is also quite possible, that electrolysis of Platinum in Hydrochloric acid will do the trick.

really,i thought Pt was one of the most inert metals,this is interesting

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Usually just a sealed flask, with Pt, H2, solvent and a stir bar.

sealed flask with gaseous products,a chemist's version of a time bomb dont you think ,with NaBH₄ around

but you should read this book(pg 31) under "Appendix 2 Watched Chemicals,
it lists palladium black as a watched chemical

Attachment: Nimble.pdf (251kB)
This file has been downloaded 840 times

[Edited on 1-10-2014 by CuReUS]

zed - 1-10-2014 at 16:53

Platinum is pretty inert, but not to elemental chlorine.

CuReUS - 3-10-2014 at 02:31

Platinum is pretty inert, but not to elemental chlorine.

so does that mean gold is the most inert metal?
many books list gold above platinum in the reactivity or the electrochemical series

violet sin - 3-10-2014 at 02:40

iridium, wiki:
http://en.wikipedia.org/wiki/Iridium
"is the most corrosion-resistant metal, even at temperatures as high as 2000 °C"

zed - 3-10-2014 at 16:53

I would expect gold also to react with elemental Chlorine.

CuReUS - 3-10-2014 at 22:23

Quote: Originally posted by violet sin

iridium, wiki:
http://en.wikipedia.org/wiki/Iridium
"is the most corrosion-resistant metal, even at temperatures as high as 2000 °C"

that's why they use Pt/Ir alloy for making the standard weight of 1 kg at the SI units office at paris

CuReUS - 3-10-2014 at 22:24

I would expect gold also to react with elemental Chlorine.

is elemental chlorine even more reactive than a chlorine free radicle?

zed - 4-10-2014 at 13:09

Don't know. Just know that precious metals can be leached from crushed ores, via elemental Halogens. Some techniques call for the generation of those Halogens, via the action of Oxone (pool shock) on Halogen Salts. Might be a spendy way to go. But, you can bet your ass that the manufacturers of Oxone, think it is a mighty fine idea.

As for the practicality of dissolving Pt in HCl with the assistance of an electrical current, unless the literature contains a good procedure, I'd have to experiment.

Maybe it is workable, maybe not.

Nice article posted elsewhere on this board. http://www.technology.matthey.com/article/57/4/289-296/

[Edited on 4-10-2014 by zed]

[Edited on 4-10-2014 by zed]

CuReUS - 5-10-2014 at 05:37

btw ,why is fe or Sn preferred over Zn for reducing agent although Zn lies above both of them in the electrochemical series

Nicodem - 5-10-2014 at 06:36

btw ,why is fe or Sn preferred over Zn for reducing agent although Zn lies above both of them in the electrochemical series

Why would the electrochemical series be that relevant for the reduction of nitro compounds? The electron transfer from the metal surface to a neutral organic compound is not that similar to the electron transfer from the surface to a metal cation, hydronium ion, or water. There are more important factors at play.

as i take it ,you must make a pd catalyst bed ,pass H₂ over that,the stream of gas should be steady,it has to be purified(dust,foreign objects kill the catalyst),and having a H₂ cylinder or a generator is like sitting on a time bomb

taking a beaker,dumping in your nitro compound and HCOOH,and adding Zn in portions seems much easier,and it is as i have already done it ,but with Zn/HCl (may be not faster but wayyyyyyyy easier)

It is quite obvious from your prejudices that you have never done a hydrogenation in your life. Comparing something as simple and straightforward as a hydrogenation over a balloon with something as tedious as a metal dissolving reaction on a substrate that gives a product so difficult to isolate is totally unreasonable. With a metal dissolving reaction, you will most likely consume most of your material just to develop a working isolation procedure, while a hydrogenation would give you near quantitative yields and no fuss whatsoever with any kind of development. For an amateur chemist with limited resources and equipment, hydrogenation is probably the only useful method on such a substrate.

CuReUS - 6-10-2014 at 03:45

Quote:

btw ,why is fe or Sn preferred over Zn for reducing agent although Zn lies above both of them in the electrochemical series

Why would the electrochemical series be that relevant for the reduction of nitro compounds? The electron transfer from the metal surface to a neutral organic compound is not that similar to the electron transfer from the surface to a metal cation, hydronium ion, or water. There are more important factors at play.

yes ,now i realize that i was a fool to come to such a silly conclusion.
it would be very helpful if you could tell more about the other factors

Quote:

It is quite obvious from your prejudices that you have never done a hydrogenation in your life

yes i have never done it and have no right to come to such stupid conclusions,i am terribly sorry

[qoute]Comparing something as simple and straightforward as a hydrogenation over a balloon

so in Pd hydrogenation what is the source of hydrogen.is it from a cylinder?.

Quote:

With a metal dissolving reaction, you will most likely consume most of your material just to develop a working isolation procedure

that is true ,considering the 3:1 ratio of Zn-nitro and the separation of ZnCl₂ from the mixture would be difficult(as you could not displace it with some easily available metal which is also more elctropositive than Zn)although idont understand this logic
suppose you used Fe and you displaced the FeCl₃ formed with Sn or Al foil,how would you separate the Sn/Al from the mixture now.do they form some insoluble salt that you can just filter off.

also could we add an excess of ZnCl₂ to the mixture to salt out the reduced organic compound from the aqueous layer(if only HCl is used as i did)or the HCl+ethanol layer(but rabodon mentioned on page 1 that HCl+ethanol could give some side products and goo formation)

i have salted out acetone and IPA(which are so soluble in water) so why cant the same logic be applied here?

also i have to confess that i was wrong in thinking that H₂S could only reduce one of the nitro groups in the dinitro as crowjford has used it to reduce tetranitro to tetraamine(see page 1) .

although you say that Pd hydrogenation is the best bet,i am not capable of doing it just yet because i still have a lot to learn about the procedure and getting Pd is not possible
so i am thinking of doing the sulphide reduction for my next experiment(reducing 4 -nitrosophenol to 4-aminophenol for making paracetamol)
so while doing the sulphide reduction,do we mix the sulphide salt(Na₂2) with the nitroso and acidify the solution?

PS- nicodem,i initially thought that you were a rude know-it-all type of person but after reading this previous post i know that you are far from that.you saved that guy's life ,if you hadn't pointed out polyammonium sulphides corrode steel ,he would have been dead by now.although people may think you are rude,your comments actually prevent mistakes( and correct crazy misunderstandings-like mine

)

your comments leave two choices to the reader,to wisen up and prevent furthur disasters, or to simply ignore or fight back with remarks like arrogant and ignorant children(like the guy in that post) and then carry on experimenting,hoping against hope that something doesn't blow up on their face(which eventually does happen and which puts a stop to their experiments for good)

i chose the former path and i am already becoming much smarter.maybe after another 1000 properly directed comments

,i can one day hope to achieve your level of knowledge .your replies to any post(including mine) are comprehensive, exhaustive and answer all our queries and live no doubts in the minds of the reader

chemistry always works,but not always in the way you want it to,so it is better to take good advice before its too late

[Edited on 6-10-2014 by CuReUS]

[Edited on 6-10-2014 by CuReUS]

[Edited on 6-10-2014 by CuReUS]

Nicodem - 6-10-2014 at 07:25

yes ,now i realize that i was a fool to come to such a silly conclusion.
it would be very helpful if you could tell more about the other factors

I don't know enough on the topic. There are several review articles on the topic of metal dissolving reductions, perhaps you can find some relevant information there. I posted two reviews in this thread, though they are not about nitro to amino reductions.

Quote:

suppose you used Fe and you displaced the FeCl₃ formed with Sn or Al foil,how would you separate the Sn/Al from the mixture now.do they form some insoluble salt that you can just filter off.

The isolation procedure is obviously dependable on the product properties. Now, you product is amphoteric, water soluble, has a very low logP, is oxygen sensitive, potentially metal chelating, and so on. For this reason I suggested hydrogenation as the simplest solution. I would never bother with anything else, but if for some reason I would have to, I would opt for iron powder in methanol. I would probably use a few mol% of saturated FeSO₄(aq) to kick start the reaction (acetic acid might do as well). After the reduction is complete, you filter off the hydrated iron oxides and any unreacted iron, wash with some methanol. You filter the filtrate trough celite or silicagel and rotavap it. Recrystallize from wherever and avoid too much oxygen exposure.
Not sure it would work, but that is what I would try first. In case of failure, I would use iron in acetic acid and proceed the same way. It would most likely give more iron contamination and the product might coordinate with Fe. To minimize complexation, I would use a large excess of iron (Fe to Fe(II), but without Fe(III) formation).

Quote:

i have salted out acetone and IPA(which are so soluble in water) so why cant the same logic be applied here?

I don't say it is not possible to remove Zn or Sn salts. I just said it would require a lot of development for no particular advantage. It sounds simple when describing such a mess with words, but doing it in real life is something else. Besides, zinc chloride is too acidic to allow the product out of the aq. phase and is also quite soluble in alcohols. At the proper pH, the mixture might be a mess with precipitated zinc hydroxide and so on.

PS: Please pay more attention to the quotation formatting. You make it difficult to read your replies.

CuReUS - 8-10-2014 at 01:09

I would expect gold also to react with elemental Chlorine.

so can that reaction be used to replace aqua regia ,by putting two gold electrodes in HCl or sulphuric acid and turning on the power ,the efficiency will not be that good though

because some one wants to replace aqua regia to strip gold from computer parts in this thread
http://www.sciencemadness.org/talk/viewthread.php?tid=36959

zed - 11-10-2014 at 15:24

I would expect all of the anodized Gold (or Platinum)to eventually dissolve as a Chloride salt. The trick might be....in preventing dissolved metal from eventually plating out on the opposite electrode. Perhaps a Semi-permeable membrane would help.

The guys in Techno-Chemistry could have better insight. Barring that, a website on the topic of Electroplating.

Might require experimentation. Just because something should work, doesn't mean it will.

In the case of dissolving Silver via HCl and electricity, I would expect that the reaction might be stopped by insoluble Silver Chloride clogging up the surface of the electrode.

I've designed lots of interesting experiments. Most failed to achieve the results I originally envisioned.

Well, back to the side issue. A few minutes of searching yielded the following.

Pt electrolysis with HCl. It wasn't very hard to find. I gotta think it's kind of obvious, and considering the late date of the patent, possibly not patent worthy. But....... http://www.google.com/patents/US5423957

But, we were talking about the possibility of using hydrogenation to achieve your goal. Think about it.

[Edited on 11-10-2014 by zed]

[Edited on 12-10-2014 by zed]

CuReUS - 12-10-2014 at 01:40

I would expect all of the anodized Gold (or Platinum)to eventually dissolve as a Chloride salt. The trick might be....in preventing dissolved metal from eventually plating out on the opposite electrode. Perhaps a Semi-permeable membrane would help.

yes,i have a design in my head which i saw in bromic acid's book ideahttp://www.bromicacid.com/bookprogress.htm
under electrolysis using a bottle to make copper sulphate
also we could use one electrode as graphite so that it does not deposit on that

Quote:

In the case of dissolving Silver via HCl and electricity, I would expect that the reaction might be stopped by insoluble Silver Chloride clogging up the surface of the electrode.

but in aqua regia reaction,gold is eventually converted to chloroauric acid so i think it will be soluble.also have you tried wrapping the electrodes with steel wool(or glass wool,i cant remember) ,that might prevent it from clogging

Quote:

I've designed lots of interesting experiments. Most failed to achieve the results I originally envisioned.

wouldnt be bad if you could share some of your ideas and the outcomes

Quote:

But, we were talking about the possibility of using hydrogenation to achieve your goal. Think about it.

yes ,i agree that nicodem was right ,but as i said in my previous post to nicodem,i cant do that because i dont understand the procedure yet(hydrogenation over a balloon?)

now i am thinking about using some sulphide salt as a possible reducing agent as the metal/acid reduction takes a lot of time,and you also need a lot of the metal(3:1 ratio of metal -nitro compound)

Nicodem - 12-10-2014 at 07:16

)

http://chemistry.tutorvista.com/organic-chemistry/carboxylic...

yes ,i agree that nicodem was right ,but as i said in my previous post to nicodem,i cant do that because i dont understand the procedure yet(hydrogenation over a balloon?)

"Hydrogenation over a balloon" is just a phrase for a normal hydrogenation at atmospheric pressure. It only takes a flask, a magnetic stirrer, a septum, a needle and a balloon. Nothing special, except perhaps an inert gas to purge out the air, but even that can be improvised in an amateur setting. I did this kind of a hydrogenation in my bathroom when I was much younger (This does not mean that I (still) approve of using the bathroom for chemical experiments! I got wiser now.).
If you are afraid of hydrogen, you can use CTH with cyclohexene instead (such a preparation of 2,4-diaminophenol is described in DOI: 10.1039/JR9540003586).

An alternative amateurish method is the reduction at the cathode. We have a thread on this topic. Apparently the 2,4-diaminophenol dihydrochloride is poorly soluble in concentrated hydrochloric acid so that would make for a good electrolyte. You would maybe have to use some methanol as a cosolvent which may affect the dihydrochloride solubility, but should be easily removable by concentration. In fact, the only reliable procedure for the metal dissolving reduction of 2,4-dinitrophenol to 2,4-diaminophenol employs this trick with the dihydrochloride to isolate the product from the reaction mixture (using Sn and conc. HCl; DOI: 10.1039/P19870000851). This procedure is simple and gives a good yield of the product as the dihydrochloride. Liberating the aniline could perhaps be done with Na₂CO₃ in methanol under nitrogen, followed by filtration and solvent removal.

By the way, electrochemical reduction of m-dinitrobenzene in acidic media also gives 2,4-diaminophenol (Current Science, 12, 151-153). An alternative using Al is described in US2525515, but no yields are given (we have two threads on the topic of such aminophenols from nitrobenzenes syntheses that you might want to check).

[Edited on 12/10/2014 by Nicodem]

zed - 12-10-2014 at 15:47

Like that.

http://www.orgsyn.org/demo.aspx?prep=cv9p0589

If the pressure gauge were replaced by a balloon, you would have a very simply built hydrogenator. The rest of the article doesn't much apply to what you are doing, but at least you have a picture.

[Edited on 12-10-2014 by zed]

CuReUS - 13-10-2014 at 04:44

nicodem
yes ,i also used to experiment in the bathroom, that to in the dead of night until a little :mad:

accident wisened me up
although i must say that i feel a bathroom is one of the safest places to work as the walls and floors are tiled making it fire proof and also easy to clean in case of a mess
with one or two halon fire extinguishers with thermal fuses,what more could you ask for

also there is a shower station in case the chemical god is not pleased with you

i didnt give much importance to the electrochemical reductions due to the long reaction times ,also in some e- reductions ,i think you have to use a clay pot with a semi permeable diaphragm and also are electrochemical reductions efficient,but now i will look into it

that you are telling me that 2,4-DAMP is insoluble in HCl comes as a bit of a surprise because when i did my Zn/HCl reduction and filtered the solution i got a clear to slightly pinkish solution although the original solution had not become colorless (as i had imagined) but a tan yellow, almost tea color ,meaning that some of the nitro compound was still not reduced.

i did not put any colsolvent like ethanol or IPA because i was scared that a side reaction would take place so i dont know if the solubility of the nitro compound would have improved or not

but the last reaction you talk about is actually beautiful

i have read about the bamberger rearrangement of n-phenyl hydroxylamine to para-amino phenol in presence of sulphuric acid and catalyst but meta dinitrobenzene to DAMP ,just amazing

ZED
thanks for the link,but it is not opening now ,i will try again later
also in our electrochemical discussion ,i had another idea for preventing silver choride depostion if the wool idea didnt work
why cant we try to covert the silver chloride into a complex compound that can be later broken down to give the silver with the help of strong acids

zed - 13-10-2014 at 13:43

One problem at a time. Silver was just an aside remark. Like anodizing Aluminum.

zed - 16-10-2014 at 13:08

Oh, in response to your complex Silver compound idea......DON'T! Unless you really know what you are doing, complex salts of Silver can be quite dangerous to work with. They like to explode. Famous for it, in-fact. Moreover, you may be unaware that you have formed a complex-salt. This can be simple as mixing Silver Nitrate and Ammonia.

http://en.wikipedia.org/wiki/Tollens%27_reagent

These explosive tendencies may be shared by the complex salts of other metals, Nobel metals especially. Always good to check.

[Edited on 16-10-2014 by zed]

[Edited on 16-10-2014 by zed]

[Edited on 16-10-2014 by zed]

CuReUS - 17-10-2014 at 08:25

i know that silver diazonium compounds can explode ,but complexes themselves,that is news
i feel it is counter-intuitive ,as we are taught that complexes are very stable compounds(Fe(CN)₆^4- is not toxic although it has cyanide ion

zed - 20-10-2014 at 15:53

Ummm. Don't let 'em dry out. Some of these complex ions, like to "simplify" themselves into materials that are very unstable.

As for Ferri-cyanides....they are sometimes utilized as components, in some impressive explosives.

Alas, we have gone way off topic. And, I'm not really an explosives guy. My interest is in avoiding explosions.

CuReUS - 23-10-2014 at 01:34

yesterday i saw nurdrage synthesis of luminol
http://www.youtube.com/watch?v=58Ve69s0qD0

he uses Na₂S₂O₅ and Al to reduce the nitro to the amino to get luminol .

so can we use Na₂S₂O₃ with Al to get the same result with 2,4 DAMP

CuReUS - 15-11-2014 at 21:44

in the hope of reviving this thread ,i ask a question that is bothering me for quite sometime now

how powerful a reducing agent is HI

can it reduce COOH to methyl directly (until recently i thought it couldn't but recently i read that it could.

CuReUS - 28-12-2014 at 23:54

Do you have a reference for a non-CTH or non-catalyzed reduction of nitroaromatics with H₃PO₂? I have only seen CTH reductions with this reagents

maybe you already know this reaction,but i am posting it anyway
read this article,they use H₃PO₂ along with HI to reduce aromatic nitro group

Attachment: molecules-19-08039-v2.pdf (403kB)
This file has been downloaded 575 times

Nicodem - 29-12-2014 at 05:24

maybe you already know this reaction,but i am posting it anyway
read this article,they use H₃PO₂ along with HI to reduce aromatic nitro group

The article in Molecules 2014, 19, 8039-8050 mentions the reductions of some nitrophenols with hydriodic acid. The hypophosphorous acid appears to be there only to quench the iodine which is the side product of the reduction (while it also recycles the iodine back to HI). This example does not indicate that the hypophosphorous acid can reduce nitro groups. If anything, it might indicate the opposite.

Quote:

The nitrophenol compounds 8b–13b were then heated under reflux with 57% HI (10 mL) in the presence of 30% H₃PO₂ (1.0 mL).

Dr.Bob - 29-12-2014 at 12:47

There are much gentler ways to reduce nitro groups than "reflux with 57% HI (10 mL) in the presence of 30% H3PO2 (1.0 mL). " Sodium dithionate (Na2S2O5) works fine, even without Al (which I had not seen added before), Raney Nickel and many reductants, Sn, Fe, H2, etc. While it is always interesting to read about another essoteric method, I don't think 57% HI is any easier to find or use than other methods. I can't think of many things more common and iron and HCl, although I will admit that they form a mess and are not the ideal reducing agent, but a nitro group is pretty easy to reduce.

CuReUS - 29-1-2015 at 23:43

could someone explain why sometimes formic acid can be used as a reducing agent and sometimes Al/hg and acid is used to reduce imines.Both can reduce imimes,formic acid in eschenweiler-clarke and Al/hg +acid for reductive amination.so can they be used interchangebly ?
also,Zn/HCl can reduce C-C double bonds,but I think the yield will be small
https://books.google.co.in/books?id=AcpPyv0HWRsC&pg=SL1-...
go to the next page(A-98) and read the example of the clemmeson reduction of cyclic 1,3-diketone

Darkstar - 30-1-2015 at 02:30