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Rosco Bodine
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Sodium picramate is such an intense dye and so much
redder and more soluble than free picramic acid that
it can act as its own color change indicator for marking
the titration endpoint when adding acid . IIRC you can actually make DDNP by first titrating the sodium picramate solution until you get a color shift
to a very pale yellow supernatant solution over a pigment fine
precipitate of the less soluble free picramic acid which
is an orange brown dull and drab color much different from the intense deep oxblood red color of sodium picramate . The diazotization can then be
performed
simply by adding sodium nitrite solution . Adding it
all at once gives the amorphous product , but I would
expect that by using sufficient dilution to get the free
picramic acid back into solution , or entering solution
in the reaction zone at a temperature that is correct
for the limited rate of addition of the sodium nitrite ,
that crystallization might be slowed sufficiently for
better crystal development . It is probably all
about reaction rate control and solubilities which
determines the crystal form as much as any order of addition , although it is not certain that this is so .
It may be that the only way to get decent crystals
is to follow the Urbanski outlined method in every detail .
It could be worthwhile to try different dilutions and
see how the titration method may perform at similar temperatures and reaction volumes and addition rates
as is described by Urbanski .
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Mason_Grand_ANNdrews
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I`ve read a document, picramic acid was made by the reduction with iron. I guessing iron is corrosive, but didn't think this method will work better.
Dissolve 1g of picric acid in 100 ml of glacial acetic acid at room themperature and this is stirred until all is dissolved. 0,5 g of finely powdered
iron is added over a period of 24 hours and the mixture is stirred papidly. The liquid is stirred until the mixture turns to slight dark red and all
iron is dissolved. The liquid is than evaporated by distillation.
I belive the result is better obtained when the mixture is diluted with H2O and the crystals are precipitated by cooling to 0 gegree celsius.
Is the result picramic acid and will this method give a purer product ? Some hints would help. 
[Edited on 21-6-2006 by Mason_Grand_ANNdrews]
[Edited on 21-6-2006 by Mason_Grand_ANNdrews]
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Rosco Bodine
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That's one huge waste of glacial acetic acid , IMO .
Reportedly ferrous sulfate will work in aqueous solution .
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Axt
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| Quote: | Originally posted by Mason_Grand_ANNdrews
I`ve read a document, picramic acid was made by the reduction with iron. |
Near bottom of first page in this thread I've attached an article giving conditions for 96% yield from PA using water/NaCl/iron turnings. I've never
tried it, though looks easy enough.
0.5g NaCl, 50ml water, 25g PA & 18g Fe, heat for 5hr @ 82-85°C --> 96% PAA
[Edited on 22-6-2006 by Axt]
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Rosco Bodine
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That reaction mixture will be a slurry , like porridge
probably and will likely be required to be stirred
for the duration of the reduction .....and it will probably
need makeup water to be added periodically to maintain the volume .
The reacted iron will probably be the black oxide which
is quite insoluble and will be intimately mixed with the
picramic acid which is also nearly insoluble , perhaps
a signifcant portion of the product being present in combined form as ferrous picramate . To isolate the
desired product in pure form it will be necessary to
dilute and digest the spent reduction mixture with an acid in order to convert any oxidized or combined iron
to a highly soluble ferrous salt which will be easy to
filter away from the free picramic acid . Using pool grade hydrochloric acid of 31.45% concentration for
this purpose 65 ml would be the minimum amount of
theory , but using 75ml would probably be better ,
and even as much as 100 ml to 110 ml would liklely be fine for a diluted spent reduction mixture . This digestion
will probably require heating the mixture to or near the
boiling point and stirring for a few minutes to complete ,
and the mixture can be cooled and diluted further before filtering . The excess of HCl is a good idea since it
will accommodate the likely oxidation of some of the
ferrous chloride to the ferric chloride from exposure to air and heating and stirring , and will keep all the iron in solution as the ferric chloride
is even more soluble than the ferrous chloride expected as the initial product of the digestion .
My german isn't good enough to pick out whether this
was described in the article ....but take my word for it
that if it wasn't it should be . And HCl may not even do the trick of solubilizing the oxidized iron .....nitric may
be required , or the addition of a nitrate salt to the HCl
may provide sufficient nascent " aqua regia " to do
the trick . Sometimes the oxidized iron particularly if
it is the black oxide can be surprisingly " inert " as if
all the " fight " was gone from that poor iron after
being so brutally oxidized  , ravaged by hordes of
rampaging horny nitrobrutes .
I have done a few of these reductions of other nitro compounds using iron , and FeCl3 as a catalyst ,
and driving the reaction directly with an HCl drip
while heating at the bp and stirring violently to
keep the iron in suspension and the insoluble nitro
compound emulsified in the mixture .
It may be as simple as it seems from the article
just stirring the slurry of the iron and the picric acid
since for this reduction the nitrocompound is soluble ,
but the isolation of the picramic acid product is
what will be the the trick .
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The_Davster
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Why not just basify to get the soluble picramate, filter out the iron and iron oxide, then acidify the picramate to get back the picramic acid? Seems
much easier. Can even control the size of the picramic crystals this way.
[Edited on 22-6-2006 by rogue chemist]
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Rosco Bodine
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You could try that , but I'm betting on an unfilterable
ferrous hydroxide or other complication with that approach because there will likely be enough soluble iron which drops out when you basify ....but
maybe boiling would break it up .....so yeah good idea . Would require greatly diluting the
mixture , maybe to a liter or two .....I'd have to check the solubility of sodium picramate at boiling .
One thing for sure , you will have a separation to look forward to . So .... does anybody speak enough german here to see if the article sheds any
light on this ?
[Edited on 22-6-2006 by Rosco Bodine]
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The_Davster
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I don't know how picramic would behave here, but with adding a bit of peroxide to ferrous hydroxide, no matter how much of an ooze it is, will make it
much easier to filter iron (III) oxide. However oxygen is also released which might reoxidize the picramic.
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Rosco Bodine
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That article may be a german journal parallel publication
of an american journal article , because the authors
have american names and the laboratory work was done
in the US . Maybe sombody could find the english version published material if it was also published in an english language journal . Axt ?
Anyway , the separation using a base will depend on how finely divided is the oxide and if it is heavy enough to settle
out so the rest can be decanted . Any iron hydroxides
mixed with the sodium picramate would be no problem
since those will readily be sent into solution as chlorides
by HCl , while the picramic acid will precipitate on acidification .
I still think the acid separation will be more straightforward ,
and sulfuric alone or sulfuric with a bit of nitrate or nitric
should work fine too . It would make for some interesting experiments to find what works best .
[Edited on 23-6-2006 by Rosco Bodine]
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Mason_Grand_ANNdrews
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I was also thinking about how to obtain picramic acid.
Is that correct, the addition of finely
powdered sulfur to a warm mix of picric acid/NaOH solution would be sodium picramate ?
I guessing, serveral steps will needed. The NaOH/sulfur should neutralised and filtered complete from the slurry
to prepricate the sodium picramate.
You are right, the described method with the iron powder was somethimes crap. Very low yield.
What is the result, dissolved phenol in NaOH solution was nitrated with dilute HNO3, second step - 70% HNO3.
A article says it is 2,4-dinitrophenol. This will be not a sodium salt ?
Even though, that during the formation of variably results by ratio dinitrate/trinitrate, HNO3/concetration by acid, H2SO4/HNO3. Why not picramic acid
by 4-chloro-2,6-dinitrophenol. 
[Edited on 24-6-2006 by Mason_Grand_ANNdrews]
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The_Duke
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| Quote: | Originally posted by Mason_Grand_ANNdrews
I was also thinking about how to obtain picramic acid.
Is that correct, the addition of finely
powdered sulfur to a warm mix of picric acid/NaOH solution would be sodium picramate ? |
That will not work.
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Mason_Grand_ANNdrews
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I have just done a search on the net for information about the result but but i didn`t found
somehwat. Nasty H2S will bubble off sulfur is added. I belive that will work when the slurry is serveral cleaned
and contents are removed.
Sulfur/soluble in CCl4
NaOH/neutralization by HCl
I hope that will work. Picric acid is added to NaOH solution at 60 degeree celsius until
addition is saturated. Finly powdered sulfur is stirred to the mixture until nothing will dissolve.
To this, some dilute HCl and any ml of CCl4 will stirred in the mix. I hope the result can be obtained when,
the liquid is careful vaporizised or the slurry is diluted with water in a ratio 1/3, filtered and the crystal are prepricated
by cooling to 0 degree celcius. I'm not sure, alternative ways to obtaining the results are adding a large access of CCl4 to the mix and this will prepricate the picrate, adding HCl to neutralizing the salt and the picramic
acid will prepricate or the mix will than diluted with H2O and this is cooled to 0 gegree celsius.
4-chloro-2,6-dinitrophenol
5g of 4-chlorophenol is careful added to a mix of 60 ml 90-95% HNO3 / 120 ml 96-98% H2SO4 and the mix
is careful heated and stirred over a period of 4 hours to 100 degree celcius. The crystals of 4-chloro-2,6-dinitrophenol are prepricated by adding
1000 ml cold water to the mix.
Several washings thoroughly with water will clean the crystals. As a possible alternative to that, 4-chlorophenol will be refluxed for two hours yield
a purer result and don`t have remains of a mononitrate of 4-chlorophenol.
[Edited on 27-6-2006 by Mason_Grand_ANNdrews]
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Rosco Bodine
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| Quote: | Originally posted by Mason_Grand_ANNdrews
I have just done a search on the net for information about the result but but i didn`t found |
Searching the net should have included searching this thread including the
link posted near the end of the first page , concerning Mr. Anonymous " dry method " for making
the Sodium Polysulfide reagent . The experimental method
is pasted below .
As promised, there is some info I can share regarding the polysulfide route to picramic acid. I will preface by saying there are better, more
efficient uses for picric acid, from what I have observed about the usefulness of DDNP, which is what I presume is the ultimate object.
A good quality of deep red crystalline sodium picramate in good yields is possible via the sodium polysulfide reduction of sodium picrate. Several
times I have repeated the experiments and found that slight adjustments in reaction conditions can improve the results, so I have not yet determined
what conditions are optimum.
Please feel free to tweak the general process, if you want to do the work. The polysulfide reduction is quite similar to the synthesis described in
your library. The problem that I have seen in the online descriptions of the polysulfide reduction, is a lack of detail about the correct method of
preparation for the sodium polysulfide reagent. A thorough, intimate mixing of the correct proportions of NaOH and sulfur, being first thoroughly
mixed as DRY ingredients, which absorb moisture from the air very gradually, darken in color, and initiate a spontaneous highly exothermic reaction
while being stirred is the required approach for producing a good polysulfide reagent. If atmospheric moisture is low, a trigger mister can be used to
get things going. The idea is to get the reaction going from a stirred dry powder which becomes crumbly as it warms and darkens and then a drop or two
of water is added, the mixture stirred very well and a few more drops of water added, whereupon the reaction then proceeds on its own to form the
polysulfide very quickly as a dark red but transparent liquid which looks bright yellow in thin layers. The stoichiometry for reactions involving
polysulfides is not fully known. The goal is to get a good reduction without a great precipitation of elemental sulfur as a contaminant. My own theory
is that if the alkalinity is just right, the higher polysulfide which is decomposed in the reduction can be converted to a lower polysulfide and
remain in solution, instead of precipitating free sulfur. The polysulfide may possibly even reform from its fragments after acting as an unstable
intermediate compound in the reduction. I am uncertain that the actual mechanism for the reaction involving polysulfide is even known, beyond the
knowing that it just works somehow.
The following is from my old lab notes, with commentary ideas included.
Experimental:
On a hotplate stirrer is placed an 800ml beaker and with stirring, 22.9 grams, (.1 mole) picric acid is dissolved in 400ml boiling water. Heating is
stopped. To the stirred still hot solution is added a solution of 4.2grams NaOH (.105 moles) in 25ml water.
comment: easy solution was noted so less water may be useful in subsequent syntheses.
While the slightly alkaline sodium picrate solution is cooling, a sodium polysulfide reagent is prepared as follows:
NOTE: All of the following procedures should be done with good ventilation, toxic gas is produced.
Into a 100ml beaker is placed 13 grams NaOH fine prills and 10.1 grams powdered sulfur (flowers of sulfur USP) Using a glass stirring rod the granular
materials were manually mixed dry as thoroughly as posssible, and as the stirring was continued the mixture began to take up moisture from the air and
darken in color slightly, and the physical texture changed as the mixture became stiffer and more difficult to stir. The particles become adherent to
each other and the mixture begins to warm.
A couple of drops of water are fed from an eyedropper onto the stirring rod and stirred into the mixture, then two drops more, and stirring is
assertively done between dropwise additions to blend the very gradually increasing moisture into the reactants. The induction of a highly exothermic
reaction occurs concurrently with the slight dampening of the mixture which may need to be stirred yet a little more if any "dry lumping" is observed.
The pasty mixture gets really hot and darkens quite rapidly, with an evolution of intense "sulfur fumes" from the melting and reacting sulfur. Hold
the beaker by the upper rim where it is cool and do not get burned by touching the walls of the beaker near the reaction mixture. The addition of
water two or three drops only, in each addition may be continued portionwise, with stirring between these small additions, in order to maintain the
heat by reaction and heat of dilution, until a dark red transparent solution results. The hot reaction mixture should become a thin and mobile enough
liquid that further mixing and dilution can be done by manually swirling the beaker lightly.
Once the pasty mixture has cleared to a hot solution (melt would probably be more accurate description), then gradual additions of water in increasing
amounts should be made by the eyedropperfull until the volume of the resulting solution is about 40ml volume. If a dark red melt clear of solids fails
to form completely on its own heat of reaction, at this point DO NOT add a lot more water and "boil" or a partly crystallized failed to complete
reaction mixture will probably result.
If 1 or 2 ml of added water is insufficient to "kick" the reaction by heat of dilution, then supplemental heat will be required to drive the reaction
to completion, before further dilution to a volume of 40 ml. This dilution should be sufficient to prevent the reagent from crystallizing upon
cooling. Keep the polysulfide reagent from contact with the air after it is prepared. Air may degrade and cause precipitation of elemental sulfur from
the polysulfide reagent if it is left standing uncovered. The prepared reagent is put into a separatory funnel and supported over the still warm
sodium picrate solution prepared earlier. A piece of plastic wrap is secured over the top of the beaker with a rubber band and the plastic wrap is
puntured in the center to admit the tip of the separatory funnel. This is done to exclude air from circulating freely around the surface of the
solution in the beaker during the addition of the polysulfide solution. A seal is not needed here, a loose covering is sufficient.
To the stirred sodium picrate solution at 44 degrees centigrade, was added the sodium polysulfide at a rate of one drop per second to one drop per two
seconds, with stirring continued for one hour. The mixture was then covered to the complete exclusion of air, and allowed to stand in the cold
overnight, chilled to 5 degrees centigrade, filtered and the crystals of sodium picramate and the filter paper and filter cake were further dried by
placing on a stack of paper blotters. The crystals were dark red prismatic and very fine granulation, and were used without further purification for
the diazotation reaction.
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Mason_Grand_ANNdrews
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Nice work, if you want to know some chemical information what any explosives are souluble in water. This will advise some to the extraction and
solublity in chemicals.
2-nitrophenol 21 g/l
2,4-dinitrophenol insoluble, around 100 mg/l
2,4,6-trinitrophenol around 10 g/l at room themperature, 11g/l at 20 gegree celsius
sodium picrate and picramate around 5g/l to 6g/l
Looks like that the way by NaOH are always exotherm and will require a precise calculation by weight to the NaOH solution. Well known are any content
of NaOH in the result can pumping out moisture from the air and the result will melt away.
[Edited on 28-6-2006 by Mason_Grand_ANNdrews]
[Edited on 29-6-2006 by Mason_Grand_ANNdrews]
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Rosco Bodine
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| Quote: | Originally posted by Mason_Grand_ANNdrews
Nice work, |
Not optimized , but close enough for " government work "
and a lot better than the old " black book " method .
I don't know where you get your solubility figures ,
but IIRC sodium picrate is * more soluble * than picric acid ,
and so are the lower nitrophenols .
| Quote: |
Looks like that the way by NaOH are always exotherm and will require a precise calculation by weight to the NaOH solution. Well known are any content
of NaOH in the result can pumping out moisture from the and the result will melt away. |
Something is lost in the translation there . I do not
understand what you are saying .
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Mason_Grand_ANNdrews
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Sorry about the lost word in the post, some login trouble. 
Any solubility in H2O will tell the safety data sheets but to exposives, precise infos will hard to get that what exactly solublityes are. I would
guess what you read somewhere will not correct always.
Also i belive, picrates are better obtained by a carbonate and will be better to store. Some stuff will decompose to fast on the open air by water.
Whats going on topic ?
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Axt
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| Quote: | Originally posted by Rosco Bodine
but IIRC sodium picrate is * more soluble * than picric acid ,
and so are the lower nitrophenols .
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Picric acid = 1.4g/100ml @ 30°C (PATR 2700)
Na-Picrate = 5.58g/100ml @ 30°C (JACS; 1939; 61(12); 3302-3303; attached)
[Edited on 5-7-2006 by Axt]
Attachment: Solubilities of Sodium and Potassium Salts of Nitrophenols and Related Acids.pdf (257kB)
This file has been downloaded 1823 times
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Mason_Grand_ANNdrews
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Thanks for uploading the PDF. I guess some methods will have interest. I belive there are more possibilities to obtain picramic acid. I will thinking
about.
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Rosco Bodine
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There are some related patents which should be
listed as also having application to the production
of picramic acid by way of sulfides / polysulfides .
While these patents were published with the focus
upon selective reduction of one nitro group in order to produce aniline or nitroanilines from nitro or polynitrobenzenes , the same reduction reagents
and methods are applicable to the selective reduction of one of the nitro groups of picric acid to produce picramic acid .
US1878950
US1689014
US1765660
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Rosco Bodine
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A highly relevant article
The preferential reduction of nitro-groups in polynitro-compounds. Part III. Picric acid and 3 : 5-dinitro-o-cresol. An almost quantitative
preparation of picramic acid
Herbert H. Hodgson and Edward R. Ward
J. Chem. Soc., 1945, 663 - 665
This study showed an optimum molar ratio of sulfur on a molar basis to the nitro compound of 2.3 to 1 ......
which is precisely the same ratio as found to give nearly quantitative yields in another reference for a similar reduction , example 2 of US1878950
.
So the somewhat preliminary molar ratio of Sulfur to picrate
of about 3 to 1 which I used in my dry method polysulfide ,
is not wildly different nor greatly excessive , even though
I knew it was not yet optimized ....it was generally in the ball park . And my direction of next increasing the alkalinity
tracks as well .
The Hodgson article also seems to agree with my own
thinking on the matter of the hydrosulfide of sodium being
the actual reducing agent .
There is a Thiokol corporation patent ( yes the same SRB propellant folks ) , US2796325 , which is very informative
about how NaOH reacts with Sulfur , and how polysulfides
of various sulfur content or " sulfur ranking " are gradually
reduced on long heating to lower and lower ranking , until
the hydrosulfide is reached .
Attachment: J[1]. Chem. Soc., 1945, 663 - 665, .pdf (344kB)
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Rosco Bodine
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Some further details on this method are on page 12 of the attached file , which reviews the Zinin reaction in general .
Attachment: The Zinin Reduction of Nitroarenes , H. K. Porter.pdf (777kB)
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Rosco Bodine
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concerning the origins of the " dry method "
When I was trying by trial and error
to work out a simple method for quickly making
an active polysulfide reagent and came up with
the technique of thoroughly mixing the dry solids ,
gradually moistening and initiating a highly exothermic
reaction to a melt then gradually diluted .......
it appears I was " reinventing the wheel "
with regards to that idea .
As it turns out it was indeed ancient art , patented 1913 ,
US1068769 , and that patent reissued later after it expired .....so it evidently was a useful method .
Anyway the patent is attached for the original " dry method "
as it has been called by others ....and seems appropriate .
The analysis of the result of the reaction , given in the patent
is incomplete IMO , as the 36.98% of so called " Free sulfur
which is soluble in water " is no such thing at all ,
but would be a combination of reducing sulfur compounds
which do have solubility in water probably Na2S2 and NaHS
for the most part . The actual analysis of these mixtures
will be variable , depending upon the alkalinity relative to the
sulfur content , the amount of water present , the temperature of formation and how long the mixture was heated ......and especially how much exposure
to air the
mixture received . The minimizing of air exposure also
minimizes the formation of thiosulfate and sulfite , to the
benefit of a higher yield of " reducing sulfur compounds "
in the mix . From all the patents and references I have
studied ....the conclusion remains with me that the actual
composition of these " polysulfides " is ambiguous and
variable ....depending upon how they are made and the
ratio of alkali to sulfur .
Update: I have done some numerical analysis and studying of the percentage analysis provided by the patent , in order to " reverse engineer " the
likely reaction quantities which would have produced that analysis I believe is in error .
It appears that the analysis provided would have applied
to a reaction involving on a gram basis for example ,
40.4 g NaOH and 55.16 g Sulfur ....
and the dubious percentile figure stated for " Na2S " when
*added* to the equally dubious " soluble sulfur " percentage , sums nicely to about what should be the expected yield of Na2S4 ....or a blend of
alkali and sulfur rankings of several polysulfides approximating Na2S4 as an average for their composition , or on a gram basis 65.45 g ,
of the Na2S4 equivalent . This analysis and conclusion was
based in part on the information disclosed in a more modern Thiokol corporation patent US2796325 .
In my own estimation , a much better polysulfide reagent for performing reductions would require additional alkali sufficient at least to bring that
Na2S4 ranking 4 equivalency component down to Na2S2 , and possibly even lower .
I am continuing to review the available literature to gain further insight and make an educated guess about the
correct proportions for polysulfide reagent to be used in the next Zinin reduction experiment . I am not certain of this , but it appears that it may
be best to first make the higher ranking sulfur compound such as Na2S3 , Na2S4 , or even Na2S5 , since the higher sulfides form more rapidly ....and
then after the higher sulfide has formed , to add more NaOH to form the lower sulfides desired with longer heating in the absence of air . This
strategy might reduce the side reaction
which produces the byproduct sulfite and/or thiosulfate ,
tying up 10 to 20% of the sulfur as non-reducing sulfur compounds . The patent process above has a byproduct
loss of sulfur of 11.8% as non-reducing sulfur compounds ....
so it actually isn't a bad starting mixture for subsequently added alkali to make it a useful reducing reagent . The inventory of alkali lost to the
byproduct formation has to be accounted for in calculating the requirement of additional alkali for adjusting the composition of the polysulfides to
a lower sulfur ranking .
[Edited on 30-1-2007 by Rosco Bodine]
Attachment: US1068769 Original Dry Process Sodium Polysulfide.pdf (174kB)
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Sickman
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I found a journal abstract that would agree with FRITZ post earlier in this thread that glucose is a valuble (and cheap) reducing agent for "alkaline picrate" (sodium picrate) forming picramic acid
directly as a major byproduct.
The following is that abstract from PubMed:
"Effect of glucose upon alkaline picrate: a Jaffe interference.Viraraghavan S, Blass KG.
Department of Chemistry, University of Regina, Saskatchewan, Canada.
The reactivity of glucose in aqueous alkaline picrate was investigated by spectrophotometry and polarography at 25 degrees C in 0.51 mol/l sodium
hydroxide. Thin-layer chromatography and infrared spectroscopy studies have conclusively identified the presence of picramic acid in 5:1 and 10:1
glucose picrate test solutions incubated at 25 degrees C. The polarographic data of an alkaline picrate blank with a concentration of 0.284 mmol/l,
show three well-defined nitro group reduction waves with approximate half-wave potentials of -0.62 V, -0.78 V, and -0.93 V and a fourth broad wave
appearing near -1.31 V versus a saturated calomel electrode. The addition of glucose to alkaline picrate resulted in a decreased diffusion current for
reduction waves 1-3, with little change in reduction wave 4. The reactivity of test solutions containing glucose:picrate in 1:1, 2:1, 5:1 and 10:1
molar ratios was investigated at varied time intervals between 10 and 180 minutes. The absorption spectra of a 10:1 glucose:picrate solution shifted
from 356 nm to 375 nm and a broad tailing shoulder absorbance formed in the 450-600 nm region. An orange coloured minor product, separated by
thin-layer chromatography, was observed to fluoresce. The maximum excitation and emission wavelengths were 318 nm and 545 nm, respectively. A major,
red-coloured product was isolated and identified as picramic acid by infrared spectroscopy. For 10:1 glucose:picrate test solutions incubated at 25
degrees C, picramic acid formed within 10 minutes. Within the first minute, the colour was observed to change from yellow to orange and then to red.
PMID: 2329319 [PubMed - indexed for MEDLINE]"
Hope it helps with the pursuit of an easy way to picramic acid! I wonder what
the yield of picramic acid would be compared to the other products of the reaction? I'm still trying to interperet the reactions described in this
absract, I guess a few tests to see what we get couldn't hurt.
Sickman
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Rosco Bodine
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a theory distilled from the references ......
It would be nice if glucose would work to produce a high yield of crystalline picramate as well as giving a positive color test , indicating that some
of that dyestuff has been produced . It may work to produce practical yields in the same way as does vitamin C , or it may not work that efficiently
. That is an experiment which should also be done , since if it does work efficiently it would be the simplest and most economical method . I have
continued to study what is reported concerning the polysulfide method in an effort to refine it , based upon the increased information gleaned from
the few references which are relevant .
According to the Thiokol patent US2796325 ( attached below )
The mixture of NaOH solution or solid NaOH and Sulfur
follows two principal reaction routes which are dependant
upon the concentration of the NaOH and temperature .
for lower concentrations of NaOH < 30% and temperature < 110C
10 S + 6 NaOH ------> 2 Na2S4 + Na2S2O3 + 3 H2O
for higher concentrations of NaOH > 35% and reaction at > 100C to < 320C
10 S + 6 NaOH ------> Na2S4 + Na2S5 + Na2SO3 + 3 H2O
According to US1068769 ( attached above ) which describes a dry method preparation using " substantially equal proportions " , a mixed product
results having byproducts which indicate that *both* the above reactions have taken place , and on a molar basis that nearly equal amounts of
thiosulfate byproduct are produced , concurrently or subsequently to the sulfite byproduct . As a result of these byproducts , 27% of the NaOH and 12%
of the Sulfur
used for the reaction wished to produce the polysulfide(s) is diverted to the formation of these byproducts . This appears to be an unavoidable loss
which is necessary to the synthesis and inherent to the nature of the reaction .
Therefore , it would seem that an implied strategy for preparation of the polysulfide reagent should be to first make the mixed higher polysulfides ,
according to the dry method , using a 27% additional amount of NaOH and a 12% additional amount of sulfur to " makeup " for the amounts which will
form byproduct thiosulfate and sulfite , instead of Na2S4 which will be the principal or average sulfur ranking 4 polysulfide product . The target
amount of reducing sulfur compounds as product will contain 2.3 gram atoms of sulfur as S1 , or a slight amount more if desired , for each mole of
nitroaromatic to be reduced .
The highest yields reported for the Zinin reduction are using both S2 and S1 ranking reducing sulfur compounds of sodium . See US1878950 for an
example using an S2 ranked polysulfide reagent in the reduction of dinitrobenzne to nitroaniline . See the Hodgson and Ward 1945 JCS article attached
to my preceding post for an S1 example more specific to producing sodium picramate from sodium picrate . Both of these high yield syntheses , using
Na2S2 and NaSH respectively , use 2.3 gram moles of combined sulfur based on S1 , per mole of nitroaromatic compound , the highest yield for picramate
using NaSH , which is derived from Na2S and NaHCO3 in aqueous solution .
To the initial product of higher polysulfides would then be added more NaOH sufficient to reduce its sulfur ranking to 1 , the compound Na2S . To
this Na2S would then be added an equimolar amount of NaHCO3 to form the reducing reagent in aqueous solution . It would be expected that the initial
melt would be very dark red colored due to the presence of higher sulfides such as Na2S5 particularly and also Na2S3 in substantial amounts in the
mixture , but the mixture should lighten in color as the reaction proceeds with time and subsequent alkali additions intended to lower the sulfur
ranking to S1 as the principal end product to be used as the reducing reagent .
The picric acid is dissolved in methanol , 25 grams in 250ml , at 55C , and neutralized to sodium picrate with 4.36 grams NaOH . The reducing reagent
amounting to .25 mole of NaSH in 100 ml H2O is added gradually with stirring to the methanol solution of sodium picrate over 10 to 15 minutes
at 55 to 60 C . The mixture is cooled to 10C and diluted with 375 ml H2O , the sodium picramate filtered and washed with cold salt water . Yield
reported is 96% when the reducing reagent is made up from pure Na2S and NaHCO3 . The yield should be high and hopefully close to that 96% , even when
using this more improvised reagent containing its indigenous impurity of thiosulfate and sulfite originating from its preparation . These impurities
shouldn't interfere
with the reduction and the expectation is that their presence will cause no problem , particularly as regards the thiosulfate , since it is a
byproduct of the reduction anyway and is going to be present as such in the spent reaction mixture .
Though the ratio of 2.3 gram atoms S1 ranked reducing sulfur compound per mole of nitroaromatic is reported to give highest yield ....this is a
minimum , and it does not hurt to use slightly more , so bearing that in mind as well as allowing for some possible incompleteness of reaction for
the improvised polysulfide reagent , I am increasing 10% beyond that theoretical to 2.52 to 1 , also because it is convenient in the measuring of
exactly 10 grams of sulfur from which the composition will be made .
Based on these informations I can propose the following as a valid experimental for the improvised polysulfide reagent possibly having an
effectiveness of the .25 mole of NaSH reagent used as described above .
Experimental :
Xylene could be useful for providing a vapor blanket to protect this reaction mixture from excessive exposure to air . Perhaps 20 - 30 ml would be
fine for this purpose .
It would likely be best not to add the xylene in the greater part until after all the NaOH has been added , because the initial exotherm and the
reaction benefits from a
temperature allowed to rise well above the bp of xylene , which if present in too great an amount would limit the temperature of reaction in the early
couple of minutes where the exotherm should be allowed to proceed unhindered .
10 grams of flowers of sulfur are thoroughly mixed dry with 7.6 grams NaOH , the reaction initiated with a few drops of water and the exotherm
maintained by additional minimum dilution ( 10ml H2O ) and supplemental heating , in the absence of air . The mixture is kept hot and liquid for 20
minutes , a further portion of 22.6 grams NaOH in 20ml H2O is gradually added . The mixture is kept hot for an additional 30 minutes . And then 13
grams of NaHCO3 in 100ml hot H2O is added , followed by 10 grams additional solid NaHCO3 , the mixture is stirred and heated an additional 10 minutes
, then allowed to cool , keeping from exposure to air .
[Edited on 30-1-2007 by Rosco Bodine]
Attachment: US2796325 NaOH or Ca(OH)2 + Sulfur Polysulfide and Sulfite Manufacture.pdf (276kB)
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Rosco Bodine
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further information on Na2S
If it should prove unsuccessfull concerning my hopeful
" one pot " strategy for the formation first of a higher polysulfide Na2S4 , and then by adding alkali attempting to lower it to Na2S by further
reaction .......there is an alternative method which can be used to produce and
isolate the Na2S .
This method is a bit more demanding on equipment ,
as I would expect that teflon or inconel would be needed
to resist the 50% NaOH at 140-150C used for the reaction ,
which would probably be more than labglass will withstand .
Anyway this patent is very similar to the Thiokol patent
US2796325 posted earlier , but it discloses much more specific details with regards to the conditions required
for producing *not* a polysulfide but rather the conditions for producing the monosulfide
which is the thing desired . In spite of the more demanding
conditions for the reaction ....this is actually the most pertinent reference to be found so far describing the convenient synthesis of Na2S in pure
crystalline form .
[Edited on 1-2-2007 by Rosco Bodine]
Attachment: US2705187 Sodium Monosulfide from alkali and sulfur.pdf (613kB)
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