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Author: Subject: Crystal growth and preparative details of nitrophenols (stypnic, picric acid)
quicksilver
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[*] posted on 9-9-2005 at 07:00
Crystal growth and preparative details of nitrophenols (stypnic, picric acid)


One of the most useful (but very short) patents that I have used was US2275172 (1940), in it the author discribes both styphic salts and the ability to control crystal shape (for a pourable true cubic shape, one uses Al in the sulphonization process...amongst others... there are some good ideas there) and effects of bases on the process as a whole. The patent deals with styphic salts but does provide information on a generalized foundation that I felt useful.

This was the provess that I worked with and posted (I think to E&W or here...I don't remember) some years back. It can be scaled up or down and has been the result of a lot of work on my part find the ratios to work well w/ resorcinol. I am actually proud of it as a little lab synth because it really provides consistent bright yellow prisms (good looking crystals!) and it's really my own work. By tweaking it with some of the sulphonization process in US2275172 I have gotten some GREAT crystal shape results!

-----------------
Styphnic Acid

Needed are:
24 grams Resorcinol
30ml H2SO4 @ 95% - 55.5 gr
45ml H2SO4 @ (72%) – 75 grams
175 NHO3 @ 70%
+ H2O

Add 24 gr Resorcinol and 30 ml of H2SO4 (concentrated) to a 250ml beaker and stir at 50C (158 F) for 30 minutes (sulfonation process)*. After the solution has been sitting at this temperature, stir and watch for solidification (it should turn to a brownish pink solid, somewhat creamy). After the material has stood and started to solidify, it is broken up & diluted with 40ml H2O: clean the sulfonation vessel and all is added to the nitration beaker (this also serves to loosen the solid mass of Resorcinol / H2SO4 that occurs as part of the sulfonation process: a mix of H2O and the sulfonated Resorcinol). Here you should have a 500ml beaker with the broken sulfonated Resorcinol and poured into it, 40ml H2O. At this point it is appropriate to further stir the Resorcinol mixed solution from a solid mass to a solution again, add. 46 ml of 62% sulfuric acid (75 grams) to the product and mix /stir as thoroughly as possible then it is ready for nitration. Pour the solution from the mixing vessel into another 500-mL beaker. To review: we have a sulfonated product that is broken into chips and 40ml H2O is added to it, producing a red solution (all is dissolved) and that is readied to be nitrated by adding 62% H2SO4 (45ml /75gr). Then placing this in a water bath, using a separator funnel add 175 ml of 70% nitric acid. Add the acid very slowly, a drop at a time (see note). The addition of nitric acid will cause a vigorous reaction and release toxic gas, use a fume hood or process outdoors. When all of the acid has been added and the reaction has subsided, the mixture is heated for 2 hours on a steam bath or hot plate at 110 C (238 F) to complete the nitration (continue to stir). When this is completed the beaker is placed in another water bath (10 C) and covered. After 8 to 12 hours the Styphnic Acid crystals should have separated. These crystals will need to be filtered with glass filter paper because of the solutions high acidity. Otherwise, pour off most of the acid, dilute with water and filter with regular filter paper. Wash the crystals with several small portions of water and allow it to dry in the open air. Product will be yellow / orange high grade Styphnic Acid.
NOTE: Several elements are very important to the success of this process. First, that the sulfonation be very through. When the H2SO4 is added to the Resorcinol a complete stirring take place so as o create a pink cream solid. This is the basis for sulfonation for Resorcinol. After which H2O is added in correct proportion and the pink solid is allowed to dissolve into the H2O thus creating a red solution of sulfonated Resorcinol. This is the basis for nitration. Any thing less that total solution is bound to oxidize much of the product. Second, is imperative that after nitration takes place with the addition of HNO3 that the solution be heated; this is the element of the nitration process and must be present to achieve a reagent grade material. After that has been accomplished the product will precipitate from the nitration acids and may be filtered off (after a period of time, wherein the whole is allowed to return to room temp). Third: it is very important to the yield percentage that the heat be monitored; too hot and oxidization will occur, too cold and the Styphnic Acid product will not be nitrated to the fullest extent possible and the product will have a high hydrogen content (as would be the case if alkali impurities were introduced to the mix. A critical element in Styphnic acid production is controlling the reaction temperature. A vigorous reaction from nitration will result in loss and low yield through oxidation. Thus it very important to nitrate slowly with corresponding low levels of heat and NO fumes.
Following these steps exactly and this process will result in reagent grade material with consistency. Turning inexpensive technical grade Resorcinol in very expensive, pure, Styphnic Acid crystals!

* This proportion of H2SO4 & Resorcinol may solidify very quickly, thus creating sulfonation. Maintain observation! The pink solid must be achieved (Resorcinol Sulfate) and that broken & dissolved into 40 ml H2O. Proportions may be multiplied or divided to achieve lager or smaller lots. MAINTAIN THESE PROPORTIONS!
------1/21/01

[Edited on 19-9-2005 by chemoleo]




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Rosco Bodine
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[*] posted on 9-9-2005 at 08:55


Here is a method which I used a few times for styphnic acid which would consistently produce a 90% yield of recrystallized pure product .

10 grams of resorcinol is swirled into and dissolved in 50 ml of concentrated H2SO4 .
The dissolution is moderately exothermic due to the spontaneous sulfonation . After a few minutes a lavender colored precipitate forms and the mixture is allowed to stand for 2 hours . Then the mixture is cooled to 0 C by ice bath and
nitrated by dropwise addition of 20 ml of HNO3 d 1.4 ~68-70% to the stirred mixture kept below 35C until all is in solution except for small amount of end product which may be appearing . On recooling to 10C , 20 ml fuming HNO3 d 1.5 ~ 97% is added dropwise to the stirred mixture keeping temperature below 25C . The stirring is stopped and the mixture allowed to stand in the cold bath for a few minutes . The reaction mixture is then removed from the cooling bath and the temperature allowed to rise
from the exotherm . Some end product should be seen precipitating at about 28C and the mixture will foam and increase in volume and temperature .
The temperature rise will accellerate at an induction point of about 38C , really accelerating at 45C and from there spiking upward to 75C . Only an intermittent stirring should be done during the exotherm because the gas bubbles actually dilute the volume density and tend to regulate the reaction . Stirring the mixture causes the temperature to spike again by reconcentrating the mixture . Only stir periodically when the reaction temperature is falling and stirring down the foam will kick the reaction and temperature back up again . Generally only stir the mixture if the temperature drops below 40C from the unaided exotherm of the reaction itself . When the reaction temperature ceases to rise above 35C when stirred , allow the mixture to stand without stirring for a half hour and then dump the reaction mixture onto 250 grams of ice cubes and rinse the flask with 200 ml ice water , everything added together in one crystallizing bowl .
After 30 minutes the mixture is filtered and the crystals rinsed on the filter with about 40 ml ice water . The crude styphnic acid is redissolved in about 900 ml of boiling water , and on cooling deposits about 20 grams of hexagonal plates of pure very pale yellow styphnic acid . Yield is 90% of theoretical based on resorcinol . This method works fine for small batches but is possibly not directly scalable upwards without some provisions for temperature control . For a batch this size , a 500 ml flask is sufficent ,
a 250 ml size is marginal and will threaten to overflow at the peak of the reaction , likely would overflow without any stirring down the mixture which at times forms a solids filled curd , more than being a liquid consistency . The mixture becomes more liquid again as the reaction completes .
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[*] posted on 19-9-2005 at 06:33


Quote:
Originally posted by Rosco Bodine
Here is a method which I used a few times for styphnic acid which would consistently produce a 90% yield of recrystallized pure product .

I tryed yours and (as usual) it was excellent. The resultant was a much higher final yield. Should you ever have the chance, in patent US2275172 there is a section wherein the author describes the use of additions to the sulphonation process to alter crystal shape (to allow for ease of pouring the product) he adds Al and the crystal form is a well formed cube. For long rectangular prisms he uses catechol. Which profides a shape that "flattens" when compressed.
The one area wherein I have heard mixed opinions was that temprature affected crystal SIZE. I have heard often enough that colder environments produced smaller crystals. Indeed in my lab posted above, my crystals were small and uniform, yet the batches from your lab were not smaller even though the temp was lower. Thinking that it would produce larger crystal forms (do to lower temp): it DID produce a higher yield.
However, it has not been my experience that this generalization occured in nitrated phenols....your thoughts here would be a help...




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[*] posted on 19-9-2005 at 15:07


The higher nitration stage using fuming HNO3 sure does put a nice finishing touch on this particular styphnic acid synthesis .

Fuming HNO3 d 1.5 , has its usefulness , and this is one of those times .

This is actually a pretty well optimized synthesis , but I deliberately avoided calling it that up front because from experience I knew that posting an unpublished synthesis under the banner of " optimized " would soon have me busy defending the proportions , temps , and every other detail , including the d 1.5 HNO3 for the nitration " kicker " . There were several experiments where I gradually worked it out what was needed to push the final stage nitration to completion , at relatively mild temperatures which would not favor oxidation byproducts and
therefore prevent contamination of the desired endproduct , so that it could be obtained pure and nearly colorless in good yield from only one recrystallization .
After a half dozen experiments and charted results compared and notes studied , that was about the best I could do ....so it probaby is " optimized " :D

Styphnic Acid is much less soluble than is picric acid and it is easier to crystallize in dense gritty well formed crystals from its strong solutions in boiling distilled water .
A similarity it shares with picric acid is a very very pale yellow color when pure , and dry . But even a trace of moisture or any impurity will greatly intensify and darken the color , and can also complicate obtaining the dense crystals which will form from hot solutions allowed to stand undisturbed while slowly cooling . For both materials , the largest crystals form in the very hot solution and have mostly completed forming while the solution is still slightly warm .

In near saturated solutions very near the boiling point , I have observed nascent crystals of picric acid first appearing as merely a pinpoint of reflected light grow to flat rectangular plates with pointed ends attain 10 mm length in 5 minutes . In bright light , a spiraling ribbon " mirage effect " in the liquid off the pointed ends of the crystals can be observed as the telltale sign of current in the liquid dragged along by the depositing molecules which build the crystal larger at a barely perceptible visible rate . The rate slows down drastically at lower temperatures and you cannot actually watch an individual crystal grow in length .

IIRC the purpose of the adulterants added to the sulfonation or nitration mixtures for styphnic acid was to produce a deliberately impure product where the impurities were found beneficial as modifiers of crystallization in the lead styphnate which would be the ultimate end product . Various crystal forms of the lead salt were found to have different firing properties when used in primers .
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[*] posted on 19-9-2005 at 16:32


Quote:
Originally posted by Rosco Bodine

IIRC the purpose of the adulterants added to the sulfonation or nitration mixtures for styphnic acid was to produce a deliberately impure product where the impurities were found beneficial as modifiers of crystallization in the lead styphnate which would be the ultimate end product . Various crystal forms of the lead salt were found to have different firing properties when used in primers .


Indeed: I noticed that in the various crystal forms of the lead salt in the "clathrate-patent"; that appeared to be the intention. Frankly I had a damn hard time finding some of the various salts....and I have access to a fairly good lab.
I have been using a microscope to closely examine some of the crystals and those from batchs w/ impurities are quite irregular. In fact, consistently inconsistent in form. However using a fairly crude method of determining mp of the various batches of picric acid I find that it is still tri-nitrated (my varience goes no lower than 122-123 C). It had been my thought that the impurity (s) would alter the final product to a mix of di & tri nitrated product. I was wrong; according to mp temp.
Now I have a supply of PHLOROGUCANOL & had wanted to work on trinotrophloroglucanol but when I looked at a patent the sulfonation used a ridiclous amount of H2SO4 (1 LITER per 50 grams!). This would make lead salts of TNPG completely inappropriate for commercial usage. But yet, it found itself in patents for rifle primers in Europe.....(?) What gives?:o
Is the sulfonization of Phloroglucanol REALLY in need of such an excess?




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[*] posted on 19-9-2005 at 20:37


The presence of impurities in picric acid substantially increases the solubility of the mixed material beyond what would be the solubility for the amount of pure picric acid the mixture contains . But the impurities are * slightly * less soluble at the boiling point of a saturated solution of the unpurified picric acid , so boiling down a saturated solution of the crude picric acid will begin to precipitate the dark colored material and the precipitation will continue to a point , but then it will stop precipitating , even as the boiling down continues , until further along a combined precipitate will occur which appears to be a eutectic melt of the impurity but is mostly picric acid and a small percentage of the impurity . Removing what is mostly
the precipitated dark colored impurity without precipitating the bulk of the picric acid can be done by a special technique of manipulating the slightly different solubilities at and just below the boiling point of the saturated solution of crude picric acid .

Observe when boiling down the saturated solution of crude PA and note when the red colored oily impurity precipitates but seems to stop increasing in accumulation as the boiling continues
for perhaps three more minutes past the time steady accumulation ceases . Remove the flask from the hotplate and
set it on pad to cool slightly , and the solution should become milky and opaque having the appearance of rusty water .
This is an emulsion of the impurity separating from solution and it is a persistent emulsion which will be destabilized by reheating just to the boiling point , but not brought to a free boil . The flask containing the cloudy liquid
and having cooled just a few degrees is returned to the hotplate and as it warms the emulsion will break and more of the dark red oil will settle out as the liquid heats and clarifies . The flask is removed from the hotplate and returned to the pad . If the flask is tilted all of the dark red impurity will settle in a single globule ,
where it will solidify on cooling slightly ,
just before the clear solution above it begins to cloud again which should be avoided since that will be mostly picric acid . A small stirbar can be dropped into the tilted flask and the cold stirbar will help set up the globule of impurity . The supernatant still very hot solution of picric acid can be decanted away from the soldified glob of impurity or it may be removed by sliding it up the wall of the flask using a magnet against the outside .
The flask is returned to the hotplate and
the boiling down is continued and the process repeated until the solution has been stripped of the dark colored impurity
and the solution color is yellow to slightly orange . The boiling solution will only precipitate a few tiny droplets of the impurity , not even one full drop when it has been substantially stripped of the
" red goo " . The saturated boiling solution may then be diluted with an added portion of distilled water about one fourth its volume , and then to the hot solution brought just again to the boiling point is added about one fortieth the total volume of 31.45% HCl with stirring . A greatly purified product will
be precipitated on slow cooling .

A subsequent recrystallization of the product from plain distilled water will require a good bit more water for the dissolution of the highly purified picric acid , than was the original volume of the solutions of crude product from which it was obtained .
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[*] posted on 23-9-2005 at 06:54


Quote:
Originally posted by Rosco Bodine
The presence of impurities in picric acid substantially increases the solubility of the mixed material beyond what would be the solubility for the amount of pure picric acid the mixture contains .


This is an extremely important concept (the whole of the post, not just the snip). Too many people don'tl continue with their synth at the precise stage where they can make a difference.
I think anyone who has been working with nitrated phenols and has had a bit of trouble should read over that pervious post.




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[*] posted on 23-9-2005 at 08:53


There is a solubility difference for the impurities at the boiling point of saturated solutions and I described a way to exploit the solubility difference for precipitating the impurity .

But from what I have been seeing , the solubility for the impurity is actually somewhat greater than the solubility of picric acid , for solutions of the crude picric acid which are well below saturation at whatever temperatures . So the way the
precipitation proceeds , and the way it is
more favorable for either precipitation of the impurity , or more favorable for precipitation of the picric acid , will vary depending on the relative concentration of each to the other , and the level of saturation of the combined system at
a given temperature . Trying to pin down the most efficient sequence and conditions for the purification is like trying to nail jello to a wall because the mutual solubility dynamic varies with temperature and concentration and pH . The more impure is the crude picric acid from nitration , the more difficult and tedious is the purification process . This is precisely why it is desirable that the crude product gotten directly from the nitration mixture should be as pure as possible , since that greatly simplifies everything to follow .

If a very complete nitration producing very few byproducts is accomplished as the source for the crude picric acid , then the crude picric acid can be obtained pure
directly from the first recrystallization from boiling water . But any inefficiency in the nitration causes an exponential increase in the difficulty of purifying the crude product , which will be heavily contaminated with impurities which are inclined to co-crystallize as mixed and entrapped occlusions , adversely affecting the color and density and crystal quality of the end product .

The level and nature of the impurities varies with both the nitration process and the precursor used , so what details are worked out as best for one synthesis do
not necessarily apply to another synthesis . The one priority that is completely evident is to perform the nitration as cleanly and completely as possible , which eliminates right there so much " crystallization algebra " as is otherwise going to follow if the nitration isn't everything it should be .
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[*] posted on 24-9-2005 at 07:30


Quote:
Originally posted by Rosco Bodine
There is a solubility difference for the impurities at the boiling point of saturated solutions and I described a way to exploit the solubility difference for precipitating the impurity .

-=snipped for brevity=-

The level and nature of the impurities varies with both the nitration process and the precursor used , so what details are worked out as best for one synthesis do
not necessarily apply to another synthesis . The one priority that is completely evident is to perform the nitration as cleanly and completely as possible , which eliminates right there so much " crystallization algebra " as is otherwise going to follow if the nitration isn't everything it should be .


While the idea of using ammonium nitrate is a very interesting one (& a one I would like to attempt) I don't know what AN would be used but the most cost effective is, of course, prills. And with that the clay and coating there-upon. That may be at issue where we look at the impurity issue vs. cost efficiency. The extra step of purifying the AN prior to usage in nitration would eliminate this obviously but the extra step would set us back time/cost-wise.
I have wanted to emulate your experiment with AN and as I was about to proceed I realized that I had prills to work with. Crushing them and purifying them would involve some serious time usage. The larger question to me is would it be worth the time?
Sodium Nitrate is available via a hardware store (USA- ACE) purchace of a brand of lawn & garden supply product marketed by a company called:"BONIDE", they make a "Nitrate of Soda" (15-0-0) that comes in a box form of several pounds for about $1 or 2 a lb..... but here again I noticed that they are prills!
The thing is that all these methodologies involve the possablity of introducing impurites via the materials used in nitration. :( After all what's the point of using very high end products to achive a high end resultant? Where is the challenge?
Extraplolating the least expensive technique for the best product I keep coming back to the added work involved in initial purification. I don't know if there is even a source for wool that has not been contaminated by something. And even though I could get raw wool from the County Fair - would that raw animal organic matter be appropriate for nitation? When I examine the various NC patents they point to highly refined sources (bleached cotton batting, etc). Could it also be that oil of wintergreen also needs an additional step prior to nitration that has been missed; something unique to a fliud?
My comment heads in that direction due to my noticing that there is an acute difference between Reagent grade resorcinol which is a hardened flake, somewhat crystaline and Technical grade product that is fiberous almost looking like fine hairs or fiberglass. Indeed, when they are nitrated using the same technique the Technical grade is a slight "peach" yellow, while the Reagent grade is a very bright yellow prism. :o




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[*] posted on 24-9-2005 at 11:19


The use of nitrates as concentrated solutions does simplify addition of the nitrate to the sulfuric acid solution of
the sulfonated organic material to be nitrated . I have mentioned that using
a solution of two or more different nitrates
can make possible an even more concentrated solution having less water content which would dilute the nitration mixture . Such solutions of mixed nitrates have been developed to provide a liquid oxidizer phase having low water content for use in manufacture of emulsion explosives . Some of these solutions are
essentially a eutectic salts mixture which
also exhibit a enhanced cosolubility in the presence of a small amount of water , similarly as they have a much lowered melting point even in the absence of water altogether . Whether this is commonly true for many or all the eutectics I do not know , but I suspect it is common for there to be a parallel .

Many such mixtures are likely , but I do not have them all listed or charted . One that I can mention is from US5454890 ,
which is an oxidizer salt solution consisting of 77% NH4NO3 , 11% NaNO3 , and 12% H2O . I do not know what is the
minimum temperature at which the mixed solution begins to crystallize but suppose that even if a few per cent more water was needed for room temperature stability , it would still have less than half the water content of a plain NH4NO3 solution .

I know I have seen other compositions mentioned and I will share any others I find .
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[*] posted on 25-9-2005 at 00:01


I'm about to do a synthesis, so I'll try the mixture from the patent that Rosco just posted.

Is there any advantage to using HNO3 instead of nitrates? Also, has anyone tried using HNO3 extracted by the methylene chloride method, without first removing the methylene chloride (the patent mentions that a number of nitrations can be performed without that removal)?

[Edit] This far, I'm having trouble getting the nitrate mix to dissolve fully, despite using a hot water bath and fast stirrer.

[Edit] Even increasing water to 20% and heating in microwave until steam appears, the solution crystallizes into a soft, semi-liquid mass. I guess I'll just give up and use it as is.

[Edited on 25-9-2005 by Quince]




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[*] posted on 25-9-2005 at 06:12


Those proportions aren't working for me either . I am trying some adjustments to the ratio of nitrates with the NH4NO3 in higher percentage like 91-94% to see if the desired " salting effect " can be obtained . Sorry for the bum proportions from that patent . Evidently those are proportions used for some sort of crystallization control instead of solubility
enhancement . However I am certain that the salting effect does occur for solutions of mixed nitrates in certain proportions . It may require some experiments to determine what ratios are good if such systems can't be found published somewhere .

At worst case a heating tape can be used to warm an addition funnel above 60C , where straight solutions of NH4NO3 are
stable as 80% solutions .

From what I have observed of these strong solutions of nitrates , they will best be prepared a couple of days in advance and allowed to stand and filtered before use , since they tend to cloud and precipitate any impurities when
simply allowed to stand for awhile .

It could also be useful to dissolve NH4NO3 in HNO3 in order to provide an additional source of HNO3 without the introduction of excess water . NH4NO3 is very soluble in HNO3 , to an extent of 50%
at 15C . For example see PATR , A-329 for a chart . This could be a very useful method of
" stretching " and reenforcing the nitrating capacity of ordinary concentrated nitric acid , by in effect forming an additional amount of fuming HNO3 in situ , when the addition is being made to a sulfonate in sulfuric acid . This
may be adaptable to the styphnic acid synthesis , as a substitute for the d 1.5 fuming acid addition , simply by dissolving the equivalent amount needed of NH4NO3 in the ordinary d 1.4 acid , and
proceeding . It would not be as efficient ,
and it would have to be tested to see how well this would work .

[Edited on 25-9-2005 by Rosco Bodine]
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[*] posted on 25-9-2005 at 14:49


Different procedures I've found have differing amounts of H2SO4 specified for a given amount of ASA. What's the minimum? At the moment, I have 82 g of ASA in 470 mL H2SO4, waiting to add the nitrate mix, but I'm wondering if I need to add any more H2SO4 (boiled drain cleaner), especially given the water content in the nitrate mix (it would be hard, though, as I'm about to overflow my largest flask...).

[Edited on 25-9-2005 by Quince]




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[*] posted on 25-9-2005 at 16:58


When I use solid nitrate as NaNO3 , the right amount of 92% H2SO4 is 4 ml for each 1 gram ASA , and 1.8 grams NaNO3 .

You are using somewhat more H2SO4 , which will help compensate for the extra water in the nitrate solution , and both those added liquids should give a much thinner reaction mixture . I would still recommend a reaction flask at least 3 times the total volume of the completed reaction mixture because you are going to get foaming from the decarboxylation .
Go very slowly with the additions because there is a time lag in the response of the reaction , with the foaming not immediately appearing according to real time tracking the rate of addition , but lagging two or three minutes later . It is very easy to add to much , observing no immediate reaction , and then a couple of minutes later you see the effect ....too late to slow the addition rate increase if you have overcompensated , which will cause an overflow . In general you need to push the temperature during the entire nitration , but let the appearance of red fumes be your indicator that the temp and/or addition rate needs to be decreased to avoid the loss of nitrogen .

The decarboxylation foaming may occur predominately during the first half of the nitration or it may continue through the entire nitration . Push the temperature during the second half of the nitration ,
maintaining at least 105 C , and finish at 120 C , holding the completing reaction at ~120 C for 15 to 30 minutes , and continue stirring the mixture as it cools .
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[*] posted on 25-9-2005 at 18:14


Well, I guess I'll have to use my French coffee press, as it's the only Pyrex vessel I have that large. I guess if my coffee tastes too bitter, I'll know I didn't wash it well...

[Edit] This semi-liquid mush is not working very well. The problem is that unlike powdered nitrates, the drops here are too big and don't mix in fast enough in the acid, resulting in lots of NOx.

[Edited on 26-9-2005 by Quince]




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[*] posted on 25-9-2005 at 20:46


Quote:
Originally posted by Quince
Is there any advantage to using HNO3 instead of nitrates? Also, has anyone tried using HNO3 extracted by the methylene chloride method, without first removing the methylene chloride (the patent mentions that a number of nitrations can be performed without that removal)?

[Edit] This far, I'm having trouble getting the nitrate mix to dissolve fully, despite using a hot water bath and fast stirrer.

[Edit] Even increasing water to 20% and heating in microwave until steam appears, the solution crystallizes into a soft, semi-liquid mass. I guess I'll just give up and use it as is.
Quote:


I had wondered about the methlene chloride issue for a while now. I believe that in a nitration of a phenol it may not be a good idea due to the flamability issue and heat produced by the process. MC boils at a very low temp (40C) and I have heard some horror stories with simple distilltion where that was not closely monitored... However I have heard that the use of same (with HNO3) in the preperation of nitramines (& cycllic nitramines) that had been great. - No problems ! It's been my understanding that the nitration itself would not be curtailed by MC but that it presents a significant fire hazard. At cool temps it would be a boon to a nitration involving higher strength nitric acid.
Dealing w/ the solid nitrates; I also have had a very mixed bag. The method I settled on was prior preperation using a quality magnetic stirred / hotplate and when my solution was mixed to my satisfaction I would cool it and use it at a later time. Unfortunatly this procedure & making sure of the purity of the nitrate in question lengthens & complicates the whole synth. I really like the idea of using solid nitrates but for reasons of economy. And therefore I have to work with prills. They have a wax or clay coating (or both) and that presents a problem with both the solution prep and the purity issue.

On another note I have used a process wherein picric acid is prepared by nitration of a nitrosophenol intermediate by preparing the phenol with sodium hydroxide and sodium NITRITE. The resulting nitrosophenol intermediate is then nitrated by a standard nitration process using strong HNO3 - and in this instance methlene chloride / HNO3 may not be exposed to much heat. Or a H2SO4 / solid nitrate mix may work. In any instance it is ment to be processed a much lower temp.
Unfortunatly it comes from a UK patent application (#365, 208 David Salter, 1973) so I am having trouble getting a PDF file....:(
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[*] posted on 25-9-2005 at 21:08


Quote:
Originally posted by Rosco Bodine
The use of nitrates as concentrated solutions does simplify addition of the nitrate to the sulfuric acid solution of
the sulfonated organic material to be nitrated . I have mentioned that using
a solution of two or more different nitrates
can make possible an even more concentrated solution having less water content which would dilute the nitration mixture . Such solutions of mixed nitrates have been developed to provide a liquid oxidizer phase having low water content for use in manufacture of emulsion explosives . Some of these solutions are
essentially a eutectic salts mixture which
also exhibit a enhanced cosolubility in the presence of a small amount of water , similarly as they have a much lowered melting point even in the absence of water altogether.

I know I have seen other compositions mentioned and I will share any others I find .


I was unawair of the "mixed-nitrates" concept...and PLEASE; if you do find material related I would deeply apprieciate seeing it!


- I too use the PATR but find that patents are making much more impact in finding answers, new proceedures, & use of my time. Some of the most interesting stuff I have found have come from US patents thus far.

As I have the same trouble accessing UK patents, as you have noted yourself, that site is a real pain. But the older, valuable patents (where they were nitrating everything under the sun) and the older techniques, seem to originate in the UK.




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[*] posted on 26-9-2005 at 01:03


Considering the amount of water needed for the purification step, I ended up using a stainless steel vessel as I don't have any Pyrex to fit 2 L. From what I've found on the Web, most stainless steel alloys are listed as resistant to picric acid, so I'm hoping that even at the higher temperature, contamination of the picric acid from the stainless steel will be minimal.



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[*] posted on 26-9-2005 at 02:06
picric acid from sulfanilic acid


@quicksilver

I couldn't find that patent under the number or the name you gave above ,
but while searchingI did find something similar which may give the most pure picric acid directly from nitration , of any of the processes I have ever seen described . And the sulfanilic acid precursor is a mundane , non-hazmat type of starting material which definitely fits in this discussion of alternate precursors and methods .

Attachment: GB16371 Picric Acid from Sulfanilic Acid.pdf (138kB)
This file has been downloaded 958 times

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[*] posted on 26-9-2005 at 07:27


Quote:
Originally posted by Rosco Bodine
@quicksilver

I couldn't find that patent under the number or the name you gave above ,
but while searchingI did find something similar which may give the most pure picric acid directly from nitration , of any of the processes I have ever seen described . And the sulfanilic acid precursor is a mundane , non-hazmat type of starting material which definitely fits in this discussion of alternate precursors and methods .


Thnak you for posting that one.....
I tried to find the nitroso intermediate thing also...Patent applications are even tougher than secured patents at that site. I will keep trying as it's a good one.

In the instance of the patent you posted I believe that sulphanlic acid is used in the dye industry; is there an OTC source?




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[*] posted on 26-9-2005 at 08:25


This is practically off topic, however:
I would be interested to know how long it takes the crystals of SA to come out of solution. I would have thought that the crystallization of the bulk of the product would be almost immediate when the solution of nitrated product is cooled to 10*C. Am I missing something? What is the purpose of the (relitively) long sitting time at low temperatures?

With respect to the question about the effect of temperature on crystallization;
It has always been my experience that the slower a solution is cooled down - the larger and more uniform crystals are produced. I understood that as the solubility of the solution <html><i>slowly</i></html> decreaces, the product is 'forced' out of solution 'onto' a crystal seed more slowly, giving a more ordered crystal. Entropy has a part to play in there somewhere too IIRC.

Sooo, perhaps letting your solution quench very slowly (stop heating the water bath even! taking a matter of hours to cool down) by my logic yeilds bigger, more uniform crystals. For what it's worth.

- D




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[*] posted on 26-9-2005 at 14:23


Having left a batch of picric acid (precipitated with the help of HCl) to dry in a stainless steel vessel, this morning I woke up to find the crystals touching the metal have turned black and brown...

Will a recrystallization be able to separate most of this out, or should I throw the whole batch away?

[Edit] The reaction only happened where the crystals had completely dried, around the sides, and the metal had somewhat corroded. On the bottom, where the crystals were still wet, there was no reaction with the steel at all. Can someone explain this?

[Edited on 26-9-2005 by Quince]




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[*] posted on 26-9-2005 at 19:19


Metal Picrates were most likely formed. The residual HCl in Picric Acid most likely attacked the steel and once the HCl had evaporated the Picric Acid attacked the steel forming Metal Picrates. Picrate salts cannot survive in an acid medium; they are converted back to Picric Acid.
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[*] posted on 27-9-2005 at 03:14


Thanks, that made it all clear.

Why do people seem to prefer the long needle-like crystals? Wouldn't they be more sensitive, due to breakage when moving and packing them?

Also, during boiling down for the second batch, it seems some picric acid is evaporating along with the water, as a cool surface above the boiling liquid accumulates a yellowish condensate from just the steam, without there being any spray (even if I remove from the heat so boiling stops).

In regards to storage, is alcohol as effective a desensitizer as water? I ask as it's much faster to dry alcohol.

[Edited on 27-9-2005 by Quince]




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[*] posted on 27-9-2005 at 07:05


Quote:
Originally posted by Ramiel
This is practically off topic, however:
I would be interested to know how long it takes the crystals of SA to come out of solution. I would have thought that the crystallization of the bulk of the product would be almost immediate when the solution of nitrated product is cooled to 10*C. Am I missing something? What is the purpose of the (relitively) long sitting time at low temperatures?

With respect to the question about the effect of temperature on crystallization;
It has always been my experience that the slower a solution is cooled down - the larger and more uniform crystals are produced. I understood that as the solubility of the solution <html><i>slowly</i></html> decreaces, the product is 'forced' out of solution 'onto' a crystal seed more slowly, giving a more ordered crystal. Entropy has a part to play in there somewhere too IIRC.

Sooo, perhaps letting your solution quench very slowly (stop heating the water bath even! taking a matter of hours to cool down) by my logic yeilds bigger, more uniform crystals. For what it's worth.

- D

There is a ratio of time vs yield as you pointed out regarding the PA coming out of solution. It certainly could be formed right away. I don't know if there exists a greater possibity of lower yields if the material is forced out via pouring into cold water, the nitrated mix; but it has been my personal experience that for the best yield slow is the way to go for shape and consistency.
I believe that you are correct in you second query. However PA, per se' preents little danger if moist and the larger crystals allow the individual to use certain mp apperatus more effectivly. For myself I enjoy seeing the differing structure of the crystal in various compounds I frankly attempt to grow them larger and well formed (except primares, peroxides, & things of that nature). Shape also helps determine the purity of the compound in certain instances as well. I continue to use a microscope in conjuntion w/ many synths... It really has helped & I just find it facinating.




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