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Quince
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I got my replacement thermometer a few days ago. I noticed it had a small gap in the mercury column, so I was shaking it, and of course it broke,
right where my thumb was. Took me ten minutes to stop the bleeding. That's the second thermometer I break in a couple of weeks.  Worst is no one sells them here, so I have to wait and pay for shipping from the US...
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Rosco Bodine
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HCl is excellent crystallization enhancer
Earlier in the thread I mentioned the difficulty which can be encountered in
getting a good clean crystallization of picric acid , and I have rediscovered the secret I had learned once before and then forgotten , concerning the
usefulness of a small amount of HCl as a crystallization modifier for aqueous solutions of picric acid . The solubility of picric acid in hot , even
boiling hot water is
dramatically reduced by even a small percentage of HCl , which radically alters also the entire temperature solubility curve , so that the picric acid
may be precipitated readily from very hot and more dilute solutions , in a controlled manner by small portionwise additions of HCl . The precipitated
crystals are the
dense gritty freeflowing and readily filterable form having a sparkling fine
mesh just coarse enough to result in a freeflowing microcrystalline form when dry . The crystals precipitated in the presence of a small percentage
of HCl are
light in color and highly pure , more consistent in granulation size than are the range of crystals which precipitate from plain aqueous solutions
which are slowly cooled . The temperature range is smaller over which the bulk of the crystallization occurs and the temperatures at which
crystallization begins and is mostly completed is much higher in solutions containing a small amount of HCl . Freeing the more concentrated solutions
of dark colored impurities is also facilitated by adding small amounts of HCl sufficient only to effect a small precipitation which drops out mostly
the impurities , which redissolve more slowly on reheating and may be filtered from the picric acid solution . Reboiling will drive off some of the
HCl and increase the solvency , and the level of saturation can be manipulated with additions of water and HCl to accomplish the selective
precipitation of dark tea colored impurities , lightening the color of the purified solution from which the picric acid may be precipitated . A
boiling hot solution of picric acid in water which is no more than perhaps two thirds saturated , will show the dramatic effect of a small amount of
HCl added to the boiling hot and well stirred solution . Adding one sixtieth to one fiftieth the volume of the aqueous solution , of 31.45% HCl into
the vortex of the rapidly stirred solution at just below the boiling point by a half degree , the solution will cloud upon cooling by another 2
degrees and the precipitation of glittering crystals will begin . The precipitation of glittering crystals of picric acid will develop steadily
and nearly all of the precipitation will occur
in the narrow yet elevated temperature range of 95 downwards to 75 C , below which little further precipitation will occur .
Contrast this sharp precipitation range at
an elevated temperature which favors consistent crystal formation , in the presence of a small percentage of HCl ,
with the rather broad and sluggish precipitation for plain aqueous solutions .
The HCl containing solution is for the most part finished precipitation at a temperature where the plain aqueous solution is at about the midpoint of
a rather wide range for crystallization which goes much more slowly and forms a wide range of crystal sizes getting smaller and smaller with
decreasing temperature .
So the usefulness of HCl is established for forcing the crystallization of picric acid from hot aqueous solutions in a desirable crystalline form .
HCl in this use could be thought of as a crystallization catalyst .
In COPAE , Davis hinted at the usefulness of HCl in producing light colored and pure crystals of picric aicd , but Davis did not elaborate on the
usefulness of HCl as a solubility modifier and the mechanism for accomplishing the crystallization .
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Quince
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That's great! I'm going to try this in my next batch, as soon as I get my Gregar extractor finished so I can purify more aspirin.
However, upon reboiling, if the solution is boiling, how can you refilter? Or is it sufficient to just decant the PA solution from the precipitated
impurities?
[Edited on 29-8-2005 by Quince]
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Rosco Bodine
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The cloud point of the solution is possible
to be maintained stable enough at a moderately warm temperature by adding the HCl in very small amounts and waiting a minute or two to observe the
change .
The clouding is in my estimation largely the impurities which can be filtered both
as precipitated solids or as the suspended
matter at the cloud point , or some of both simultaneously . The use of temperature and the carefully added small amounts of HCl can be used to
manipulate the solubility of warm and hot solutions so you can conveniently work with the solutions across a wider range of concentrations and
temperatures . There is different solubility for the impurities and the picric acid , and you can selectively precipitate the impurities and or
redissolve
any also precipitated picric acid by cycling the solution with temperature changes ,
and additions of water or hydrochloric acid . You will see when you work with the technique how the presence of HCl can be used to facilitate the
selective precipitation of the picric acid or the impurities . Once you understand from observation how the solubilities can be manipulated , using
HCl will become routine . The color and or physical form of the precipitated impurities is quite different from the sharply crystalline crisp form
of picric acid crystals , and tar or heavy oily material which redissolves on resumed heating and dilution more slowly than any picric acid which may
also precipitate and comingle with the impurities as a melt . This is the sort of
separation that has to be finessed with
a bit of skill , but having the HCl to use as a tool makes the process much simpler .
The first crystallization from a good nitration procedure is not difficult because the impurites are not at sufficient concentration to complicate
things . But when the residual liquid from the first crop is boiled down to perhaps a third or less of its volume is when the impurities will begin
to be troublesome and precipitate on cooling . Being able to accomplish the precipitation in hotter and more dilute solutions , by use of the HCl ,
by itself reduces the problem significantly of precipitated impurities in the second crop of crystals . It also reduces the length of time and energy
requirement for not having to boil down the residual solution from the first crystallization to as small a volume as would be required without the
added HCl . The technique can likely be generalized to a step by step which works well for a given batch size , but I can give no more details
except to say try it , and learn from what you see occur with the solutions , the fuzzy logic of solubility manipulations ,
which applies to your particular batch .
I cannot yet describe a standard method because I am still working it out myself
the best technique . But even the not fully developed idea in experimental practice is a huge improvement over no idea at all , that a little HCl
makes much shorter and rewarding work of your picric acid crystallizations .
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chemoleo
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That's very interesting.
What is the basis of precipitation? I can't quite figure it out, the precipitate has to be the full acid (including the proton), so what is
causing the picric acid ion to protonate? The excess H+ I suppose. Still odd. I never understood these issues (common ion effect and such) too well
Never Stop to Begin, and Never Begin to Stop...
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The_Davster
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Is the batch that the HCl precipitated from a KNO3/H2SO4 batch or a HNO3/H2SO4 batch? I have had difficulties with the KNO3 method for a reason I
believe to be because potassium picrate had formed. I have a feeling Rosco's HCl idea would have fixed it.
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Rosco Bodine
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Memory fails me on where I read it first , but I know later that Philou Zrealone also has mentioned that picric acid can exist in different forms
depending upon the pH of the solution .
A lower pH favors the less soluble and less colored form of picric acid , IIRC it is called an enol form , and I don't recall the other form . A
similar solubility and pH relationship exists for sulfuric acid added to solutions of picric acid , and Urbanski and PATR have that solubility
relationship charted with minimal solubility at 18% H2SO4 . But of course H2SO4 would also tend to contaminate the crystals with its
low volatility residue , and HCl probably does the same thing more effectively in recrystallization scenarios . The H2SO4 data is useful for efficent
quenching of nitration mixtures to determine the optimum dilution for the first crystallization of the crude material , with least loss in the
dilution water , washings
from the first filtration . Industrial practice recycles everything , including that wash water , using it in subsequent nitrations .
Anyway , yes the picric acid was made using the nitrate and sulfuric acid method .
It may be possible that an alkali-trinitrosulfonic intermediate is formed
and that somehow HCl catalyzes the decomposition to picric acid ....I wondered about that myself , but then the observations on solubilities
don't reconcile with that idea of what is occuring when HCl is present .
I'll have to go with the pH sensitivity / enol formation idea , and wish I could learn more about this . A possible clue
is in the formation of different colored forms of ammonium picrate , one yellow and one red . This may be a different aspect of the same pH
sensitivity causing a different crystal form and color for a picric acid salt , while the effect is being manifested from the picric acid itself .
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Rosco Bodine
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picric acid as indicator dye for pH 0.3 to pH 0.4 transition
According to Merck , picric acid is not only
a dye , but is a pH sensitive indicator dye with a change from yellow to colorless at
pH decreasing below pH of 0.4 , listed in the attached table as the indicator shown
seventh down the list . So for sure there is a sharp transition point in pH which results in a fading of color from the solutions of picric acid ,
and indeed I have observed literally chalk white crystals clinging to the stirbar , which are probably
the fully transitioned material mentioned by Davis in COPAE . This information squares with my own observations and sheds light on what is occurring
with added HCl . Picric Acid is itself a very strong acid , about as strong as phosphoric acid , so solutions of picric acid alone approach the
transition point if they are strong enough , but don't quite get there to achieving the low enough pH to make the transition to the colorless and
lower solubility form . Adding HCl nudges the pH still lower the little extra needed for the transition to occur , and that changes the entire nature
of the system solubility , in favor of crystallization .
All in all a very neat trick 
Attachment: table_phindic.pdf (100kB)
This file has been downloaded 1370 times
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GODhack
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ahh I know that it is almost totally offtopic but please help. Also sorry for my not very good english. So I maked TNP, NC, NG, EG... and it was realy
fun. Two weeks (or ewen more) ago I had contact with NO2. I holded TNP reaction bath in my hand (~100ml) and NO2 fumes cames out. I droped all in
large amont of water and moved avay for about10 minutes. Because I am silly I camed back and vorked in same plase for another few hours. Evrything was
ok same day, another day...
But yesturday my body teprerature reached 37.3C and lots of red spots occured on skin. Yesturday also I tassed some exotic food so I buyed and drinked
some antihistamin (not shure how it is colled in english) drugs. They helped me a lot. This day skin is red again and I drinked even double dose. I
begin to think that it is not alergy but I am poisoned. Because I am realy scared few hours ago I asked my good frend and he dumped ALL chemicals in
my lab that I produced.
Questions:
Am I realy poisoned?
How long skin will be red-spoted?
Is it serious?
How much is it seriuos?
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Quince
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I'd think that NO2 won't cause red spots on your skin. I've had several times nitrated my skin by accident, and it turns brown. After
accidental releases of NO2, I took a breath of ammonia to neutralize it. Sounds like you have a rash, either allergic reaction to some chemical, or
some sort of infection. The NO2 causes lung damage instead, and possibly death.
[Edited on 4-9-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Taaie-Neuskoek
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| Quote: |
After accidental releases of NO2, I took a breath of ammonia to neutralize it.
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 You took a breath of ammonia?? I cannot advise this method, NO2 is already
taken up in your lungs when you have breathed a couple of times more... It goes in your blood and does nasy things, I've read some literature on
it.
Red spots on the skin is not something usual for NO2, if you've inhaled NO2 you feel sick, and your lungs hurt... no symptoms concerning the skin
(exept from dying maybe) are described.
Thanks for the recristalising info Rosco, very helpfull. (I'm about to make some TNP...)
[Edited on 4-9-2005 by Taaie-Neuskoek]
Never argue with idiots, they drag you down their level and beat you with experience.
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quicksilver
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| Quote: | Originally posted by Rosco Bodine
-=snipped for brevity=-
All in all a very neat trick |
Rosco: I have been following your posts for years now (mr. anonymous) and as I have been such a lurker have never told you that much of what you have
experimented with / such have I..... indeed much of what you have expounded upon tracks with what I have worked with in-so-far as crystal growth, etc.
Some years back I posted a styphnic acid sulphonation and worked with styphic acid as you have picric. My experiences have been much the same
in-so-far as crystal size, shape, and temp issues. I was lucky to have some kg of resorcinal...so I just went at it. Most of the styphic acid patents
didn't provide for sulphonization in a manner that could be scaled up or down. Eventually I was able to reproduce beautiful, large yellow
crystals of a variety of shapes. I have also made an attempt at picric using indigo, as I found a dye mfg that had some for pennies. Being a solid I
did not have the challenges that oil of wintergreen presented and am possably going to use that next.
That being said I wanted to thank you for the work you have posted as I save much of the notes and experiences of others and even remember the
clathrate post for some years back!
I have found that the toughest thing is to record mp temp when completing an experiment as I am limited as to equipment and have wondered if you have
a "kitchen- fix" or some methodology regarding mp temp....(?)
I have found a method to change crystal shape from needle to a more pourable (cube, etc) without sacrificing size or consistency.
My issues with crystal growth are such that I found that the investment in a quality hotplate was nesessary.... as you have said that temp control was
virtually primary; other factors being equal. And I simply wanted to add that your posts through out the years have been apprieciated.
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quicksilver
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| Quote: | Originally posted by chemoleo
That's very interesting.
What is the basis of precipitation? I can't quite figure it out, the precipitate has to be the full acid (including the proton), so what is
causing the picric acid ion to protonate? The excess H+ I suppose. Still odd. I never understood these issues (common ion effect and such) too well
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I do now believe that it (and much of the "red goo" issue) _WAS_ H+. This was discussed several years ago and I believe that it was a member
here who brought about some proofs. I can't remember who it was but I remember some of the remarks.
The final form is a bit stabilised by hydrogen bonding between the H of
=N(O)-OH and theO of O=C.
Orange color sometimes comes from NH3, or another base which produce a
tiny amount of the cetonitronic form (possibly more sensitive!)
You know the process for CH3-NO2 (uncolored but yellow to dark
brown when exposed to bases:
CH3-NO2 + NaOH -- H2C=N(O)-ONa
Thus
H3C-NO2 <==-- H2C=N(O)-OH (proton jump from the CH3 to the O)
Excessive Hydrogen may also account for same color.
Same occurs in TNT when subjected to alkaline fusion...a sensitizor
colored form appears:
-C(CH3)=C(NO2)- <==---- -C(=CH2)-C(=N(O)OH)-
Same phenomenon occurs with mono, di and trinitrophenol.
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Rosco Bodine
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The red goo is one of several byproduct impurities attendant to the synthesis of picric acid which are analogous to the byproducts formed with
styphnic acid , and described in several patents . There are also other byproducts not mentioned ,
which tend to form a melt with some of the picric acid , which dissolves more slowly than the pure picric acid does when
forming a * saturated * solution in water gradually heated to boiling . The removal of the red goo impurity is best accomplished by fractional
dissolution , sacrificing whatever picric acid is entrapped as a melt and slow to dissolve in boiling water , decanting the more nearly pure saturated
or nearly saturated picric acid solution from the red goo which will solidify as a single solid chunk adhering to the bottom of the flask set upon a
cool surface for a minute or two , allowing the still nearly boiling hot picric acid solution to be decanted . This is really the only effective way
of removing the impurities which will otherwise discolor and adhere to the picric acid which precipitates if gotten from a mixture where " all is
in solution " including the impurities . The precipitate of impure picric acid will on redissolving in
water gradually heated again to boiling leave the bulk of the impurities as the last thing to dissolve , again forming a melt which puddles on the
bottom of the vessel . By cycling the dissolution and precipitation , nearly all of the impurity may be removed . Pure picric acid solutions are
pure yellow in color without a trace of orange or brown . Even the saturated boiling solution will be pure primary color yellow . And the crystals
which separate from these pure yellow solutions will be more nearly perfect in purity than the crystals which form in more
orange colored impure solutions . These observations still apply to the solutions where HCl is used as a solubility modifier .
I have noticed that the more desirable crystals tend to drop out while the solution is still warm and this is really where the added HCl has benefit
by shifting higher the temperature range over which most of the crystallization completes , and leaving much less remainder to be gotten from the
filtered solution if it is boiled down for a second crop . Instead of 10% of the yield having to be gotten by boiling down the residual solution from
the first recystallization , there is only maybe an additional 2 or 3 % there , which makes the second crystallization hardly even worthwhile for
smaller sized batches .
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Rosco Bodine
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To get a more pure crude picric acid product from the first filtration of the diluted nitration mixture , I have underway an experiment which appears
to be working . The experiment at early purification of the product is being done on a 1 mole scale according to a slight variation of Experiment 2
above using 1 mole of methyl salicylate for the nitration .
The sulphonation was done at a higher temperature ( 169 C ) for a longer time ,
several hours , using 40% the amount of sulfuric acid , and then adding more sulfuric before the nitration , but using only 90% the total amount H2SO4
on a molar basis as in Experiment 2 . An extra amount 20 grams of solid NH4NO3 was added to the spent nitration mixture before it was raised to 120
C for a half hour in finishing the nitration . After standing overnight , the two thirds solidified mixture of lumpy solids and spent acid was
diluted with 1150 ml distilled water and heated to 110 C to redissolve the bulk of the crystals , but leaving a layer of darker melt and impurities at
the bottom of the hot mixture . As the gentle boiling proceeded , the saturated solution gradually lightened and clarified above the melt pooled on
the bottom , as small globules would rise and fall in the saturated solution " lava lamp style " .
There was a considerable amount of the melt at the bottom of the flask containing the spent nitration mixture total volume now about 2250 ml . The 3
liter Erl containing the boiling hot saturated solution was removed from the hotplate stirrer and set on a stack of newspaper
with one edge of the bottom of the flask raised slightly by a 1" thick block of wood ,
in order to tilt the flask so the melted material and the stirbar would roll across the bottom and settle at the low spot . The low spot was rested
on a damp paper towel to more rapidly cool the puddled melt and stirbar . The flask was rocked gently to observe when the melt solidified , and when
this occured , the saturated solution was clouding and
was quickly decanted from the solidified impurities , into a 4 liter beaker . A stirbar was placed into the beaker to keep the hot solution stirred
as it precipitated the
crystals of picric acid .
The solidified chunk of impure picric acid encased the stirbar , and it was half the size of a fist , containing much picric acid ,
though contaminated with impurities . The impure material was covered with a fresh portion of 1500 ml distilled H2O and reheated to boiling . The
similar effect as observed in the first dissolution repeated ,
only this time , a small volume of much darker melt was the result , estimated to be maybe 5 or 6 grams of impurity . The
1500 ml of boiling hot solution was handled exactly as was done before , decanted away from the impurity melt
just as it solidified clinging to the stirbar .
The hot saturated solution was decanted into a 2 liter beaker , and the residual 5 ot 6 grams of impurity was discarded .
The contents of the 2 liter beaker were
then added to the product from the first
decantation in the 4 liter beaker , total
volume of the combined material is about
3700 ml .
The crude material having been freed from probably 90% of its impurity
by this workup of the nitration mixture ,
should give a very fine quality end product
after subsequent recrystallization from
boiling water and HCl .
I wanted to describe this process since
no complete details of how this is done have been described before .
The quantities for the process described are for 1 mole of precursor , so it should be easy math to determine quantities for other batch sizes .
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((Blasta))
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my first picric acid synth, did I do something wrong?
So I tried to create phenolsulfonic acid by first heating my concentrated sulfuric acid to around 300C. I then allowed the acid to cool off to 210C
then I added my 100 extra strength Asprin tablets, at 32.5 grams. The solution began to attack the asprin quite quickly and within several minutes the
acid-asprin solution went very dark and a few white fumes evolved. The end solution after cooling is still very dark but when I turn the flask to the
light the acid-asprin solution appear to have a dark redish copper color to it. Did I overcook my solution? Is this normal? The smell of this liquid
reminds me of photographic grade acetic acid...
update* I wonder if I used too little sulfuric acid? After adding in 100ml more acid the solution began to lighten some what...
[Edited on 12-9-2005 by ((Blasta))]
use caution---explosives in transport
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Quince
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Isn't that too hot?
[Edited on 13-9-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Mumbles
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That sounds normal to me. Everytime I have seen the phenol(or substitute) reacted with sulfuric acid it takes on a dark red color, to a black color
if th sulfuric acid is impure. I assume the phenol-4-sulfonic acid has a dark red to black color. As far as the lightening, it could be because you
had too little. I feel there is a much stronger chance that it is because of simple dilution. If you have a colored solution, and you add more
solvent it tends to lighten in color.
As far as the acetic acid smells that is normal. The asprin is hydrolysed to salicylic acid and acetic acid. It is then decarboxalated and
sulfonated. The heat you had on the sulfuric acid/asprin mix was probably high enough to boil off some of the acetic acid thus explaining the odor.
[Edited on 9-13-2005 by Mumbles]
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Rosco Bodine
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The phenolsulfonic acids are dark red and appear nearly black in anything but a thin layer which allows some light to reveal the color . Aspirin
sulfonates easily and rapidly and at a fairly low temperature . It may be beneficial to actually leave as much of the acetic acid as possible by not
sulfonating aspirin for too long or too hot ,
as its solvent properties and its evaporation is probably helpful to the nitration particularly in the first half of the nitration .
Using plain aspirin tablets will reduce your yield and result in purification problems if your experience follows mine . Picric acid can be difficult
to isolate in pure form since any impurities tend to get trapped in the crystals . The difference can be whether one or three recrystallizations will
be needed if the pure material is what is desired .
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((Blasta))
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humm, I'll try nitrating the mixture and see how much Picric acid I recieve... I'll let you all know.
use caution---explosives in transport
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Quince
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I want to save on solvent, so I'm wondering if an extraction using a solvent apparatus is usable for aspirin extraction, or would the filter be
too clogged by the fine solids for this to work (or can I perhaps use a layer of several filters of increasing fineness to decrease the clogging
effect)?
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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((Blasta))
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...pleasently surprised
Well, the experiment wasn't a loss after all. The black phenolsulfonic acid nitrated easily and produced a bright yellow crystalline precipitate.
The crystals were washed in deionised water and dried. The end product was fairy pure after filtration. I estimate that the yield was ~60%, so I
don't think it was terriable for my first try. I've since made
Ammonium Picrate and tested a COB device at the firing range. Quite powerful stuff and quite easy to make too!
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Rosco Bodine
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My initial optimism about methyl salicylate being a good precursor for picric acid is much in question now after three experiments have each failed to
produce nearly as good yields of simply isolated pure product compared to the use of aspirin as the precursor . The process using methyl salicylate
goes much more slowly both in the nitration and doubly slowly in the purification . It may be that the optimum conditions for the sulfonation and
nitration have simply not been identified , but indications are that the problem is more involved than just that . The methyl group of the ester is
what appears to itself be causing problems , possibly due to a byproduct during sulfonation which then causes losses during nitration , along with way
too much of an oily contaminant in the end product which is difficult to eliminate .
Future experiments may refine the method for methyl salicylate to a point it will become useful , but presently the yield of purified end product is
only about half the amount obtained using aspirin , and the quality is not as good . If I make any progress at refining the method to a point it is
worthwhile , I will share the information . But from what I have observed with three experiments so far the methyl salicylate is much inferior to
aspirin as a precursor for picric aicd .
I am considering saponifying the methyl salicylate with NaOH and then acidifying with HCl to convert it to salicylic acid , and eliminate the methyl
group which I believe is the source of the trouble .
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quicksilver
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| Quote: | Originally posted by Rosco Bodine
My initial optimism about methyl salicylate being a good precursor for picric acid is much in question now after three experiments have each failed to
produce nearly as good yields of simply isolated pure product compared to the use of aspirin as the precursor . The process using methyl salicylate
goes much more slowly both in the nitration and doubly slowly in the purification . It may be that the optimum conditions for the sulfonation and
nitration have simply not been identified , but indications are that the problem is more involved than just that . The methyl group of the ester is
what appears to itself be causing problems , possibly due to a byproduct during sulfonation which then causes losses during nitration , along with way
too much of an oily contaminant in the end product which is difficult to eliminate .
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My attempt yielded a slightly darker yellow (but indeed the yield was low. I am in the process of working w / HCI and that attempt at salvage.
However....I live in a very rural area and if you have access to a vet supply or a feed & grain store there is a product that is Asprin (pure) for
cattle that sells for $8. It is made by Priority Care (it is Asprin for Cattle) called Asprin Boluses. This is pure ASA for $8 and it is 2.5 lbs of
asprin....yes; one Kg of ASA for $8. It has been my source for experiments for a few years now.
You can find it on the web as well (Re-order #1OM010PCARE - second digit is the letter o the fourth is a zero). Thus you could spend about $20
(including shipping and get two kilos of ASA !
And that, my friend is VERY inexpensive. I have made a list of OTC sources in the USA and some items are unusally low cost; asprin is one of them.
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Rosco Bodine
Banned
Posts: 6370
Registered: 29-9-2004
Member Is Offline
Mood: analytical
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Yeah I think ASA is definitely the better precursor and it does produce a very pure picric acid in high yield by a fast process .
I haven't yet tested the ASA nitration using the nitrate as a concentrated solution of ammonium nitrate . Another
idea I want to try is a mixed solution of ammonium nitrate with some sodium nitrate , which may allow a more concentrated solution . I know there is
an optimum water content and an optimum spent acids composition , any departure from which can be adverse to the yields . It can be a lot of work
testing the variables and finding the conditions which work best , but I have seen it happen that the quality of the process can make a huge
improvement when the details are worked out just right .
One thing I am getting with methyl salicylate is a clear oily precipitate which contaminates the end product , and also there is a soapy detergent
like byproduct of sulfonation which results in a persistence to the foaming , at times the nitration is like trying to stir whipped cream or shaving
cream , which is very annoying and troublesome , making the additions go tediously slow to allow continued mixing . There are very significant
viscosity problems to manage
during the nitration , much worse than is the case for ASA .
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