aromaticfanatic
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Why are sulfuric acid ratios the same for nitrate salt and nitric acid?
I have been perplexed by this for years. Why is it that sulfuric acid amounts are similar or the same for nitrations using nitric acid as well as
nitrate salts.
Shouldn't the nitrate salt require more sulfuric acid to form the nitric acid in situ and protonate it than if the sulfuric acid just has to protonate
the nitric acid in a typical mixed acid bath?
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Antigua
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Are you looking at molar rations or gram ratios?
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aromaticfanatic
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molar and gram
for ETN people often use 15g erythritol and 100-120mL of sulfuric acid no matter if nitric acid or nitrate salt
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Fyndium
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I'm also curious about this. I consider reagent saving a big factor in reaction efficiency, and there seem to be some fluctuation in sulfuric acid
amount used.
Some synthesis appears like it is used in well excess, as high as 35-fold in volume, but a better question is, what is the minimum amount that can be
used without detrimental effect on yield?
I never liked the idea of whipping stuff together in order to obtain something desired. Instead, I love perfected processes where everything is used
just the required amounts, and even better if some parts can be recycled, if worthy.
[Edited on 14-1-2021 by Fyndium]
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Sulaiman
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I assume that a major part of such a reaction is the capture of water by the sulphuric acid,
if you add a nitrate salt some sulphuric acid will be required to convert it to HNO3
If you add nitric acid then it is 31% w/w water, that needs to be 'removed' by the sulphuric acid.
I'll let others do the math.
As commercial sulphuric acid is cheap, excess is used.
I often use excess of one reactant, usually the cheap one to ensure that all of the more expensive reactant is used.
If you use stoichiometric quantities of all reactants,
the reaction will slow down as it nears completion due to dilution / molecules of reactants rarely meeting.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Fyndium
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So it is practically always more economical to use nitrate salt, as nitric acid requires basically double step consumption of sulfuric acid.
If overhead stirring is used, can it be too vigorous? Considering the salt method tends to form a paste over the course.
[Edited on 15-1-2021 by Fyndium]
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stamasd
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Don't forget that the resulting salts (sodium or potassium sulfate/bisulfate, depending on which initial nitrate is used and in which proportions)
also have an assisting effect in trapping water - especially the sodium one. They are not completely inert as to the nitration reaction and can help
driving it forward by providing an amount of dehydrating effect.
All your acids are belong to us.
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Boffis
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They aren't and you can't generalize aout such things but you are probably looking at ill designed and poorly tested procedures. There are many
issues that affect the ratio of sulphuric acid to nitrating agent. Sulphuric acid acts as a solvent, dehydrating agent and as the generator of the
nitrating species. One of the advantages of alkali nitrates is that the reaction with sulphuric acid generates sodium hydrogen sulphate and hydrogen
nitrate; no water, so higher nitration species concentration (nitronium ions?). On the other hand the problem of the separation of the sodium salt
from the mixture can be a problem as I reported recently in another thread. It was not a problem when nitration was carried out at higher temperatures
because of increased solubility of the salt but this may not be an option in many nitrations. Your options are then to increase the amount of solvent
(sulphuric acid) or turn to nitric acid. You have to design you nitration mixture to match the needs of the conditions you bare trying to achieve.
This is a bit of a dark art but there is plenty of quality literature on the subject available (probably more than for any other procedure!!).
Generally however, I find that unless you have a quality procedure to follow you have to do a bit of small scale trial and error.
Overhead stirrers certainly help with heterogeneous mixtures and in general the more vigorous the better. I recently posted on the nitration of
p-dichlorobenzene with sodium nitrate; here an overhead stirrer with a propeller type stirrer is essential. In the thread on the nitration of
bromobenzene I found that the addition of dichloromethane, more sulphuric acid and partial use of nitric acid in place of some of the sodium nitrate
can be used to make the nitration mixture stirrable by a magnetic stir-bar which in my case is essential as the reaction is carried out under reflux,
hence enclosed equipment. (I don't a sealed stirrer gland for the overhead stirrer).
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Fyndium
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Reflux does not mean enclosed, it just means you need a longer stirrer shaft. 
Yes, there are number of variables here, and likely there are some generalizations of what dehydrates and how effectively.
Maybe I haven't had time to read enough of the forum, but there appears to be more of surface-scratching than actual studying and documentation of
different procedures. This reminds me of when I was younger and into energetics - I was more interested in the results, not the kinetics - if x + y
gets z, it will suffice. A library of studies and documentations would be invaluable to any chemist whatsoever, as tried and true methods make working
and developing new things a lot more efficient. Here, it would mean trying out different amounts of reagents, different salts of nitrates (sodium,
potassium, calcium, etc) and measuring if more solvent is needed or not, or does it affect the yield, etc. I'm not sure if there are inert solvents
apart from sulfuric acid (inert may be poor choice of words per se) which would liquefy the reaction.
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Pyro_cat
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Isnt HNO3 kind of a nitrate salt itself ? HNO3 or KNO3 its still one atom stuck to an NO3
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katyushaslab
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Quote: Originally posted by Boffis  | | They aren't and you can't generalize aout such things but you are probably looking at ill designed and poorly tested procedures.
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A LOT of the nitration procedures for polyols/etc (think: mannitol, erythritol, pentaerythritol, glycerin) seem to be basically "folk knowledge"
levels of optimisation/design, where one of two things happens:
1. some poster on some forum gets it working via trial and error with a decent yield and it gets copied around as gospel forever.
2. its the procedure found in "some book", gets posted/used, and becomes gospel. Often with the original reference lost. This may feed into "1".
As kind of an aside: with some nitrations, mixed-acid works better than straight-HNO3 not only due to dehydration effects, but also sulphonation of
the thing being nitrated as an intermediate step. With others, the amount of sulphuric acid used is larger than needed because stirring/solvency...
[Edited on 20-1-2021 by katyushaslab]
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Fyndium
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There are some scientific research papers where ETN was prepared by various means, and they have descriptions of synthesis, so there should be
legitimate sources for ratios and methods available with somewhat professionally optimized results.
Although, when performed in mmol scale, they tend to use huge excess of solvents mainly due to ease of handling. The actual productive scale would
limit the amount of solvent a lot.
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Nitrosio
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Attachment: ETN4.pdf (11kB)
This file has been downloaded 388 times
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caterpillar
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I made TNP via H2SO4 + KNO3 and definitely could have used less amount of H2SO4. One needs some experiments. But there is another way- to make mixed
acid from H2SO4 and dehydrated Ca(NO3)2.
Women are more perilous sometimes, than any hi explosive.
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Microtek
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Apart from the lower viscosity, another advantage to HNO3/H2SO4 over XNO3/H2SO4 is that the sulfuric acid can be recycled (unless it is contaminated
during the reaction). This works best if the HNO3 is distilled out of the mixed acid before the reaction, and used neat. Then the remaining fraction
can be concentrated at a higher pot temperature to reconcentrate the sulfuric, which is then ready for another run.
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MineMan
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| Quote: Originally posted by Microtek | | Apart from the lower viscosity, another advantage to HNO3/H2SO4 over XNO3/H2SO4 is that the sulfuric acid can be recycled (unless it is contaminated
during the reaction). This works best if the HNO3 is distilled out of the mixed acid before the reaction, and used neat. Then the remaining fraction
can be concentrated at a higher pot temperature to reconcentrate the sulfuric, which is then ready for another run. |
In an industrial setting sure
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night429
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I've made TNP with potassium nitrate as well using less sulfuric acid than I normally do, the volume of 93% sulfuric acid was double the mass of
potassium nitrate used, if I'm remembering right. I got what I believe was potassium picrate crystallizing with the picric acid, including after
recrystallizing from water. I haven't had this issue while using more sulfuric acid, about three times the mass of potassium nitrate.
So, I think the amount of sulfuric acid prevents other salts from precipitating out, but I wonder if something else, like HCl, could be used during
the workup instead.
In a free fall of fire and ice with explosions in the sky
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katyushaslab
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Recycling reaction mixes is something that can also be done on an amateur setting to reduce waste - the disposal of which can be quite expensive or
draw attention. I also think this will become more important in future for people in countries where acids are becoming harder to get ahold of.
Waste management is one of those things I spend a not inconsiderable amount of time thinking about when planning an experiment. Chem-waste disposal is
expensive, dumping it down the drain is irresponsible, etc.
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MineMan
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| Quote: Originally posted by katyushaslab | Recycling reaction mixes is something that can also be done on an amateur setting to reduce waste - the disposal of which can be quite expensive or
draw attention. I also think this will become more important in future for people in countries where acids are becoming harder to get ahold of.
Waste management is one of those things I spend a not inconsiderable amount of time thinking about when planning an experiment. Chem-waste disposal is
expensive, dumping it down the drain is irresponsible, etc. |
What is the right way then?
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Texium
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Thread Moved
13-8-2021 at 05:49 |
Herr Haber
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The one that suits you !
Still thinking about how to deal with the 15 liters of highly concentrated copper nitrate waste I have from silver refining.
When I think in SM mode I giggle thinking about the kilograms of CaC2 I have and what would happen if... Or... did I just think NH4, NaN3 ?
When I get a little bit more serious, I think about reclaiming some HNO3, but that would imply H2SO4 that could also be reclaimed afterwards. Then I
think about all the long hours and the electricity bill. Not so "green" anymore !
When all I really need is the copper.
I'm pretty sure that in reality I will end up flushing down iron nitrate instead of copper...
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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