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niertap
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HNO3 is a terrible NO3- source...why use it?
In most energetic material synthesis' 70% HNO3 is used. Why doesn't everyone just use KNO3 or NaNO3? There will be a considerable amount of water
that will not have to be removed from the reaction, decreasing the amount of H2SO4 needed.
A 3.8L jug of 98% H2SO4 can be purchased from the hardware store for around $25. Why would someone not in an analytical setting use anything
different?
Ignorance is bliss
Outliers in life are modeled by chemical kinetics
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Bhaskar
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Hi,
Your suggestion is quite right, I quite agree but how can the acidification of a nitrate salt form nitric acid above it's aezotrope? I don't know
myself so as your suggestion says, you must be knowing the maximum concentration reached by a nitrate salt on acidification, say sulfuric acid in
nitrations?
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Bot0nist
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Nitrations are not a "one size fits all" reaction, and are tailor fitted to the substrate. In some nitrations sulfuric acid can not be used at all,
like hexamine.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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Bhaskar
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Quote: Originally posted by Bot0nist  | | Nitrations are not a "one size fits all" reaction, and are tailor fitted to the substrate. In some nitrations sulfuric acid can not be used at all,
like hexamine. |
He's just asking wether he can use nitrate salts for performing nitrations, how is what you just said the answer to the question?
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barley81
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The answer is yes. Search for the syntheses of nitrocellulose and picric acid on this forum and you will find that some use nitrate salts.
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Bot0nist
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| Quote: Originally posted by Bhaskar | | Quote: Originally posted by Bot0nist | | Nitrations are not a "one size fits all" reaction, and are tailor fitted to the substrate. In some nitrations sulfuric acid can not be used at all,
like hexamine. |
He's just asking wether he can use nitrate salts for performing nitrations, how is what you just said the answer to the question?
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No, he asked why is nitric acid used at all. I assumed that the OP was not completely dense and was capable of utfse. If he is capable of such a
seemingly difficult feat for most, then he would already know the answer to the question you thought he asked. I, however, was attempting to answer
the question he actually asked. I Think.
How could we employ nitrate salts in a nitration without dissolving then in concentrated sulfuric acid?
What if there is issues with you isolating your nitrated product due to the contaminates (potassium sulfate, etc) you added?
The easiest answer to these two questions is to distill nitric acid from the nitrate salt and sulfuric acid. No added contaminates during the
nitration, and no need to use sulfuric, like when it's not compatible with the substrate, intermediate, or target.
[Edited on 12-3-2012 by Bot0nist]
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Bhaskar
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I see... 
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Pulverulescent
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If one is unable, or unwilling (too lazy) to prepare strong HNO<sub>3</sub> by distillation then nitration by
H<sub>2</sub>SO<sub>4</sub>/nitrate-salt mixtures would seem to be a doable alternative, poor though it is . . .
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
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Bhaskar
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| Quote: Originally posted by Pulverulescent | | If one is unable, or unwilling (too lazy) to prepare strong HNO<sub>3</sub> by distillation then nitration by
H<sub>2</sub>SO<sub>4</sub>/nitrate-salt mixtures would seem to be a doable alternative, poor though it is . . .
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Use of fuming nitric acid for nitrations is unprofitable in a way as if one can perform successful nitrations using nitrate salts then why not?The
extremely precious fuming counterpart can be used for other syntheses...
I wonder the difference in yield using nitrate-salt mix. and using aezotropic nitric acid method. Anyone?
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Pulverulescent
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| Quote: | | The extremely precious fuming counterpart can be used for other syntheses... |
If you have the glass, the alkali nitrate and the sulphuric acid why would it be precious?
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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Bhaskar
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Good point, my bad.
I was talking about it's price for buying as a reagent.
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garage chemist
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There are several reasons why nitrating mixtures with "real" HNO3 are preferable over those from sulfuric acid and an alkali metal nitrate, even
despite the increased water content when using 70% HNO3.
One is recyclability of the spent nitrating acid, a decisive factor in industry. If you use a nitrate salt, the spent acid will be full of alkali
metal bisulfate and cannot simply be boiled down to
recycle the sulfuric acid. With HNO3, the spent acid can be freed of HNO3 and water by distillation and used over and over again, without losses
except for what adheres to your filtered solid product, or almost no losses in the case of liquid nitrated products.
Another one is viscosity of the nitrating mix. A solution of KNO3 in H2SO4 is a relatively thick and slurry-like, and does not so easily wet things
like cellulose, forming a mass that has to be kneaded. With HNO3, the nitrating acid is thin and fluid, rapidly and easily wetting all of the
precursor.
Have you ever directly compared nitrocellulose made from acid and nitrate mix with the product from conc. H2SO4 and 65% HNO3? The product made with
HNO3 is significantly better, despite more water being present in the nitrating mix!
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phlogiston
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Would adding a little water to the mix to decrease the viscosity help, then?
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Bot0nist
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Using ammonium nitrate instead of potassium greatly reduces the viscosity, IME.
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quicksilver
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Just from a discussion standpoint; I see every reason (if you do have the glass) to distill your acid. One maintains a variety of controls from that
agenda.
Sometime back there was a discussion as to the efficiency of varying alkali nitrates used in a mixed acid distillation. Of course there is a small
learning curve also as the mixture of a solid nitrate and another acid such as sulfuric acid appears to provide a better yield when the distillation
is started from a clear solution of both materials (beginning from a weighted solid simply dumped into a flask of sulfuric creates several problems).
I did a small experiment a long time back testing the proportionate yield of nitric acid with a vacuum applied, cooling in the receiving flask and
cooling in the condenser (as well as condenser design) and removed.
However, given that a fairly equipped lab would have more than kitchen utensils available, the resultant nitric acid eventually could be substantially
inexpensive with a marginal initial investment.
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caterpillar
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I used satls and sulphuric acide where it was possible. Moreover, salts plus aforementioned sulphuric acid are more powerful nitrating agents than
HNO3 + H2SO4. The only reason to prepare conc HNO3 by distillation is syntesis of such compounds like RDX and HMX, that are destoyed by H2SO4.
Women are more perilous sometimes, than any hi explosive.
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Pulverulescent
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| Quote: | | The only reason to prepare conc HNO3 by distillation is syntesis of such compounds like RDX and HMX, that are destoyed by H2SO4.
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Mixed acid nitration gives higher yields and better purity . . .
Only one more reason!
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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AndersHoveland
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The reason that 70% HNO3 is typically used is because it is completely soluble. Potassium nitrate can have some trouble dissolving in concentrated
sulfuric acid. The potassium bisulfate that forms apparently does not have a very high solubility under these conditions because of the common ion
effect.
Anhydrous (100 percent concentrated) nitric acid would be the most ideal, but usually these high concentrations of nitric acid are not readily
obtainable. Higher concentrations of HNO3 are more difficult to make, and have less stability, having a tendancy to irreversibly decompose in the
presence of light. Anhydrous lithium nitrate would also be a good choice, but this is more expensive and not commonly available.
Ammonium nitrate is sometimes used in nitrations because it has such a high solubility and readily dissolves, but in the presence of concentrated
sulfuric acid, some of the NH4NO3 can be dehydrated and decompose into nitrogen oxides, reducing yields.
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Bhaskar
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Depends on what salt you are using, but it will lead to dilution of the nitration mix. and destroy it. That's what we are talking about, the use of
anhydrous nitric acid is preferable to it's aezotropic counterpart as it contains less water.
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Bhaskar
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Won't the salt-acid mix. reduce the purity of the nitrated product and can pose problems for it's synthesis?
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AndersHoveland
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| Quote: Originally posted by Bhaskar | Won't the salt-acid mix. reduce the purity of the nitrated product and can pose problems for it's synthesis?
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Potentially yes, but typically this is not so much of a problem. It depends on what the nitrated product is. If making cellulose nitrate, the salt can
be rinsed out when it is neutralised with sodium bicarbonate solution. If making nitroglyerin, the nitroglycerin separates out as oily droplets which
the salt is not soluble in.
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caterpillar
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| Quote: Originally posted by Pulverulescent | | Quote: | | The only reason to prepare conc HNO3 by distillation is syntesis of such compounds like RDX and HMX, that are destoyed by H2SO4.
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Mixed acid nitration gives higher yields and better purity . . .
Only one more reason! |
It is a strange idea. Who told you it? How do you determine this yield? It can be calculated in different ways. You need generally more H2SO4, and
according to it yield will be, yeah, lower. But mixture of salt + H2SO4 is more powerful nitrating agent- less amount of water, and this factor
usually increase yield. All sulphates can be deleted by water- they are not reason for impurity.
Women are more perilous sometimes, than any hi explosive.
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Bhaskar
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| Quote: Originally posted by AndersHoveland | | Quote: Originally posted by Bhaskar | Won't the salt-acid mix. reduce the purity of the nitrated product and can pose problems for it's synthesis?
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Potentially yes, but typically this is not so much of a problem. It depends on what the nitrated product is. If making cellulose nitrate, the salt can
be rinsed out when it is neutralised with sodium bicarbonate solution. If making nitroglyerin, the nitroglycerin separates out as oily droplets which
the salt is not soluble in. |
That's a relief to hear. Nitroglycerine isn't soluble in water right?
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AndersHoveland
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That is correct, it is not.
But nitroglycerin can very slowly hydrolyse in water, especially if there is plenty or residual acid left in the aqueous solution. This is a
charactaristic of all esters (nitroglycerin is a nitrate ester of glycerol).
The solubility of nitroglycerin in ethanol is reportedly 1 part nitroglycerin to 3.2 parts by weight ethanol.
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Bhaskar
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| Quote: Originally posted by AndersHoveland |
That is correct, it is not.
But nitroglycerin can very slowly hydrolyse in water, especially if there is plenty or residual acid left in the aqueous solution. This is a
charactaristic of all esters (nitroglycerin is a nitrate ester of glycerol).
The solubility of nitroglycerin in ethanol is reportedly 1 part nitroglycerin to 3.2 parts by weight ethanol. |
So after the nitration of glycerol, I am supposed to wash it in water to clean it, right?
I want to make my first nitroglycerine so that's why I asked...
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