Rbick
September 15th, 2007, 10:06 PM
I think I have finally figured out the age old question as to why KNO3 creates a thick syrup that’s impossible to manage when used in a nitration reaction. No its not because you let the temperature get to high or because you added too much Potassium Nitrate... It really seems quite simple, I just never really looked in to it. I will also being going over a few things about nitrations that I have always wondered about. The reaction between H2SO4 and KNO3 goes as follows:
H2SO4 + 2KNO3 ---> K2SO4 + 2HNO3
The resulting compounds are obviously Potassium Sulfate and Nitric Acid. The Sulfate is not of use, and it is the Nitric acid that we are after. Now lets look at a nitration mixture with Ammonium Nitrate and Sulfuric Acid, which is known for not becoming a thick slurry during the nitration process:
H2SO4 + 2NH4NO3 ---> 2(NH4)2SO4 + 2HNO3
These products are Ammonium Sulfate and Nitric acid. Ok… Well what is the big deal? I believe that part of the answer is in the properties of the two byproducts: Ammonium and Potassium Sulfate.
Potassium Sulfate is described as being a very hard substance. Along with that, it also only dissolves at about 11g per 100 mL of water. If there isn’t enough water for the Potassium Sulfate to dissolve into, then it will obviously come out of solution as a solid. 11g per 100 mL is very low considering if we look at Ammonium Sulfate, which dissolves at 70g per 100mL of water. The one thing I am unsure of is how much each dissolves in Sulfuric Acid or whether they do at all. I don’t think this would change my conclusion in this matter.
Well where does the water come from? Hopefully I will be able to answer that using ETN as an example. In the process of nitration, a byproduct is often water. This can be seen here in the following example. I will use pure HNO3 in the equation for clarity. Also, Erythritol has the formula of C4H10O4 and is a natural sweetener. Four nitro groups replace four of the H atoms and bond to the Oxygen, creating C4H6N4O12. This is known as an O-nitration.
4HNO3 + C4H10O4 ---> C4H6N4O12 + 4H2O
The water seen in this reaction would actually be absorbed partially, if not fully, by the Sulfuric acid. In a nitrating mixture involving no nitrate salt, this is a reason for the Sulfuric Acid (I’ll get into this later). However, one thing I have noticed is that the directions for nitration reactions using a nitrating salt either don’t have enough Sulfuric Acid, or they use too much. Usually the latter. Of course it cannot be assumed that you can get everything perfect, but I sure as hell like to try. Anyway, the water from the resulting nitration is what I assume is part of what dissolves the byproducts in the reactions. With Potassium Sulfate not dissolving nearly as well as Ammonium Sulfate, and being classified as “brittle and hard”, it comes out of solution and makes a hard, thick solid mess. I also took a look at some pure Ammonium Sulfate in my chemistry class, and it seems to be a soft, fine white powder. I assume this is why KNO3 is not suitable for nitrations. In conclusion, I would much rather use Ammonium Nitrate in my nitrating mixes, as I prefer swirling as opposed to breaking stirring rods. But if I had no other options, Potassium Nitrate still gets the job done. You just have a little extra work to do.
Now as for the role of Sulfuric Acid: As mentioned earlier, the Sulfuric is used to absorb water from the resulting nitration and act as a catalyst, driving the reaction. Unless of course if you are using a nitration salt, in which case the Sulfuric is also used to make HNO3 through the reaction with the nitrating salt. Sulfuric Acid is not always needed in some reactions. For instance, RDX and PETN can use 95% or higher HNO3 alone. What happens when the Sulfuric Acid mixes with the water is as follows:
H2SO4 + H2O --> H3O+ + SO4 -
This creates a positively charged Hydronium ion and a negatively charged Sulfate ion. The two bond to form Sulfuric Acid Hydrate, or H2SO4*H2O. This is how Sulfuric Acid absorbs the water. If you can, visualize the Water and Sulfuric Acid “sharing” a Hydrogen atom. Sulfuric acid hydrate can be turned into steam from the exothermic reaction with water, which is corrosive and dangerous. Remember, add acid to water, not water to acid :D.
I think that excess Sulfuric Acid could be partially responsible for bad yields with nitration salt mixtures. In this case, the unused Sulfuric might react with un-nitrated Erythritol (like it does with other organic substances), pulling out the Hydrogen and Oxygen to make water, and leaving a carbon byproduct.
H2SO4 + C4H10O4 ---> 4C + 4H2O + H2
Other mols of Sulfuric would react with the 4 mols of water to form Sulfuric Acid Hydrate.This is why when Sulfuric comes into contact with anything organic, it leaves a black residue, or in the case of skin, causes a burn. This makes Sulfuric Acid useful to make compounds anhydrous. I think this is what happened once while I was making ETN. I left the nitrating mix to go get a drink with my buddy and came back a few hours later. I didn’t think I’d be gone that long… But the mixture turned into a clear liquid with some black stuff floating at the bottom. This is just an assumption, but it makes sense.
So hopefully this is why Potassium Nitrate serves as such a bad nitration salt in nitration reactions. If this is completely wrong or you have more to add, by all means, correct me. I would also like to hear any other nitrating salts others have found to work well in this type of nitration.
H2SO4 + 2KNO3 ---> K2SO4 + 2HNO3
The resulting compounds are obviously Potassium Sulfate and Nitric Acid. The Sulfate is not of use, and it is the Nitric acid that we are after. Now lets look at a nitration mixture with Ammonium Nitrate and Sulfuric Acid, which is known for not becoming a thick slurry during the nitration process:
H2SO4 + 2NH4NO3 ---> 2(NH4)2SO4 + 2HNO3
These products are Ammonium Sulfate and Nitric acid. Ok… Well what is the big deal? I believe that part of the answer is in the properties of the two byproducts: Ammonium and Potassium Sulfate.
Potassium Sulfate is described as being a very hard substance. Along with that, it also only dissolves at about 11g per 100 mL of water. If there isn’t enough water for the Potassium Sulfate to dissolve into, then it will obviously come out of solution as a solid. 11g per 100 mL is very low considering if we look at Ammonium Sulfate, which dissolves at 70g per 100mL of water. The one thing I am unsure of is how much each dissolves in Sulfuric Acid or whether they do at all. I don’t think this would change my conclusion in this matter.
Well where does the water come from? Hopefully I will be able to answer that using ETN as an example. In the process of nitration, a byproduct is often water. This can be seen here in the following example. I will use pure HNO3 in the equation for clarity. Also, Erythritol has the formula of C4H10O4 and is a natural sweetener. Four nitro groups replace four of the H atoms and bond to the Oxygen, creating C4H6N4O12. This is known as an O-nitration.
4HNO3 + C4H10O4 ---> C4H6N4O12 + 4H2O
The water seen in this reaction would actually be absorbed partially, if not fully, by the Sulfuric acid. In a nitrating mixture involving no nitrate salt, this is a reason for the Sulfuric Acid (I’ll get into this later). However, one thing I have noticed is that the directions for nitration reactions using a nitrating salt either don’t have enough Sulfuric Acid, or they use too much. Usually the latter. Of course it cannot be assumed that you can get everything perfect, but I sure as hell like to try. Anyway, the water from the resulting nitration is what I assume is part of what dissolves the byproducts in the reactions. With Potassium Sulfate not dissolving nearly as well as Ammonium Sulfate, and being classified as “brittle and hard”, it comes out of solution and makes a hard, thick solid mess. I also took a look at some pure Ammonium Sulfate in my chemistry class, and it seems to be a soft, fine white powder. I assume this is why KNO3 is not suitable for nitrations. In conclusion, I would much rather use Ammonium Nitrate in my nitrating mixes, as I prefer swirling as opposed to breaking stirring rods. But if I had no other options, Potassium Nitrate still gets the job done. You just have a little extra work to do.
Now as for the role of Sulfuric Acid: As mentioned earlier, the Sulfuric is used to absorb water from the resulting nitration and act as a catalyst, driving the reaction. Unless of course if you are using a nitration salt, in which case the Sulfuric is also used to make HNO3 through the reaction with the nitrating salt. Sulfuric Acid is not always needed in some reactions. For instance, RDX and PETN can use 95% or higher HNO3 alone. What happens when the Sulfuric Acid mixes with the water is as follows:
H2SO4 + H2O --> H3O+ + SO4 -
This creates a positively charged Hydronium ion and a negatively charged Sulfate ion. The two bond to form Sulfuric Acid Hydrate, or H2SO4*H2O. This is how Sulfuric Acid absorbs the water. If you can, visualize the Water and Sulfuric Acid “sharing” a Hydrogen atom. Sulfuric acid hydrate can be turned into steam from the exothermic reaction with water, which is corrosive and dangerous. Remember, add acid to water, not water to acid :D.
I think that excess Sulfuric Acid could be partially responsible for bad yields with nitration salt mixtures. In this case, the unused Sulfuric might react with un-nitrated Erythritol (like it does with other organic substances), pulling out the Hydrogen and Oxygen to make water, and leaving a carbon byproduct.
H2SO4 + C4H10O4 ---> 4C + 4H2O + H2
Other mols of Sulfuric would react with the 4 mols of water to form Sulfuric Acid Hydrate.This is why when Sulfuric comes into contact with anything organic, it leaves a black residue, or in the case of skin, causes a burn. This makes Sulfuric Acid useful to make compounds anhydrous. I think this is what happened once while I was making ETN. I left the nitrating mix to go get a drink with my buddy and came back a few hours later. I didn’t think I’d be gone that long… But the mixture turned into a clear liquid with some black stuff floating at the bottom. This is just an assumption, but it makes sense.
So hopefully this is why Potassium Nitrate serves as such a bad nitration salt in nitration reactions. If this is completely wrong or you have more to add, by all means, correct me. I would also like to hear any other nitrating salts others have found to work well in this type of nitration.