Can potassium nitrate and sulfuric acid be used to nitrate organics?

If we are doing a classic nitration to produce glyceryl trinitrate, one uses a mix of concentrated sulfuric and nitric acids. Additionally, one can produce concentrated nitric acid by distilling it from a mixture of potassium nitrate and sulfuric acid.

So, is it possible to do a nitration by mixing the glycerol with sulfuric acid and then adding potassium nitrate?

Disclaimer

In case anyone is wondering, I am not going to try this, and I do know how to make many better and safer explosives since I used to be a member of the alt.engr.explosives group way back.

• @NilayGhosh No. I know how to make that. My explosive of choice would be Kinepak. It's a LOT simpler – Dirk Bruere Jun 13 '20 at 12:34
• I'd rather add nitrate first, as H2SO4 would start reacting with glycerine immediately, or at least be quick with adding the salt. – Mithoron Jun 13 '20 at 16:19

A simple, but dangerous path to nitrating a metal oxide (say MgO) is to treat with NO2 gas (caution: toxic and corrosive), as to quote Wikipedia on Nitrogen dioxide:

NO2 is used to generate anhydrous metal nitrates from the oxides:[10]

$$\ce{MO + 3 NO2 -> M(NO3)2 + NO}$$

where heating mix of Cu, KNO3 and H2SO4 will generate NO2.

A safer path to nitrating, starts with the introduction of the powerful radicals, like the hydroxyl radical (•OH). The latter can transform commonly available nitrate salts (like KNO3) to the nitrate radical (•NO3) especially in the presence of an acid catalyst per the reaction:

$$\ce{•OH + NO3- <=> OH- + •NO3}$$

A supporting source reference, Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol. Per the paper's abstract:

Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere.

Also, see The Reactivity of the Nitrate Radical (•NO3) in Aqueous and Organic Solutions, by Stephen P. Mezyk, Thomas D. Cullen, Kimberly A. Rickman and Bruce J. Mincher, per the abstract to quote:

ABSTRACT Rate constants for the nitrate (•NO3) radical reaction with alcohols, alkanes, alkenes, and several aromatic compounds were measured in aqueous and tert‐butanol solution for comparison to aqueous and acetonitrile values from the literature. The measured trends provide insight into the reactions of the •NO3 radical in various media. The reaction with alcohols primarily consists of hydrogen‐atom abstraction from the alpha‐hydroxy position and is faster in solvents of lower polarity where the diffusivity of the radical is greater. Alkenes react faster than alkanes, and their rate constants are also faster in nonpolar solution. The situation is reversed for the nitrate radical reaction with the aromatic compounds, where the rate constants in tert‐butanol are slower. This is attributed to the need to solvate the NO3− anion and corresponding tropylium cation produced by the •NO3 radical electron transfer reaction. A linear correlation was found between measured rate constants in water and acetonitrile, which can be used to estimate aqueous nitrate radical rate constants for compounds having low water solubility.

With respect to the hydroxyl radical, the UV photolysis of a photocatalyst like TiO2 in aqueous KNO3, could be a path to the powerful, but very transient, hydroxyl and nitrate radicals.

Nitration reactions rely on the absence of water to proceed efficiently, in fact part of the purpose of the sulfuric acid in the mixture is as a drying agent to remove the water produced by the nitration reaction. Because potassium nitrate (and potassium sulfate for that matter) is not meaningfully soluble in concentrated sulfuric acid, it is impossible to create the dry solution required by this reaction in this way.

• In that case, why can one add pure sulfuric acid to potassium nitrate and get nitric acid, in the abscence of water? – Dirk Bruere Jun 13 '20 at 12:35
• This is thoroughly incorrect. – Mithoron Jun 13 '20 at 16:20
• Could you please correct me, or at least offer insight into what exactly is incorrect then? – WindowHero Jun 13 '20 at 16:36
• I realize that by some definitions what's being discussed here isn't even technically nitration, since nitration can specifically refer to aromatic structures, and that the primary role of sulfuric acid in either case is the formation of the nitronium ion, but I wouldn't consider either of those to be strictly in the scope of the question. – WindowHero Jun 13 '20 at 16:46