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Author: Subject: Alternate routes to FOX-7 precursors
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[*] posted on 4-4-2017 at 10:11
Alternate routes to FOX-7 precursors

The two main precursors that are nitrated to FOX-7 are 2-methylimidazole (or 2-methylimidazolidinedione) and 4,6-dihydroxy-2-methylpyrimidine.

By far the easier precursor to acquire or make is 2-methylimidazole.

Most of the preparation instructions I've seen for this precursor are acetimidine + glyoxal (for the imidazole) or acetimidine + diethyl oxalate (for the imidazolidinedione).

Diethyl oxalate can be purchased, or synthesized via Fischer esterification of oxalic acid and ethanol (though I haven't seen an exact procedure for such).

Acetimidine, however, seems to be a strictly DIY project. And the imidine is very susceptible to hydrolysis, giving the rather useless acetamide.

I suppose you could use a 1:1 molar ratio of acetonitrile to NH4Cl and heat it to ~400 C in a sealed tube to produce acetimidine hydrochloride, but I'm more interested in something completely different:

A whole class of antibiotics is based on 2-methylimidazole, so, digging around, I found this:

Attachment: kraft1989.pdf (290kB)
This file has been downloaded 314 times

It uses ethylenediamine, acetic acid, and calcium oxide to form the imidazoline, then a nickel catalyst to dehydrogenate the C-C bond and thus produce the imidazole.

I: 2-methylimidazoline (2-methylimidazole with the C-C double bond hydrogenated)
II: 2-methylimidazole

2-Methyl-4,5-dihydroimidazole (2-Methylimidazoline).
A 1- to 1.05-mole portion of AcOH (glacial or in the form of 20-85% aqueous solution) was added with water cooling and stirring to 0.5 mole of ethylenediamine (in the form of a 20-85% aqueous solution). The mixture was boiled with the simultaneous evaporation of water, while the temperature was increased to 220-240ºC and at the end was heated for 30-40 min at 240-250ºC until water ceased to separate out. The technical grade N,N'-diacetylethylenediamine obtained (mp in a sample 176-177) was cooled to 180-185ºC, 43 g (0.75 mole) of 97.5% calcium oxide was added, and the downward condenser was replaced by an air-cooled reflux condenser. Heating of the hot mass was continued at 220-265ºC whereby I was soon formed and the whole mass began to boil (the bp of I is 197-200ºC) The mixture was boiled for 2 h, cooled to 185-190ºC, the reflux condenser was replaced by an air-cooled downward condenser, and I was distilled off at atmospheric or reduced pressure. Compound I can also be separated by dissolution of the mass in an anhydrous organic solvent (isopropanol, dichloroethane, diphenyl ether, etc.). Yield 37-43 g (88-95%) of I, mp 101-104ºC, which was suitable for the preparation of II without additional purification. According to the data in [14], the mp of I is 105ºC.

Then they give a procedure for the dehydrogenation of the imidazoline to form the 2-methylimidazole, both of which involve nickel catalysts.

Raney nickel can be a fickle beast, so their second procedure utilizing nickel formate would be more attractive; however, the second procedure requires temperatures as high as 200 Celsius, so the number of solvents that could be used is limited. They used diphenyl ether (m.p. 26ºC, b.p. 258ºC), but Ph2O is expensive to buy and difficult to synthesize (AlCl3 + Br2 + PhH, followed by PhBr + PhONa + Cu).

However, since FOX-7 doesn't care if you use straight imidazole or the dione, I'm wondering whether the imidazoline could be used directly in the nitration, or oxidized before use via some other mechanism that is simpler than dehydrogenation via Raney nickel (or nickel formate in diphenyl ether).

[Edited on 4-5-2017 by Chisholm]
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PHILOU Zrealone
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[*] posted on 4-4-2017 at 14:28

The important part of the process is the need for a structure -NH-C(CH3)=N- or -NH-C(=CH2)-NH- after isomerisation.
To allow for -NNO2- and addition-elimination-oxidation of HNO3, HNO2 to the double bond and formation of the dinitromethylen =C(NO2)2.

While FOX-7 is very stable and safe explosive on the contrary the intermediaries are not gentle compounds since some trinitromethyl , dinitromethyl and nitrosonitrocompounds are involved aside with nitramides...all of those are sensitive explosives towards heat, shock and process is quite risky...

If you really want to perform a new process take care to make it in low quantity and even if it succeeds be very cautious if you want to scale up process (even by a factor 2).

Oxydation of imidazoline into the process will make the all process more succeptible to I think it is better to perform oxydation step prior to nitration.

I guess that another good starting material would be oxalic acid diamide (oxalamide) and acetic anhydride or chloride to get CH3-CO-NH-CO-CO-NH-CO-CH3 then by further heating CH3-C(*)=N-CO-CO-NH(*) (ring closure via (*)) + CH3-CO2H.
This molecule contains the feature of the two starting material for FOX-7...the N=C(CH3)-NH sequence and the -NH-CO- sequence found as a discrete version into 4,6-dihydroxy-2-methylpyrimidine...
-NH-C(=O)- <==> -N=C(-OH)- (remember than phenol is an enol so as discrete structure phenol is also a keton)

PH Z (PHILOU Zrealone)

"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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