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Would 2,5-dinitropyrrole be a product of nitration of pyrrole with $\ce{H2SO4/HNO3}$? It seems that 2,5-dinitropyrrole is not formed when using $\ce{Ac2O/HNO3}$ (ref 1). Is this just because of the mild conditions used, or does this reflect the pyrrole ring being more deactivated by the first nitration than a benzene ring would be?

1 Cooksey, A. R.; Morgan, K. J.; Morrey, D. P. Nitropyrroles—II : The nitration of pyrrole. Tetrahedron 1970, 26 (21), 5101–5111. DOI:10.1016/S0040-4020(01)93163-1

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    $\begingroup$ Pyrrole is more activated towards electrophilic aromatic substitution, due to the electron donation of nitrogen atom. $\endgroup$ – Jori Apr 22 '15 at 8:08
  • $\begingroup$ Yes, but is 2-nitropyrrole activated towards electrophilic substitution relative to nitrobenzene? I assume it would be but then unfunctionalized dinitropyrroles should be relatively easy to make (unless the harsh conditions cause other side reactions). Sorry if I was being unclear ! $\endgroup$ – J. LS Apr 22 '15 at 8:32
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Would 2,5-dinitropyrrole be a product of nitration of pyrrole with $\ce{H2SO4/HNO3}$?

I doubt it and would rather expect a lot of tar to be formed here. Pyrrole tends to undergo acid-catalyzed polymerization!

For decades, acetyl nitrate, formed by addition of fuming nitric acid to acetic anhydride, is the reagent of choice.

Mononitration of pyrrole predominantly gives 2-nitropyrrole, accompanied by minor amounts of 3-nitropyrrole. (K.J. Morgan and D.P. Morrey, Tetrahedron, 1966, 22, 57–62. DOI).

In the case of 1-methylpyrrole, the yield of the 3-nitropyrole is somewhat larger (H.J. Anderson, Canad. J. Chem, 1957, 35, 23–29). In you want even more of the 3-nitro isomer, a more bulky alkyl substituent (t-Bu) or N-silylation with $\ce{((CH3)CH)2SiCl}$ is a viable approach.

Nitration of 2-nitropyrrole at −15 °C with nitric acid in acetic anhydride furnishes a 4:1 mixture of 2,4- and 2,5-dinitropyrrole with a total yield of 61%. (R. Alan Jones, Gerritt P. Bean, The Chemistry of Pyrroles: Organic Chemistry: A Series of Monographs, Vol. 34, Academic Press, p. 124)

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    $\begingroup$ Safety concerns should be indicated here, particularly operating with concentrated nitric acid and any organic layers. $\endgroup$ – Geoff Hutchison Apr 22 '15 at 12:50

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