6-Membered rings – 1N 3177.6 6-Membered rings – 1N – pyridines
N
HN
HO 2 NO 2 NNO 2NO 2NO 2O 2 NN
HN
HO 2 N
O 2 NO 2 NNO 2NO 2NO 2O 2 N2 N NHFuming HNO 3DMF168
1692,4,6-(NO 2 ) 3 C 6 H 2 Cl170
(PYX)NH 2 NNO 2NFigure 7.63The synthesis of polynitro derivatives of pyridine and other six-membered nitrogen hetero-
cycles by electrophilic aromatic substitution is often not feasible due to electron deficiency in
these rings; pyridine is nitrated to 3-nitropyridine only under the most vigorous nitrating con-
ditions. A solution to this problem is to incorporate electron-releasing groups into the pyridine
ring. Such an approach is seen during the synthesis of the thermally stable explosive known as
PYX (170); 2,6-bis(picrylamino)pyridine (169) is di-nitrated at the 3- and 5-positions under
relatively mild nitrating conditions.^107 ,^108 PYX (VOD∼7450 m/s,d= 1 .75 g/cm^3 , m.p.
460 ◦C) is now commercialized in the US and is manufactured by Chemtronics under licence
from Los Alamos National Laboratory for use in thermally stable perforators for oil and gas
wells.^109
N NHHNNHNO 2NO 2NO 2NO 2 NO 2O 2 NNO 2O 2 NO 2 NO 2 NNNO 2NO 2NO 2NO 2O 2 NO 2 NO 2 NO 2 NNN NN172171
(PADP)
NO 2Figure 7.64PADP (171), an explosive synthesized from the reaction of 3,5-dinitro-2,6-bis-
(hydrazino)pyridine with picryl chloride in DMF followed by oxidation with nitric acid, also
exhibits high thermal stability.^110 2,4,6-Tris(picrylamino)-3,5-dinitropyridine (172) exhibits
much lower thermal stability than both PYX (170) and PADP (171), a consequence of in-
creased steric crowding around the pyridine ring.^108