Nucleophilic aromatic substitution 171must not be used for the recrystallization of 2,4,6-trinitrophenetole and vice versa. Thetrans-
etherification of 2,4,6-trinitroanisole with ethanol and 2,4,6-trinitrophenetole with methanol
goes via the same Meisenheimer intermediate (131) which is stable enough to be isolated.^270
Both 2,4,6-trinitroanisole and 2,4,6-trinitrophenetole and similar picryl ethers slowly form
picric acid in the presence of moisture, so inhibiting their use in munitions destined for long-
term storage. The formation of 2,4,6-trinitroaniline from the reaction of 2,4,6-trinitroanisole
or 2,4,6-trinitrophenetole with ammonia is too slow to be synthetically useful.
Aryloxy groups are much easier to displace compared to primary and secondary alkox-
ide anions and so, aryl ethers are generally more useful in displacement reactions. Amine
nucleophiles react with unsymmetrical aryl ethers to form the amine of the heavier nitrated
moiety.^271 Accordingly, 2,4,6-trinitrodiphenyl ether reacts with ammonia to expel phenoxide
anion and form 2,4,6-trinitroaniline.
CH 3
O 2 N NO 2NO 2
132OMeO 2 NCH 3 CH 3
NO 2 NO 2NH 2 NO 2
NO 2
56NH 3 , MeOH O^2 NNO 2
57H 2 SO 5 , 100 °C74 %Figure 4.54The displacement of alkoxy groups from polynitroarylenes has been used for the indi-
rect synthesis of some highly nitrated polynitroarylenes. Holleman^272 synthesized 2,3,4,6-
tetranitrotoluene (57) by treating 3-methoxy-2,4,6-trinitrotoluene (132) with ammonia in
methanol, followed by oxidation of the resulting product (56) with peroxymonosulfuric acid.
4.8.3.3 Other displacements
Some synthetically useful reactions exploit the displacement of sulfonate esters from polyni-
troarylenes. Thep-toluenesulfonate (tosyl) group is readily introduced into aromatic systems
from the reaction of phenols with tosyl chloride. The tosyl group is an excellent leaving group
and is readily displaced by a range of nucleophiles. When polynitrophenols are reacted with
tosyl chloride in the presence of pyridine the intermediate tosylate is too reactive to be iso-
lated, and instead, the tosylate reacts with the pyridinium chloride formed during the reaction
to form an arylpyridinium salt.^273 Such salts are synthetically useful because the pyridinium
group is readily displaced by various nucleophiles. The chemistry of picrylpyridinium chloride
and 2,4-dinitrophenylpyridinium chloride has been discussed in Sections 4.8.1.2 and 4.8.1.3
respectively.
Cl
NO 2NO 2
106ClO 2 NOHOHO 2 N NO 2NO 2
5O pyr
NO 2O pyr
NO 2
133O 2 N
POCl 3 , heat98 %pyridine, Et 2 O94 %Figure 4.55