Physicochemical properties of DNAN and its products
Table 2 summarizes the physicochemical properties (Sw, pKa,
and Kow) measured herein for DNAN and its amino derivatives
2-ANAN, 4-ANAN, and DAAN. Relevant parameters of the more traditional
explosive TNT are also gathered in Table 2 for comparison.
The aqueous solubility of DNAN and its major products follows
the order: DNAN < 2-ANAN < 4-ANAN < DAAN (Table 2). Sequential
reduction of the nitro groups into amino groups increased the
water solubility of the aromatic chemical. However, while the solubility
of 4-ANAN (4.43 ± 0.06 g L1) was twenty times higher than
that of DNAN (0.213 ± 0.012 g L1), that of 2-ANAN (0.252 ±
0.008 g L1) was only slightly higher than DNAN. Two chemical
phenomenons might explain these different solubilities: 1/the para
isomer might have an ability to form solute–solvent intermolecular
H-bonding that the ortho isomer cannot form due to the intramolecular
H-bonding mentioned above, or 2/the para isomer is more
easily protonable than the ortho isomer. In water, substituted
aminoaromatics (ArNH2) equilibrate with their acidic protonated
forms (ArNH3 + ) and the dissociation constant (pKa) of the latter
depends on the relative position of the NH2 group and other
substituents, AMeO and ANO2 in the present case, on the aromatic
ring. The pKa values measured herein show that 4-ANAN (pKa 3.50)
will be more protonated and hence more soluble than 2-ANAN (pKa
2.55) in distilled water (pH 5.5). As for DAAN (pKa1 = 2.61;
pKa2 = 5.46) half of the chemical is expected to be monoprotonated at the water pH of 5.5, thus explaining its markedly higher water
solubility. TNT was the least soluble of all chemicals