CONTROL OVER m-NITROTOLUENE CONCENTRATION IN PRODUCTS
ecules and, therefore, of the complexes with the ni-
2071
tronium ion, increases in the order o-NT < m-NT <
p-NT. Therefore, addition of the electrolytes should
primarily affect the meta and para selectivity, which
is confirmed by the experimental data (Fig. 8; Table 7,
run nos. 56 59, 62 65, and others).
The effect of the salt additives on the regioselec-
tivity of toluene nitration decreases in the order Na+ >
Li+ > K+. The maximal increase in the m-NT yield
and the maximal decrease in the ortho/para ratio were
observed as the concentration of sodium nitrate in
the acid mixture increased, but not with increasing
concentration of lithium nitrate, as would be expected,
i.e., this trend is inconsistent with the order in which
the cation charge density grows (Fig. 7). Evidently,
the lithium cation is considerably more strongly sol-
vated in the acid mixture than the sodium cation. As
a result, the effective radius of the lithium solvate is
higher, and, therefore, it is more weakly adsorbed at
the interface and increases the charge of the electric
double layer to a lesser extent, compared to the so-
dium solvate. Thus, the increase in the contribution of
the interfacial nitration is more clearly pronounced in
the presence of the sodium cation.
Fig. 8. m-NT yield vs. the stirring rate N (rpm) in het-
erogeneous nitration of toluene with the acid mixture of
composition (mol %): H SO 35.70, HNO 0.83, and
2
4
3
H O 63.47 in the presence of alkali metal nitrate addi-
2
tives (1.58 M): (1) LiNO , (2) NaNO , and (3) KNO .
3
3
3
HNO /toluene molar ratio 1.04, 50 C.
3
effect on the total reaction rate and to raise the con-
tribution of the interfacial reactions. This can be done
lowering the reaction temperature, raising the sulfuric
acid concentration in the acid mixture, and raising
the stirring rate to 3000 5000 rpm, when a gas-filled
emulsion is formed the reaction mass is saturated with
air bubbles).
Upon addition of LiNO3, which has a higher affin-
ity for water and exists as a crystal hydrate under
ambient conditions, the m-NT yield increases against
the reference experiment, and the dependence of the
m-NT yield on the stirring rate passes through a max-
imum (Fig. 8). As the stirring rate is raised above
2000 rpm, i.e., when the gas content of the reaction
mass starts to be an important factor, the m-NT yield
decreases, probably due to a rise in the contribution
of the interfacial nitration, as demonstrated by an in-
crease in the p-NT yield and a decrease in the ortho/
para ratio (Table 7, run nos. 62 65 and others).
(3) Addition of alkali metal nitrates affects the rates
of both the interfacial and bulk nitration. The former
effect is caused by an increase in the positive charge
in the electric double layer at the interface, and
the latter effect, by a decrease in the steady-state
toluene concentration in the bulk of the acid phase
(salting-out effect).
(4) Introduction of alkali metal nitrates raises
the yields of meta- and para-nitrotoluenes by promot-
ing the nitration at the para and meta positions of
the aromatic ring, since the corresponding reaction
intermediates have a higher dipole moment, compared
to ortho-nitrotoluene.
Presumably, these salts bound water to form stable
hydrates, thus making higher the nitration activity of
the acid mixture and shifting the reaction zone toward
the interface, i.e., promoting the interfacial nitration
and raising the para selectivity.
CONCLUSIONS
REFERENCES
(1) Para-selective two-phase toluene nitration with
sulfuric nitric acid mixtures proceeds in the charged
interfacial monolayer, in which the nitrating agent
reacts with the spatially oriented toluene molecules,
while the formation of ortho- and meta-nitrotoluenes
occurs essentially in the bulk of the acid phase.
1. Hermann, H. and Gebauer, J., Nitration: Recent Lab-
oratory and Industrial Development, Albright, L.F.,
Carr, R.V.C., and Schmitt, R.J., Eds., ACS Symp.
Ser. 623, Washington, DC: Am. Chem. Soc., 1996,
pp. 234 249.
2. Orlova, E.Yu., Khimiya i tekhnologiya brizantnykh
vzryvchatykh veshchestv (Chemistry and Technology
of High Explosives), Lenningrad: Khimiya, 1973.
(2) To reduce the meta-substitution rate in toluene
nitration, it is necessary to diminish the mass-transfer
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 12 2007