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312 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Kinetics of the nitration of dinitrotoluene to trinitrotoluene............

DINITROTOLUENE TO TRINITROTOLUENE

From the results of their studies on the kinetics of the nitration of 2,4-dinitroto-

luene to 2,4,6-trinitrotoluene Bennett and his co-workers [109, 110] inferred that

the reaction is of the third order, represented as follows:

DNT + NO 2 + + HSO 4 - -> TNT + H 2 SO 4 (17)

DNT + NO 2 + + H 2 SO 4 ->TNT + H 2 SO 4 (18)

In the presence of oleum the reaction

DNT + NO 2 + + HS 2 O 7 -> - TNT + H 2 S 2 O 7 (19)

may also take place.

The rate of the nitration reaction in the presence of sulphuric acid can be re

presented by :

d[TNT]

dt

= k[DNT][NO 2 +][HSO 4 - ] + k’[DNT][NO 2 +][H 2 SO 4 ] (20)

The constants k and k’ are independent of the medium and of the concentration

of sulphuric acid. If Q denotes the proportion of nitric acid dissociated into NO 2 +

ions, then :

[NO 2 +] = Q [HNO 3 ] (21)

From this the following equation for the rate of nitration can be derived:

d[TNT]

dt

= {k[HSO4-] + k’[H 2 SO 4 ]}[DNT][HNO 3 ]Q (22)

At a constant concentration of sulphuric acid the nitration rate can be repre-

sented by a second order reaction equation:

d[TNT]

dt

= k 2 [HNO 3 ][DNT] (23)

where k 2 is the rate constant of a second order reaction.

From equation (22) Bennett and his co-workers derived the following general

equation valid when oleum is used:

d[TNT]

dt

= k [HSO 4 - ] + k’[H 2 SO 4 ] + k''[HS 2 O 7 - ][DNT][HNO 3 ]Q (24)

Values of k, k’ and k” for concentrations of sulphuric acid ranging from 87.4%
H 2 SO 4 to oleum containing 29.1% SO 3 , at temperatures from 60°C to 120°C,

have been determined experimentally.

The experiments are in agreement with the equations derived. In particular,
the equations show that an increase in the reaction rate due to decreasing the con-