Alkaline hydrolysis of trinitrotoluene, TNT

Abstract

The kinetics of the alkaline hydrolysis of trinitrotoluene, TNT, in an aqueous solution is a possible approach to destroying the active agent in unwanted munitions. The kinetics are shown to have a rapid initial step, step A, in which a highly coloured species, X (max=450 nm) is formed via an equilibrium reaction: TNT+OH-X. The bimolecular rate constant for the forward part of this equilibrium process, k1, is: 0.099±0.004, 0.32±0.02 and 1.27±0.05 dm3 mol-1 s-1, at 25, 40 and 60°C, respectively. The activation energy for the forward process is 60 kJ mol-1. The first-order rate constant for the reverse of this process, k-1, is: (5.3±2.6)×10-4, (1.2±1.0)×10-3 and (7.7±2.9)×10-3 s-1 at 25, 40 and 60°C, respectively. The activation energy for the overall equilibrium process (k1/k-1) is ca.-5 kJ mol-1. The subsequent alkaline hydrolysis of X to form the final product P, i.e. step B, is much slower than step A and appears to comprise two processes coupled in series, i.e. steps B1 (X+2OH-Z) and B2 (Z+OH-P). At 25°C, Step B1 appears rate determining throughout the decay process. At 45°C and, more so, at 60°C, step B appears increasingly biphasic with increasing alkaline concentrations, as step B2 begins to compete with step B1 for position as the rate determining step. The trimolecular rate constant for step B1 is: 0.017±0.001, 0.0085±0.0002 and 0.0011±0.0001 dm6 mol-2 s-1 at 25, 40 and 60°C, respectively, and the process has an activation energy of 64 kJ mol-1. The transition from uniform kinetics, described by step B1, to mixed kinetics, described by steps B1 and B2, as the reaction temperature and alkali concentration are increased most likely occurs because (a) step B2 has a lower activation energy than B1, although it was not possible to measure the former parameter, and (b) step B2 has a lower (1st) order dependence upon [OH-] compared with that of step B1 (2nd). The bimolecular rate constant for step B2 is 0.0035±0.03 dm3 mol-1 s-1 at 60°C. A brief NMR study of the initial hydrolysis product in water, acetone and chloroform, coupled with UV/visible spectra, provides evidence that species X is a Meisenheimer complex

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“…But no by-products investigation was reported in the study of Saupe et al [18]. Recently, Mills et al [19] performed a kinetic study of the TNT removal rate under alkaline conditions and provided evidence that one of the molecules formed was a Meisenheimer complex.…”

Spread, Behavior, and Ecosystem Consequences of Conventional Munitions Compounds in Coastal Marine Waters

“…Because photolysis and Fenton reaction mechanisms tend to produce different reaction Figure 6. References: a, Lenke et al (2000) and Mills et al (2003); b, Symons and Bruce (2006), Lenke et al (2000), Ziganshin et al (2007), and Rieger et al (1999); c, Williams et al (2004) and Wittich et al (2008); d, Williams et al (2004).…”

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“…Currently, TNT continues to be a major component of ordnance used by the military and terrorists, which causes environmental damage and threatens public security. [145][146][147] Therefore, the development of practicable analytical platforms for monitoring ultra-trace levels of TNT is urgently necessary. Zhang et al 148 successfully synthesized Nrich CDs via a microwave-assisted pyrolysis method and employed them in both the uorescence and the electrochemical determination of TNT.…”