The deuterium isotope effect was applied to condensed-phase thermochemical reactions of HMX and HMX-8 by using isothermal techniques. Dissimilar deuterium isotope effects revealed a mechanistic dependence of HMX upon different physical states which may singularly predominate in a specific type of thermal event. Solid-state HMX thermochemical decomposition produces a primary deuterium isotope effect (DIE), indicating that covalent C-H bond rupture is the rate-controlling step in this phase. An apparent inverse DIE is displayed by the mixed melt phase and can be attributed to C-H bond contraction during a weakening of molecular lattice forces as the solid HMX liquefies. The liquid-state decomposition rate appears to be controlled by ring C-N bond cleavage as evidenced by a secondary DIE and higher molecular weight products. These results reveal a dependence of the HMX decomposition process on physical state and lead to a broader mechanistic interpretation which explains the seemingly contradictory data found in current literature reviews.
Xenon difluoride (XeF2) reacts with methanol to form an unstable reactive species CHgOXeF (1). Formaldehyde is produced quantitatively by disproportionation in the absence of unsaturated hydrocarbons or with unreactive alkenes. Hydrogen fluoride generated in situ complexes with 1 to form 2 which reacts with unsaturated hydrocarbons of intermediajte reactivity such as cisor trtms-l-phenylpropene (5c, 5t), indene (6), 2,3-dimethyl-l,3-butadiene (7), and norbornene (8) as an apparent fluorine electrophile and Markovnikov fluoromethoxy products are found.Reaction of XeF2 with methanol in the presence of boron trifluoride as catalyst forms the complex 3 which disproportionates to formaldehyde. Intermediate 3 reacts with unsaturated hydrocarbons of intermediate reactivity (5c, 5t, 6, 7, and 8) as a positive oxygen electrophile to give anti-Markovnikov fluoromethoxy products. However, very reactive (electron rich) alkenes such as dihydropyran ( 9) react rapidly with XeF2 to give a carbocation species before the intermediate 1 (or its complex 2 or 3) can be formed.Recently1® we reported on the methanolysis of xenon
The appearance of a significant deuterium isotope effect during the combustion of the solid HMX compound verifies that the chemical reaction kinetics is a major contributor in determining the experimentally observed or global burn rate. Burn rate comparison of HMX and its deuterium labeled HMX‐d8 analogue reveals a primary kinetic deuterium isotope effect (1° KDIE) at 500 psig (3.55 MPa) and l000 psig (6.99 MPa) pressures and selectively identifies covalent carbon‐hydrogen bond rupture as the mechanistic step which ultimately controls the HMX bum rate under the static combustion conditions of this experiment. The 1° KDIE value further suggests the rate‐limiting CH bond rupture occurs during the solid state HMX decomposition/deflagration portion of the overall combustion event and is supported by other independently published studies. A possible anomalous KDIE result at 1500 psig (10.4 MPa) is addressed. This condensed phase KDIE approach illustrates a direct link between lower temperature/pressure thermal decomposition and deflagration processes and their potential applicability to the combustion regime. Most importantly, a new general method is demonstrated for mechanistic combustion investigations which selectively permits an in‐situ identification of the compound's burn rate‐controlling step.
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