Glyphosate (GP) is a widely used herbicide worldwide, yet accumulation of GP and its main byproduct, aminomethylphosphonic acid (AMPA), in soil and water has raised concerns about its potential effects on human health. Thermal treatment, in which contaminants are vaporised and decomposed in the gas-phase, is one option for decontaminating material containing GP and AMPA, yet the thermal decomposition chemistry of these compounds remains poorly understood. Here, we have revealed the thermal decomposition mechanism of GP and AMPA in the gas phase by applying computational chemistry and reaction rate theory methods. The preferred decomposition channel for both substances involves the elimination of P(OH)₃ to yield the imine N-methylene-glycine (from GP) or methanimine (from AMPA), with relatively low barrier heights (ca. 45 kcal mol⁻¹). The half-life of GP and AMPA at 1000 K are predicted to be 0.1 and 4 ms respectively, and they should be readily destroyed via conventional incineration processes. The further decomposition of N-methylene-glycine is expected to also take place at similar temperatures, leading to N-methyl-methanimine + CO₂, with a barrier height of ca. 48 kcal mol⁻¹. The imine decomposition products of GP and AMPA are expected to react with water vapour to form simple amines and carbonyl compounds.

中文翻译：

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草甘膦（GP）及其代谢产物氨基甲基膦酸（AMPA）的热分解动力学。

草甘膦（GP）是全球范围内广泛使用的除草剂，但是GP及其主要副产物氨甲基膦酸（AMPA）在土壤和水中的积累引起了人们对其潜在危害人类健康的担忧。热处理（其中污染物在气相中蒸发并分解）是对包含GP和AMPA的材料进行净化的一种选择，但是对这些化合物的热分解化学了解仍然很少。在这里，我们通过应用计算化学和反应速率理论方法揭示了GP和AMPA在气相中的热分解机理。两种物质的优选分解通道均涉及消除P（OH）₃以产生亚胺N-亚甲基-甘氨酸（来自GP）或甲胺（来自AMPA），具有相对较低的势垒高度（约45 kcal mol ^-1）。预计GP和AMPA在1000 K下的半衰期分别为0.1 ms和4 ms，应通过常规焚烧工艺将其轻易破坏。N-亚甲基-甘氨酸的进一步分解预计也会在相似的温度下发生，从而导致N-甲基-甲亚胺+ CO ₂的势垒高度约为1。48 kcal mol ^-1。GP和AMPA的亚胺分解产物有望与水蒸气反应形成简单的胺和羰基化合物。