Diazo compounds see wide use as metal-carbene precursors, due to the varied and powerful transformations they can achieve. Despite their popularity in academia, this chemistry is rarely transferred to scaled synthetic processes. Their use in industry is often avoided owing to concerns over their instability, exothermic decomposition and potential explosive behaviour. Unlike the well-studied diazo transfer reagents used to prepare them, there is only a handful of existing reports of thermal analysis on diazo compounds, which are varied and often missing experimental detail that would allow replication of the results. This work presents a rigorous Differential Scanning Calorimetry (DSC) dataset of 44 diazo compounds, enabling direct comparison to other energetic materials to provide a clear reference. The results presented give valuable knowledge of the practical hazards posed by diazo compounds to those wishing to harness their reactivity. The thermal stability variation heavily depended on the electronic effect of substituents and the amount of charge delocalisation. A statistical model based on the Hammett substituent constant was developed to predict the thermal stability of differently substituted phenyl diazoacetates with a reasonable degree of accuracy before synthesis of the compound ever takes place. The average enthalpy of decomposition (ΔHD) was determined for diazo compounds without other energetic functional groups, indicating those &gt; 300 g mol–1 would be classed as medium risk. Both the Yoshida correlation and a more conservative modification were applied to DSC data for each diazo compound in order to provide the most accurate prediction of both their impact sensitivity (IS) and explosivity. This data is interpreted for discussion of the practical implications for laboratory chemists.

Explosive hazards of diazo compounds and what practical precautions are necessary

ACS Fall 2020 Virtual Meeting

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