Reactive chemical hazards of diazonium salts

• The reactive chemical hazards of diazonium salts were systematically discussed.
• Twelve cardinal rules were provided to mitigate the hazards of diazonium salts.
• An example of quick experimental determination of the hazards of such compounds was provided.

Many diazonium salts are thermally unstable and sensitive to friction and shock. Most diazonium salts are known for their violent decomposition hazard in the solid state. There are many industrial and laboratory incidents caused by this group of chemicals. For safety purposes, the hazards related to the preparation and the handling of diazonium salts are discussed. Twelve cardinal rules are provided:1. Use only a stoichiometric amount of sodium nitrite when generating diazonium salts, avoiding excess sodium nitrite.2. Check for the excess of nitrous acid by starch–potassium iodide papers and neutralize it.3. Minimize the presence of nitrous acid by combining amine and acid first, then subsequently adding the sodium nitrite.4. Keep the temperature below 5 °C.5. Always vent the gases generated.6. Determine the thermal stability of diazonium compounds in your system.7. Understand the explosive properties of diazonium salts. If unknown, always assume they are explosive.8. Never allow the undesired precipitation of diazonium salts out of solution.9. Analyze the residual diazo compounds in the final product, especially for new process conditions.10. Quench the remaining diazonium salts before any further treatments.11. Isolate no more than 0.75 mmol of explosive diazonium salts at one time; also consider the addition of an inert material to stabilize the diazonium salts.12. Use a plastic spatula when handling the solid. The dried powder should not be “scratched” with a metal spatula or ground finely.An example of a testing strategy and data interpretation is provided for a process which has multiple steps and two diazonium compounds. Differential Scanning Calorimetry (DSC) and Heat of Mixing calorimetry (HOM) successfully serve as efficient tests to screen thermal stability and gas generation, identifying the candidates for advanced tests.