The UC Center for Laboratory Safety

What Happened?

A student synthesized 750 mg of di-tert-butyl peroxyoxalate (CAS:1876-22-8), which is used as a low‐temperature radical initiator in synthetic reactions. Following its synthesis, di-tert-butyl peroxyoxalate should be stored dissolved in a solvent for later use. However, that final step was omitted and the compound was kept in a solid form. Later in the day, the student wanted to weigh out a sample of the di-tert-butyl peroxyoxalate. When the student tried to transfer the compound to a balance using a metal spatula, a violent exothermic reaction occurred causing the glass vial containing the di-tert-butyl peroxyoxalate to shatter. The student sustained minor lacerations and abrasions to their neck, arms and both hands, so was taken to the hospital. At the time of the incident, the student was wearing a flame resistant (FR) lab coat, safety glasses and disposable gloves, but no face shield. The student was also not working behind a blast shield.

What Was The Cause?

Di-tert-butyl peroxyoxalate is a shock sensitive chemical, especially when in a dry crystalline state. Instead of dissolving it in a solvent as the procedure stated, the compound was kept in a solid state for a period of time which allowed it to dry out. When the compound was pressed while being transferred with the metal spatula it detonated. 

Note that if a shock sensitive crystal is pressed by a small spatula with a contact area of 1 mm2 and a force of only 1 lb, that is equal to a force of 625 psi. Also, some explosive compounds are specifically sensitive to metal, as opposed to plastic, spatulas, but that is not likely with di-tert-butyl peroxyoxalate.

What Corrective Actions Were Taken?

• All activities involving di-tert-butyl peroxyoxalate synthesis and use were halted until a safety review of the procedure was performed.
• The PI discussed the incident with lab members.
• The PI consulted with the EH&S department for advice on using this compound.
• A risk assessment was conducted and mitigation measures were identified.
• An SOP for the synthesis and use of di-tert-butyl peroxyoxalate was generated using all the gathered information.
• Additional safety training was provided to lab members regarding preparation and use of organic peroxides.

How Can Incidents Like This Be Prevented?

• Follow all steps of the written procedures for synthesizing of new compounds.
• Laboratories preparing and using sock sensitive compounds such as di-tert-butyl peroxyoxalate should have full SOPs for their preparation and use.
• Laboratories preparing and using sock sensitive compounds should have administrative controls in place to ensure that  inexperienced workers do not inadvertently work with them.
• Laboratories preparing and using sock sensitive compounds such as di-tert-butyl peroxyoxalate should ensure that they are stored correctly.
• Researchers should work behind a blast shield and wear all required PPE when working with shock sensitive chemicals.
• If a blast shield is not used, consider using a face shield in addition to eye protection such as goggles.
• Many shock sensitive compounds are less shock sensitive when moist with a solvent, however, that does not guarantee safety. Therefore, always use full protective measures when working with shock sensitive compounds

Resources

• Di‐t‐butyl peroxyoxalateentry in Encyclopedia of Reagents for Organic Synthesis
• Di‐t‐butyl Peroxyoxalate in PubChem database
• Canadian Centre for Occupational Health and Safety fact sheet on organic peroxides
• SOP for Organic Peroxides Chemical Hazards and Risk Minimization from the University of Nebraska, Lincoln