On 3 February 2017, a graduate student in the School of Chemistry at the University of Bristol was carrying out a literature procedure to oxidise an aldehyde to the carboxylic acid using aqueous acidified chlorite. The experiment was carried out on a 5 mmol scale (just under 1g of aldehyde) and risk assessments identifying all hazards had been undertaken and signed off by both student and supervisor. The reaction solvent was acetone (50 mL).
Part of the procedure involved adding a quantity of 30% hydrogen peroxide (H2O2) solution to remove some of the by-products of the reaction, whose presence was (apparently) associated with a yellow colour (possibly including chlorine dioxide). The literature indicated that H2O2 be added until this yellow colour had disappeared, which should have required about 1 mL of peroxide solution.
The student, focusing on the yellow colour, which did not completely disappear, continued to add hydrogen peroxide solution until about 50 mL had been added. During workup to remove the solvent, the student realised that the solvent volume was not decreasing and that the liquid was becoming viscous, and so likely contained far more “product” than was expected. GCMS analysis indicated the presence of triacetone triperoxide (TATP), and it was estimated that this could amount to 30-40g if all the excess H2O2 had reacted with the acetone solvent.
At that point, the graduate student immediately alerted the supervisor, who escalated this to the Head of School. A series of decisions were made and actions taken that resulted in the disposal of the suspected TATP by means of a controlled explosion carried out by the emergency services.
Nobody was injured and no damage was done in the lab. Although the TATP presented an explosion hazard, the risk of explosion was considered minor due to all material remaining in solution; TATP is far more sensitive to detonation as a solid. Immediate disposal was warranted, however, due to the risk of precipitation/crystallisation of a solid material.The authors have some statements that I will summarize (errors made are mine)
- The student was overfocused on removing the yellow color in the reaction, even as the risk of H2O2 + acetone had been identified.
- The role of the acetone was overlooked.
- When the student recognized how they had made an error, they reported it immediately to their supervisor. "This was highly responsible – the most important thing done – and shows the value of investing in developing and fostering a culture in which colleagues recognise errors and misjudgements, and they are supported to report near misses."
I'd sure like to know what the "workup to remove the solvent" was. Did the student put this material on a rotary evaporator?
This incident reminds me of a favorite list of "what if" questions from McConville's "Pilot Plant Real Book", including the question "Consider the possibility of operator error - over charging or undercharging raw materials, adding materials in the wrong order, omitting a component, overheating, holding for too long at reaction temperature, opening or closing the wrong valve, etc."
Finally, it would be great if there was some kind of central repository of chemical incident information. This report would certainly be a good candidate for inclusion in it. I wonder if the chair of the department of chemistry at UCLA has such a report to file?