Trimethylaluminum Ignites When Syringe for Transfer Separates

What happened?

A researcher attempted to add 0.6 mL of trimethylaluminum (TMA) to their reaction using a syringe. However, the syringe needle became clogged and the researcher applied pressure to force out the TMA. This caused the needle to separate from the syringe’s barrel and TMA was released, igniting upon exposure to air. Despite the mishap, the researcher attempted the same procedure again using a different needle and syringe only to have the same result, a release of TMA which immediately ignited in the fume hood due to separation of the needle from the barrel. The researcher suffered only a minor injury to a finger, and no damage occurred to the laboratory fume hood.

What was the cause?

The direct cause of the separation and release appears to have been applying pressure on a syringe with a clogged needle. But was caused the clog? When reviewing the procedure, the research team realized that the reaction to which the needle with the TMA was inserted was kept at —78 °C, which is far below the freezing point of TMA (15 °C). It is likely that the TMA froze inside the syringe needle causing the clog.

How can incidents like this be prevented?

  • Check the physical properties, such as boiling point, freezing point, etc., of all components of a reaction to understand the physical state all chemicals in the reaction.
  • Understand how your experimental conditions may affect the physical state of your chemicals and what impact that may have on your reaction.
  • When working with syringes, especially if they contain pyrophoric chemicals, be sensitive to resistance in the syringe as it may indicate clogs.
  • When working with pyrophoric materials in syringes, consider using syringes with a Luer-Lock which are threaded to prevent accidental detachment of needles. These are different than syringes with a “Luer-Slip” or “Luer Fitting.”
  • Consider wearing flame-resistant glove liners underneath your chemical-resistant gloves. Note that disposable gloves, when on fire, will melt to the skin. Wearing flame-resistant liners is a Cal/OSHA requirement for research involving pyrophoric chemicals in California.

Tips for Working with Pyrophoric Chemicals

  • Add the reagent to the headspace above the cold solution, the needle should never be inserted into the actual reaction solution. This prevents needle clogs by freezing reagent or reaction at the tip of the needle.
  • Consider diluting the TMA in hexane or toluene prior to adding it to the reaction. This will greatly reduce the freezing point and also reduce the pyrophoric reactivity.
  • When adding a highly pyrophoric reagent to a reaction via syringe make sure no active reagent is at the tip of the syringe needle while moving the syringe in the air as it can react or catch fire.  So, after filling the syringe with reagent from the reagent container, draw a plug of inert gas from the reagent container headspace before removing the needle. Then after delivering the pyrophoric reagent to the reaction again draw a plug of inert gas from the reactor headspace before removing the needle.
  • Finally, take precautions with the syringe after delivering the pyrophoric reagent as it still contains some amount of active reagent!  Insert the needle into a small flask of hexane or toluene and draw insolvent to dilute the pyrophoric reagent and rinse the syringe. The diluted pyrophoric reagent can now be safely quenched in isopropanol.

Precautions

  • Never assume accidents are flukes and re-attempt a failed experiment. Pay attention to details and discuss unexpected experimental problems with your PI or other experienced researchers.
  • If a mishap occurs, consider it a near miss that did not cause an injury, but had the potential to do so. Do not attempt the same or similar procedure again. Causes of near misses should be analyzed and discussed!

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