Detonation during Fischer esterification

Title

December 2020

Situation

A researcher was attempting to implement a Fischer esterification procedure that had been well established within the same research group. This class of reaction had been carried out multiple times without incident by others in the group on scales ranging from 10-100 g of the product ester. Here, the reaction was carried out with a new substrate, propargyl alcohol (an alkyne) on a 35 g scale. Following addition of the propargyl alcohol to a cooled reaction mixture containing a carboxylic acid and sulfuric acid, the flask was placed in an oil bath that had been preheated to ca. 70 °C. About 30 minutes into the warming phase, a violent detonation occurred. Because the researcher was working on another experiment inside the same hood, the hood sash was raised. The researcher was sprayed with chemical liquid, resulting in first degree burns on exposed skin, and received some cuts from flying broken glass. Fortunately, the main force of the detonation was directed toward the back corner of the hood. The researcher was wearing safety goggles but not a lab coat. They proceeded to a nearby safety shower, where other labmates assisted in washing with water, calling 911, and escorting the researcher to the medical respondents waiting outside of Smith Hall.

Suggestions

When performing new reactions (even established reactions with new substrates) always first do so on a small scale, and gradually scale up.
Recognize additional hazards and exercise further caution with respect to scale when working with high-energy functional groups: alkynes, azides, nitro groups, etc—be aware that even common functional groups can release significant energy via unwanted reaction pathways.
Isolate reactions considered higher risk (e.g. large scale, high temp/pressure, new chemistry, highly reactive chemistry, etc.) while running. It may be prudent to position it behind a blast shield in cases where performing other chemistry is required.
Reading more than one version of a SDS (or MSDS) is advisable because they do not all contain the same information. For example, it is mentioned in some (but not all) SDSs that propargyl alcohol and Brønsted acids such as sulfuric acid can result in “potentially explosive reactions,” although we have not been able to locate primary sources that discuss this.
Lab coats should always be worn when practicing chemistry in the lab. In this case, some types of injuries such as burns or cuts might have been avoided if a lab coat is worn. Make sure that it is suitable for the type of hazards that you may encounter during your experimentation.