Rotary Evaporator exploded
The incident
During a preparation of 4-aminobutanol, a solvent strip was carried out in a 50 litre rotary evaporator. During the night the main flask exploded destroying the associated condenser, and setting off the smoke alarms.
The Investigation
The preparation has proceeded normal, but the final product was problematic in obtaining a low water content. The product was therefore dissolved in dichloromethane, dried with magnesium sulphate, filtered, and the strip of the DCM carried out on the rotary evaporator.
Subsequent searches in the literature indicated instability of dichloromethane and amines at a certain level of DCM in the amine. DSCs were therefore carried out on this mixture and on several other amines. It was found that nearly all amines and anilines are unstable with dichlormethane, but the majority have such high onset temperatures that the presence of dichloromethane would be unlikely. However 4-aminobutanol has a low onset.
It was also concluded that the flask had been left hot after the vacuum was removed, as the means for cooling (with a fixed water bath) are limited.
Therefore a combination of the low stability coupled with the mixture being left hot and unstirred (thus increasing the trend to adiabatic conditions) further coupled with the mixture being low in dichloromethane led to a runaway reaction causing the material to boil and over pressurize the flask.
Lessens Learnt
- Dichloromethane should not be used to extract amines, unless previous thermal analysis proves the mixture is stable
- Change control and Hazard evaluation should apply to all stages of a process, not just the main reaction.