Explosion, rotary evaporator

The submitters concentrated the reaction mixture by vacuum distillation (100 mm, bath temperature 70°C, vapor temperature 51°C). The weight after concentration was ca. 120 g. The checkers used rotary evaporation with a bath temperature of 65 to 70°C without any problems, and employed an explosion shield as a safety precaution. 

During rotary evaporation of solvent (from an ethyl acetate extract of a fermentation culture) at 55°C/50 mbar, the flask exploded. (It seems likely that some unsuspected peroxidised material may have been present in the extract, or perhaps the flask was scratched or cracked, and imploded [1].) Several fires and explosions suggest that ethyl acetate may be a worse generator of static electricity than its measured conductivity would indicate [2],... 

Dining the preparation by solid phase interaction of tetramethylammonium hydroxide and potassium superoxide [1] by tumbling for several days in a rotary evaporator flask, a violent explosion occurred [2], This may have been caused by ingress of grease or other organic material leading to contact with potassium superoxide, a powerful oxidant. 

An explosion was experienced dining work up of an epoxide opening reaction involving acidified sodium azide in a dichloromethane/dimethyl sulfoxide solvent. The author ascribes this to diazidomethane formation from dichloromethane [1]. A second report of an analoguous accident, also attributed to diazidomethane, almost certainly involved hydrogen azide for the cold traps of a vacuum pump on a rotary evaporator were involved this implies an explosive more volatile than dichloromethane. It is recommended that halogenated solvents be not used for azide reactions [2]. 

Two hundred milliliters of ether and diazomethane are removed before transfer for rotary evaporation. Diazomethane in a rotary evaporator can cause explosions. 

Powders milled in solvents were either dried in trays using a forced air explosion proof dryer or in a rotary evaporator. Dried cakes were then granulated by screening through an 80 mesh nylon screen. 

As an additional precaution for the very delicate CB determinations a nitrogen gas flow of 10 mL/min through the condenser should be maintained during extraction. The flask is then cooled to approximately 0 °C, preferably in a freezer, before the solvent is removed by rotary evaporation at 0.1 hPa. TTie boiling chips stay in the flask, because removal is a potential source of contamination. At the low temperature of the solvent they will not induce boiling. A layer of ice growing on the outside of the flask retards the evaporation of the solvent (boiling point 76 °C at atmospheric pressure). It may be removed by immersion in a water-bath at 30 °C after 15 min. It is important to allow for this delay as aqueous acetonitrile tends to bump or boil explosively. 

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