Prolonged distillation of 2-bromo-4-isopropylaniline
Some poor quality product was being fractionated in the high efficiency still at high vacuum and around 150°C in the flask. All was well until the third day when the operator came back from break to find the vacuum was failing, large amounts of acidic gases were rushing up the column and the flask temperature was 50°C above the jacket. The system was shut down without any problems and the still had to be stripped down to clean out a lot of tarry material.
Subsequently a DSC of the crude charge showed an onset (where the slope > 1 x 10-3 W/g/°C) of 200°C and about 200 kJ/kg in size. Therefore a maximum temperature of 125°C was assigned to this material for future use - which was 25°C above the distillation temperature. It is not known if the instability is due to the material or some impurity.