Loss of batch overnight
Three litre lab batch found in morning as black mess
The experiment was run overnight at reflux, however the solvent was slowly lost, either by too fast a nitrogen purge or inadequate condenser. By the morning the mixture was >200°C and a black tarry mass. No other damage but a loss of an important batch.
Unattended experiments often complete without problems, however when there is a deviation there is no one about to correct the problem. Therefore greater consideration should be given as to the possible deviations. Reactions at reflux are often used in the lab, but often the same result can be achieved by running the reaction at just 1-2°C below the boil, thus reducing the chance of an unwanted temperature rise.