Answer from Radleys FAQ : Scientists commonly over heat solvents. However, because they are typically using a large or ‘over sized’ water condenser and lots of cooling water, the condenser may adequately contain the solvent and therefore they do not normally pay attention to careful temperature control. There is no benefit to the chemistry in overheating the solvent. Indeed the chemistry cannot get any hotter than the boiling point of the solvent, no matter how high the temperature. Standard ‘good laboratory practise’ when heating solvents is that the hotplate or block temperature should be no more than 20°C above boiling point of the solvent for high boiling point solvents (>80°C), or 10°C above boiling point for lower boiling point solvents (<80°C). For applications where an oil bath is being used, the hotplate or oil bath temperature should be no more than 10°C above the boiling point of solvent for high boiling point solvents (>80°C), or no more than 5°C above boiling point for lower boiling point solvents (<80°C). In all cases particular care should be taken if the heating control is not fully calibrated, or does not have precise settings.