Peroxide formation

Materials that are susceptible to peroxide formation (i.e., auto-oxidation) are ones that typically react with air, moisture or impurities and produce a change in their chemical composition in normal storage. The peroxides that form are less volatile than the solvent itself and thus tend to concentrate. This is particularly dangerous if peroxides are present during a distillation, where the applied heat to the concentrated solution may trigger a violent explosion.
Reference: Chemical Process Safety – Fundamentals with Applications, 2nd Ed., Daniel A. Crowl/Joseph F. Louvar
Science/Chemical Reactivity/Reactive Interactions