(CAS NO. ) is difficult to purify and keep pure. The purification usually contains added inhibitors (such as a trace of hydroquinone). Washed with aqueous NaOH to remove inhibitors (e.g. tert-butanol), then with water, dried for several hours with MgSO₄ and distd at 25 °C under reduced pressure in the presence of an inhibitor (such as 0.005% p-tert-butylcatechol). It can be stored at -78 °C. It can also be stored and kept anhydrous with Linde type 5A molecular sieves, CaH₂, CaSO₄, BaO or sodium, being fractionally distd, and distd in a vacuum line just before use. Alternatively styrene (and its deuterated derivative) were passed through a neutral alumina column before use.