Most ethers are generally considered to be very unreactive. They are unreactive towards most bases and only react with very strong bases where they undergo cleavage of the ether bond. Ethers, however, form peroxides when stored with oxygen for long periods. For example, a bottle of ether once opened will be filled with air and over time the oxygen can convert a small amount of ether to ether peroxide. Ether peroxides are very unstable and can explode at slight heating. To overcome this problem, old ether solvents are always refluxed with sodium metal (a very strong reducing agent) to convert the ether peroxides to alkoxides before they are distilled.
A grad student was refluxing THF (tetrahydrofuran) with sodium metal and a small amount of benzophenone. After a couple of hours, all of the ether in the distillation flask turned dark purple. Is there an explanation for this change in color?