1,2-Dioxane or o-dioxane is an organic compound with the molecular formula (CH2)4O2, classified as a cyclic peroxide.

Its synthesis was reported in 1956 by Criegee and Müller, who prepared it by reacting butane-1,4-diol bis(methanesulfonate) with hydrogen peroxide and distilled it as a colorless liquid.

Acids and bases decompose it to gamma-hydroxybutyraldehyde.

[1] Substituted 1,2-dioxanes have also been prepared, and some have been isolated from natural sources.

This article about a heterocyclic compound is a stub.