1,3-Dioxane or m-dioxane is an organic compound with the molecular formula (CH2)4O2.

It is a saturated six-membered heterocycle with two oxygen atoms in place of carbon atoms at the 1- and 3- positions.

[1] The parent 1,3-dioxane is prepared by the reaction of formaldehyde and 1,3-propanediol in the presence of Brönsted or Lewis acid catalysts.

Substituted derivatives can be used as protecting groups for carbonyl compounds.

are prepared from the reaction between a ketone or an aldehyde with 1,3-diols.