Abstract: Dioxane is prepared by reaction of polyethylene glycols in a catalytically active liquid reaction medium comprising a mixture of partial phosphate esters of a polyethylene glycol, and ammonium salts of partial esters of a polyethylene glycol. Along with dioxane, valuable co-products, including the compound 5-ethyl-2-methylpyridine, are formed from which the dioxane is readily separated in highly pure form. The catalytically active liquid reaction medium is derived from the reaction of ammonium dihydrogen phosphate with a polyethylene glycol at temperatures preferably in the range from 190.degree. to 225.degree. C. Temperatures of reaction between the polyethylene glycol and the catalytically active liquid reaction medium to form the dioxane and co-products are preferably in the range of from about 225.degree. C. to about 275.degree. C.