Azeotrope water-dioxane solutions

Water-dioxane solutions form a minimum-boiling-point azeotrope at atmospheric pressure and cannot be separated by ordinary distillation methods. Benzene forms no azeotrope with dioxane and can be used as an extraction solvent. At 298 K the equilibrium distribution of dioxane between water and benzene is as follows (Treybal, 1980) ... 

For quinoaxaline itself (Expt 8.44) glyoxal is the dicarbonyl component. The interest in this synthesis is that 2,3-dihydroxy- 1,4-dioxane is employed as a stable reagent equivalent for anhydrous glyoxal. It is prepared by the azeotropic removal of water from a benzene solution of aqueous glyoxal and ethylene... 

A solution (or slurry) of the sample is refluxed for 4h. A sample/reagent ratio of <0.01 is recommended. The boiling point of the dioxane-water azeotrope (81.6% dioxane) is 87.8°C. Losses of solvent due to evaporation during the treatment should be avoided (Susarev and Guseva 1964, Froment and Robert 1970). (Note 1). 

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