Treating m-dioxanes with H2 in the presence of hydrogenation catalysts at elevated temperature (preferably 200°-280°) and pressure (preferably >100 atm.), sometimes in the presence of inert solvents or diluents gives primary alcohols; 2 moles H2 are consumed per mole of the dioxane derivative, and the cleavage of the dioxane nucleus results in the formation of 1 mole each of MeOH and the higher-molecular alcohol. Heating 4.4-dimethyl-m-dioxane 100 and a Cu-Cr oxide catalyst 5 parts by weight in an autoclave with H2 at 200 atm. and 260° gives, after removal of the catalyst and distillation, 80-90% iso-AmOH, b. 131°, besides MeOH. Similarly are prepared: 2,3-dimethyl-1-butanol, b. 145°, from 4,4,5-trimethyl-m-dioxane; 2,2,3-trimethyl-1-butanol, b. 156°, from 4,4,5,5-tetramethyl-m-dioxane; BuOH, b. 117°, from 4-methyl-m-dioxane.