Abstract: The preparation of propylene oxide or other epoxides by reaction which comprises the introduction of oxygen and olefin as reaction ingredients and the removal of the epoxide as it is formed in which iodine reacts with the olefin in a first reaction step to form iodohydrin and hydrogen iodide, converting the iodohydrin to the epoxide with the further production of hydrogen iodide in a second reaction step, and converting the hydrogen iodide to iodine for recycle to the first reaction step in a third reaction step in which an imidazole-copper complex is used as a catalyst in the third reaction step and which finds beneficial use in the first and second reaction steps to enable joinder of said reaction steps.