A reactor which comprises a vessel (1) with a vessel bottom (2), a stirrer (3) arranged in the vessel, an emergency discharge valve (4) arranged in the vessel bottom for emptying the reactor in less than 600 seconds and at least one filtration device (5) arranged in the vessel bottom is suitable for the safe preparation of organic peroxides. The process for preparing an organic peroxide comprises the steps of preparing a solid hydroperoxide in the form of a suspension in the reactor, filtering the suspension through the filtration device (5) arranged in the vessel bottom (2) while retaining the solid hydroperoxide in the reactor and reacting the hydroperoxide with an alkylating agent, an acylating agent or a carbonyl compound.