Versatile and conveniently operated microreactor devices, suitable for long term chemical synthesis for both laboratory and industrial use, are described. Direct fluorination of ethyl acetoacetate by fluorine gas is used as a model reaction to illustrate the successful application of reactors having either 9, 18 or 30 microchannels, with all channels supplied from single reagent sources, to provide significant quantities of fluorinated products. Convenient reactor maintenance, simple design, versatility and the enhanced safety features of using such modular microreactor devices, make these systems appropriate for synthesis on the large scale.