Design calculations are presented for a single-pass high-conversion electrochemical reactor suitable for process intensification in electroorganic synthesis. The key feature of the design is the use of a segmented working electrode, combined with a small anode–cathode gap. Each working electrode segment is operated at an optimal local current density, defined with respect to the local diffusion–limited current density of the reacting species. Two reactor configurations are considered: (i) an adiabatic reactor, and (ii) an isothermal reactor with integrated heat exchange. Calculated results for the devices in a classical electroorganic synthesis system, the methoxylation of 4-methoxy-toluene, are presented and the general features and performance characteristics of the cell are compared with those of a more conventional capillary-gap cell, currently used industrially. For an electrode gap of 0.1 mm, the average current density attainable in the novel design is of the order of 2700 A m−2 in the adiabatic reactor and of the order of 7100 A m−2 in the isothermal reactor, respectively, 5 and 14 times higher than the current densities applied in the current industrial process. In addition to process intensification, other advantages of the proposed technology are the absence of reactant recycle, short residence times and plug flow of the reagents, all of which contribute to improved process selectivity.