In this study, a heat pipe was integrated with a mesoscale oscillatory baffled reactor for the passive temperature control of an exothermic reaction. The thermal/chemical performance of this new Heat Pipe Oscillatory Baffled Reactor (HPOBR) was compared to a conventional jacketed OBR (JOBR) using central composite experiment designs for an imination reaction between benzaldehyde and n-butylamine, in the absence of solvent. The variables in the experimental designs were reactant het flow rate (Re-n= 4-20), fluid oscillation intensity (Re-o = 123-491) and heat pipe fill ratio (FR = 11.5-26.5; methanol working fluid). In the JOBR, the fill ratio factor was replaced with jacket temperature (4-20 degrees C). Both reactors were able to reduce the maximum reaction temperature below the butylamine boiling point in all experiments. Overall, a 20-fold reduction in reactant volume and 13-fold improvement in reaction rate were obtained in the HPOBR for this imination reaction, compared with the same reaction using a solvent. Advantages of the HPOBR demonstrated here are isothermal operation and passive thermal control. Both reactors offer accelerated reaction rates and the potential for screening exothermic reactions. The HPOBR is a novel reactor design that provides a new approach for achieving green chemistry through solventless operation. (C) 2016 Elsevier B.V. All rights reserved.