The synthesis of 1-ethyl-3-methylimidazolium ethyl-sulfate ([EMIM]EtSO 4 ) from 1-methyl-imidazole and diethyl sulfate suffers from highly exothermal behavior. Once the activation energy barrier is reached (E A = 89 kJ mol À1 ), the bimolecular reaction accelerates with a high reaction enthalpy (ΔH = À130 kJ mol À1 ). 1À3 The excess of heat has to be concurrently dissipated to avoid hot spots or thermal runaways. Depending on the volume flow velocity of the reactants and the applied reactor temperature, the reaction zone can be shifted inside the reactor from the inlet to the outlet and vice versa. Therefore, a sophisticated thermal control, oscillating between providing activation energy and intense cooling of the reaction mixture, is required. Heat pipes intrinsically allow both fast dynamic bidirectional heating and cooling. A stainless steel chiplike setup equipped with an externally heated, modified heat pipe system was used. 4 Independently from the reactant volume flow, a colorless and 1 H NMR clean product could be obtained by setting a self-controlled optimal operating temperature of about 100 °C.