Simultaneous Back-and-Forth Dual Reflux Apparatus for Complete Removal of Water and Alcohol in Equilibrium Systems

Many chemical reactions generate alcohol or water as byproducts under equilibrium conditions. For complete conversion, it is necessary to remove these protic byproducts entirely from the equilibrium system, which can often be challenging. To address this issue, we developed an “simultaneous back-and-forth dual reflux apparatus” consisting of two reactors (Reactor A and B), each connected to a separate condenser (Condenser A and B). The key feature of this design is that the liquid condensed in Condenser A is returned to Reactor B, while the liquid condensed in Condenser B is returned to Reactor A. Using this apparatus, [Cr(EtOH)4Cl2][B(C6F5)4] was efficiently converted on a large scale to [CrCl2][B(C6F5)4]·6.5(CH3CN). In this reaction, the EtOH formed in Reactor A was transferred, along with CH3CN serving as both solvent and reactant, via Condenser A to Reactor B containing (iBu)3Al in CH3CN, where the transferred EtOH was destroyed. The versatility of this apparatus was demonstrated in the conversion of various hydrated metal complexes, [Ni(H2O)6][ClO4]2, CrCl3·6(H2O), CeCl3·7(H2O), and NiBr3·3(H2O) into their aprotic donor congeners, Ni(ClO4)2·5.8(CH3CN), CrCl3·3.0(THF), CeCl3·1.5(THF) (or CeCl3·2LiCl in THF solution), and NiBr2·1.0(DME), respectively. Additionally, the apparatus proved effective in imine formation reactions where water is produced as a byproduct under equilibrium conditions.