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

Abstract

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.