KINETIC STUDY OF SYNTHESIZING UNSYMMETRIC ACETALS UNDER PHASE TRANSFER CONDITIONS

Abstract

An effective method was proposed to determine the two organic-phase rate constants of the primary and secondary reactions which have differences in rates. The goal was achieved by employing the reaction of two mixed l-alcohols and dibromomethane in an alkaline solution of KOH/chlorobenzene two-phase medium under phase transfer catalysis. A new product of unsymmetric acetal was obtained in this work. The intermediate ROCH₂Br (a-haloalkyl ether) was not detected during or after the reaction when using high reactive alcohols. This result indicated that ROCH2Br was more reactive than the organic reactant CH₂Br₂. This high reactive a-haloalkyl ether implied that the rate constants of secondary reactions are larger than those of the primary reactions. The resistance of mass transfer of the catalyst ((C₄H₉)₄NBr, QBr) and the active catalyst, ((C₄H₉ )₄NOR, QOR R: c₄h₉and C₈h₁₇) transferring from the aqueous phase to the organic-phase and vice versa were found to be negligible. The organic-phase reaction is a rate-determining step of the phase transfer catalytic reaction, A measured constant concentration of tetrabutylammonium alkoxide (QOR) during the reaction leads to the application of pseudo-first order rate law. The reaction rate constant of ROCh₂Br acts 10⁴ larger than that of CH₂Br₂.

Keywords:

• Symmetric and unsymmetric acetals
• phase transfer catalysis
• rate constants

Notes

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