Phase Transfer Catalysis of Synthesizing Dialkoxymethane at Low Alkaline Concentration

Abstract

The phase transfer catalyzed reaction of 2,4,6-tribromophenol and dibromomethane to synthesize α-bromomethyl 2,4,6-tribromophenyl ether and di-(2,4,6-tribromophenoxide) methane by quaternary ammonium salt was carried out in an alkaline solution of low KOH content/dibromomethane two-phase medium. Dibromomethane acts both as the organicphase reactant and the organic solvent; thus, no extra organic solvent is required. A large conversion of 2,4,6-tribromophenol is obtained at a region of low KOH content. During the reaction, two products, i.e., the mono-substituted product (α-bromomethyl 2,4,6-tribromophenyl ether) and the bi-substituted product (di-(2,4,6-tribromophenoxide)methane) were detected. In the reaction, the active catalyst (tetrabutylammonium 2,4,6-tribromophenoxide, ArOQ), which was produced from the reaction of 2,4,6-tribromophenol, potassium hydroxide and tetrabutylammonium bromide (TBAB or QBr), is purified as the crystalline product from the reaction solution. Based on the experimental data, a kinetic model is developed to describe the behaviors of the two organic-phase reactions. The two intrinsic rate constants of the two organic-phase reactions are determined. Effects of the reaction conditions, such as: agitation speed, amount of water, amount of TBAB catalyst, amount of dibromomethane, catalysts, temperature and inorganic salt KBr, on the conversion and the reaction rate are investigated in detail.