Search

Phase-transfer catalytic reactions of the derivatives of benzyl halide and 2,4,6-tribromophenol have been successfully carried out in an organic solvent/alkaline solution of KOH two-phase medium. The main purpose of this work is to study the effects of the leaving groups, orientations, and functional groups of the derivatives of benzyl halide on the reaction rate and the product yield. To identify the reaction rate in the organic phase, 2,4,6-tribromophenol is employed as the nucleophilic reagent under phase-transfer catalytic reaction. Reactions of aqueous phase and organic phase can be separately carried out to determine the reaction rate constants. Results obtained from the single organic-phase reaction are compared with those obtained from the two-phase phase transfer catalytic reaction. According to the experimental data, simplified models for representing the single-phase reaction and the two-phase reactions were proposed and derived. The reaction rate constants for the single-phase model (ks) and the two-phase model (kT) were compared to show their consistency. The kinetics of the reactions of the derivatives of benzyl halide and 2,4,6-tribromophenol were also studied. The effects of the leaving group, orientation, and functional group of the organic substrate on the reaction rate constant were also investigated in detail. A satisfactory explanation was arrived at to account for the experimental evidence. [ABSTRACT FROM AUTHOR]

In this work, the synthesis of dichlorocyclopropane, from a phase-transfer catalyzed reaction of chloroform and olefins (1-octene or 1,7-octadiene), was carried out in an alkaline solution of NaOH/chloroform two-phase medium. Trialkylammonium propansultan, a zwitterionic compound, acts as a new phase-transfer catalyst of high reactivity to produce high yields of dichlorocyclopropane. Dichlorocarbene (:CCl2), which is an active species to react with olefins to produce dichlorocyclopropane in the organic phase, is generated from the reaction of chloroform, sodium hydroxide, and trialkylammonium propansultan as phase-transfer catalyst at the interface between two phases. The dichlorocyclopropanation is dramatically enhanced by adding a small quantity of trialkylammonium propansultan. An interfacial reaction mechanism was proposed to explain the reaction characteristics. A pseudo first-order rate law is used to describe the reaction rate at high alkaline concentration solution (>50 wt% NaOH). There is detailed investigation of the reaction kinetics, including the effect of the reaction conditions—the agitation speed, temperature, phase-transfer catalysts and their amounts, the amount of chloroform, the amount of 1-octene, inorganic salt (NaCl and Na2SO3), and alkali concentration—on the conversion of 1-octene. [ABSTRACT FROM AUTHOR]

The phase-transfer catalytic reaction (PTC) of 2,4,6-tribromophenol and dibromomethane by quaternary ammonium salt was carried out in a high alkali content of KOH/dibromomethane two-phase medium. A large conversion of 2,4,6-tribromophenol is obtained at a region of high KOH content. Dibromomethane acts both as the organic-phase reactant and the organic solvent; thus, no extra organic solvent is required. Two main products, i.e., α -bromomethyl 2,4,6-tribromophenyl ether (mono-substituted product) and bis-(2,4,6-tribromophenoxide)methane (bis-substituted product), were detected in the solution during the phase-transfer catalytic 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. A kinetic model is developed to describe the behaviors of the two organic-phase reactions on the basis of the experimental observation. The two intrinsic rate constants of the two organic-phase reactions, which are the rate-determining steps of the whole reaction system, are determined. Effects of the reaction conditions, such as agitation speed, amount of water, amount of TBAB catalyst, temperature, and amount of dibromomethane, quaternary ammonium salts, and inorganic salt KBr, on the conversion of 2,4,6-tribromophenol and the reaction rate are investigated in detail. [ABSTRACT FROM AUTHOR]