Researchers have begun to recognize phase-transfer catalysis (PTC) as an invaluable methodology in organic syntheses in recent years, and its scope and application are the subject of current research interests. Ether, which is a high additive-value chemical, is widely used in various industries as a petroleum chemical additive or extractant (Sato et al., 1967;Dehmlow and Dehmlow, 1983). The complicated ethers can be easily synthesized from the reaction of alcohol and halogenate alkane using phase-transfer catalyst under mild conditions. This study synthesizes diether from the reaction of a,a 0 -dibromo-o-xylene and 1-butanol in an alkaline solution of KOH and organic solvent two-phase medium under PTC conditions. The organic-soluble active catalyst, tetrabutylammonium butanoxide ((C 4 H 9 ) 4 N + -OC 4 H 9 Γ , QOR), which forms in an aqueous phase, transfers to the organic phase for reaction with bromoalkane to produce the ether product. Quaternary ammonium salt is then regenerated in the aqueous phase. The reaction mechanism is proposed as
The hydration molecules of QOR decrease the organic solubility of QOR, and thus affect the reaction rate. As a result, the amount of potassium hydroxide and organic solvents has significant effects on the concentration of QOR in organic phase, which plays an important role in the etherification reaction.
2. Experimental
Previous research reports the synthesis of monosubstituted and disubstituted products of a,a 0 -dibromo-o-xylene in detail (Wang and Chang, 1993). The molecular weight of these products was identified by GC mass spectroscopy, and IR and NMR revealed the functional groups. Previous study also proves the extraction reaction mechanism and estimation of rate constants using the pseudo-first-order rate law. This study focuses on the effects of the hydration number and biphasic distribution of QOR on phasetransfer-catalytic activities.
2.1. Measurement of the distribution of QOR in organic phase
Measured quantities of potassium hydroxide (18-72 mmol), 1-butanol (40 mmol), and TBAB (0.62 mmol of tetrabutylammonium bromide, QBr) were dissolved in a mixture of organic solvent (40 mL) and water (20 mL) in a flask in an isothermal vibrating (100 rpm) water bath. QBr reacts with 1-butanol in the alkaline solution to produce the QOR product, which is an organic-soluble compound and extracted into the organic phase. This study maintains constant values of [QOR] org and [QBr] org during the reaction period by using a large excess amount of