Reaction of 4,4′-bis(chloromethyl)-1,1′-biphenyl and phenol in two-phase medium via phase-transfer catalysis

Kinetic study of the phase-transfer catalyzed etherification of 4,4′-bis(chloromethyl)-1,1′-biphenyl with phenol in an alkaline solution of KOH/organic solvent two-phase medium was investigated. The reaction was carried out in a stirred batch reactor under mild operating conditions. During or after completing the reaction, the mono-substituted product (4,4′-(chloromethylphenoxy-methyl)-1,1′-biphenyl) and the di-substituted product (4,4′-bis(phenoxymethyl)-1,1′-biphenyl) are both produced. Effects on the reaction due to various operating conditions, such as agitation speed, amount of water, amount of organic solvent, amount of phase-transfer catalyst, amount of potassium hydroxide, kind of phase-transfer catalyst, kind of organic solvent, inorganic salt and temperature were studied in detail. A rational mechanism of the etherification was proposed based on the experimental observation and a kinetic model was developed. In examining nine kinds of phase-transfer catalyst, tetraoctylammonium bromide was found to be the best for increasing the reaction rate. The inorganic salts, such as potassium iodide or sodium iodide play an important role in enhancing the reaction rate. Hoffmann elimination is used to explain the peculiar behavior in studying the effect of the KOH on the apparent rate constants. The apparent activation energies for the etherification were Ea1 = 23.7 kcal/mol and Ea2 = 31.5 kcal/mol, respectively, using tetra-n-butyl-ammonium bromide (TBAB) as the catalyst.

Graphical abstractThe overall reaction of the etherification of 4,4′-bis(chloromethyl)-1,1′-biphenyl with phenol is Figure optionsDownload full-size imageDownload as PowerPoint slideTetra-n-butylammonium bromide was used as a liquid–liquid phase-transfer catalyst (LL-PTC, Q). Potassium phenoxide (PhO−K+) was synthesized in situ directly by reacting phenol with potassium hydroxide in the aqueous phase. 4,4′-(Chloromethylphenoxymethyl)-1,1′-biphenyl was first synthesized by reacting phenoxide with 4,4′-bis(chloromethyl)-1,1′-biphenyl in an organic solvent. Afterward, 4,4′-bis(phenoxymethyl)-1,1′-biphenyl was produced by further reacting phenoxide with 4,4′-(chloromethylphenoxymethyl)-1,1′-biphenyl.