Study On Hydroarylation Of Styrenes Over Acidic Cation-exchange Resins

1,1-diarylalkanes are important for the synthesis of many pharmaceuticals, agro-and fine chemicals. Many natural products and synthetic molecules with uniquebiological and pharmacological activities have such structure motifs. Therefore, it isquiet important to synthesis these compounds.4-(1-Phenylethyl)-1,3-resorcinol, also called SymWhite377, which was foundto be stable and to inhibit mushroom tyrosinase22times more effectively than kojicacid, it is one of the most efficient tyrosinase inhibitor up to date found in theliterature. In this paper, we first investigated the reaction of resorcinol with styreneover H2SO4to get pure4-(1-phenylethyl)-1,3-resorcinol with simple work-upprocedure. The effects of solvent, reaction time and the work-up procedure wereinvestigated. Optimal reaction conditions as follows: a mixture of resorcinol andstyrene(molar ratio was2:1) in1,2-dichloroethane was catalyzed by catalytic amountof concentrated H2SO4, after refluxing for4h, the HPLC yield of the target productwas70%. In the work-up procedure, based on the little difference of physicalcharacter between resorcinol,4-(1-phenylethyl)-1,3-resorcinol and4,6-bi(1-phenylethyl)-1,3-resorcinol, the method of extraction was used to separate thesecompound from the mixture. All of them were obtained with high purity, therecovered resorcinol and4,6-bi(1-phenylethyl)-1,3-resorcinol could be reused, afterrecrystallization, the desirable product with the purity of99%was obtained, and theyield of it was43%.Owning to the fact that the H2SO4can bring about many disadvantages, a seriesof acidic cation-exchange resins were used for the model reaction of resorcinol withstyrene (the mole ratio of them was3:1), in which both resin D072(30wt%, based onstyrene) and resin NKC-9(20wt%, based on styrene) exhibited the excellent catalyticperformance in this reaction with the selectivity of90%for target product. Both ofthem were applied to the hydroarylation of various electron-rich arenes with styrenes,the hydroarylated products were quantitatively obtained. They could be used for fourconsecutive runs with slight decrease in activity.What’s more, the continuous process for hydroarylation of styrenes over resinD072in a fixed-bed reactor was established, as for the reaction of resorcinol withstyrene, the selectivity for the target product was94%, which was higher than that batch conditions, this green continuous process is potentially applicable to large-scaleproductions.