Supramolecular Self-assembly And Properties Of Six-membered Cucurbit Rings And Heteropolyacids

Heteropoly acid has the properties such as acidic,redox properties and pseudoliquid behavior.Therefore,it has a good application prospect in the fields of separation,identification,adsorption and catalysis.Because of the excellent solubility of heteropoly acid,it is difficult to separate from the product in the reaction,and it is not easy to recover,so it cannot be reused.Usually,heteropoly acid is loaded on insoluble solid carrier to form solid heteropoly acid material.So,through the"outer-surface interaction"between the positive electro-potential outer surface of cucurbit[n]urils(Q[n]s)with heteropolyacid anions.Supramolecular self-assembly of heteropoly acid and Q[n]s is a new method was made into a new solid Q[n]s-HPAs material with stable properties,which not only retained the original structural characteristics of Q[n]s and heteropoly acid,but also maintained the multifunctional characteristics of acidity,oxidation and catalysis of heteropoly acid,which is one of the research hotspots in the field of polyacidification.The supramolecular assemblies of substituted cucurbit[6]uril{Q[6]s include(OH)₁₂Q[6],TMe Q[6],Q[6]},Keggin-type silicotungstic acid(H₄Si W₁₂O₄₀,STA)and phosphomolybdic acid(H₃PMo₁₂O_40,PMA)were selected as self-assembly modules.The structural characteristics,and functional properties of Q[6]s-HPAs self-assembly were investigated.The main research contents are as follows:1.(OH)₁₂Q[6]and Keggin type STA,are selected as building blocks,(OH)₁₂Q[6]-STA supramolecular self-assembly system was constructed,and the structure of the supramolecular self-assembly was characterized by X-ray single crystal diffraction,XRD and FT-IR.The results showed that supramolecular self-assembly{(HO)₁₂Q[6]-STA,(HO)₁₂Q[6]-K⁺-STA,(HO)₁₂Q[6]-Ba²⁺-STA,(HO)₁₂Q[6]-octyl diamine-STA}all through the outer-surface interaction of cucurbit[n]urils(i.e.typical hydrogen bonds,atypical hydrogen bonds,ion-dipole interaction and electrostatic interaction between(HO)₁₂Q[6]-Mⁿ⁺cation and STA anion.)2.The supramolecular self-assemblers of TMe Q[6]-STA,TMe Q[6]-PMA,Q[6]-STA and Q[6]-PMA were obtained by the reaction of Symmetric tetramethyl Q[6](TMe Q[6])or regular Q[6]with silicotungstic acid(STA)and phosphomolybdic acid(PMA),respectively.A series of self-assemblers were characterized by XRD,SEM,FT-IR and other methods.The properties of Q[6]-STA self-assemblers were investigated by BET and TG-DSC methods.The results show that in the Q[6]s-HPAS self-assembly system,both Q[6]s and HPAs maintain the original structure.Compared with HPAS,the specific surface area of the Q[6]s-HPAS self-assembly system is significantly increased.3.Because heteropoly acid has a very strong Br?nsted acid and is commonly used as catalyst for esterification reactions.Q[6]s-HPAs was used as solid acid catalyst in the esterification reaction system for the synthesis of Butyl p-hydroxybenzoate(BP),and its catalytic performance was investigated.The effects of the reaction time,the loading of catalyst and the molar ratio of alkyd on the synthesis of BP were systematically investigated by single factor experiments,and the optimal reaction conditions were selected.Q[6]-STA,TMe Q[6]-STA,(OH)₁₂Q[6]-STA,TMe Q[6]-PMA and Q[6]-PMA were used to catalyze the synthesis of butyl p-hydroxybenzoate(BP)under optimized conditions,and the yields were95.78%,93.63%,93.2%,91.30%and 84.96%,respectively.The results show that the Q[6]s-HPAs self-assembled system has good catalytic activity in the esterification system,and has the characteristics of high recovery and reutilization.