Synthesis Of SO₃H-functionalized Ionic Liquids And Their Catalytic Performance

To achieve substainable development of economy and the whole society,it is important to develop green chemistry in the 21 century.Ionic liquids,known as new environmental benign materials,have attracted great attention for their unique physical and chemical properties.In the recent decades,there were numerous research about using ionic liquids as catalyst and solvent in the reaction of isomerization,alkylation and other organic synthetic chemistry.Ten different SO₃H-functionalized ionic liquids have been synthesized by using tri-alkylamine,methylimidazole,pyridine with inexpensive industrial materials 1,4-propane sultone as source.Their structures,thermal stabilities were characterized by NMR,Q-TOF,TG-DTA respectively.The results exhibit that ionic liquids are in good agreement with those expected and display high thermal stability.The decomposition temperatures are higher than 300℃,and there are no obvious weight loss observed.Compared with conventional organic solvent,ionic liquids have less pollution to environment due to no vapour pressure.Therefore, ionic liquids can be viewed as green solvent.Tert-butyl-penols are important fine chemicals,which are used in the manufacture of resins,antioxidants,printing inks,petroleum additives,ultraviolet absorbers,heat stabilizers for polymeric materials,food additives etc.Catalytic performance of the SO₃H-functionalized ionic liquids for the alkylation of catachol and o-cresol with tert-butanol(TBA) were investigated.Reaction conditions were optimized and their catalytic performance are compared with conventional acid(sulphuric acid or p-toluenesulfonic acid) and solid acid (H-β,H-ZSM5).Simulated calculation is carried out to explain the experimental phenomenon and propose possible reaction pathways for tert-butylation of catechol and o-cresol with TBA. The results indicate that the SO₃H-functionlized ionic liquids exhibited high catalytic activities for the alkylation of catechol and o-cresol.In the optimized reaction conditions,the conversion of catechol and o-cresol are 41.5%and 80.9%respectively,and selectivity of 4-tert-butyl-cathchol,6-tert-butyl-o-cresol were 97.1%and 44.1%respectively;compared with solid acid,reaction temperature decrease and reaction can carry on without solvent. Extraction is used after reaction to separate ionic liquids and products.The ionic liquids were recycled five times,and no change in activity.The results of simulated calculation are consistent with that from experiment,and the conclusion is that:massive ether is formed initially in the tert-butylation of o-cresol and then isomerized into other thermodynamic stable products.Unlike other tert-butylation of phenols,there is no ether detected in the tert-butylation of catechol due to hydrogen bonding and steric hindrance of[t-C₄H₉]⁺.