Abstract
The alkylation reaction of isobutane with 2-butene to yield C8-alkylates was performed using Brønsted–Lewis acidic ionic liquids (ILs) comprising various metal chlorides (ZnCl2, FeCl2, FeCl3, CuCl2, CuCl, and AlCl3) on the anion. IL 1-(3-sulfonic acid)-propyl-3-methylimidazolium chlorozincinate [HO3S-(CH2)3-mim]Cl-ZnCl2 (x=0.67) exhibited outstanding catalytic performance, which is attributed to the appropriate acidity, the synergistic effect originating from its double acidic sites and the promoting effect of water on the formation and transfer of protons. The Lewis acidic strength of IL played an important role in improving IL catalytic performance. A 100% conversion of 2-butene with 85.8% selectivity for C8-alkylate was obtained under mild reaction conditions. The IL reusability was good because its alkyl sulfonic acid group being tethered covalently, its anion [Zn2Cl5]− inertia to the active hydrogen, and its insolubility in the product. IL [HO3S-(CH2)3-mim]Cl-ZnCl2 had potential applicability in the benzene alkylation reaction with olefins and halohydrocarbons.
Highlights
As a type of green solvent/catalyst, ionic liquids (ILs) have attracted much attention for applications in chemistry and industry because of their chemical stability, thermal stability, low vapor pressure, and high ionic conductivity properties.[9,10] ILs, especially acidic ILs, are recognized as promising candidates to overcome shortcomings of industrially employed traditional liquid catalysts and solid catalysts in many reactions, such as esteri cation, polymerization, and alkylation
A 95.8% C8-alkylate selectivity and 90.4% TMP selectivity were achieved when HCl gas was bubbled into the Lewis acidic IL triethylamine hydrochloride–aluminum chloride/cuprous chloride [(C2H5)3NH]Cl–AlCl3/CuCl.[17]. These results indicate that the addition of a Brønsted acidic compound was an effective way to improve the catalytic activity and selectivity of Lewis acidic IL
The good catalytic performance may be attributed to the appropriate acid strength of the IL and the synergistic effect originating from the Brønsted and Lewis acids of IL
Summary
As a type of green solvent/catalyst, ionic liquids (ILs) have attracted much attention for applications in chemistry and industry because of their chemical stability, thermal stability, low vapor pressure, and high ionic conductivity properties.[9,10] ILs, especially acidic ILs, are recognized as promising candidates to overcome shortcomings of industrially employed traditional liquid catalysts and solid catalysts in many reactions, such as esteri cation, polymerization, and alkylation. The conversion of 2-butene reached 91.0%, but the selectivity of C8-alkylate was only 50.5% and only 10% trimethylpentane (TMP) selectivity was obtained.[13] Many other chloroaluminate ILs were investigated in the alkylation reaction of isobutane/2-butene.[13,14] the amounts of TMP in the alkylation products were seldom greater than 75 wt%. The TMP selectivity is close to 80% in commercial alkylation.[1] To improve the catalytic performance of chloroaluminate IL, HCl or Brønsted acidic IL 1-methyl-3(4-sulfobutyl)-imidazolium hydrogen sulfate [HO3Sbmim] [HSO4] were used as co-catalysts in the alkylation reaction of isobutane/2-butene.[15,16] The TMP selectivity increased from
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