Molecular design and experimental study on the alkylation of benzene with C6 olefin dimer with Lewis acidic monoamine ionic liquids and its sulfonate surfactant properties

Long-chain alkyl benzene (LAB), conventionally manufactured by petrochemical routes, is an important intermediate for the synthesis of high-value chemicals, especially detergents and oil displacement agents. The preparation of LAB from coal-based olefins has attracted extensive research interest. In this work, the alkylation activity of four Lewis acidic monoamine chloroaluminate ionic liquids (LAMCILs), designed by AlCl3 and monoamine hydrochloride with alkyl chains of different lengths, was predicted by quantum chemical calculations using the synthesis of 1-methyl-1-butylheptylbenzene (MBHB) with benzene and C6 olefin dimer as a model reaction. The HOMO*-LUMO* gap indicated that the alkylation activity was enhanced with increasing alkyl chain length of the organic amine molecules in the LAMCILs, in the following order: [n-C6H13NH3]Cl-AlCl3 > [n-C4H9NH3]Cl-AlCl3 > [n-C3H7NH3]Cl-AlCl3 > [C2H5NH3]Cl-AlCl3. These four LAMCILs were successfully synthesized and used to catalyze the alkylation of benzene with the C6 olefin dimer. The experimental results are consistent with the calculated results. The UV/VIS characterization showed that their Hammett acidity function (H0) increased as the alkyl chain of organic monoamine molecules in the LAMCILs extended. Therefore, a two-way correlation between the HOMO*-LUMO* gap, MBHB yield and Hammett acidity function can be established. Furthermore, the effect on the yield of MBHB was investigated by the method of metal chloride modified [n-C4H9NH3]Cl-AlCl3 ionic liquids. The results showed that the CuCl2-modified [n-C4H9NH3]Cl-AlCl3 ionic liquid had better catalytic activity in this study. Under optimal reaction conditions, the conversion of the C6 olefin dimer and selectivity toward MBHB reached 100 % and 91.34 %, respectively. Finally, the surfactant properties of sodium 1-methyl-1-butylheptylbenzene sulfonate (SMBHBS) were examined, and the results indicated that its surfactant properties were basically comparable to those of commercial LAS.