Syntheses of naphthyl-based quaternary ammonium surfactants and their catalytic properties in chloromethylation of naphthalene

Abstract

Two naphthyl-based quaternary ammonium surfactants Naph-GS and Naph-MS were synthesized by reaction of bis(chloromethyl)naphthalene and chloromethyl naphthalene with N, N-dimethyl long-chain alkyl tertiary amine. The purified products were characterized by FT-IR and ESI-HRMS. The critical micelle concentration and surface tension (γCMC) at the critical micelle concentration (CMC) of Naph-MS and Naph-GS are 3.70 mmol/L, 27.90 mN/m; 0.89 mmol/L and 31.60 mN/m, respectively. The CMC of Naph-MS is about four times higher than that of Naph-GS. The sizes of most micelles of Naph-MS and Naph-GS aqueous solution at 1.1 CMC are both <1 nm. While at the concentration of 11 CMC, most of the Naph-MS, the Naph-GS micelles aggregate forming particles with an average size of 1.2 nm and 10 nm, respectively. The Naph-MS and Naph-GS were used to promote the chloromethylation reaction of naphthalene. The conversion of naphthalene was 77% when the reaction was catalyzed by Naph-MS (2.5 mol% of naphthalene at 48 mmol/L) at mole ratio of naphthalene/paraformaldehyde/NaCl/H2SO4 being 1.0:1.0:1.7:6.3 at 70 °C for 12 h. At the same condition, the conversion of naphthalene was 82% when the reaction was promoted by Naph-GS (0.53 mol% of naphthalene at 10 mmol/L). When the mole ratio of naphthalene/paraformaldehyde was increased to 1.25, the conversion of naphthalene increased to 90%, and the positioning selectivity (1-chloromethyl to 2-chloromethyl) is 94.8%. The gemini surfactant Naph-GS has better catalytic performance than conventional Naph-MS in the chloromethylation of naphthalene. The inorganic aqueous solution can be recycled by simple separation, and the conversion of naphthalene can still remain at 85% after 5 cycles.