Synthesis of Bis-Quaternary Ammonium Salts

12.8 g (60 mmol) of amine 4 and 73.2 g (300 mmol) of 1,6-dibromohexane 5 were added to acetonitrile (100 mL). The temperature of the reaction mixture was raised to 65 °C and stirred under N₂ for 24 h. After acetonitrile was removed, the excess of dibromohexane was removed under reduced pressure. The residual mixture was washed with ether (50 mL) in two steps and later dissolved in 50 mL of hot acetone. A white solid (2.5 g, 12%) was found after bis-quaternary salt 7 crystallized upon cooling of the ether-washed reaction mixture. When acetone was removed from the filtrate, mono-cationic salt 6 was found to be a white solid (22.5 g, 82%). MP 58–59 °C. (Found: C 52.2; H 9.6; N 3.0%. C₂₀H₄₃Br₂N requires C 52.52; H 9.48; N 3.06%); ν_max (KBr): 3409, 2920, 2855, 1465, 1242, 1143, 1053, 964, 893, 779, 728, 637, 497, and 472 cm⁻¹. FTIR spectrum is displayed in Fig. S2.†δ_H (D₂O) 0.71 (3H, t, J 6.8 Hz), 1.10–1.50 (22H, m), 1.57 (4H, m), 1.76 (2H, m), 2.98 (6H, s), 3.16 (4H, m), 3.39 (2H, J 6.4 Hz); δ_C (D₂O) 14.82 (1C), 22.99 (1C), 23.17 (1C), 23.57 (1C), 25.80 (1C), 26.94 (1C), 28.17 (1C), 30.01 (1C), 30.41 (1C), 30.47 (1C), 30.76 (3C), 32.88 (1C), 33.11 (1C), 35.80 (1C), 52.89 (2C), 63.11 (2C) (dioxane: δ 67.4 ppm).