1,3-Dimethyl-1H-Benzimidazolium Salts

[769-15-3] C9H11N2+ (MW 147.2) InChI = 1S/C9H11N2/c1-10-7-11(2)9-6-4-3-5-8(9)10/h3-7H,1-2H3/q+1 InChIKey = DSPUBTKMQXMJCI-UHFFFAOYSA-N [7181-87-5] C9H11IN2 (MW 274.1) InChI = 1S/C9H11N2.HI/c1-10-7-11(2)9-6-4-3-5-8(9)10;/h3-7H,1-2H3;1H/q+1;/p-1 InChIKey = RQGURHMTNSNBQX-UHFFFAOYSA-M (reagent used in Umpolung reactions to convert an electrophilic aldehyde to a nucleophile in the benzoin condensation, Stetter-type reaction, and SNAr reaction; the generation of homoenolate species from α,β-unsaturated aldehydes; formylation; and in coupling reactions) Physical Data: mp 200–201 °C,1 201–202 °C (methanol),2 200–201 °C (ethanol);3 1H NMR (60 MHz, DMSO-d6) δ 9.65 (s, 1H), 7.50–8.10 (m, 4H), 4.09 (s, 6H).2, 4 1H NMR (500 MHz, D2O, 50 mM acetate buffer pH 5.6) δ 9.17 (br s, 1H), 7.86 (m, AA′XX′, 2H), 7.70 (m, AA′XX′, 2H), 4.10 (d, J = 0.6 Hz, 6H).5 13C NMR (60 MHz, DMSO-d6) δ 9.65 142.9 (d), 131.5 (s), 126.2 (d), 113.2 (d), 33.3 (q).4 IR (KBr, cm−1)λ 3095, 1597, 1572.3 Solubility: sol THF, MeCN, acetone, H2O, DMSO, and methanol. Known Forms: the iodide salt is the most widely used form. Other counteranions such as chloride, bromide, perchlorate, hydroxide, tetrafluoroborate, and trifluoroacetate are also known. Most of the benzimidazolium salts are not commercially available. The iodide salt can be synthesized from commercially available 1-methylbenzimidazole. Preparation and Purification: 1,3-dimethyl-1H-benzimidazolium iodide was prepared by methylation of 1-methylbenzimidazole with an excess amount of iodomethane2, 4, 5 To an oven-dried pressure tube equipped with a stir bar was added 1-methylbenzimidazole (1.0 equiv) and iodomethane (5.5 equiv). The tube was sealed and heated to 100 °C for 1 h. The reaction was cooled to room temperature and concentrated under vacuo. The product was recrystallized from acetone, methanol, or a mixture of MeCN-toluene and dried under vacuum in the presence of P2O5. The iodide salt was obtained as light yellow crystals. Handling, Storage, and Precautions: the iodide salt can be stored in the dessicator and handled quickly in air.6