Methyl p-toluenesulfonate → Benzothiazolium, 3-methyl-2-(methylthio)-, 4-methylbenzenesulfonate (1:1)

Participants

Reaction Steps

In the first step, 2-methylthiobenzothiazole (Aldrich Chemical Company, Milwaukee, Wis.) is quaternized by heating at 120° C. with an equivalent of methyl p-toluenesulfonate to yield N-methyl-2-methylthiobenzothiazolium p-toluenesulfonate (Compound 1A is also commercially available from TCI, Portland, Oreg.). N-(3-iodopropyl)-4-methylpyridinium iodide (Compound 1 B) is prepared by heating 4-methylpyridine (1.00 g) with 5 mL of 1,3-diiodopropane without a solvent at 120° C. for about 1 hour. Ethyl acetate is added and the product is filtered. Compounds 1A and 1B are condensed to yield 1'-(3'-iodopropyl)-3-methyl-4'-thiacyanine iodide (Compound 1C) using methods known in the art [e.g. Brooker, et al. J. AM. CHEM. SOC. 64, 199 (1942)]. For instance when 2.93 g of 1A is stirred with 3.3 g of 1 B with the addition of 1.15 mL of triethylamine in 20 mL of CH2Cl2 for 16 hours at room temperature followed by the addition of 80 mL of ethyl acetate about 1.1 g of 1 C is obtained.

Provenance & Evidence