Process for Preparing Tribromomethylsulfonylpyridine

An aqueous solution consisting of sodium methanethiolate (0.24 mol), 95% NaOH (0.15 mol) and water (0.15 mol) was added to 2-chloropyridine (0.20 mol) and tetrabutylammonium bromide (2.3 g) over 2 hours at 80-90°C. Thereafter, the mixture stirred 5 hours at 90-100°C. The two layers were separated and the product isolated in 95% yield. 

A 27% solution of sodium hypobromite (1.2 mol) was prepared by adding bromine to 30% aqueous sodium hydroxide and then adding it to 95% sodium hydroxide (0.12 mol). 

Thereafter, the mixture was cooled to 0°C, the product from Step I (23.8 g) added over 2 hours, and the mixture stirred for 5 hours at 5-10 °C. The product precipitated out as crystals and was isolated in 99% yield, mp = 160-161 °C. 

2-Methylthiopyridine was prepared in this two phase system using tetrabutylammonium bromide as the phase transfer catalyst. 

In a subsequent investigation by others (1), tetrabutylphosphonium bromide was used as the phase transfer catalyst. 

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