TRIMETHYLAMMONIOMETHANESULFINATE AND TRIMETHYLAMMONIOMETHANESULFONATE, THE SIMPLEST SULFINIC AND SULFONIC ACID BETAINES. REVISION OF THE STRUCTURE OF THE TRIMETHYLAMINE OXIDE–SULFUR DIOXIDE PRODUCT

Abstract

Bromomethanesulfinic acid (1) reacted with excess trimethylamine to give trimethylammoniomethane-sulfinate (3) which was converted by aqueous chlorine into trimethylammoniomethanesulfonate (4). Compounds 3 and 4 are (a) the first examples of sulfino- and sulfo-betaines in which the sulfur and quaternary nitrogen are bound to the same carbon, and, at the same time, are (b) the parent compounds of the respective classes of the sulfinic and sulfonic acid betaines. Reaction of 1 with dimethylamine followed by aqueous chlorine yielded a compound which (a) proved to be identical to the product of the reaction of trimethylamine oxide with sulfur dioxide, and also to the formaldehyde-bisulfite-dimethyl-amine adduct, and (b) gave 4 on methylation with dimethyl sulfate. We conclude that the sulfur dioxide-trimethylamine oxide product, contrary to an earlier proposal, is dimethylammoniomethane-sulfonate (8). The pK′_a of 8 and the equilibrium constant for the reaction Me₂NCH₂SO₃ ⁻ + H₂O ⇄ Me₂NH + HOCH₂SO₃ ⁻ (in H₂O, ionic strength 0.5 M with NaCl), were found from ¹Hmr spectra to be 6.05 (at 19.2°C) and 1.20 × 10⁻⁴ M (at 20.8°C), respectively.