Reactions of 1, 2, 2, 6, 6-Pentamethyl-4-oxothianium Tetrafluoroborate with Alkali Metal Halides in a Solid State

Abstract

The solid-state reaction of the ground mixture of 1, 2, 2, 6, 6-pentamethyl-4-oxothianium tetrafluoroborate [ 3] with some alkali metal halides has been examined in comparison with the corresponding reaction in aqueous solution. Each ground mixture was prepared by a mill or an agate mortar. At room temperature, changes were recognized in the infrared spectra as the time proceeds in KC1 and KBr, but were little observed in KI and NaCl. The reaction of [3] with KCl occurred via ion exchange and afforded mainly 2, 6-dimethy1-6methylthio-2-hepten-4-one [4], α β-elimination product, and 2, 6-dichloro-2, 6-dimethy1-4heptanone [6]an HCl adduct of 2, 6-dimethyl-2, 5-heptadien-4-one [5]. On heating the system, the chief product was [4] in KCl and NaCl. In KBr, products were [4], 2, 2, 6, 6tetramethylthian-4-one [8] and [5]. The reaction products in KI were nearly exclusively [8] which was formed by the attack of S-methyl group at the oxothianium ring. On the other hand, the reaction in aqueous solution afforded only [4]for all alkali metal halides employed. Based on the facts described above, it became clear that the reactions in the solid state are different from those in solution, and that chloride, bromide and iodide ion act as hard, borderline and soft base, respectively. Furthermore, it was found that the reactivity of halide ions was changed by the substituent group on 2- and 6-position of the 4-oxothianium ring.