The chemistry of N,N′-dimethylformamidine. I. Formation from potassium methylamide and its thermal stability

Abstract

The thermal decomposition of methylamine solutions of potassium methylamide (PMA) to form the potassium salt (PDMFA) of N,N′-dimethylformamidine (DMFA) has been studied as a function of PMA concentration at 60 °C. Although concentrated solutions yield normal pseudo-first-order plots (analysis by ultraviolet–visible spectrophotometry), dilute solutions (< 0.05 mol L−1 PMA) show an increase to a new rate after about 20 h reaction.The mechanism for this novel amidine salt synthesis is discussed in terms of rate-limiting β-hydride elimination from the PMA ion pair. The relatively sharp rate increase with time for the low concentration runs may arise from a slow build up of one or more intermediates. The resulting inverse dependence of kobs on PMA concentration is probably related to ion pair–dimer association phenomena.Pure DMFA has been produced by this reaction, and its thermal stability examined. DMFA decomposes above 100 °C to form bis-N-(N′-methylmethylenimine)methylamine and methylamine; the series of equilibria involved have been shown to be reversible.