Quaternization of Pyrazine, Pyridazine, and Pyrimidine with Alkyl and Polyfluoroalkyl Halides: Formation of Low Melting Salts

Abstract

Pyridazine (1a), pyrazine (1b), pyrimidine (1c) and 1,4-dimethylpiperazine (1d) were quaternized at N-1 with alkyl iodides and polyfluoroalkyl halides under either neat or solvent conditions at 10-110 °C to form N₁CH₂CH₂C_mF_2m+1 (m = 0, 1, 6, 10) diazinium iodides, and N₁CH₂CH₂F diazinium bromides in moderate to excellent isolated yields. Metathesis of these alkyl and monopolyfluoroalkyl substituted diazinium halides with other salts led to the formation of new quaternary compounds, some of which fall into the ionic liquid class (mp <100 °C), where [N₁(R_fCH₂CH₂)⁺]Y^- (Y = NTf₂, PF₆, OTf, NO₃, ClO₄). 1,4-Dimethylpiperazine with 2.5 equivalents of 1-bromo-2-fluoroethane in DMSO gave the diquaternized N₁, N₄-(CH₂CH₂F)₂ product. All compounds were characterized by ¹H, ¹³C, ¹⁹F NMR, MS, elemental analyses, and density measurements (for liquids). The phase transition and decomposition temperatures of the quaternized compounds were determined by DSC.

Key words

quaternization - ionic liquids - diazine - fluoroalkyl - polyfluoroalkyl

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