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 N 1CH2CH2CmF2m+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(RfCH 2CH2)+]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.