Nonaromatic heterocyclic cations

In Tables 126,37- 1,43,46,56,73-115 and n 57.90.9.4,..6-.34 pKr+ values currently available for heterocyclic cations are listed in order of increasing complexity of the heterocyclic system. Aromatic and nonaromatic heterocyclic cations are considered separately in Tables I and II, respectively. Only data for strictly aqueous solutions or for aqueous solvents containing small proportions of nonnucleophilic organic solvents are included in Tables I and II. A number of data reported for aqueous alcoholic solutions are discussed separately in Section VI,A. Equilibrium constants in such media can only be considered as apparent constants since no allowance is made for the existence of the pseudobases in these solutions as mixtures of the corresponding hydroxide and alkoxide adducts. The presence of an organic solvent is sometimes necessary to promote sufficiently the solubility of the pseudobase for pXR+ determination. In such cases, interpretation of data relative to strictly aqueous solutions is more straightforward if nonnucleophilic cosolvents such as acetonitrile and dioxane, are chosen in preference to alcohols. 

As indicated in Table II, only scattered data are available for nonaromatic heterocyclic cations however, some trends are apparent. If one assumes that a pKR+ of 8, as indicated for the first three cations in Table II, is typical of an isolated C=N bond, then any stabilization of such cationic systems via resonance or other electronic effects would be expected to result in higher p/CR+ values. Thus, p/CR+ > 8 is observed for the 1,3-diphenylimid-... 

We have recently developed some new RTILs by combining fluorohydrogenate anions and some nonaromatic heterocyclic cations such as Ar-aIkyl-//-methylpyrro-lidinium (RMPyr) and A -alkyl-A -methylpiperidinium (RMPip) ions [10, 11]. 

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