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Abstract
introduction, a brief review on methods for the preparation of N-acyliminium salts 1, and on the physical and chemical properties of these salts is presented (163 references).
The own results are reported in the Theoretical Part. Ritter reaction of a-chlorocarbenium salts 43 with nitriles 44 affords nitrilium salts 45, which undergo fast 11,3] -chlorotropic rearrangement to funish the chloro substituted 2-azoniaallene salts 46.
This new tandem reaction has been used for the preparation of twelve stable hexachloroant^monates 46 {P 51). With electron-rich nitriles the 2-azoniaallene salt 46 react further to give the rather stable salts 47 (p 51), respectively 49 (p 54). The new salts 46, 47, 49 are characterized by elemental analyses, 1H- and 13C-NMR spectra, as well as by their IR spectra, which show broad, characteristic absorptions for the C=N=C stretching frequency between 1600 and 1850 cm”1. Because of low stability, i3C-NMR spectra of the 1,3-dichloro substituted 2-azoniaallene hexachloroantimonates 46, derived from the pentachloropropenium salt C^OCCl-CCi^SbCl^” could not be obtained. Chloro substituted 2-azoniaallene cations 46 are strong Lewis acids, which compete with SbCl5 for the chloride ion. In most cases SbClg is the stronger Lewis acid, that is, compounds 46 are really salts. However, if R3 is a strongly electron-withdrawing substituent (CClj) it is observed that the cation abstracts a chloride anion from SbCl^- to give the unpolar compound 41 (p 57).
The polar character of the salts 46 has been studied in detail using an exchange reaction with tetraalkylammonium chlorides. Instances,for both unpolar and polar chlorides 46 have been observed. The results suggest a correlation of the geometry of chloro substituted 2-azoniaallene salts with the polar character of their chlorides.