General Properties and Spectra

The A-fluoropyridinium salts are crystalline species with melting points ranging from 90°C for lc to above 300°C for le (86TL3271). With the notable exception of perchlorates, such as If, they are shock-resistant, thermally stable, and nonhygroscopic. Care must be taken in work with the perchlorates because in dry form they can undergo a violent explosion if touched, even with a soft Teflon spatula (94UP1). 

The salts are stable indefinitely when stored under strictly anhydrous conditions. The solutions in dry degassed dichloromethane, tetrahydrofu-ran, or acetonitrile are also relatively stable. The salts undergo a slow decomposition when dissolved in dimethyl sulfoxide, A, A-dimethylform-amide, alcohols, or water (94UP1). For example, a half-life of 13 days for the triflate lb in D20 at room temperature has been reported (90OS129). Tertiary amine-mediated decomposition is rapid at room temperature. 

The stability of the nitrogen-fluorine bond (58MI1) and the nature of the A-fluoropyridinium cation have been discussed in terms of back- 

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