Dediazoniations of Arene Diazonium Ions in Homogenous Solution. Part IV: Change-over from a heterolytic to a homolytic mechanism in 2,2,2-trifluoroethanol pyridine mixtures

✍ Scribed by Peter Burri; Hana Loewenschuss; Heinrich Zollinger; Gene K. Zwolinski

• Publisher: John Wiley and Sons
• Year: 1974
• Tongue: German
• Weight: 484 KB
• Volume: 57
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19740570214

✦ Synopsis

Abstract

There are only two dediazoniation products of benzenediazonium tetrafluoroborate in 2,2,2‐trifluoroethanol (TFE), namely phenyl 2,2,2‐trifluoroethyl ether (1) and fluorobenzene (2). The reaction kinetics are strictly first‐order with respect to the diazonium salt. The addition of increasing amounts of pyridine to the system results in a gradual decrease in the yields of 1 and 2 and an increase in the yields of the homolytically formed products, benzene (3), biphenyl (4), isomeric phenylpyridines (5) and diazo tar (6). The reaction kinetics show that the rate of dediazoniation of the benzene diazonium salt increases with increasing amounts of pyridine. The reaction with added pyridine is no longer first‐order with respect to the diazonium ion.

The product analyses and the kinetic data are consistent with the view that in pure TFE this diazonium salt decomposes completely by a heterolytic mechanism. The addition of pyridine brings about a competitive homolytic mechanism which becomes increasingly dominant as the concentration of pyridine increases.