Schiemann reaction improved

Scavenger s. Water scavenger Schiemann reaction, improved... 

Schiemann reaction, improved 16, 608 17,624 Schiff bases s. Azomethines Schmidt reaction 17, 524 —, lactams from ketones,... 

Introduction of a fluorine atom is achieved using the Schiemann reaction. Originally, the reaction involved gently heating the solid diazonium fluoroborate (Scheme 8.18), but improved yields result from the thermal decomposition the hexafluorophosphate, ArN2 PF, or hexa-fluoroantimonate, ArN2 SbFg, salts. 

Fluoro-l,2,4-traizole was also prepared by the photochemical Schiemann reaction. Yields were improved over the original method by increasing the concentration of fluoroborate ion in the reaction mixture. 

Improved Schiemann reaction—Diazotization in tetrahydrofuran or dimethyl sulfoxide s. 16, 608... 

Hexafluorophosphoric acid Replacement of amino groups by fluorine Improved Schiemann reaction... 

Selective introduction of fluorine into an aromatic ring is often achieved by thermal decomposition of diazonium fluoroborates, which is called the Balz-Schiemann reaction (Scheme 37). 25 i26 jjie scope of the reaction is wide and includes heterocyclic compounds (equation 47). The Bp4 salts are unusually stable for diazonium salts and yields are usually high. In some cases, however, use of Pp6 or Sbp6 salts gives improved yields. ... 

Bis-(N-methyl-N-nitroso)terephthalamide and N,N -dimethyl-N,N -dinitrosooxamide are convenient precursors of diazomethane. From N,N -dinitrosooxamides, other diazoalkanes have been prepared as well . Improved yields in the Schiemann reaction have been obtained with hexafluorophosphoric acid . Reaction of dia-zonium salts with nickel carbonyl and acetic acid may provide a single-step alternative to the Sandmeyer reaction, especially where the nitriles from the latter contain other groups susceptible to hydrolysis . The highly reactive 1,2,4-thiadiazolediazonium salts have permitted an extension of diazonium salt chemistry by new reactions . 

---