KF-alumina surface

Alcohols and amines have been regenerated by MW-promoted deavage of sulfonates (83-90%) and sulfonamides (76-85%) respectively, on basic KF-alumina surface (Scheme 6.16) [58],... 

Scheme6.16 Cleavage of sulfonates and sulfonamides on a basic KF-alumina surface.

Among various polyaryls, Basu et al. [201] reported microwave-assisted Suzuki coupling on a KF-alumina surface starting from 1,6-dibromopyridine to give 1,6-diphenylpyridine. 

KF impregnated on alumina (KF-alumina) has been shown to act as solid heterogeneous base to catalyze various organic reactions. A facile and expedicious solvent-free synthesis of libraries of quinoxalines promoted on KF-alumina surface has been realized from the condensation of a-hydroxy-, a-haloketones, or 1,2-diketones with aryl... 

Several solvent-free N-alkylation reactions have been reported which involve use of tetrabutylammonium bromide (TBAB), as a phase-transfer agent, under micro-wave irradiation conditions, an approach that is developed in Chapter 6 [36]. An experimentally simple microwave-assisted solvent-free N-arylation of primary amines with sodium tetraphenylborate or arylboronic acids, promoted by inexpensive cupric acetate on the surface of KF-alumina, has been reported. The reaction is selective for mono-N-arylation and a variety of functional groups are tolerated in the process (Scheme 8.4) [37]. 

It must also be pointed out that other basic materials have been synthesized which present no surface oxygens and hydroxyls, but other types of active sites whose exact nature remains controversial. These type of solids are, for example, impregnated imides and nitrides on zeolites and alumina, amorphous oxynitrides obtained by treatment with ammonia or aluminium orthophosphate, zirconium phosphate, aluminium vanadate or galloaluminophosphate, and KF supported on alumina/1,3,41 One of the main advantages of these solids with respect to basic oxides is their resistance to carbon dioxide or water. 

Whereas KF can be considered as a weak base, when impregnated on alumina, it becomes very strong and is able to ionize extremely weak carbon acids (up to pKa 30) [27]. This enhancement in basicity results from ionic dissociation K+F K+-i-F on the surface of alumina due to its amphoteric character (Scheme 6). 

If a KF-AIF3 electrolyte is used, it has a eutectic with a melting point of 560 °C [6, 21, 22]. In that electrolyte, no crust is formed on the cathode, and the alumina solubility is higher than in the NaF-AlF3 eutectic, at 5 wt% [23, 24]. There are two reasons for the absence of crust from the cathode surface. 

---