Microwave activated with graphite

Consequently, a lot of research has been carried out in this area in order to find convenient catalysts, i.e. those able to activate the acylating reagent while giving labile complexes with ketones, in particular in hot conditions. Ferric chloride is the most common catalyst when the reaction is achieved in this manner (refs. 7, 8). With this same view, Friedel-Crafts acylation in the presence of small quantities of catalysts (for example FeCl3), is strongly activated by microwave irradiation, in particular when the catalyst is on a graphite substrate (ref. 9). 

Table 5.4), prepared from reduction of Pd(II) salts with potassium graphite. The results suggested that this catalyst was not very active. However, some years later Jikei and Kakimoto [73] prepared a more active Pd/CGr based on a smaller crystallite size. In 2002, Kohler et al. [74] studied a variety of Pd/C catalysts with different properhes (Pd dispersion, oxidation state, water content, conditions of catalysts preparation etc.) in the Heck reaction of aryl bromides with olefins (entry 4, Table 5.4). The authors pointed out the hypothesis that the leached Pd from the support is the active species and the solid Pd/C catalyst acts as a reservoir that delivers catalytically active Pd species into solution. All catalysts were obtained by wet impregnation (5% Pd loading). The Heck reaction can also be conducted in ionic liquids through promotion by microwave irradiation. Moreover the reaction of iodobenzene with methylacrylate in NMP was reported to be accelerated by ultrasound [75]. The ionic liquid containing the catalyst system was used five consecutive times with only a slight loss of activity (entry 5, Table 5.4) [76]. Perosa [77] reported the addition of a phase transfer catalyst to an ionic liquid as a method to accelerate the C-C coupling reaction. As far as we know, only by using ionic liquids has Pd on carbon been recovered and reused with success.

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