Benzoic anhydride, cross-coupling

A co-solvent that is poorly miscible with ionic liquids but highly miscible with the products can be added in the separation step (after the reaction) to facilitate the product separation. The Pd-mediated FFeck coupling of aryl halides or benzoic anhydride with alkenes, for example, can be performed in [BMIM][PFg], the products being extracted with cyclohexane. In this case, water can also be used as an extraction solvent, to remove the salt by-products formed in the reaction [18]. From a practical point of view, the addition of a co-solvent can result in cross-contamination, and it has to be separated from the products in a supplementary step (distillation). More interestingly, unreacted organic reactants themselves (if they have nonpolar character) can be recycled to the separation step and can be used as the extractant co-solvent. 

A Rh(I) catalyst has likewise been found to promote cross-coupling between readily available benzoic acids as arylating agents and arenes bearing N-based directing groups such as pyridinyl, heteroaryl, and iminyl moieties (Scheme 22.34). The process involves the intermediacy of a mixed anhydride formed in situ by the reaction between the benzoic acid and (f-BuCO)jO [49]. 

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