Palladium-catalyzed carbonylation of benzyl chlorides to phenylacetic acids - A new two-phase process

Palladium-catalpzed carbonylation of substituted benzyl chlorides in a two-phase system at atmospheric carbon monoxide pressure generates the corresponding phenylacetic acids in 80-94% yield. The palladium catalyst is dissolved in the aqueous phase by using water-soluble phosphine ligands. The turnover numbers (TON) are higher than 1500 and turnover frequencies (TOF) of 135 h(-1) are reached. The length of the induction period observed is in inverse order to the phosphine-palladium ratio. The reaction rate is strongly dependent on the temperature and the initial substrate concentration. Continuous addition of substrates is increasing the life time of the catalyst. The proposed active species is generated via chloride- and hydroxy-bridged palladium dimers.