Contribution of phase transfer to resolve the problem of separation between the catalyst and the product in the catalytic carbonylation of halides.

Study of carbonylation of benzyl bromide in a biphasic liquid-liquid system shows that the catalytic ion pair Bu₄N⁺Co(CO)₄^? stays in the organic layer and that the carbonylated product C₆H₅CH₂CO₂^? stays in the aqueous one.