The Mechanism of Palladium-catalyzed Oxychlorination of Propylene

Abstract

The mechanism of oxychlorination of propylene over supported metallic palladium catalyst was studied. The change in the products formation with time was observed after the supply of one of the reactants (oxygen or hydrogenchloride) was stopped. If the feed of oxygen was stopped, the rate of allyl chloride formatidn fell slowly to zero in about 30 miutes, whereas that of isopropyl chloride did not change. On the other hand, if the feed of hydrogenchloride was stopped the rate of allyl chloride formation fell $lowly to zero in about an hour, wbereas that of isopropyl chloride fell to zero in a few minutes. These observations suggested that the chloride species participating in allyl chloride formation were held strongly on palladium surface, but those related to isopropyl chloride were comparatively held weakly. The fact that considerable amount of palaladium chloride was formed in the catalyst during oxychlorination and the amount of it depended on the reaction condition suggested the chloride species concerning allyl chloride formation being chloride anion which has been oxidatively adsorbed on the palladium.
Some cocatalysts (active carbon, cupric chloride and nitric acid) which had been considered to promote the oxidation of palladium, accelerated the rate of allyl chloride formation.
The mechanism was analyzed by the kinetic method.