Study On Dehydration Of Amides Catalyzed By Palladium Catalysts

Nitriles are important raw materials for organic synthesis,and they can be converted into primary amines,carboxylic acids,amides,esters and nitrogen-containing heterocyclic compounds.It is of great significance to develop more simple method for the preparation of nitriles in order to reduce pollution and cost of production.In this paper,the new development in the preparation of nitriles by catalytic dehydration of amides is reviewed,and the catalytic effect of resin-supported palladium catalyst on the dehydration of amides was studied.Because 4-hydroxybenzonitrile has been widely used in the preparation of medicine,pesticide and liquid crystal materials,the factors influencing the dehydration reaction of4-hydroxybenzamide catalyzed by palladium were studied in detail,which laid a foundation for industrial applications.Firstly,a method for preparing polymer supported palladium catalyst was investigated using ion-exchange resin as a carrier,and it was prepared using highly acidic ion-exchange resin(001?7 H)and palladium chloride.The correlations of loading amount of Pd on resin with the type of ion-exchange resins,Pd sources,adsorption time,p H value and so on were investigated.Under the optimized conditions,the resin-supported palladium catalyst can effectively catalyze the dehydration of various amides to corresponding nitriles at 60 °C,with acetonitrile as dehydrating agent and mixture of water and acetonitrile as solvent.The yield is mostly between 60%～80%,and the yield of 4-hydroxybenzonitrile is the highest(up to 96%).The reaction conditions are mild,and water is used as solvent.There is no waste acid and gas produced;the catalyst is easy to reuse.It is an environment-friendly method.Based on the above research,the catalytic behaviors of two different palladium catalysts for dehydration of 4-hydroxybenzamide was further studied.The first is the self-made resin-supported palladium catalyst,which is easy to recover and reuse.It was found that the deactivation of the catalyst was related to the residual ammolnium salt in the raw material.Purification of 4-hydroxybenzamide can increase the yield of dehydration reaction and the times of catalyst recycle.When 4-hydroxybenzamide purified through adsorption of resin was used as raw material,yield of 4-hydroxybenzonitrile still reached 90% after the self-made supported palladium catalyst was reused 5 times.However,if the catalyst continues to be reused,the effect of the catalyst will be greatly reduced.The second is unsupported palladium chloride which was used in the dehydration of 4-hydroxybenzamide.The conditions of the dehydration reaction and the regeneration method of deactivated palladium chloride were studied.4-Hydroxybenzonitrile was synthesized by dehydration of 4-hydroxybenzamide purified by strong acid resin in 94% yield using palladium chloride(5 mol %)as catalyst.The deactivated palladium chloride can recover its catalytic activity when it is deaminated at high temperature under vacuum or atmospheric pressure.