Studies on the Silk-Palladium Catalyst. II. General Properties

Abstract 1. The silk-palladium catalyst was found to catalyze the hydrogenation of aliphatic C=C double bonds, aldehyde, nitriles and nitro groups directly attached to aromatic rings, azobenzene, and some oximino groups, but relatively weakly that of aliphatic nitro groups. The catalyst was completely inactive to aromatic C=C double bonds, aliphatic carbonyl (with the exception of α-ketoglutarate which was reduced to glutamate in the presence of ammonia), nitriles, and several oximes. 2. The catalyst, when used once, considerably increased its catalytic activity and this elevated activity persisted after several repeated uses. 3. Ethyl mercaptan was poisonous to the catalyst probably due to its combination with the active palladium atoms. Ferric and cupric ions inhibited the catalyst by forming chelate linkages with the carrier protein. The inhibition by these metal ions could be restored by ethylenediamine tetraacetic acid. Acetylation of the catalyst with acetic anhydride markedly reduced the activity, although the treatment of silk fibroin with acetic anhydride prior to the preparation of the catalyst gave a strongly active catalyst.