Urushibara cobalt catalysts are modifications of the Urushibara nickel catalysts, just as Raney cobalt is a congener of Raney nickel. Their activities compare with that of Raney cobalt and have properties very similar to the corresponding useful nickel catalysts. However, they are less useful for general purposes, as their activities are somewhat less and they are more expensive. In catalytic reduction of nitriles or oximes Raney cobalt surpasses Raney nickel in depressing the formation of accompanying undesirable secondary amines. Likewise, the U-Co-B catalyst was used for the same purpose and proved to be more effective than U-Ni-B. In general, the cobalt catalysts are known to be less active than the nickel catalysts for hydrogenation of the ethylenic bond, U-Co-B can effect the selective reduction of unsaturated nitriles to unsaturated amines, leaving the ethylenic linkage intact.

It should be remembered that U-Co-B is entirely inactive when used in ethanol saturated with ammonia. Therefore, ammonia should be precluded from U-Co-B, even in the reduction of nitriles for which the presence of ammonia is usually preferable.

Urushibara Cobalt Catalysts

The preparative methods for Urushibara nickel catalysts can be applied without modification to the preparation of Urushibara cobalt catalysts, except that nickel chloride is replaced by cobalt chloride. Just as in the nickel catalysts, U-Co-B and U-Co-A are obtained from cobalt chloride with zinc dust; U-Co-BA is prepared using aluminum grains instead of zinc dust. As the atomic weights of cobalt and nickel are almost the same, the quantities described in the preparations of Urushibara nickel catalysts can be employed without alteration.

Preparation 19: U-Co-B

A 10 ml hot aqueous solution (90-100° C) containing 4.04 g of cobalt chloride (CoCl2 · 6H20) is added all at once with vigorous stirring to a hot mixture (90-100° C) of zinc dust (10 g) and water (4 ml) placed in a 100 ml flask on a boiling water bath. The reaction product (precipitated cobalt) is transferred to a 300 ml beaker and washed with 200ml of hot water. After 160 g of 10% sodium hydroxide solution has been added, the mixture is heated at about 50-55° C on a water bath for 15 minutes with occasional stirring. The supernatant liquor is then decanted and the residue is washed with two 100 ml portions of hot water, and then with two 50 ml portions of ethanol. About 6.5-7 g of catalyst, containing cobalt (ca. 1 g), zinc, zinc oxide, and a trace amount of alkali is obtained.

Preparation 20: U-Co-A

The precipitated cobalt obtained in Preparation 19 is treated with 160 ml of 13% acetic acid. The mixture is stirred for approximately 5 minutes until the evolution of hydrogen ceases and a solid rises to the surface of the solution, which in turn develops a pink color. To obtain an active catalyst, the coloration stage is indispensable. The solid is collected on a sintered glass filter and washed with 200 ml of hot water, then with 100 ml of ethanol. About 1-1.2 g of catalyst, containing about 0.8 g of cobalt together with small quantities of zinc and zinc oxide, is obtained.

Preparation 21: U-Co-CB

Similar to Preparation 7 (U-Ni-CB), except that the nickel chloride is replaced by cobalt chloride (CoCl2·6H2O), the weight being the same.

Preparation 22: U-Co-CA

Similar to Preparation 8 (U-Ni-CA), except that nickel chloride is replaced by cobalt chloride, and the volume of 10% acetic acid is changed to 150 ml. The precipitated cobalt can also be prepared from 4.04 g of cobalt chloride CoCl2 · 6H20 and 10 g of zinc dust as in Preparation 7.

Preparation 23: U-Co-B(s)

U-Co-B(s) is a U-Co-B catalyst prepared from crystalline cobalt chloride and zinc dust by a simplified method. To a mixture of zinc dust (5 g) and water (1 ml) placed in a 50ml beaker, add 2.02 g of commercial cobalt chloride crystals, CoCl2·6H20, (corresponding to 0.5 g of cobalt). The mixture is stirred well with a glass rod. A mild exothermic reaction begins to take place and the mixture becomes slushy in about 5 minutes. The precipitated cobalt is washed with 100 ml of cold water, and the washing water is removed by filtration or decantation. The precipitated cobalt is transferred to a 200 ml beaker and heated for 15 minutes at 50° C on a water bath with 80g of 10% sodium hydroxide solution. The supernatant liquor is decanted, and the remaining solid is washed twice with 50 ml of warm purified water, then twice with the same amount of ethanol.

Preparation 24 : U-Co-A(s)

The precipitated cobalt (corresponding to 0.5 g of cobalt) prepared by Preparation 23 from cobalt chloride crystals is placed in a 200 ml beaker to which 75 ml of 15% acetic acid is added, and the mixture is stirred at room temperature. In several minutes, the evolution of hydrogen ceases and a black solid comes to the surface of the solution, which becomes pink. The solid is collected on a sintered glass filter and washed with 200 ml of cold water, then with 100 ml of ethanol.

Preparation 25: U-Co-A(s) (HCl)

Precipitated cobalt (Preparation 23), corresponding to 0.5 g of cobalt, is placed in a 500 ml beaker, and stirred at room temperature with 200 ml of 0.75 N hydrochloric acid. Stir well to prevent the vigorous evolution of hydrogen, which tends to get out of control. Within one minute, a black solid comes to the surface of the solution, which becomes pink. At this stage, the solid is collected immediately on a sintered glass filter and washed with 200 ml of cold water, then with 100 ml of ethanol.

[1] "New Hydrogenation Catalysts" - by K. Hata, Halsted, New York (1971)