Acetaldehyde

aka U-Nickel

Uses

Primary

• Hydrogenation / Reduction reactions, particularly of nitro groups

vs Raney Nickel

It is not pyrophoric which distinguishes it from Raney Nickel.

Regarding the differences with Raney nickel (R-Ni), surface characterization by means of XPS had shown that R-Ni catalysts contain metallic aluminium in the activated phase as well as oxidized aluminium, while U-Ni catalysts contain metallic zinc in the activated phase in addition to oxidized zinc. Also, U-Ni catalysts can be described as supported nickel catalysts, while R-Ni catalysts are shown to have the well known skeletal structure.

The activity of U-Ni catalysts is very similar to R-Ni catalysts, both in nature of the reaction catalysed and in the rate of catalysis. One of the advantage of U-Ni is their simplicity of preparation, while R-Ni catalytic synthesis requires a long time. Despite this, U-Ni catalysts are also not very sensitive to impurities, so they can be prepared from commercial chemicals of ordinary grade, and they can be stored for a long time without decreasing the activity. Another advantage is the safer handling, since U-Ni catalysts are not inflammable upon contact with air, in contrast to Raney catalysts which are pyrophoric. This allows the catalyst to be recovered and regenerated. However, it should be noted that U-Ni catalyst durability is not satisfactory during the reaction, but this is also the case of R-Ni catalysts, so there is not really a big difference when it comes to practical use, maybe slightly supporting the use of U-Ni vs R-Ni as the former is less expensive and easy to produce and regenerate. The only real disadvantage of U-Ni catalysts is that for some particular reductions, they show less activity than R-Ni catalysts, favouring one reaction over another, for example U-Ni catalysts particularly favours the partial hydrogenation of acetylenic compounds to ethylenes

Natural Occurrence

• Does not occur naturally

Hazards

• Toxic in quantity

Production

Urushibara-A

Urushibara-A is used for reduction of nitro groups. The "A" comes from "acid", which is used to partially free the zinc from its nickel shell.

1. Dissolve nickel salts in an excess of hydrochloric acid to produce nickel chloride
2. Prepare a nickel chloride / hydrochloric acid solution, noting the amount of nickel in solution
3. Prepare a 5:1 molar excess of zinc proportional to the nickel
4. Rapidly immerse the zinc in the solution, producing (soluble) zinc chloride, as well as zinc particles partially coated in nickel
5. Filter
6. Discard filtrate
7. Dry residue
8. Prepare 15% v/v acetic acid solution
9. Immerse residue in solution
10. Agitate solution until it changes color from grey to faintly greenish (30-ish minutes)
11. Filter
12. Wash residue with distilled water
13. Wash residue with ethanol

See Also

• Original definition:Urushibara, Yoshiyuki (1952) "A New Method of Catalytic Hydrogenation"
  Bulletin of the Chemical Society of Japan 25(4); pp280. 
  DOI:10.1246/bcsj.25.280
  link courtesy Chemical Society of Japan.
• Raney nickel