Nickel(II) Acetate

(AcO)2Ni.4H2O

[6018-89-9]  · C4H14NiO8  · Nickel(II) Acetate  · (MW 248.87)

(autoxidation catalyst;1 hydrogenation catalyst;2 catalyst for isomerization of aldoximine4 to amides;3 template for Schiff base condensations4)

Physical Data: decomposition above 250 °C; d = 1.798 g cm-3.

Solubility: sol H2O and MeOH; insol most organic solvents.

Form Supplied in: widely available as tetrahydrate in high purity as a green powder or small crystals.

Purification: anhydrous nickel acetate can be obtained by heating the tetrahydrate to 100 °C under vacuum over P2O5 or other desiccants.

Handling, Storage, and Precautions: excellent shelf life, carcinogen, toxic.

Autoxidation of Benzoin.

Anhydrous nickel acetate in methanol can be used to catalyze the autoxidation of benzoin to benzil.1 The reaction is first order in nickel acetate and in benzoin, and extensive mechanistic studies suggest that a complex is formed between nickel acetate and benzoin that subsequently reacts rapidly with dioxygen. Both formaldehyde and H2O2 were identified as byproducts. No other a-hydroxy ketones have been studied.

Hydrogenation.

A heterogeneous catalyst for hydrogenation can be prepared from Sodium Hydride, RONa, and Ni(OAc)2 and used for hydrogenation of alkynes, alkenes, and carbonyl compounds at room temperature and atmospheric pressure.2 The catalyst is prepared by adding a stirred suspension of 1 equiv anhydrous Ni(OAc)2 in THF to 6 equiv NaH. After heating to 45 °C, 2 equiv of the desired alcohol, for example t-pentyl alcohol, is added and heating is continued for 3 h. The resulting solution is used directly for reduction of 1 equiv of substrate at room temperature for reaction times of 5-60 min. This catalyst selectively reduces alkynes to cis-alkenes in reaction times of 10-20 min. Conjugated dienes react more slowly, so that a mixture of dienes may be selectively reduced as well. Ketones are reduced to alcohols more slowly, requiring 2-9 h for completion of the reaction. See Sodium Hydride-Nickel(II) Acetate-Sodium t-Pentoxide.

Isomerization of Aldoximes to Amides.

Aldoximes are isomerized to amides by heating in xylenes in the presence of 0.2-5.6 mol % Ni(OAc)2 as catalyst.3 For example, benzaldoxime is converted to benzamide in 91% purified yield by heating to reflux in xylenes for 5 h with 2 mol % catalyst (eq 1). Aliphatic oximes, including acid-sensitive ones, and aromatic oximes with either electron-donating or -withdrawing substituents are all good substrates for this reaction.

Schiff Base Condensations.

Simple nickel(II) salts such as Ni(OAc)2 are used as templates for Schiff base condensation of amines with carbonyl compounds to form polydentate nickel chelates.4 In particular, acetylacetone and its analogs will condense with 1,2-Diaminoethane to form a macrocyclic complex. The reaction is exemplified with phenyldiazomalondialdehyde (eq 2).


1. Hammond, G. S.; Wu, C. S. JACS 1973, 95, 8215.
2. Brunet, J. J.; Gallois, P.; Caubere, P. JOC 1980, 45, 1937.
3. Field, L.; Hughmark, P. B.; Shumaker, S. H.; Marshall, W. S. JACS 1961, 83, 1983.
4. L'Eplattenier, F. A.; Pugin, A. HCA 1975, 58, 2283.

Cynthia J. Burrows & Shiow-Jyi Wey

State University of New York at Stony Brook, NY, USA



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