Nickel(II) Peroxide1

NiO2

[12035-36-8]  · NiO2  · Nickel(II) Peroxide  · (MW 90.69)

(reagent for oxidation of alcohols,2 phenols,3 and amines,4 and for dehydrogenation of heterocycles5)

Physical Data: black hydrous powder, reportedly a mixture of higher nickel oxides.

Form Supplied in: supplied as nickel peroxide hydrate, NiO2.xH2O, with Ni content >25%, active oxygen content >30%.

Preparative Methods: by treatment of alkaline nickel sulfate with sodium hypochlorite.2

Handling, Storage, and Precautions: as with most nickel compounds, a presumed carcinogen which should be handled with extreme care. Irritating to mucous membranes and upper respiratory tract. Causes dermatitis and may cause allergic respiratory reactions. Use in a fume hood.

Alcohol Oxidations.

Nickel peroxide has been used as a mild, selective reagent for the oxidation of a variety of primary alcohols to the corresponding carboxylic acids in alkaline medium. Saturated primary aliphatic alcohols oxidize cleanly, but some unsaturated alcohols, such as allyl alcohol, give mostly cleavage products. The scope of the reaction is illustrated by the oxidation of 1-butanol and cinnamyl alcohol to the corresponding acids (eqs 1 and 2).6 Oxidation of 6-hydroxymethyl-1-methyl-2-thiouracil to 1-methylorotic acid also involves replacement of sulfur by oxygen in the thiocarbonyl group (eq 3).7

When organic solvents such as petroleum ether or benzene are used in place of water, conversion of alcohols to the corresponding carbonyl compounds is observed. Although the reaction is poor with simple aliphatic alcohols, good to excellent yields of allylic or benzylic aldehydes and ketones are obtained using 1.0-1.2 equiv NiO2. Allyl alcohol, furfuryl alcohol, benzyl alcohol, and diphenylmethanol in benzene are all smoothly converted to the corresponding aldehyde or ketone in 78-98% yield.6 Oxidation of 3-phenylpropargyl alcohol under these conditions reportedly gives the aldehyde in 70% yield.8 The conversion of geraniol to citral (eq 4) is illustrative of the selectivity of this process.6 Oxidation of vitamin A1 to retinene6 and monooxidiation of the terpenoid diol lutein to 3-hydroxy-3-a-carotene9 are similarly achieved. Related alcohol oxidations were recently reported using NiO2 deposited on alumina.10 Oxidation of polyhydroxy compounds with NiO2 gives rise to various cleavage products similar to periodate oxidations, depending on the solvent and reaction conditions.11

Oxidation of Phenols.

Treatment of most simple phenols with NiO2 leads to polymerization, although oxidation of sterically cluttered phenols may lead to dimers, oligomers, or quinonoid structures, depending on the substitution pattern of the phenol.12 Thus oxidation of 2,6-di-t-butyl phenol gives rise to the dimeric 4,4-diphenoquinone (eq 5),12 while oxidation of more hindered phenols affords 3,5-disubstituted fuchsones (eq 6).3 NiO2 also oxidizes 4-cyanocatechol to the corresponding ortho-quinone, whereas Ag2O oxidation fails.13

Amides from Alcohols or Aldehydes.

Primary allenic alcohols are cleanly oxidized to the corresponding aldehydes with NiO2 in benzene (eq 7), but are converted to amides when the oxidation is carried out in the presence of ammonia (eq 8).14 Secondary allenic alcohols give the corresponding ketones when oxidized.

Oxidation of allylic and benzylic aldehydes with NiO2 in ether at -20 °C in the presence of ammonia also gives the corresponding amides in good yield, as illustrated by the conversion of piperonal to piperonamide (eq 9).15 At higher temperatures, an intermediate imine forms which is oxidized to the corresponding nitrile.15 In the absence of ammonia, oxidation of aldehydes leads to the corresponding acid,16 while oxidation of ketones in some cases affords 1,4-diketones via a dehydrodimerization process.17

Amine Oxidations.

NiO2 oxidation of primary aliphatic and benzylic amines affords the corresponding nitriles, while primary aromatic amines afford the symmetrical azo compounds. Thus oxidation of n-heptylamine gives n-hexyl cyanide (eq 10), while p-nitroaniline gives 4,4-azonitrobenzene (eq 11).4

Secondary aromatic amines undergo oxidative dimerization, affording the symmetrical hydrazines (eq 12).18

Oxidation of 1,2-diaminoaromatics leads to ring-opened dinitriles, although the yields are uniformly poor.19 Thus oxidation of o-phenylenediamine with NiO2 gives cis,cis-1,4-dicyano-1,3-butadiene (eq 13), whereas oxidation with Manganese Dioxide gives only 2,2-diaminoazobenzene.20

Heterocycle Synthesis.

Early work indicated that pyrazolines21 or indolines22 could be dehydrogenated to pyrazoles or indoles using NiO2 in refluxing benzene. Subsequent efforts showed that a variety of partially reduced oxygen-, sulfur-, and nitrogen-containing heterocycles could be cleanly dehydrogenated in hydrocarbon or halogenated solvents using NiO2.5 These findings included the previously unreported conversion of oxazolines to oxazoles. More recently, it has been found that dihydrotriazoles23 and flavanones24 are converted to triazoles and flavones, respectively, by oxidation with NiO2. Table 1 shows some representative examples of these transformations.5

Treatment of Schiff bases derived from o-aminophenols and benzaldehyde with NiO2 in benzene leads to benzoxazoles via an intramolecular oxidative cyclization (eq 14).25 The monoimines derived from o-phenylendiamine and substituted benzaldehydes are similarly cyclized to benzimidazoles.26 Hydrazones of pyridine-2-carbaldehyde and 2-acetylpyridine are also oxidatively cyclized to ring-fused triazoles by NiO2 in benzene (eq 15).27

Miscellaneous Reactions.

NiO2 oxidizes benzophenone hydrazone to diphenyldiazomethane in quantitative yield28 and, in the absence of solvent, converts diphenylmethane and fluorene to benzophenone and fluorenone in 79% and 66% yields, respectively.21 Thiols and sulfides give disulfides in high yield when treated with the reagent.29,30


1. George, M. V.; Balachandran, K. S. CRV 1975, 75, 491.
2. Nakagawa, K.; Konaka, R.; Nakata, T. JOC 1962, 27, 1597.
3. Becker, H. D. JOC 1967, 32, 2943.
4. Nakagawa, K.; Tsuji, T. CPB 1963, 11, 296 (CA 1963, 59, 3827).
5. Evans, D. L.; Minster, D. K.; Jordis, U.; Hecht, S. M.; Mazzu, A. L.; Meyers, A. I. JOC 1979, 44, 497.
6. Nakagawa, K.; Konaka, R.; Nakata, T. JOC 1962, 27, 1597.
7. Warrener, R. N.; Cain, E. N. TL 1967, 4953.
8. Atkinson, R. E.; Curtis, R. F.; Jones, D. M.; Taylor, J. A. CC 1967, 718.
9. Jensen, S. L.; Hertzberg, S. ACS 1966, 20, 1703.
10. Kim, K. S.; Cho, S. B.; Hahn, C. S. Bull. Korean Chem. Soc. 1991, 12, 116.
11. Nakagawa, K.; Igano, K.; Sugita, J. CPB 1964, 12, 403 (CA 1964, 61, 1789).
12. Sugita, J. Nippon Kagaku Zasshi 1966, 87, 603, 607, 741, 1082 (CA 1966, 65, 15522, 15262, 15522; CA 1967, 66, 94777).
13. Ansell, M. F.; Gosden, A. F. CC 1965, 520.
14. Bertrand, M.; Gil, G.; Viala, J. TL 1979, 1595.
15. Nakagawa, K.; Onoue, H.; Minami, K. CC 1966, 17.
16. Nakagawa, K.; Mineo, S.; Kawamura, S. CPB 1978, 26, 299.
17. Hawkins, E. G. E.; Large, R. JCS(P1) 1974, 280.
18. Sugita, J. Nippon Kagaku Zasshi 1967, 88, 659 (CA 1968, 69, 10319).
19. Nakagawa, K.; Onoue, I. TL 1965, 1433.
20. Bhatnagar, I.; George, M. V. JOC 1968, 33, 2407.
21. Balachandran, K. S.; Bhatnagar, I.; George, M. V. JOC 1968, 33, 3891.
22. Jansen, A. B. A.; Johnson, J. M.; Surtees, J. R. JCS 1964, 5573.
23. Kadaba, P. K.; Edelstein, S. B. S 1990, 191.
24. Mallik, U. K.; Saha, M. M.; Mallik, A. K. IJC(B) 1989, 28, 970.
25. Nakagawa, K.; Onoue, H.; Sugita, J. CPB 1964, 12, 1135 (CA 1965, 62, 541).
26. Balachandran, K. S.; George, M. V. IJC(B) 1973, 11, 1267.
27. Mineo, S.; Kawamura, S., Nakagawa, K. SC 1976, 6, 69.
28. Nakagawa, K.; Onoue, H.; Minami, K. CC 1966, 730.
29. Sugita, J. Nippon Kagaku Zasshi 1967, 88, 1237 (CA 1968, 69, 2640).
30. Nakagawa, K.; Shiba, S.; Horikawa, M.; Sato, K.; Nakamura, H.; Harada, N.; Harada, F. SC 1980, 10, 305.

Gary W. Morrow

The University of Dayton, OH, USA



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