Copper1

Cu

[7440-50-8]  · Cu  · Copper  · (MW 63.54)

(reagent for the cyclization and/or coupling of various functional groups;1 decarboxylation;10 preparation of a-alkynic alcohols;12 cyclopropanes,13 nitriles,15 ketones by benzylic oxidation10)

Physical Data: mp 1083 °C; d 8.94 g cm-3.

Solubility: slowly sol aq NH3.

Form Supplied in: reddish, lustrous solid; ingots, sheets, wire, or powder (most synthetic reactions require the use of the powder form); widely available.

Analysis of Reagent Purity: by electrolytic assay,21 or EDTA/iodometric titration.1d

Handling, Storage, and Precautions: should be stored in the absence of moisture; in moist air it gradually becomes coated with copper carbonate. The powder may be flammable when exposed to excessive heat or flame.

Ullmann Reaction.

Alkyl halides containing electron-attracting substituents may be coupled in the presence of copper in good yields.1 The reaction is believed to proceed through organocopper intermediates, in an oxidant addition, rather than radicals.2 Details for the activation of the copper catalyst by iodine in acetone are described along with the Ullmann coupling of 2-chloronitrobenzene to yield 2,2-dinitrobiphenyl.3

Procedures for the preparation of unsymmetrical biaryls from a mixture of halides have been described.4 Similarly, the coupling of vinyl bromides by copper in a stereospecific synthesis of conjugated dienes has also been reported.5 A highly reactive copper powder has been developed that is particularly effective for Ullmann reactions.6

Other Ullmann-type coupling reactions include the reaction of phenols with aryl halides to yield diaryl ethers,7 the synthesis of triarylamines through the coupling of diarylamines with aryl halides,8 the cross coupling of allylic and benzylic bromides with acid chlorides,6b and the cyclization of epoxyalkyl halides.9

Decarboxylation.

Commercial copper powder in quinoline solution is a standard reagent for decarboxylation reactions.10 In some instances, decarboxylation and dehydration occur to produce an exocyclic alkene.11

a-Acetylenic Alcohols.

Heating 1,4-diformyloxy-2-butyne with copper and adipic acid followed by treatment with acid and methanol gives 2-butyn-1-ol.12

Cyclopropanes.

In the presence of copper, a-diazo ketones decompose and react with alkenes to yield cyclopropyl ketones by intermolecular or intramolecular cyclization.13 Also, copper assists the reaction of alkenes with gem-dihalides to produce cyclopropanes.14

Nitriles.

Nitriles may be prepared from aromatic aldehydes by reaction with copper powder and ammonium chloride (in situ preparation of CuCl2 and NH3).15

Ketones.

The formation of ketones has been reported to result from benzylic oxidation using a copper powder catalyst (eq 1).16 The initial oxidized product (2) may further cyclize to (3) by continued use of the same reagent. The latter reaction is similar to tetramethoxydibenzofuran formation resulting from heating 4-bromo-5-iodoveratrole with copper in nitrobenzene.17

Other minor reactions of copper include its use as a catalyst in the synthesis of azo compounds from diazonium tetrafluoroborates,18 rearrangements of bicyclic hydrocarbons,19 and in the classic Gattermann version of the Sandmeyer reaction for the conversion of arenediazonium salts to halides.20

Related Reagents.

Copper Bronze; Sodium Iodide-Copper.


1. (a) Fanta, P. E. CRV 1964, 64, 613. (b) Fanta, P. E. S, 1974, 9. (c) Sainsbury, M. T 1980, 36, 3327. (c) Miayano, S.; Tobita, M.; Hashimoto, H. BSF(2) 1981, 54, 3522; SC 1993, 23, 2463. (d) Dictionary of Organometallic Compounds; Buckingham, J., Ed.; Chapman & Hall: New York, 1984; Vol. 1, p 569. For reviews of properties, uses, and inorganic chemistry of copper, see, e.g. (e) Massey, A. G. In Comprehensive Inorganic Chemistry; Trotman-Dickenson, A. F., Ed.; Pergamon: New York, 1973; Vol. 3, pp 1-78; (f) Tuddenham, W. M.; Dougall, P. A. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Wiley: New York, 1979; Vol. 6, pp 819-869. For further reviews of the use of copper in organic synthesis, see, e.g. (g) Young, G. B. In Comprehensive Organometallic Chemistry; Wilkinson, G.; Stone, F. G. A.; Abel, E. W., Eds.; Pergamon: New York, 1982; Vol. 9, p 1529 and references cited therein.
2. (a) Cohen, T.; Poeth, T. JACS 1972, 94, 4363. (b) Cohen, T.; Cristea, I. JACS 1976, 98, 748.
3. Fuson, R. C.; Cleveland, E. A. OSC 1955, 3, 339.
4. (a) Brown, E.; Robin, J.-P. TL 1977, 2015. (b) Brown, E.; Robin, J.-P. TL 1978, 3613.
5. (a) Cohen, T.; Poeth, T. JACS 1972, 94, 4363. (b) Lewin, A. H.; Zovko, M. J.; Rosewater, W. H.; Cohen, T. CC 1976, 80.
6. (a) Rieke, R. D.; Rhyne, L. D. JOC 1979, 44, 3445. (b) Ebert, G. W.; Rieke, R. D. JOC 1984, 49, 5280.
7. (a) Ungnade, H. E.; Orwoll, E. F. OSC 1955, 3, 566. (b) Lindley, J. T 1984, 40, 1433.
8. (a) Hager, F. D. OSC 1941, 1, 544. (b) Gauthier, S.; Fréchet, J. M. J. S 1987, 383.
9. (a) Wu, T.-C.; Rieke, R. D. TL 1988, 29, 6753. (b) Rieke, R. D.; Wehmeyer, R. M.; Wu, T.-C.; Ebert, G. W. T 1989, 45, 443.
10. (a) Manecke, G.; Rotter, U. CB 1973, 106, 1116. (b) Smith, N. R.; Wiley, R. H. OSC 1963, 4, 337. (c) Burness, D. M. OSC 1963, 4, 628. (d) Wiley, R. H.; Smith, N. R. OSC 1963, 4, 731. (e) Walling, C.; Wolfstirn, K. B. JACS 1947, 69, 852.
11. Vilkas, M.; Abraham, N. A. BSF(2) 1960, 1196.
12. Himmele, W.; Fliege, W.; Fröhlich, H. S 1973, 615.
13. (a) Novák, J.; Ratuský, J.; &SSbreve;neberk, V.; &SSbreve;orm, F. CCC 1957, 22, 1836. (b) Ratuský, J.; &SSbreve;orm, F. CCC 1958, 23, 467. (c) Novák, J.; &SSbreve;orm, F. CCC 1958, 23, 1126. (d) Stork, G.; Ficini, J. JACS 1961, 83, 4678. (e) Doering, W. Von E.; Fossel, E. T.; Kaye, R. L. T 1965, 21, 25. (f) Baldwin, J. E.; Fogelsong, W. D. TL 1966, 4089. (g) Monahan, A. S. JOC 1968, 33, 1441.
14. Kawabata, N.; Naka, M.; Yamashita, S. JACS 1976, 98, 2676.
15. Capdevielle, P.; Lavigne, A.; Maumby, M. S 1989, 451.
16. Farrell, P. G.; Moskowitz, D.; Terrier, F. SC 1993, 23, 231.
17. Baker, W.; Barton, J. W.; McOmie, J. F. W.; Penneck, R. J.; Watts, R. L. JCS 1961, 3986.
18. Cadogan, J. I. G.; Hibbert, P. G.; Siddiqui, M. N. U.; Smith, D. M. JCS(P1) 1972, 2555.
19. Burger, U.; Mazenod, F. TL 1976, 2885.
20. Bigelow, L. A. OSC 1941, 1, 135.
21. Reagent Chemicals: American Chemical Society Specifications, 8th ed.; American Chemical Society: Washington, DC, 1993; pp 272-274.

Edward J. Parish

Auburn University, AL, USA



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