Copper Bronze1

Cu

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

(Ullmann coupling;6 thermal decomposition of diazo compounds;9 vinyl ether synthesis;10 Guerbet reaction3)

Physical Data: mp 1083 °C; bp 2595 °C; d 8.95 g cm-3.

Solubility: slowly sol in ammonia water.

Form Supplied in: copper-colored, finely ground powder; commercially available.

Preparative Methods: copper bronze can be activated either by the method of Vogel1a or by addition of a 2% solution of iodine in acetone.2

Handling, Storage, and Precautions: may lose its activity due to aging. Flammable when exposed to heat, sparks, and open flame. Irritant. May discolor on exposure to air and moisture. Incompatible with strong acids, strong oxidizing agents, acid chlorides, and halogens. Use of safety goggles and chemical-resistant gloves is strongly recommended. Avoid breathing the dust. Avoid contact in eyes, on skin, on clothing.

Guerbet Reaction.

Preparation of ethylhexanol from butanol occurs within an autoclave at autogenous pressures of 50-60 atm and temperatures of about 300 °C in the presence of the hydrogenation-dehydrogenation catalyst, copper bronze. Butanol is first dehydrogenated to an aldehyde in the presence of sodium and copper bronze before undergoing aldol condensation and subsequent dehydration. The resulting a,b-unsaturated aldehyde is then hydrogenated, yielding 2-ethylhexanol.3

Ullmann Coupling.

Under Ullmann conditions,6 halogen-substituted aromatic compounds react with organic halides in the presence of activated copper bronze1b,2,4 to give the corresponding coupled products in moderate yields. A recent example is the synthesis of perfluoroalkyl-substituted aromatic aldehydes via the coupling of two different substrates (i.e. perfluorooctyl iodide and p-iodobenzaldehyde) (eq 1).5

Thermal Decomposition of Diazo Compounds.

Copper bronze can promote the intramolecular cyclization of diazo ketones in boiling cyclohexane (eq 2); anhydrous Copper(II) Sulfate in boiling THF can also be used.7 Other diazo compounds that have been shown to undergo copper-catalyzed thermal decomposition include ethyl diazopyruvates in the presence of enol ethers or alkynes8 and diazoacetates (eq 3).9

Vinyl Ether Synthesis.

Rearrangement of b-alkoxycyclopropanecarboxylates in the presence of copper bronze catalyst produces vinyl ethers (eq 4). Vicinal alkoxy and ethoxycarbonyl groups activate the substrate as the reaction proceeds.10

Related Reagents.

Copper.


1. Vogel's Textbook of Practical Organic Chemistry, 5th ed.; Wiley: New York, 1989; p 426. (b) Ref. 1(a), p 837. (c) FF 1967, 1, 155; 1972, 3, 62; 1974, 4, 100; 1984, 11, 49; 1986, 12, 140.
2. Fuson, R. C.; Cleveland, E. A. OSC 1955, 3, 339.
3. Weizmann, C.; Bergmann, E.; Sulzbacher, M. JOC 1950, 15, 54.
4. Weber, E.; Csöregh, I.; Stensland, B.; Czulger, M. JACS 1984, 106, 3297.
5. Paciorek, K. J. L.; Masuda, S. R.; Shih, J. G. JFC 1991, 53, 233.
6. Fanta, P. E. S 1974, 9.
7. Chakrabortty, P. N.; Dasgupta, R.; Dasgupta, S. K.; Ghosh, S. R.; Ghatak, U. R. T 1972, 28, 4653.
8. Wenkert, E.; Alonso, M. E.; Buckwalter, B. L.; Sanchez, E. L. JACS 1983, 105, 2021.
9. Joshi, G. S.; Kulkani, G. H.; Shapiro, E. A. CI(L) 1989, 424.
10. Doyle, M. P.; Van Leusen, D. JACS 1981, 103, 5917.

Edward J. Parish & Stephen A. Kizito

Auburn University, AL, USA



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