Benzene copper catalysts

In the 1930s, the Raschig Co. in Germany developed a different chlorobenzene-phenol process in which steam with a calcium phosphate catalyst was used to hydrolyze chlorobenzene to produce phenol (qv) and HCl (6). The recovered HCl reacts with air and benzene over a copper catalyst (Deacon Catalyst) to produce chlorobenzene and water (7,8). In the United States, a similar process was developed by the BakeHte Division of Union Carbide Corp., which operated for many years. The Durez Co. Hcensed the Raschig process and built a plant in the United States which was later taken over by the Hooker Chemical Corp. who made significant process improvements. 

Raschig (2) Also called Raschig-Hooker. A two-stage regenerative process for making phenol from benzene. The benzene is first chlorinated with hydrochloric acid in the presence of air, at 200 to 260°C, over a copper catalyst on an alumina base ... 

Another method for preparing 2-phenylbenzofurans through o-hydroxydeoxybenzoins (without isolating the latter) is the rearrangement of diazoacetophenones with a copper catalyst in the presence of phenol in benzene,400 which gives directly 63% phenoxyacetophenone and 26% 2-phenylbenzofuran [Eq. (1)]. 

A different approach that even obviates the use of a preformed silyllithium reagent takes advantage of the cleavage of the Si-Si bond of a disilane by a copper salt. Hosomi and co-workers185 have reported on the reaction of various enones or enals 250 with hexamethyldisilane or l,l,2,2-tetramethyl-l,2-diphenyldisilane, catalyzed by copper(i) triflate-benzene complex (Scheme 61). The transformation requires heating to 80-100 °C in DMF or DMI and the presence of tri-/z-butylphosphine in order to stabilize the copper catalyst under these harsh conditions. The addition products 251 were obtained with high yield after acidic work-up. The application of the method to alkylidene malonates as the Michael acceptor was recently disclosed.1... 

A -Cycloalkene-lA ioiits. a,couple intramolecularly to cyclic ene-l,4-diones in the presence of Cu(acac)2 in benzene at 60°. Other copper catalysts are unsatisfactory. The procedure fails when n is S or 6, but is satisfactory V ien n is 4 and >6. Both cis- and trans-isomers are formed, with the latter predominating exeept when n is 4. The products are reduced by sodium dithionite to cycloalkane-1,4-diones, which can be cyclized by NaOH to fus d-ring cyclo-pentenones when n is 7, 9,10, and 16. 

Only moderate yields of biphenyls result from the Gomberg reaction, in which an acidic solution of a diazonium salt is made alkaline with sodium hydroxide solution in a two-phase mixture with an aromatic hydrocarbon such as benzene (Scheme 8.20). A variation of this reaction uses a copper catalyst. The reaction is more successful in the intramolecular version and the Pschorr reaction (discussed in Chapter 12) offers a useful route to phenanthrene. 

The CuCli-CuO promoted hydrolysis is not solely limited to thioacetals—a variety of acetals are also deprotected [21]. Treatment of 26 with the copper catalysts in acetone-water afforded the spiroacetals 27 and 28 via concomitant hydrolysis of the thioacetal and benzylidene dioxy and ethoxyethyl acetals (Sch. 7) [22], Copper(II) chloride dihydrate has also been shown to hydrolyze a variety of acetals [23] and trityl groups can also be removed in the presence of copper sulfate in benzene to afford deprotected alcohols [24]. 

The copper and palladium transition metal catalysts noted in Table 18 proved to be superior to nickel, ruthenium and rhodium catalysts. The nature of the reacting species has not been unequivocally defined, but the following experimental observations may provide some insight (i) tetrahydrofuran solvent is essential for the palladium-mediated reactions, since complex reaction mixtures (presumably containing carbinols) were observed when the reactions were performed in either benzene or methylene chloride (ii) the reaction is truly catalytic with respect to palladium (2 mmol alkylaluminum, 0.05 mmol of Pd(PPh3)4), whereas the copper catalyst is stoichiometric and (iii) in the case where a direct comparison may be made (entries 1-8, Table 18), the copper-based system is superior to palladium catalysis with regard to overall yield. 

In contrast to silver-catalysed cumene oxidation, the evidence concerning the mechanism of copper-catalysed reactions favours radical initiation via surface hydroperoxide decomposition. Gorokhovatsky has shown that the rate of ethyl benzene oxidation responds to changes in the amount of copper(ii) oxide catalyst used, in a manner which is characteristic of this mechanism. Allara and Roberts have studied the oxidation of hexadecane over copper catalysts treated in various ways to produce different surface oxide species, Depending on the catalyst surface area and surface oxide species present, a certain critical hydroperoxide concentration was necessary in order to produce a catalytic reaction. At lower hydroperoxide levels, the reaction was inhibited by the oxidized copper surface. XPS surface analysis of the copper catalysts showed a... 

The magnitude of the effect is not unreasonable for promotion by nickel. The original activity was 0.040 (cm /minute at 310° and a space velocity of about 600 hour i). After 3 x lO s nvt, two samples had activities of 0.100 and 0.148 and, after repreparation, of 0.510 and 0.376. Apparent activation energies were 41 kcal/mole before irradiation, 17-18 after irradiation, and 17-20 after repreparation. Emmett and Skau (63) found zero conversion in benzene hydrogenation at 200° over a nearly pure copper catalyst (5 X 10 % Ni) and about 2% conversion on one containing 0.1 % nickel. These experiments are not easily compared quantitatively with Tet nyi s because of the different temperatures, but they demonstrate the promoting effect of a known addition of nickel. 

Figure 4.4 The specific activities of silica-supported ruthenium-copper and osmium-copper catalysts for the dehydrogenation and hydrogenolysis of cyclohexane, the former reaction yielding benzene and the latter alkanes (V. (Reprinted with permission from Academic Press, Inc.)...

Benzophen-oae, Diphenylmethanone diphenyl ketone benzoylbenzene. CwHwO mol wt 182.21. C 85.69%, H 5.53%, O 8.78%. CtHsCOCsHj. Prepd by the Friedel-Crafts ketone synthesis from benzene and benzoyl chloride in the presence of ASCI, Marvel, Sperry, Org Syn. call. vol. I (Wiley, New York, 2nd ed., 1941) p 95. By decarboxylation of o-benzoytbenzoic acid in the presence of copper catalyst L. F. Fieser, Organic Experiments (D. C. Heath Co., Boston, 1964) pp 201-203. 

It is difficult to replace aromatically bound halogen by a hydroxyl group. Hydrolysis of halobenzenes has been effected under pressure in the presence of alkali or after addition of catalytically active substances.526 There are numerous patents describing, e.g., the conversion of chlorobenzene into phenol 527 and phenols have been obtained from bromobenzene derivatives in an autoclave in the presence of copper catalysts.528 Hydrolysis of halo-benzene derivatives is easier if they contain electron-attracting substituents in the ortho- or /wra-position to the halogen. 

The copper specimen was inactive though face-centered. Pease and Purdum had previously indicated, however (23), that to obtain a copper catalyst active in the hydrogenation of benzene, the reduction of the oxide must be performed at low temperatures, and the inactivity of the catalyst of Long, Frazer, and Ott was attributed to overreduction. 

The very purest catalysts, prepared by reduction of copper sulfate solutions in an autoclave at ISO by hydrogen at 60 kg./sq. cm. pressure, consisted of large microcrystals, and would not hydrogenate benzene at 350° even at 100 kg./sq. cm. pressure. Other pure copper catalysts. 

Readily available A -r-butanesulfinylimine derivatives of aldehydes react with B2piii2 in the presence of the NHC-copper catalyst (ICy)Cu-O-t-Bu (5 mol%) to give high ratios of diastereomeric a-amino boronate estersJ Benzene is the solvent of choice, as lower yields are observed for the reaction below, run in toluene (69%), THF (50%), or dioxane (62%). Both alkyl and aryl aldimines participate to give dr s >95 5. The utility of this highly diastereoselective process was demonstrated by its application to a synthesis of bortezomib (Velcade), a U.S. Food Drug Administration (FDA)-approved and clinically useful protease inhibitor. ... 

In the first stage of this process, benzene is transformed into chlorobenzene with air and hydrochloric acid in the presence of a copper catalyst on an alumina base at 275 °C. To avoid the formation of polychlorinated benzenes as far as possible, conversion is limited to 15% and the process is operated with a large excess of benzene, so that only 5 to 8% dichlorobenzenes result. After the reaction mixture has been separated, the unconverted benzene is recycled the polychlorinated benzenes are refined to recover o-/p-dichlorobenzenes (see Chapter 5.8.2). 

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