Alumina-supported copper halides

Alkoxybenzenes were highly regioselectively halogenated by use of copper(II) halides supported on alumina to give 4-halo-alkoxybenzenes in high yield. Bromination of alkoxybenzenes with alumina-supported copper(II) bromide occurred at lower temperature than chlorination with alumina-supported copper(II) chloride (ref. 14). 

The yield increased with increasing the ratio of alumina-supported copper(II) bromide to alkoxybenzenes. The size of alkoxy group did not influence significantly the yield and the ratio of p/o. Nonpolar solvents such as benzene and hexane were better than polar solvent. Polar solvents such as chloroform and tetrahydrofiiran decreased the yield. It is suggested that these polar solvents may be strongly adsorbed on the surface of the reagent. The reaction did not proceed in ethanol to be due to the elution of copper(II) bromide from the alumina to the solution. It is known that the reaction of aromatic hydrocarbons with copper(II) halides in nonpolar solvents proceeds between aromatic hydrocarbons and solid copper(II) halides and not between hydrocarbons and dissolved copper(II) halides (ref. 6). 

Kantam et al. [59] reported the synthesis of alumina-supported copper NPs from copper(ll) acetylacetonate and aluminum isopropoxide precursors using aerogel protocol. The NPs were characterized by XRD, TEM, Al MAS NMR, X-ray photoelectron spectroscopy (XPS), and ICP-AES. Cu-AiPj NPs are used for the preparation of 1,2,3-triazoles by the reaction of terminal alines, sodium azide, and alkyl/allyl halides (Scheme 5.17). 

Surprisingly, palladium(II) salts supported on NaY zeolite produce DMC, even without halogens. The preferred support seems to be active carbon compared to zeolites because of higher DMC selectivities based on both MN and carbon monoxide, >95% in the case of active carbon and 80-90% in the case of zeolites. Palladium chloride/copper chloride on active carbon is likely used as a catalytic system in the industrial process. Because the carbonylation of MN to DMC occurs without water coproduction, the use of palladium salts as catalysts does not adversely affect selectivity. In the carbonylation reactor outlet some amount of methyl-chloroformate is present, as expected because it is known that palladium(II) chloride supported on alumina or silica catalyzes the reaction between MN, CO, and HCl to give methylchloroformate. " The presence of halide ions in the catalytic system and the methylchloroformate generation likely raise some corrosiveness issues. 

The synthesis of 1,2,3-triazole derivatives by a three-component coupling of alkyl (benzyl) halides or aryl boronic acids, sodium azide, and terminal alkynes over copper(II) sulfate supported on alumina (CU/AI2O3,10 mol%) has been developed [117]. 

---