Acylation zinc oxide

Acylation. Zinc oxide is found to be a good catalyst for acylation of ferrocene. 

The preparation of ketones from aromatic hydrocarbons and acyl chlorides in the presence of zinc metal or zinc oxide was reported by Grucareviz and Merz in the same year, and by Doebner and Stackman in 1876. Despite all authors having recognized the presence of zinc chloride in the final reaction mixture, no mention was made of the possible role of a metal halide as catalyst in the reaction. 

Table 4.14 Acylation of aromatics with acyl chlorides in the presence of zinc oxide...

Zinc oxide, an inexpensive and commercially available inorganic solid, can be utilized as an efficient catalyst in the Friedel-Crafts acylation of activated and unactivated aromatic compounds with acyl chlorides at room temperature for 5 to 120 min (Table 4.14). Acylation is claimed to occur exclusively at the para-position of the monosubstituted aromatic compounds. The catalyst can be recovered and reused, after washing with methylene chloride, for at least two further cycles, showing quite similar high yield (-90%) in the model benzoylation of anisole. Mechanistically, it seems that zinc chloride can be the true catalyst, generated in situ by the reaction of zinc oxide with hydrogen chloride. 

Sarvari, M. H. and Sharghi, H. 2004. Reactions on a solid surface a simple, economical and efficient Friedel-Crafts acylation reaction over zinc oxide (ZnO) as a new catalyst. /. Org. Chem. 69 6953-6956. 

The Friedel-Crafts reaction involves an electrophilic aromatic substitution that facilitates the alkylation or acylation of arenes (135) and heterocyclic compounds catalyzed by acidic catalysts. Zinc oxide has been found to be an effective catalyst for the Friedel-Crafts acylation of activated and nonactivated aromatic compounds (135) (Hosseini-Sarvari and Sharghi 2004) under solvent-free and room temperature conditions (Scheme 9.44). The catalyst provides a large surface area for the reaction. This Friedel-Crafts reaction is a safe and environmentally benign method which requires simple workup, mild reaction conditions and a short reaction time. 

Type of reaction C-C bond formation Reaction conditions Solvent-free, room temperature Synthetic strategy Solid-supported Friedel-Crafts acylation Catalyst Zinc oxide (ZnO) powder... 

Keywords Aromatic compounds, acid chlorides, zinc oxide powder, solvent-free, room temperature, Friedel-Crafts acylation, acyl derivatives... 

With Acyl Halides, Hydrogen Halides, and Metallic Halides. Ethylene oxide reacts with acetyl chloride at slightly elevated temperatures in the presence of hydrogen chloride to give the acetate of ethylene chlorohydrin (70). Hydrogen haUdes react to form the corresponding halohydrins (71). Aqueous solutions of ethylene oxide and a metallic haUde can result in the precipitation of the metal hydroxide (72,73). The haUdes of aluminum, chromium, iron, thorium, and zinc in dilute solution react with ethylene oxide to form sols or gels of the metal oxide hydrates and ethylene halohydrin (74). 

Synthesis of the remaining half of the molecule starts with the formation of the monomethyl ether (9) from orcinol (8). The carbon atom that is to serve as the bridge is introduced as an aldehyde by formylation with zinc cyanide and hydrochloric acid (10). The phenol is then protected as the acetate. Successive oxidation and treatment with thionyl chloride affords the protected acid chloride (11). Acylation of the free phenol group in 7 by means of 11 affords the ester, 12. The ester is then rearranged by an ortho-Fries reaction (catalyzed by either titanium... 

A few further general examples of zinc catalytic activity or reactivity include the following. Other zinc-containing systems include a zinc phenoxide/nickel(0) catalytic system that can be used to carry out the chemo- and regioselective cyclotrimerization of monoynes.934 Zinc homoenolates have been used as novel nucleophiles in acylation and addition reactions and shown to have general utility.935,936 Iron/zinc species have been used in the oxidation of hydrocarbons, and the selectivity and conditions examined.362 There are implications for the mechanism of metal-catalyzed iodosylbenzene reactions with olefins from the observation that zinc triflate and a dizinc complex catalyze these reactions.937... 

For example, the reaction of nitronates (123) with a zinc copper pair in ethanol followed by treatment of the intermediate with aqueous ammonium chloride a to give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating of this mixture b affords pyocoles (126). Successive treatment of nitronates (123) with boron trifluoride etherate and water c affords 1,4-diketones (127). Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5% rhodium on aluminum oxide e gives a-hydroxypyrrolidines (128) or pyrrolidines 129, respectively. Finally, smooth dehydration of a-hydroxypyrrolidines (128) into pyrrolines (130f) can be performed. 

Tetrafluoroammonium hexafluoromanganate, 4378 Tetrafluoroammonium hexafluoronickelate, 4379 Tetrafluoroammonium hexafluoroxenate, 4380 Tetranitromethane, 0543 Titanium tetraperchlorate, 4164 1,1,1 -Triacetoxy-1,2-benziodoxol-3-one, 3604 Trifluoromethyl hypofluorite, 0352 Trimethylsilyl chlorochromate, 1297 Trioxygen difluoride , 4317 Uranium hexafluoride, 4369 Vanadium trinitrate oxide, 4758 Vanadium(V) oxide, 4860 Vanadyl perchlorate, 4146 Xenon hexafluoride, 4371 Xenon tetrafluoride, 4347 Xenon tetrafluoride oxide, 4340 Xenon tetraoxide, 4857 Xenon trioxide, 4851 Xenon(II) pentafluoroorthoselenate, 4376 Xenon(II) pentafluoroorthotellurate, 4377 Zinc permanganate, 4705 ACETYLENIC PEROXIDES ACYL HYPOHALITES ALKYL HYDROPEROXIDES ALKYL TRIALKYLLEAD PEROXIDES AMINIUM IODATES AND PERIODATES AMMINECHROMIUM PEROXOCOMPLEXES BIS (FLUOROOXY)PERHALOALKANES BLEACHING POWDER CHLORITE SALTS... 

Lithium and magnesium of the metallated N-oxides 369 and 371 were readily replaced with zinc or boron. The boronic esters were very unstable undergoing deborylation. The zinc salts 373 were fairly stable and reacted with acyl chloride affording 1,2,3-triazolylketone 374 (2010UP2) (Scheme 113). 

Cyclic orthoesters derived from gem-diols offer a further route to alkenes. As part of a three-step conversion, they may be ring opened with hydrobromic acid to give O-acyl bromodeoxy compounds that undergo reductive elimination with copper-zinc. In this way, unsaturated nucleosides have been made by way of mixed 2y3,-bromo-2y3,-deoxy-3,/2, carboxyl-ates.174 A more direct route to alkenes from cyclic orthoesters involves heating in acetic anhydride together with zirconium oxide.175... 

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