Zinc chloride reagent

Zinc chloride was used as a catalyst in the Friedel Crafts benzylation of benzenes in the presence of polar solvents, such as primary alcohols, ketones, and water.639 Friedel-Crafts catalysis has also been carried out using a supported zinc chloride reagent. Mesoporous silicas with zinc chloride incorporated have been synthesized with a high level of available catalyst. Variation in reaction conditions and relation of catalytic activity to pore size and volume were studied.640 Other supported catalytic systems include a zinc bromide catalyst that is fast, efficient, selective, and reusable in the /wa-bromination of aromatic substrates.641... 

Anjaneyulu, A. S. R., Mallavadhani, U. V., Venkateswarlu, Y., and Ramaprasad, A. V. 1987. Reaction of acetic anhydride/zinc chloride reagent with phenols improved yields of hydroxyacetophenones. Ind. J. Chem. 26B 823-826. 

Robertson and Speedie were unable to sjmthesize a benzylidene acetal of methyl D-xylofuranoside, either with the benzaldehyde-zinc chloride reagent or with benzaldehyde alone at 140-150°. 

There are also a number of procedures for cross coupling of indoles. 3-Bromoindole protected with a 1-TBDMS group can be converted to 3-zinc chloride reagents by lithiation followed by... 

Add 5 mL of the hydrochioric acid-zinc chloride reagent (Lucas reagent) to about 0.5 mL of the compound in a test tube. Stopper the tube and shake it allow the mixture to stand at room temperature. Try this test with known primary, secondary, and tertiary alcohols, and note the time required for the formation of an alkyl chloride, which appears either as a second layer or as an emulsion. Repeat the test with an unknown, and compare the result with the results from the knowns. 

The lithium reduction of zinc (II) cyanide using naphthalene or biphenyl as a catalytic electron carrier yields a more reactive form of Rieke zinc. This new form of Rieke zinc is able to undergo direct oxidative addition to alkyl chlorides under mild conditions and tolerates the presence of nitriles and bulky tertiary amides [17]. Table 3.5 shows representative reactions of alkyl zinc chloride reagents with benzoyl chloride. The activation of the zinc surfeice could originate by the adsorption of the Lewis base cyanide ion on the metal surface. The adsorbed cyanide ion can affect the metal s reactivity in two possible ways. One possible mode of activation would be the reduction of the metal s work function in the vicinity of the adsorbed cyanide ion, and the second could be that the cyanide ion is acting as a conduction path for the transfer of the metal s electrons to the alkyl chloride. One or both processes could account for the observed enhanced chemical reactivity. 

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