Zinc metal reactions with

Silver can be prepared from aqueous silver nitrate by reaction with zinc metal. Zinc nitrate is formed. 

Consider, for example, the net-ionic equation (the equation showing just the chemical substances that are changed during a reaction — see Chapter 8) for a reaction with zinc metal and an aqueous copper(Il) sulfate solution ... 

The classical Reformatsky reaction consists of the treatment of an a-halo ester 1 with zinc metal and subsequent reaction with an aldehyde or ketone 3. Nowadays the name is used generally for reactions that involve insertion of a metal into a carbon-halogen bond and subsequent reaction with an electrophile. Formally the Reformatsky reaction is similar to the Grignard reaction. 

By reaction of an a-halo ester 1 with zinc metal in an inert solvent such as diethyl ether, tetrahydrofuran or dioxane, an organozinc compound 2 is formed (a Grignard reagent-like species). Some of these organozinc compounds are quite stable even a structure elucidation by x-ray analysis is possible in certain cases ... 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

Water-insoluble metal hydroxides can be brought into solution with a strong acid such as HQ. The reaction with zinc hydroxide is typical ... 

Sanders and his co-workers reported two enzymatic reactions using CPO 3 described above (Fig. 9). In the reactions, three zinc metals are incorporated into each porphyrin. The first reaction is the acylation reaction of pyridyl alcohol 18 using AT-acetylimidazole (19) [35] to afford 20. In the presence of 3, the reaction is accelerated 16 times compared to the reaction without 3. The replacement of 3 with 4 (M=Zn) gave no significant acceleration of the reaction therefore, the enzymatic reaction proceeds through a supramolecular... 

Many other oxidants give dangerous reactions with zinc. These reactions have already been mentioned by means of previously discussed transition metals. 

The direct reaction of zinc metal with organic iodides dates back to the work of Frankland(67). Several modifications have been suggested since that time to increase the reactivity of the metal. The majority of these modifications have employed zinc-copper couples(68-72), sodium-zinc alloys(73), or zinc-silver couples(77). Some recent work has indicated that certain zinc-copper couples will react with alkyl bromides to give modest yields of dialkylzinc compounds(74,73). However, all attempts to react zinc with aryl iodides or bromides have met with failure. The primary use of zinc couples has been in the Simmons-Smith reaction. This reaction has been primarily used with diiodomethane as 1,1-dibromides or longer chain diiodides have proven to be too unneactive even with the most reactive zinc couples. 

Titanium catalysts have long been used in electron transfer reactions involving epoxides, mostly as stoichiometric reagents. Gansauer et al. have developed a catalytic version of these reactions using titanocenes along with zinc metal to generate the active catalyst (Scheme 60). In situ reduction of Ti(IV) with zinc metal provides Ti(III) species 231, which coordinates... 

Let us continue with the example of copper ions in contact with copper metal and zinc ions in contact with zinc metal. This combination is usually referred to as the Darnell cell or zinc/copper couple(Fig. 6.5a). For this electrochemical cell the reduction and oxidation processes responsible for the overall reaction are separated in space one half reaction taking place in one electrode compartment and the other takes place in the other compartment. 

In an atmosphere of nitric oxide, thermal decomposition produces barium nitrite, Ba(N02)2. Reactions with soluble metal sulfates or sulfuric acid yield barium sulfate. Many insoluble barium salts, such as the carbonate, oxalate and phosphate of the metal, are precipitated by similar double decomposition reactions. Ba(N03)2 is an oxidizer and reacts vigorously with common reducing agents. The solid powder, when mixed with many other metals such as aluminum or zinc in their finely divided form, or combined with alloys such as... 

Iron(III) sulfate may be reduced to +2 oxidation state of the metal in solution in the presence of common reducing agents. For example, reaction with zinc in sulfuric acid can produce iron(II) sulfate. The molecular equation is as follows ... 

Mercury dimethyl undergoes single replacement reactions with several metals such as alkali and alkaline earth metals, zinc, aluminum, tin, lead and bismuth forming their corresponding dialkyls. 

Similarly, reaction with zinc and other reducing agents converts the oxide to metallic mercury ... 

As part of an efficient, facile and practical liquid-phase combinatorial synthesis of benzimidazoles under microwave irradiation, the reduction of a polymer bound o -nitroaniline with zinc metal in methanol was completed in a very short time (2 min)61 (Scheme 4.33). However, no detailed reaction conditions were given. 

Batteries, although they come in many types and sizes, are all based on redox reactions. In a typical redox reaction carried out in the laboratory—say, the reaction of zinc metal with Ag+ to yield Zn2+ and silver metal—the reactants are simply mixed in a flask and electrons are transferred by direct contact between the reactants. In a battery, however, the two reactants are kept in separate compartments and the electrons are transferred through a wire running between them. 

Hydrogen gas can be prepared by reaction of zinc metal with aqueous HC1 ... 

FIGURE 14.1 Preparation of hydrogen by reaction of zinc metal with dilute acid. The H2 gas, which is nearly insoluble in water, displaces the water in the collection vessel. 

Another reaction that builds a cyclopropane ring onto a carbon-carbon double bond is called the Simmons-Smith reaction. This reaction does not actually involve a car-bene, but rather a carbenoid, an organometallic species that reacts like a carbene. This species is generated by reaction of diiodomethane with zinc metal from a special alloy of zinc and copper ... 

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