Zinc metal reactivity

Zinc and Zinc Alloys. Zinc metal is highly reactive in acid solutions such as sulfuric, hydrochloric, and nitric dissolving rapidly at acid concentrations normally used to pickle steel and aluminum. Dilute (1—4%) solutions of these acids can be used with caution to remove zinc oxides. 

Further dechlorination may occur with the formation of substituted diphenyhnethanes. If enough aluminum metal is present, the Friedel-Crafts reactions involved may generate considerable heat and smoke and substantial amounts of hydrogen chloride, which reacts with more aluminum metal, rapidly forming AlCl. The addition of an epoxide inhibits the initiation of this reaction by consuming HCl. Alkali, alkaline-earth, magnesium, and zinc metals also present a potential reactivity hazard with chlorinated solvents such as methylene chloride. 

Gold ores can be concentrated by froth flotation, the resulting concentrate being roasted at 600-800°C to oxidize off sulphur and arsenic as their oxides. The product is extracted with cyanide under oxidizing conditions (using either peroxide or air itself) before displacement with powdered zinc. More reactive metals (silver etc.) can be removed by chlorination of molten gold. 

The reactivities of potassium and silver with water represent extremes in the spontaneity of electron-transfer reactions. The redox reaction between two other metals illustrates less drastic differences in reactivity. Figure 19-5 shows the reaction that occurs between zinc metal and an aqueous solution of copper(II) sulfate zinc slowly dissolves, and copper metal precipitates. This spontaneous reaction has a negative standard free energy change, as does the reaction of potassium with water ... 

Several techniques have been used to activate the zinc metal and improve yields. For example, pretreatment of zinc dust with a solution of copper acetate gives a more reactive zinc-copper couple.168 Exposure to trimethylsilyl chloride also activates the zinc.169 Wilkinson s catalyst, RhCl(PPh3)3 catalyzes formation of Reformatsky reagents from diethylzinc, and reaction occurs under very mild conditions.170... 

Zinc metal is often used to coat iron objects in a process called galvanizing. Which of these two metals do you think is more reactive Explain. 

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. 

Zinc metal is very reactive chemically. Zinc metal strips are often used as the plates in wet cell batteries. Galvanized iron is iron that has been coated with a thin film of zinc metal to protect it from corrosion. Many garbage cans and metal buckets are made of galvanized iron. 

Previous thermal analysis studies had indicated that while Sb203 did not react directly with DBDPO, there was some evidence that the reaction of a polymer substrate with the Sb203 generated a species which was very reactive (23), and that this product was antimony metal (Sb°). Therefore, simple mixtures of DBDPO with powdered antimony, bismuth and zinc metals (mole ratio of bromine to metal of 3 1) were pyrolyzed and the extent of reaction determined by CGC. 

Among protein aromatic groups, histidyl residues are the most metal reactive, followed by tryptophan, tyrosine, and phenylalanine.1 Copper is the most reactive metal, followed in order by nickel, cobalt, and zinc. These interactions are typically strongest in the pH range of 7.5 to 8.5, coincident with the titration of histidine. Because histidine is essentially uncharged at alkaline pH, complex-ation makes affected proteins more electropositive. Because of the alkaline optima for these interactions, their effects are most often observed on anion exchangers, where complexed forms tend to be retained more weakly than native protein. The effect may be substantial or it may be small, but even small differences may erode resolution enough to limit the usefulness of an assay. 

Zinc metal reacts spontaneously with an aqueous solution of copper sulfate when they re placed in direct contact. Zinc, being a more reactive metal than copper (it s higher on the activity series of metals presented in Chapter 8), displaces the copper ions in solution. The displaced copper deposits itself as pure copper metal on the surface of the dissolving zinc strip. At first, the reaction may appecir to be a simple single replacement reaction, but it s also a redox reaction. 

The formation of arylzinc reagents can also be accomplished by using electrochemical methods. With a sacrificial zinc anode and in the presence of nickel 2,2-bipyridyl, polyfunctional zinc reagents of type 36 can be prepared in excellent yields (Scheme 14) . An electrochemical conversion of aryl halides to arylzinc compounds can also be achieved by a cobalt catalysis in DMF/pyridine mixture . The mechanism of this reaction has been carefully studied . This method can also be applied to heterocyclic compounds such as 2- or 3-chloropyridine and 2- or 3-bromothiophenes . Zinc can also be elec-trochemically activated and a mixture of zinc metal and small amounts of zinc formed by electroreduction of zinc halides are very reactive toward a-bromoesters and allylic or benzylic bromides . ... 

Preparation of highly reactive forms of zinc metal. 802... 

Whenever metallic zinc is to be used in oxidative addition processes, results are affected by the metal surface activity. Two strategies for the production of active zinc metal surfaces can be adopted (i) chemical or physical activation of commercial zinc powders, or (ii) in situ production of highly reactive metal powders by reduction of a zinc salt with a suitable reducing agent. 

The authors observed that the applied quantity of electricity (0.2-0.5 F) was always lower than the expected quantity on the basis of Zn consumed (1 g atom). This difference reflects the concurrence of two processes at the anode surface, where the electrochemically promoted reaction (Figure 4) coexists with a classic zinc metal-promoted Reformatsky reaction. Indeed, the electrochemical process produces at the working anode a perfectly clean zinc metal surface, very reactive towards the a-bromoester. 

This is also a redox reaction involving the transfer of two electrons from the zinc metal to the copper ions. The zinc is oxidised to zinc ions in aqueous solution, while the copper ions are reduced. (See Chapter 5, p. 73, for a discussion of oxidation and reduction in terms of electron transfer.) It is possible to confirm the reactivity series for metals using competition reactions of the types discussed in this section. 

The most significant obstacle to be overcome in the preparation of organozinc halides by direct insertion of zinc metal into an organic halide is the intrinsic lack of reactivity of commercially available zinc metal. This is primarily due to a surface coating, for example of zinc oxide, which prevents direct reaction with an organic substrate. The success of attempts to insert zinc metal into an organic halide is entirely dependent upon the care with which the zinc metal is... 

As mentioned earlier, direct thermal dissociation of water requires temperatures above approximately 2500 K. Since there are not yet technical solutions to the materials problems, the possibility of splitting water instead, by various reaction sequences, has been probed. Historically, the reaction of reactive metals and reactive metal hydrides with water or acid was the standard way of producing pure hydrogen in small quantities. These reactions involved sodium metal with water to form hydrogen or zinc metal with hydrochloric acid or calcium hydride with water. All these... 

Ultrasound has been employed to promote the formation of o-xylylene from the reaction of zinc metal with a,a -dibromo-o-xylene." In the absence of reactive dienophiles, the transient diene produced in... 

Another method involves an electric-arc vaporizer which is >2000° C before burning (25,32). One of the features of the process is a rapid quench of the hot gas flow to yield very fine oxide particles (<0.15 nm). This product is quite reactive and imparts accelerated cure rates to mbber. Internally fired rotary kilns are used extensively in Canada and Europe and, to a limited extent, in the United States (24). The burning occurs in the kfln and the heat is sufficient to melt and vaporize the zinc. Because of the lower temperatures, the particles are coarser than those produced in the other processes. In a fourth process, zinc metal which is purified in a vertical refining column is burned. In essence, the purification is a distillation and impure zinc can be used to make extremely pure oxide. Also, a wide range of particle sizes is possible (33). 

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