Zinc dust, Zn

A grey powder, the particles of which are somewhat oxidized at the surface. Pure zinc has an atomic weight of 65.37, melts at 419°C and boils at 907°C. Its specific gravity is 7.34. 

Zinc dust is stable against water or moisture, because the film of zinc hydroxide, Zn(0H)2, or basic zinc carbonate, 2ZnC03.3Zn(OH)2., formed on the particle surface protects the metal from corrosion. It is not easily soluble in sodium hydroxide solution in water, but it is soluble in a weak alkali solution such as sodium carbonate or bicarbonate generating hydrogen gas. It is also easily soluble in ammonia solution to form a complex salt, [Zn(NH3)4] (OH) 2- Zinc is attacked by chlorides, but not by ammonium perchlorate. The main use for zinc is in white smoke, which is created by zinc chloride particles. Zinc dust is quite reactive with hexachloroethane in presence of moisture or water, and it often causes fire when manufacturing smoke composition. It is thought that a trace of hydrochloric acid in the hexachloroethane causes the reaction. 

Manufacture. (1) Metallic zinc is evaporated, collected, cooled and 

Packing and volume for storage. A strong wooden case, the inside of which is covered with zinc plate. 0.62 m per 1000 kg of zinc dust. Quite a heavy powder. 

Quality. The zinc dust of commerce is a fine powder which passes 150 mesh. It contains some matter insoluble in hydrochloric acid solution. Examples of analyses are shown as follows Made by manufacturer A metallic zinc 69.62%, total zinc 84.69% made by B metallic zinc 77.91%, total zinc 86.79% made by C metallic zinc 81.02, total zinc 87.13%. 

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Zinc dust (Zn) is not a compound but a gray powder that is used as a pigment and acts as an excellent reducing agent and catalyst. It is dangerous because it can explode when exposed to moist air and may heat up and ignite spontaneously. When mixed with dry, powdered sulfur, it makes an excellent dry propellant-type rocket fuel, but is dangerous to handle. 

Zinc dust was previously activated by the addition of carcinogenic 1,2-dibromoethane [0.026 equiv relative to zinc dust (Zn)] followed by chlorotrimethylsilane (TMSCl) (0.018 equiv relative to Zn), which gave rise to serious issues of poor reproducibility and requirement of excess iodide 80 (2.5 equiv relative to 8). Because the Fukuyama coupling reaction has been reported not to proceed with dialkyl zinc (R2Zn), the Schlenk equilibrium of the zinc reagent should lie to the left to achieve... 

Zinc is a bluish-white metal which dissolves readily in strong acids. In nature it occurs as a sulfide, oxide, or carbonate. In solution, it is divalent and can form hydrated Zn2+ cations in acids, and zincated anions — probably Zn(OH)42 — in strong bases (USEPA 1980, 1987). Zinc dust and powder are sold commercially under a variety of trade names Asarco, Blue powder, Cl 77949, Cl pigment metal 6, Emanay zinc dust, granular zinc, JASAD Merrillite, LI 5, and PASCO (USPHS 1989). Selected physical and chemical properties of zinc, zinc chloride, and zinc sulfate are listed in Table 9.2. 

In neutral or alkaline solution the conditions are altered so as to favour the immediate precursor of the final product of hydrogenation, namely, phenylhydroxylamine. This compound is obtained from nitrobenzene, suspended in ammonium chloride solution, by reduction with zinc dust. Zinc dust can decompose water with the formation of Zn(0H)2 if a substance is present which takes up the liberated hydrogen. Molecular, i e. ordinary, oxygen is capable of doing this and is thereby converted into hydrogen peroxide (M. Traube) ... 

KAu(CN)2 + Zn = K2Zu(CN)4 First patented by J. W. Simpson in 1884 and developed by J. S. MacArthur and R. W. and W. Forrest in Glasgow in 1887. The first commercial application was at the Crown Mine, New Zealand in 1889, followed shortly by mines in South Africa and the United States. If zinc dust is used, the process is known as the Merrill-Crowe process. 

Under conventional dechlorination conditions (20 equiv of zinc dust, acetic acid, 25°C or 50°C) the reduction of 4,4-dichlorocyclobutenones affords complex mixtures of products which include the desired cyclobutenones as well as significant amounts of partially reduced byproducts. He have found that the desired transformation can be accomplished cleanly provided that the reduction is carried out at room temperature in alcoholic solvents (preferably ethanol) in the presence of 5 equiv each of acetic acid and a tertiary amine (preferably tetramethylethylenediamine). Zinc dust has proven to be somewhat superior to zinc-copper couple for this reduction. The desired cyclobutenones are obtained in somewhat higher yield using this procedure as compared to the related conditions reported by Dreiding [Zn(Cu), 4 1 AcOH-pyridine, 50-60 C] for the same transformation. ... 

In the initial stages of development of smoke formulations, HCE-Zn dust-based formulations were in use for screening purposes. But as this formulation is very sensitive to moisture and accidents were reported, zinc dust was replaced by zinc oxide. 

The source of Cr2+ can be [C MeCOaMltO ],1100 aqueous Cr2+ produced by the reduction of Cr3+ electrolytically1101 or by Zn/Hg in hydrochloric acid,1099 or anhydrous or hydrated CrCl3 reduced by zinc dust in suspension in the reaction mixture.1100,1102 Presumably the ligands can displace solvent molecules more readily from the labile Cr2 species. 

Nearly pure cadmium sponge is precipitated by the addition of high-purity. lead-free zinc dust. The cadmium sponge then is redigested in spent cadmium electrolyte, alter which the cadmium is deposited by electrolysis onto aluminum cathodes. The metal is then stopped from the electrodes, melted, and cast into various shapes. Reactions which occur during the electrolytic process are (Roasting) ZnS +1,0 — — ZnO +... 

Zinc sulfide, selenide, and telluride are more pronouncedly covalent than the oxide. They can be prepared from the elemenls, or in the case of first two, by the action of H2S or hydrogen selenide upon zinc solutions. Zinc nitride, Zn N . prepared from zinc dust and NH<, hydrolyzes readily to NH3 and the oxide. Two zinc phosphides are known Zn. formed by heating the dements, yields phosphine w lth acids ZnP and ZnHP have also been prepared. 

Zinc Dust.—Commercial varieties vary much in character and are subject to deterioration they contain usually 90—95% Zn (for estimation, see p. 510) they should be preserved in airtight vessels and should be occasionally estimated. Two other forms of zinc for reducing purposes are on the market—a ground zinc, made by grinding metallic zinc, and a variety in the form of powder containing 2% of lead, which gives specially good results. Usual impurities zinc oxide, iron and arsenic. 

By passing carbon dioxide over red hot zinc C02 + Zn or iron dust A ZnO + CO... 

The active zinc was obtained by electrolysis at constant current in a one-compartment cell in DMF containing Et4NC104 using a Zn/Pt anode/cathode system. The isoprenylation of isovaleraldehyde led to the product in 68% isolated yield, higher than with a conventional procedure using zinc dust in DMF or in refluxing THF. 

Reformatsky reactions have a bad reputation as being difficult to entrain. To the authors experience, however, the reactive donors such as alkyl bromo-acetates do not pose particular problems even under rather conventional conditions. Commercial zinc dust activated by pre-treatment with either iodine of preferentially with cuprous chloride (i.e. Zn(Cu)) readily inserts into these halocarbonyl compound with formation of the corresponding zinc enolates. Protocols 1 and 2 describe prototype examples for Reformatsky reaction in the conventional two-step or Barbier-type set-up, respectively. 

AgCl (finely divided solid) + Zn (zinc dust) suspended in water. 

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