Density zinc compounds

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

Zinc Chromite, ZnO.CraOg, may be obtained in the same manner as the corresponding calcium salt. It yields dark green octahedral crystals of density 5 29 at 13° C. Two other zinc compounds are known, namely 3Zn0.2Cr20j eZnO.SCrgOg. 

The formulation of calcium chelate materials is based upon the formation of a low-solubiUty chelate between calcium hydroxide and a sahcylate. Dycal utilizes the reaction product of a polyhydric compound and sahcyhc acid. Other sahcyhc acid esters can be similarly used. Vehicles used to carry the calcium hydroxide, extenders, and fillers may include mineral oil, A/-ethyl- -toluenesulfonamide [80-39-7] and polymeric fluids. The filler additions may include titanium dioxide [13463-67-7] zinc oxide, sihca [7631-86-9], calcium sulfate, and barium sulfate [7727-43-7]. Zinc oxide and barium sulfate are useflil as x-ray opacifying agents to ensure a density greater than that of normal tooth stmcture. Resins, rosin, limed rosins, and modified rosins may serve as modifiers of the physical characteristics in both the unset and set states. 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

Y Picoline. Commercially pure y-picoline contains )S-picoline and 2 6-lutidine and sometimes traces of non-basic impurities (aromatic hydrocarbons) which cannot be separated by fractionation. The non-basic impurities are removed by steam distillation of the base in dilute hydrochloric or sulphuric acid solution (for details, see under a Picoline). The impure y-picoline is converted into the zinc chloride complexes of the component bases the 2 6-lutidine - ZnClj complex is the least stable and upon steam distillation of the mixture of addition compounds suspended in water, 2 6-lutidine passes over flrst. The complete separation of the 2 6-lutidine may be detected by a determination of the density and the refractive index of the dry recovered base at varioiu stages of the steam distillation. The physical properties are —... 

Further examples where these rules are observed are as follows. Under pressure, some compounds with zinc blende structure, such as AlSb and GaSb, transform to modifications that correspond to the J3-Sn structure. Others, such as InAs, CdS, and CdSe, adopt the NaCl structure when compressed, and their atoms thus also attain coordination number 6. Graphite (c.n. 3, C-C distance 141.5 pm, density 2.26 gem-3) pr Te diamond (c.n. 4, C-C 154 pm, 3.51 gem-3). 

Functionalized organozinc halides are best prepared by direct insertion of zinc dust into alkyl iodides. The insertion reaction is usually performed by addition of a concentrated solution (approx. 3 M) of the alkyl iodide in THF to a suspension of zinc dust activated with a few mol% of 1,2-dibromoethane and MeaSiCl [7]. Primary alkyl iodides react at 40 °C under these conditions, whereas secondary alkyl iodides undergo the zinc insertion process even at room temperature, while allylic bromides and benzylic bromides react under still milder conditions (0 °C to 10 °C). The amount of Wurtz homocoupling products is usually limited, but increases with increased electron density in benzylic or allylic moieties [45]. A range of poly-functional organozinc compounds, such as 69-72, can be prepared under these conditions (Scheme 2.23) [41]. 

Electrolytic reduction of an emulsion of the nitro compound in 1 M zinc chloride solution at high current density is another proposed method for conversion to the amine. Finely divided zinc is produced and this reduces the nitrocompound. Zinc ions also function as Lewis acid in the reduction of arylhydroxylamines [44]. 

When the electrochemical reaction is carried out in DMF solution19, in the presence of a zinc anode and at a low current intensity, the organozinc compounds CF3ZnBr and (CF3)2Zn are produced with faradaic yields higher than 100%. Interestingly, the lower the current density, the higher the faradaic yield. 

---