Chromy reaction

Mukherjee studied the gas phase equilibria and the kinetics of the possible chemical reactions in the pack-chromising of iron by the iodide process. One conclusion was that iodine-etching of the iron preceded chromis-ing also, not unexpectedly, the initial rate of chromising was controlled by transport of chromium iodide. Neiri and Vandenbulcke calculated, for the Al-Ni-Cr-Fe system, the partial pressures of chlorides and mixed chlorides in equilibrium with various alloys and phases, and so developed for pack aluminising a model of gaseous transport, solid-state transport, and equilibria at interfaces. 

Chromium hexacarbonyl is prepared by the reaction of anhydrous chromi-um(lll) chloride with carbon monoxide in the presence of a Grignard reagent. A 60% product yield may be obtained at the carbon monoxide pressures of 35 to 70 atm. Other chromium salts may be used with carbon monoxide and Grignard reagent in the preparation. The compound may also be obtained by the reaction of a chromium salt with carbon monoxide in the presence of magnesium in ether or sodium in diglyme. 

Aquo-pentammino-chromic Hydroxide, [Cr(NH3)5H20](OH)3, is known only in solution, and is formed when dry chloro-pentammino-chromie chloride, [Cr(NH3)5Cl]Cl2, is rubbed, in absence of light, with moist silver oxide and water on filtering a deep red solution, which is strongly alkaline in reaction, is left, which contains the base, Cr[(NH3)5H20](OH)3. The solution is unstable and decomposes on... 

Rapid increase in temperature is desirable at temperatures below those at which substantial liquid formation occurs (C9,B27,S21,C11,W9,G26). Most of the belite, and almost all of the other product phases, subsequently either melt or react in the presence of the melt, and there is no merit in promoting crystal growth or removal of imperfections, which would impede these processes. Slow heating may also allow the decomposition products of the clay minerals to transform into less reactive phases. It can also lead to the formation of microstructures unfavourable to the later reactions Chromy (C9) found that it allowed the belite shells around the silica particles to thicken, producing composites slow to react with lime. In contrast, rapid heating increases movement of the liquid phase, when this forms, and thus improves the mixing of the calcareous and siliceous constituents (Cl 1). 

Beckwith, R.E.J., Gravestock, M.B., and Simpkins, N.S. 2002. Nucleophilic addition reactions of bridged triene h -chromi-umtricarbonyl complexes. J Chem Soc Perkin Trans 1, 2352-2359. 

Pour an ammonium sulphide solution into a potassium chromate or dichromate solution and heat the mixture. How does the solution s colour change What is the composition of the precipitate Write the equation of the reaction. What properties does chromi-um(VI) exhibit in this reaction How does an acidified potassium chromate or dichromate solution react with hydrogen sulphide, sulphur dioxide, and an iron(II) salt Write the equations of the reactions. 

Protection of aldoses at the non-anomeric positions makes it possible to use many of the common procedures in organic chemistry for oxidizing lactols as shown with mannofura-nose 1 and glucopyranose 3 (O Table 1). The reactions can be divided into three main categories oxidations mediated by activated dimethyl sulfoxide (DMSO), oxidations with chromi-um(VI) oxides, and oxidations catalyzed by ruthenium oxides. The DMSO-mediated oxidations of alcohols can be promoted by several activators [27]. With the partially protected aldoses the activation has mainly been achieved with acetic anhydride and oxalyl chloride. Competing /3-elimination does usually not occur unless the eliminating group is an ester, e. g., an acetate or a benzoate [27]. 

Ingesting large amounts of chromium(VI) can cause stomach upsets and ulcers, convulsions, kidney and liver damage, and even death. Skin contact with certain chromium(VI) compounds can cause skin ulcers. Some people are extremely sensitive to chromi-um(VI) or chromium(ni). Allergic reactions consisting of severe redness and swelling of the skin have been noted. 

Chromium. In 1998, Boland reported a chromium(n)-catalyzed pinacol coupling reaction of aromatic aldehydes and ketones (Eq. 3.28) [46-48J aliphatic aldehydes are inert to these conditions. The turnover step relies upon a combination of manganese and Me3SiCl to regenerate CrX2 from an intermediate chromi-um(III) species (Fig. 3-3). 

These acids form dark brown amorphous masses which, in freshly prepared, dil. soln. exhibit the characteristic reactions of neither SO4"—-nor Cr04"—-radicles, slowly decompose when they do show the reactions of these radicles. Arguing by analogy, and from some observations on the heats of neutralization, it is inferred that the constitution of the chromisulphatochromic acids resembles that of the chromisulphuric acids. If the alkali chromates are employed in place of chromic acid in the preparation of the.se products then the corresponding chromisulphatochromates are formed. J. Poizat. studied the action of chromi-mouo-, -di-, and tri-sulphuric acids on hydrogen dioxide. 

Asymmetric reaction of the sulfides bearing a tricarbonyl(ri -arene)chromi-um complex was shown to be successful by Gibson and Simpkins [48,49]. The benzyhc methylene groups in tricarbonyl(ri -phenylmethyl alkyl sulfide)chro-mium(O) and tricarbonyl(ri -l,3-dihydroisobenzothiophene)chromium(0) were highly asymmetrically functionahzed by deprotonation with a chiral bis-Uthium amide and subsequent electrophihc reactions (Tables 4 and 5). 

Tables. Enantioselective reaction of tricarbonyl(ri -l,3-dihydroisobenzothiophene)chromi-um(0)...

Therefore, any cross section of typical clinker displays (1) the more or less loosely tied framework of alite crystals, (2) belite that occurs as single crystals and as concentrations, and (3) a matrix of aluminate and ferrite formed as the molten liquid cools and crystallizes. Microscopical observations clearly suggest aluminate (CjA) crystallizes after the ferrite, the latter forming a prismatic crystal mesh, the holes of which are partially filled with aluminate. Ferrite can be seen within alumi nate and, extremely rarely, vice versa. The matrix com monly contains secondary belite and shows effects of reaction with alite. Voids remain in areas not filled by the liquid, forming sites for crystallization of alkali sulfates on the cavity walls. Thus, the typical clinker is a somewhat porous mass of interlocking crystals, a truly glassless crystalline mosaic. Recent studies of the sequence of crystal development in the production of Portland cement clinker can be found in papers by Imlach and Hofmanner (1974), Moore (1976), Ono (1981, 1995), Chromy (1974, 1982), and Maki (1982, 1995). 

Chemiluminescence reactions Chemiluminescence reactions are usually redox reactions. The catalytic effect is reflected in the release of radiant energy. The best known of this type of reaction is the oxidation of luminol (5-amino-2,3-dihydrophthalazine-l,4-dione) by hydrogen peroxide, catalyzed by metal ions such as cobalt(II), copper(II), iron(II), nickel(II), chromi-um(III), and manganese(II) at pH 10-11. Detection limits of 10 to 10 mol 1 are readily achieved this way. Luminol is converted into a doubly charged anion that is subsequently oxidized to an excited singlet state that emits radiation on decomposing to... 

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