Magnesiums redistribution

The other commercially important routes to alkyltin chloride intermediates utilize an indirect method having a tetraalkjitin intermediate. Tetraalkyltins are made by transmetaHation of stannic chloride with a metal alkyl where the metal is typicaHy magnesium or aluminum. Subsequent redistribution reactions with additional stannic chloride yield the desired mixture of monoalkyl tin trichloride and dialkyltin dichloride. Both / -butjitin and / -octjitin intermediates are manufactured by one of these schemes. 

The second route (Scheme 1) is a redistribution reaction, in fact the Schlenk equilibrium. This route may be used in the reverse direction for the preparation of pure diorganomagnesium compounds from organomagnesium halides. Addition of a ligand, usually dioxane, that forms an insoluble complex with magnesium dihalide, shifts the Schlenk equilibrium completely to the left side and allows isolation of pure diorganomagnesium compounds from the remaining solution. ... 

For both cesium and barium sorption, there is reasonable agreement between the total concentrations of desorbed species and the ion-exchange capacities determined by isotopic redistribution. The small differences which exist could easily be due to the precision in the elemental analyses. (Also, the experimental technique would not have detected desorption of hydrogen ions.) The solid-phase concentrations of sodium, potassium, magnesium, calcium. 

Of the organometallic compounds of Group II elements, undoubtedly the chemistry of the magnesium compounds is best known. By contrast, the remaining elements in this group have received less attention and it is only recently that more information on organo derivatives of beryllium and, to lesser extent, of calcium, strontium, and barium has become available. Therefore, most of the observations regarding redistribution equilibria have been of more or less qualitative nature. 

In the case of a high iron content in the carbonate, olivine is formed instead of orthopyroxene. A 10% increase in magnesium content leads to a 5-8° shift of the P-T curve into the higher temperature region. The shift is relatively small, but it plays a definite role in the metamorphic redistribution of iron among the minerals, particularly in reactions in which iron oxides are formed in the absence of water ... 

The reactions usually proceeded to approximately 90% completion over a period of days, at which point the authors believe the redistribution reached equilibrium. However, substitution of the tris(3,5-dimethylpyrazolyl)hydroborato (>/ -HB(3,5-Me2pz)3) by the more sterically demanding tris(t-butylpyrazoyl)hydroborato ligand ( -HB(3- -Bupz)3) in magnesium complexes 13 prevents ligand redistribution after 7 days at 120°C. 

The spontaneity of this reaction is reflected in the AG value of — 125kJ/mol(C). The result is that the total equivalents of reduced matter produced by carbon burial are redistributed and now include some pyrite. Sulfate is removed from the water permeating the sediments and magnesium and calcium carbonates are formed. Thus, the carbon, oxygen, and sulfur cycles are coupled by a redox reaction which also includes iron. The extent of the coupling depends on the supplies of reactive organic carbon, sulfate, and reactive iron. When the reduced material is returned to contact with the atmosphere, it is oxidized and an amount of oxygen equivalent to that formed when the carbon was first buried is removed. 

Magnesium ethoxide undergoes redistribution with (h -CjH5)2Mg to give h -CjHjMgOEt in THF the product is a monomeric THF adduct, but in toluene an unsolvated cubane tetramer is formed. 

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