Magnesium oxide deactivation

Purified by chromatography on a column of deactivated alumina or magnesium oxide, or on a thin layer of silica gel G (Merck), using dichloromcthane/dicthyl ether (9 1) to develop the chromatogram. Stored in the dark and in an inert atmosphere at -20 . 

Polychloroprene rubbers are not efficiently vulcanized by sulfur. The chlorine atoms deactivate the double bonds toward reaction with sulfur. Vulcanization is achieved by heating with zinc and magnesium oxides. Crosslinking involves the loss of... 

Pure iron(iii) oxide performs rather poorly as a WGS catalyst, due to rapid catalyst deactivation by sintering. Traditional iron catalysts typically consist of iron(iii) oxide (80-90% by mass), chromium(iii) oxide (8-10% by mass) and small amounts of other stabilisers and promoters such as copper(ii) oxide, aluminium oxide, alkali metals, zinc oxide and magnesium oxide. The small fraction of chromium(iii) oxide acts to prevent catalyst sintering, and also promotes the catalytic activity of iron. Catalyst deactivation is typically caused by poisons in the feedstock gases and by deposition of solids on the catalyst surface. 

Polychloroprenes differ from other polydienes in that conventional sulphur vulcanization is not very effective. The double bonds are deactivated by the electronegative chlorine atoms and direct reaction with sulphur is limited. The vulcanization of polychloroprenes is normally achieved by heating at about 150°C with a mixture of zinc and magnesium oxides W type neoprenes also require an organic accelerator (commonly either a diamine or ethylene thiourea) but G types cure quite rapidly without acceleration. The mode of reaction has not been established with certainty, but it is generally supposed that cross-linking occurs at the tertiary allyUc chloride structures generated by 1,2-polymerization (see Section 18.8.3) and that a 1,3-allylic shift is the first step. The metal oxides may lead to ether cross-links as follows ... 

Although N sulfinyl imines can be prepared by several other methods (oxidation of sulfenimines [12] and iminolysis of sulfinates [13]), they are most conveniently synthesized by condensing aldehydes with tert butanesulfinamide in the presence of copper(II) sulfate or magnesium sulfate/pyridinium p toluenesulfonate as a Lewis add catalyst and water scavenger (Scheme 1.4) [14]. When ketones, more sterically hindered aldehydes or even electronically deactivated aldehydes are used, titanium tetraethoxide is the preferred Lewis add and water scavenger. These methods are convenient to synthesize both alkyl and aryl substituted imines. 

An apparatus for simultaneously coating a plate with two adjacent layers of different adsorbents was accomplished by placing a plastic insert into a commercial spreader, thus forming two independent chambers. For this reason, combinations of two adsorbents, such as cellulose, silica gel, alumina, charcoal, silicic acid, magnesium silicate, etc. as a function of the sample were used. Then, the two eluents systems were optimized for the two development directions, e.g., 2-D separation of some ketones on a bilayer (charcoal/ silicic acid) with benzene-ether-acetic acid (82 9 9, v/v) in the first direction (on charcoal) and with benzene-ether (85 15, v/v) in the second direction (on silicic acid). In another paper, the first adsorbent was silica gel (air-dried) and the second adsorbent was deactivated aluminum oxide. The same solvent system, toluene-ethyl acetate (3 1, v/v), was used in the two directions. In this condition, a mixture of 2,4-dinitrophenylhydrazine derivatives of hydroxycarbonyl compounds was resolved. 

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