Add time:07/24/2019         Source:sciencedirect.com

A study is described of the reaction of trimethylbromosilane and trimethyliodosilane with various esters of phosphorothioic and phosphoroselenoic acids of general structures (RO)2(RY)P=O (I) and (RO)3P=Y (II) (Y = S or Se, R = alkyl). The reaction results in replacement of the R groups by trimethylsilyl groups. NoS-trimethylsilyl andSe-trimethylsilyl substituted esters were found among the products. Thus the displacement of theO-R group in II as well as the replacement ofS-organyl orSe-organyl groups in I both lead to the correspondingO-trimethylsilyl isomer containing thiophosphoryl or selenophosphoryl groups. The following sequence of reactivity of the ester groups was observed:Download full-size imageThe process involves initially the reversible formation of a phosphonium salt intermediate in a fast step, followed by slow dealkylation. It was shown by low temperature31P FT-NMR studies that in the reaction of trimethyliodosilane with an ester bearing a P=O phosphoryl group, the equilibrium for the phosphonium salt formation lies well over towards the intermediate and so the intermediate can be observed directly. These mechanistic proposals were confirmed by conductance studies on the reaction system and by investigation of the stereochemical course of the corresponding reaction of an optically-active model thiophosphonate.In some cases the reaction of the halosilanes with the phosphates takes a selective course which allows the reaction to be used as a convenient route toO-silyl substituted esters of phosphorothioic or phosphoroselenoic acids.

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