Phosphorus enrichment requirement

In recent studies, Glindemann et al. (1999, 2000) attempted to obtain definite answers to one of the basic problems of prebiotic phosphorus chemistry were there realistic enrichment mechanisms for the phosphorus derivatives required in prebiotic syntheses Only if the phosphorylating agents were present in concentrated form could successful reactions have taken place. 

Whereas the barrier for pyramidal inversion is low for second-row elements, the heavier elements have much higher barriers to inversion. The preferred bonding angle at trivalent phosphorus and sulfur is about 100°, and thus a greater distortion is required to reach a planar transition state. Typical barriers for trisubstituted phosphines are BOSS kcal/mol, whereas for sulfoxides the barriers are about 35-45 kcal/mol. Many phosphines and sulfoxides have been isolated in enantiomerically enriched form, and they undergo racemization by pyramidal inversion only at high temperature. ... 

Plastics are not all equally flammable. Some burn as readily as fuels. Some do not burn spontaneously but when exposed to a severe fire, they can be burned. And some require enriched or pure oxygen environment before they will bum. Most plastics can be made more resistant to burning, by incorporating flame-retardant elements—phosphorus, bromine, chlorine, antimony, even water— either in the polymer molecule or in physical additives. 

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... 

It is fairly well established that enrichments of the surface layer with phosphorus tends to improve the selectivity of butane to maleic anhydride as it avoids overoxidation of the intermediates that form. Increases in the P/V ratio, however, decrease the reducibility of the catalyst and thus its ability to subsequently reoxidize. The optimal balance of activity and selectivity therefore requires an optimal P/V ratio. Centi et al.I suggest that this should be in the range 1.0-1.1. 

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