Oxygen—phosphorus bonds reactions with

This problem has been partially overcome by elimination of the phosphorus-oxygen bonds, as, for example, in the poly(phosphinoisocyanates), which have the structure shown in 6.47.42 It is also possible to form poly(metal phosphinates) with repeat unit -M(0PR20)2- by allowing a metal alkoxide to react with a phosphinic acid.43 Typical metal atoms are aluminum, cobalt, chromium, nickel, titanium, and zinc.43 Polymeric phosphine oxides can be prepared by the reactions... 

These reagents are usually prepared by treatment of a phosphine with an alkyl halide and successive addition of base, like BuLi or NaHMDS. Reaction with the ketone takes place by attack of the carbanionoid carbon of the ylide form on the electrophilic carbon of the carbonyl group via a four-membered heterocyclic transition state, the oxaphosphetane 35. The driving force for this transformation is provided by formation of the very strong phosphorus-oxygen bond. Subsequent collapse of the oxaphosphetane furnishes the desired exomethylene group under retention of geometry. 

White phosphorus reacts with oxygen to produce an oxide (P2O5). This oxide then reacts with any water that is around to form phosphoric acid. The phosphorus-phosphorus bonds of P4 are weak compared with the stronger phosphorus-oxygen bonds of P2O5 in other words, the oxide is thermodynamically much more stable than white phosphorus, and this drives the reaction to such an extent that white phosphorus spontaneously combusts in air. 

The analytical method used for parathion takes advantage of the ease with which the phosphorus-oxygen bond in that material is cleaved by hydroxide. The hydrolysis produces a mole of 4-nitrophenol for each mole of parathion originally present in solution. Because 4-nitrophenol has a well-defined absorption spectrum with a high molar absorptivity at the wavelength of maximum absorption (400 m/x) and because the reaction to form 4-nitrophenol from parathion is rapid and quantitative, the method provides a reliable and sensitive means for analyzing parathion. 

Studies by E. Vedejs (University of Michigan) indicate that the Wittig reaction takes place in two steps. In the first step (below), the aldehyde or ketone combines with the ylide in a cycloaddition reaction to form the four-membered ring of an oxaphosphet-ane. Then in a second step, the oxaphosphetane decomposes to form the alkene and triphenylphosphine oxide. The driving force for the reaction is the formation of the very strong (DH° = 540 kj moP ) phosphorus—oxygen bond in triphenylphosphine oxide. 

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