Subject elemental phosphorus

Elemental phosphorus in white or red forms is subject to attack by a variety of nucleophilic reagents. Aqueous bases provide one of the most useful reagent systems for organophosphorus syntheses, although other nucleophiles can also be used for specific synthetic processes. 

There are several allotropic forms of elemental phosphorus, the most common being the white, red, and black forms. Red phosphorus, which itself includes several forms, is obtained by heating the white form at 400 °C for several hours. An amorphous red form may also be prepared by subjecting white phosphorus to ultraviolet radiation. In the thermal transformation, several substances function as catalysts (e.g., iodine, sodium, and sulfur). Black phosphorus appears to consist of four different forms. These are obtained by the application of heat and pressure to the white form. The major uses of elemental phosphorus involve the production of phosphoric acid and other chemicals. Red phosphorus is used in making matches, and white phosphorus has had extensive use in making incendiary devices. Several of the important classes of phosphorus compounds will be discussed in later sections. 

In spite of this only since 1950 was more closely looked at the direct synthesis of organic phosphorus compounds starting from elemental phosphorus. Rauhut, in his thorough review in 1963 on this subject included 34 references. A year later, Grayson lectured on tliis subject Since that time the number of references concerning the synthesis of organic phosphorus compounds from phosphorus has more than quadrupled ( 160) which attests to the lively interest in tlris field. 

It is the purpose of this review to summarize all the syntheses of organic phosphorus compounds which used elemental phosphorus as a starting material. The literature concerning the subject of this review is covered through January 1, 1971, including patent literature so far as abstracts are available in Chemical Abstracts. 

The evidence indicates that provision of a large area of wall with high surface phosphatase activity is one, if not the most important, role for these hairs. In all cases where an organism able to develop multicellular hairs was subjected to phosphorus limitation, hairs were formed, though in some taxa they were shown experimentally to form in response to one or several other element limitations such hairs are smaller than those formed under phosphorus limitation and often look slightly different... 

There have been many studies of the crystalline structures of elemental phosphorus [10,45], and the microscopic structures of the amorphous modifications (red, black, grey vitreous) are still the subjects of considerable attention. Gas phase clusters have been of interest for many years, and Martin [19] has detected mass spectroscopically clusters up to > 6000. Nevertheless, little experimental information was available until recently on the structure of clusters with > 4, and this is also true for arsenic clustere, As . 

There has so far been only limited success in attempts to produce P-C compounds directly from elemental phosphorus, although both white and red forms are subject to attack by a variety of nucleophilic reagents. These and other synthetic methods are discussed below in this chapter. Synthesis of P-C bonds has recently been comprehensively reviewed [21]. The synthesis of P=C and P=C bonds is dealt with in Sections 6.14 and 6.15 (see also Phospha-Wittig reaction (6.445)). Carbophosphenes can be obtained from carbophosphynes and vice versa (6.631,6.631a), although these are not general methods of preparation. 

The two substances in the photograph appear very different, but they are the same element, phosphorus. On top is white phosphorus, P4, stored in water because it catches fire when exposed to air. Notice that its particulate-level structure is a collection of discrete four-atom molecules. When white phosphorus is heated, it changes to red phosphorus, shown in the bottom of the photograph. This substance is stable in air, as you can see. At the particulate level, red phosphorus is a network of phosphorus atoms with no individual molecules. How can two forms of the same pure element be so different The answer lies in understanding the differing arrangements of the chemical bonds, the subject of this chapter. 

Plants are highly sensitive to soil acidity because many equilibria involving plant nutrients are affected by pH. Phosphorus is a primary example. This essential element for plant growth occurs in soils mainly as phosphates, which are subject to phosphate-hydrogen phosphate equilibria. Consequently, phosphorus is... 

The chemistry of trivalent phosphorus compounds in which phosphorus is one or two coordinate is rapidly developing. These systems contain sp or sp2 hybridized phosphorus and multiple TT-bonds between P and other elements and until 1964 it was believed that bond formation involving ptr-pir overlap was unfavourable. Subsequently certain -P=C systems resulted from the use of charged ( 1, 2, 3) and or delocalized systems (4J but it is only in the past few years that successful syntheses of phospha-alkenes, R2C=PR , and phospha-alkynes, RC=P, have been reported. These novel compounds are the subject of this paper. 

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