Halides phosphorus

Direct reaction of phosphorus and halogen gives the trihalide (except PF3) if phosphorus is kept in excess. For example, phosphorus and chlorine give PCI3, which is a volatile, easily hydrolysed, fuming liquid  

Many other phosphorus compounds can be made from PCI3. Industrially, it is important as a source of organophosphorus compounds for oil and fuel additives, plasticizers and insecticides. 

PF3 is a colourless, odourless gas formed by the action of a metal fluoride such as Cap2 on PCI3  

The diphosphorus tetrahalides, P2X4, are also known, as are many mixed halide compounds. 

Phosphorus forms the halides PX3 (X = F, Cl, Br and I) and PX5 (X = F, Cl and Br) PI5 is unknown. Most are made by direct combination of the elements with the product determined by which element is in excess. PF3, however, must be made by reaction 15.74 and a convenient synthesis of PF5 is from KPFg (see below). The halides are all hydrolysed by water (e.g. equation 15.75), although PF3 reacts only slowly. 

PCI3 -F AsFj PF3 -F ASCI3 PCI3 -F 3H2O H3PO3 -F 3HC1 

Each of the trihalides has a trigonal pyramidal structure, 15.29. Phosphorus trifluoride is a very poisonous, colourless and odourless gas. It has the ability (like CO, see Section 24.2) to form complexes with metals and Lewis 

Box 15.5 Crystal structure disorders disorders involving F and O atoms 

Phosphorus trichloride is a colourless liquid (mp 179.5 K, bp 349 K) which fumes in moist air (equation 15.75) and is toxic. Its reactions include those in scheme 15.78. 

First look up the spin quantum number and natural abundance of 

Adjacent P nuclei will couple, and the presence of a triplet and doublet in the spectrum is consistent with a P—P—P backbone in [Psle] - The terminal P atoms must be equivalent and therefore the following structure can be proposed  

Single-crystal X-ray diffraction (at 109 K) data show that PF5 has a trigonal bipyramidal structure, 15.32. In solution, the molecule is fluxional on the NMR spectroscopic time-scale and one doublet is observed in the NMR spectrum, i.e. all F environments are equivalent and couple with the P nucleus. This stereochemical non-rigidity is another example of Berry pseudo-rotation (see Fig. 4.24). 

Electron diffraction data show that in the gas phase, PCI5 has a molecular, trigonal bipyramidal structure (P-Clax = 214, P-Clgq = 202 pm), provided that thermal dissociation into PCI3 and CI2 is prevented by the presence of an excess of CI2. In the solid state, however, tetrahedral [PCm (P—Cl =197 pm) and octahedral [PCl ]  

Phosphorus forms a wide range of compounds with the halogens, the most important of which are the trihalides and pentahalides. Phosphorus trichloride (PCI3) is commercially the most significant of these compounds and is used to prepare a wide variety of products, including soaps, detergents, plastics, and insecticides. 

Phosphorus chlorides, bromides, and iodides can be made by direct oxidation of elemental phosphorus with the elemental halogen. PCI3, for example, which is a liquid at room temperature, is made by passing a stream of dry chlorine gas over white or red phosphorus  

If excess chlorine gas is present, an equilibrium is established between PCI3 and PCI5. 

The phosphorus halides hydrolyze on contact with water. The reactions occur readily, and most of the phosphorus halides fume in air because of reaction with water vapor. In the presence of excess water the products are the corresponding phosphorus oxyacid and hydrogen halide  

Despite the fact that both contain oniy phosphorus atoms, these two forms of phosphorus differ greatly in reactivity. The white allotrope, which reacts violently with oxygen, must be stored under water so that it is not exposed to air. The much less reactive red form does not need to be stored this way. 

Which oxyacid is produced when PF3 reacts with water  

By the latter part of the 19th century, Sdiutzenbergpr and FontaineH had already noted that PQ5 was a strong oxidant. They demonstrated that phosphorus pentachloride interacts with platinum bla( to give a bridged homobinudear platinum(n) complex, Eq. 8.33  

This synthesis of [Pt2(it-Q)2Cl2(PCl3)2] was reproduced, confirmed, and described in detail by Arbuzov and Zoroastrova.1 5 has also been shown that phosphorus pentabromide,PBrs, similarly reads with platinum black to form Pt2( x-Br)2Br2(PBr3)2].ll  

Oxidative chlorination of anionic platinumdD complexes with PQ5 has been described, Eqs. 8.34 and 8.35  

Similar reactions of neutral complexes of platinum (n) are known, Eq. 8.36  

The oxidation of cationic platinum(II) complexes also can be accomplished with phosphorus pentachloride, Eq. 8.37  

The tetrakis(hydroxymethyl)phosphonium chloride so formed is the major ingredient with urea-formaldehyde or melamine-formaldehyde resins for the permanent flame-proofing of cotton cloth. 

The next member of the open-chain series P H - -2 is P3H5, i.e. PH2PHPH2, a colourless liquid that can be stored in the dark at —80° for several days. 0 an be made by disproportionation (2P2H4----- P3H5 -)- PH3) but it is dif- 

Tetraphosphane(6), P4H6, exists as an equilibrium mixture of the two structural isomers H2PPHPHPH2 in) and P(PH2)3(i), and itself reacts with P3H5 at —20° according to the idealized stoichiometry P4H6 4- P3H5 --- 2PH3 4- 

cyc/o-(PH)5. All members of the series cyc/o-P H (n = 3-10) have been detected mass spectrometrically in the thermolysis products from P2H4.  

Polycyclic polyphosphanes are often best prepared by direct protonation of the corresponding polyphosphide anions (Figs. 12.11 and 12.12) 

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The hydroxyl groups of 5-hydroxypyrazoles (498) are readily replaced by halogens by the action of phosphorus halides. 

These compounds generally exist in carbonyl forms. The oxygen function can be converted into halogen by phosphorus halides. Reactions with electrophiles are quite complex. Thus urazole (511) reacts with diazomethane quickly to yield (512), which is more slowly converted into (513). 1-Phenylurazole gives (514) however, 4-phenylurazole yields (515). Oxadiazolinones of type (516) can be alkylated at both O- and N-atoms. 

R2ASNCS, react similarly to the phosphorus halides (76RCR25). Halosilanes do not react with thiiranes. 

Table 12.3 Some physical properties of the binary phosphorus halides...

I. Reactions with Miscbli.aneous Inorganic Compounds 1. Phosphorus Halides... 

Reaction between phosphorus halides and Grignard reagents... 

Amine-phosphorus halide reactions involve hydrogen halide (or amine hydrohalide) formation. They can be complicated through acid catalysis or side reactions. Thus, the possible formation of skeletally stabilized products through transamination reactions in which no hydrohalide products are obtained is of interest. 

See Chromium pentafluoride Phosphorus trichloride Chromyl chloride Non-metal halides Fluorine Phosphorus halides Iodine chloride Phosphorus trichloride... 

Arbusov reaction of thienyl halides with phosphites in the presence of nickel catalyst [41, 42], or palladium catalyzed phosphorylation of thienyl halides [43], and some of them are commercially available (Scheme 22). 2,5-Diphosphorylthiophenes were synthesized by Arbusov reaction of thienyl halides with phosphites in the presence of nickel catalyst [44] or reaction of 2,5-dilithiothiophene with phosphorus halides followed by oxidation [45] (Scheme 23). 

The H2S03F+ ion is such a strong acid that it will also protonate phosphorus halides as well as hydrocarbons. 

When the phosphorus halide is PI3, this reaction is a convenient way to produce HI. Arsenic trihalides hydrolyze in an analogous way but the trihalides of antimony and bismuth react to produce oxyhalides. 

Preparation of diethyl 3-diphenylthiophosphoryl-2-morpholino-l-cyclohexenylphosphonous acid — Reaction of an enamine with a phosphorus halide and subsequent esterification... 

Preparation of bis(4-methoxyphenyl)phenylphosphine oxide — Reaction of a Grignard reagent with a phosphorus halide... 

Reaction of a phosphorus halide with a 2-alkynol and subsequent rearrangement to generate a hydroxyphosphonate... 

The difficulties attendant with the direct preparation from alcohol and phosphorus halide of partial ester/partial halide systems may be overcome through the use of a variety of alternative approaches. We will briefly consider a few of these here. 

Both of these types of organometallics have the disadvantages of difficulties in preparation and extreme toxicity. Their major advantage is that they provide a controlled reaction, allowing a single halogen of the phosphorus halide to be displaced, leaving the others untouched. 

Of course, the high reactivity of the Grignard reagents can be used to good advantage for exhaustive alkylation or arylation in the preparation of a wide range of phosphorus halides and esters.43 18... 

The reaction is performed most simply by the addition of the propargylic alcohol to a solution of the phosphorus halide. Rearrangement of the phosphorus ester proceeds at ambient temperature or with mild heating. When phosphorus trihalides are used, the product can be isolated as the phosphonic dichloride.168169 Aqueous workup provides the phosphonic acid.162 In most instances, however, a dialkyl phosphorochloridite with only a single halogen on phosphorus available for reaction with alcohol has been used.165 170 174... 

Reaction of an enamine with a phosphorus halide and subsequent esterification72... 

The second reaction proceeds much more energetically than the first, especially if preformed phosphorus halide is used. This is, however, not always necessary, at least not in the case of replacements by bromine and iodine in many cases the procedure is rather to produce the halide only during the reaction, either by dropping bromine from a separating funnel into a mixture of alcohol and red phosphorus or, as above, by adding finely powdered iodine. Like the former, this reaction can also be applied to polyhydric and to substituted alcohols indeed, it is possible to replace all the OH groups by halogens, and in particular also by chlorine. 

The action of phosphorus is quite different and much more complicated. The phosphorus halide which is first formed reacts with the acid to form the acid chloride and this, with a second molecule of the acid, forms the anhydride ... 

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