Phosphorus trichloride formation

Phosphorus/bromine combinations are perhaps the most effective flame retardant combination (ref. 3) and claims have been made for synergy. The formation of phosphorus trichloride or oxychloride has been postulated by analogy to that of the formation of antimony trichloride and oxychloride but there is no evidence for this mechanism. Some reports of synergy appear to be a result of a nonlinear response to the flame retardant concentration. 

The donor-acceptor formation can be considered by transfer of electrons from the donor to the acceptor. In principle one can assume donor-acceptor interaction from A (donor) to B (acceptor) or alternatively, since B (A) has also occupied (unoccupied) orbitals, the opposite charge transfer, from B to A. Such a view refers to mutual electron transfer and has been commonly estabUshed for the analysis of charge transfer spectra of n-complexes [12]. A classical example for a donor-acceptor complex, 2, involving a cationic phosphorus species has been reported by Parry et al. [13]. It is considered that the triaminophosphines act as donor as well as an acceptor towards the phosphenium cation. While 2 refers to a P-donor, M-donors are in general more common, as for example amines, 3a, pyridines, 3b, or the very nucleophilic dimethylaminopyridine (DMAP) [ 14], 3c. It is even a strong donor towards phosphorus trichloride [15]. 

A Lewis base must have valence electrons available for bond formation. Any molecule whose Lewis stmcture shows nonbonding electrons can act as a Lewis base. Ammonia, phosphorus trichloride, and dimethyl ether, each of which contains lone pairs, are Lewis bases. Anions can also act as Lewis bases. In the first example of adduct formation above, the fluoride ion, with eight valence electrons in its 2 s and 2 p orbitals, acts as a Lewis base. 

With phosphorus trichloride, a rather complex reaction results partly in the formation of [PhaP N uPPha PPhCl]+ Cl. The reactivity of the phosphorus(iii) atom is also demonstrated by its ability to desulphurize thiophosphoryl chloride, and its ready reactions with Group VI elements, diborane, and carbon disulphide ... 

The formation and reaction of peroxyl radicals derived by reaction of tervalent phosphorus compounds with oxygen have attracted interest. Photolysis of trialkyl phosphites in oxygenated solutions of aromatic hydrocarbons gives phenols. " Phosphorus trichloride reacts with 1,2-dichloroethylene, in the presence of oxygen, to give (17). It is tempting to suggest that both reactions occur via similar intermediates, e.g. (15) and (16). 

It is possible to make an acid chloride by the action of phosphorus trichloride on an acid. Three accidents have been described that involved the action of this compound on acetic, propionic and 2-furoic acids, respectively. This was explained by the formation of phosphine due to excessive heating that led to the decomposition of the phosphorus acid formed ... 

Another general method for converting alcohols to halides involves reactions with halides of certain nonmetallic elements. Thionyl chloride, phosphorus trichloride, and phosphorus tribromide are the most common examples of this group of reagents. These reagents are suitable for alcohols that are neither acid sensitive nor prone to structural rearrangement. The reaction of alcohols with thionyl chloride initially results in the formation of a chlorosulfite ester. There are two mechanisms by which the chlorosulfite can be converted to a chloride. In aprotic nucleophilic solvents, such as dioxane, solvent participation can lead to overall retention of configuration.7... 

Phosphorus tribromide Phosphorus trichloride Propionic acid Propyl acetate Propyl alcohol Propyl bromide Propyl chloride Propyl formate Propyl iodide Sodium... 

An unusual mixed lithium phosphide/lithium alkyl aggregate has been reported as arising from an attempted synthesis of Li PH(mes ) (46). Initial treatment of phosphorus trichloride with Li(mes ) is reported to give a mixture of the desired product, (mes )PCl2, and the side product (mes )Cl (via Li/Cl exchange) in an approximately 2 1 ratio. Reduction of this mixture with LiAlH4, followed by treatment with BuLi, then leads to rapid formation of Li PH(mes ), accompa-... 

The lithium salt of a substituted cyclopentadienyl anion has been used in reaction with phosphorus trichloride for carbon-phosphorus bond formation.70 The resultant simple displacement product ultimately undergoes dimerization and loss of four (from the dimer) equivalents of HC1 (Equation 4.25). 

The formation of the technically important 2 -hydroxy-3 -naphthoylanilines (Naphthol AS derivatives) is accomplished primarily by a condensation reaction between 2-hydroxy-3-naphthoic acid and an aromatic amine in the presence of phosphorus trichloride at 70 to 80°C. Appropriate reaction media are organic solvents, such as toluene or xylene. In stoichiometric terms, one mole of 2-hydroxy-3-naphthoic acid reacts with 0.4 to 0.5 moles of phosphorus trichloride. The solution is allowed to cool to room temperature, then neutralized with a sodium carbonate solution, and the Naphthol AS derivative is isolated by filtration. Mechanistically, the reaction is thought to proceed via the phosphoazo compound (11) ... 

Phosphorus containing 32P (of the order of 1 g.) was converted into the trichloride. This small-scale conversion presented considerable and unexpected difficulties, the most serious feature being the very ready production of phosphorus pentachloride. (All the reliable descriptions of the preparation of phosphorus trichloride are on a basis of ca. 200 g. of phosphorus.)6 This tendency to pentachloride formation was checked by the correct geometry of the apparatus and by the method of manipulation. 

In many cases the solid, more active and much less volatile pentar chloride is used instead of phosphorus trichloride. Then it is necessary to use a whole mole of PC15 for each mole of alcohol since the reaction leads to the formation of the much more -sluggish phosphorus oxychloride, e.g. 

The formation of phosphanylium salts (77) in the reaction of phosphorus trichloride with methylhydrazones, presumably via the intermediate chlorophosphine (76), may be assisted by aromatic stabilization of the product.61... 

It is instructive to consider why the presence of relatively bulky N-substituents results in the formation of small rings. Of the reactions of phosphorus trichloride with amines, that with t-butylamine has been widely studied (Scheme 6) Intermediates (17) and (18) have been isolated, but not (79), which evidently undergoes a facile cyclisation step to give (20). Two effects can be identified, which are expected to favour the formation of small rings. Firstly, an n.m.r. study of (18)... 

Phosphorus pentachloride purchased as pure is occasionally of inferior quality and gives poor results. It is not a difficult matter to prepare in the laboratory a product suitable for this reaction. To 1000 g. of phosphorus trichloride, chlorine is added until the increase in weight is 500 g. The gas should be added above the surface of the liquid, which is stirred occasionally during the addition. The stirring should not be continuous, however, as this tends to allow the formation of the pentachloride in the tube, which thus becomes clogged. At the end of the reaction the mixture becomes practically solid. 

Treatment of propargyl alcohols with phosphorus trichloride gives chloroallenes and these can undergo dimerization under the reaction conditions, as in the case of the formation of cyclobutanes 15 and 16.30... 

Under similar conditions thionyl chloride reacts with both red and yellow phosphorus with formation of phosphorus trichloride according to the equation ... 

The trioxide possesses marked oxidising properties, in the exercise of which it is generally reduced to the dioxide. Yellow phosphorus soon inflames in the vapour at the ordinary temperature, some of the trioxide being reduced even to sulphur.6 Phosphine is oxidised by solid sulphur trioxide with formation of phosphorus.7 Phosphorus trichloride... 

Selenium monochloride behaves as a strong chlorinating agent towards metals, metallic selenides and hydrocarbons.3 Phosphorus displaces selenium from the chloride with formation of phosphorus trichloride.4 Chlorine converts it into the tetrachloride. 

Excess of phosphorus displaces the selenium from the tetrachloride with the formation of phosphorus trichloride.7... 

Phosphorus pentaehloride acts on selenium dioxide with the formation of the tetrachloride, whilst phosphorus trichloride yields brown amorphous selenium in these reactions phosphorus oxychloride is also formed. 

H. A. Taylor f made a similar experiment with phosphorus trichloride vapour and chlorine, which in glass vessels combine almost instantaneously to give the solid pentachloride. In this instance the combination still took place with immeasurable rapidity in a vessel of paraffin wax. This combination, unlike that of ethylene and bromine, appears to be a homogeneous reaction, since when the trichloride and chlorine are mixed there is a delay of a few seconds due to supersaturation, and then the solid is formed as a cloud which settles slowly to the bottom of the vessel. Some solid formation also takes place on the walls. 

The reaction of Grignard reagents with phosphorus trichloride usually proceeds all the way to the tertiary phosphine, R3P. Stepwise alkylation is rarely observed. Examples of the latter include the formation of small amounts of the monochloro-phosphines, (n-C8 Hi7 )2 PCI2 and (C6Hn)2 PCI,3 in the reaction of the appropriate Grignard reagents with phosphorus trichloride. In... 

The immediate use of the Grignard reagent thus obtained is imperative. If it is allowed to stand for any period of time, the yield in the subsequent reaction with phosphorus trichloride is reduced drastically. Furthermore, if formation of larger amounts of a white precipitate is observed at the end of the Grignard reaction, the reaction mixture should be discarded. 

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