Phosphonous dihalides

Petersen, H., Ureidomethyl Phosphonic Dihalides for Fireproofing Materials, West German Patent Application 1,817,337, 1970. 

The Unexpected Formation of l,2-Oxaphosphol-3> ene 2-Oxides in the Reaction of Diacetone Alcohol with Phosphonous Dihalides... 

Since reaction of phosphorus with alkyl halides occurs also without a catalyst, direct attack by the alkyl halide must be possible. Support that these reactions are also radical in nature has been provided by the work of Petrov, Smirnov, and Emel yanov In the reaction of white phosphorus with Cg H5 CH2 Cl ), PhBr ) ff2-CH3C6H4Br and n-CgHi7Br in the liquid phase phosphonous dihalides are the predominant products but appreciable yields of phosphi-nous halides are also obtained. A correlation was observed between the tempera-... 

Phosphonous dihalides are nearly the exclusive products in the alkylation of white phosphorus with aJkyl and aryl halides dissolved in a phosphorus trihalide. 

The synthesis of chiral phosphine oxides has stimulated effort in a number of laboratories in recent years. An elegant new approach to the problem involves the use of sugar-derived phosphorus heterocycles. These are 1,3,2-dioxa-phosphorinan-2-ones, such as (1), formed from glucosides and various phosphonic dihalides, such as (2). The preparation of chiral phosphine oxides... 

Oxophosphines have been generated by pyrolysis of cyclic phosphine oxides, e.g. r rr-butyloxophosphine (equation 102) and oxophenylphosphine (equation 103) The thermally stable dihydrophosphole 38 gave oxophenylphosphine upon irradiation (equation 104) ". Another route to oxophosphines is the dehalogenation of phosphonic dihalides with magnesium, e.g. oxophenylphosphine from phenylphosphonic dichloride... 

The isolation and characterization of chloroaluminate complexes of the type [CgHigP ClR] [AICI4"], by other workers from reactions which involved phosphonous dihalides, RPCI2, seemed to confirm suggestions as to the reaction mechanism, and which are summarized in Scheme 6. As originally envisioned, the mechanism required the initial complexation of PCI3 and AICI3, a point in doubt, but it may be noted that the proposed intermediate 122 possesses a chlorophosphonium structure similar to that encountered in the McCormack reaction. 

The displacement of halogen from phosphonic dihalides with thiols in the presence of an appropriate base leads to 5,S-diesters rather than (9,5-isomers (equation 30 Z = 0)2-7374,375 gych a reaction has been employed in the determination of the enantiomer composition of chiral thiols. The NMR spectra for a series of phosphonodithioates 163 (Z = O, R = Me, Ph, PhCH2) and also for analogous trithiophosphonates 163 (Z = S, R = Me or Ph) in which the group R is derived from a chiral thiol, showed that the best separation of P NMR signals for the diastereoisomeric forms was achieved when R = Me. Displacement reactions which involve the loss of chlorine from R2P(Z)C1 (Z = or Se ). RP(0)(SR )CP and RP(S)(NHR )C1 by thiols in the presence of a tertiary amine base, and many more, are widely exemplified. 

In 1988, it was discovered that 3-phospholenes can be prepared directly by the reaction of zirconium metallocycles with phosphonous dihalides (Equation (50)) <88JA2310>. The synthesis of only one phospholene (3,4-dimethyl-l-phenyl) has been reported so far, but the method appears to have a good chance of possessing valuable versatility. 

The P-phenyl group of a phosphole can be directly displaced by reaction with alkyl lithium reagents in TMEDA. Both t-butyl <72T47i> and -butyl <720MR(4)171> have been placed on P by this method. With 3,4-dimethyl-1-phenylphosphole, the former reaction occurred in 70% yield, the latter in 31.5% (with some oxide) (Scheme 79). This method is of considerable value for the introduction of the t-butyl group on phosphorus, as this group cannot be used as the P-substituent in a phosphonous dihalide in the McCormack reaction because of steric restrictions. 

A widely used method of making phosphines is by the reduction of various phosphorus compounds with lithium aluminium hydride. These include phosphine oxides, phosphinous halides, phosphonous dihalides, phosphonic dihalides, phosphinic acids and phosphonous esters (6.58). In some cases increased yields can be obtained at low temperatures down to -78°C, and high yields can be obtained by using trichlorsilane or hexachlorodisilane in place of LiAlH4. 

A general method of preparation of alkyl phosphonous dihalides is the reaction of phosphorus trihalide with a dialkyl mercury, a dialkyl cadmium or a trialkyl aluminium. 

Phosphinic acids may be produced by oxidation of primary phosphines or primary phosphine oxides, but the products are liable to be contaminated with phosphonic acids (6.26). Phosphinic acids may also be produced by hydrolysis of phosphonous dihalides (6.164), phosphonous diesters (6.224) or phosphonous diamides (7.189). Good yields are obtained from the halides by adding alcohol, then refluxing with water. 

Most known phosphoranes contain more than one kind of atom directly attached to the central P atom. Alkylhalophosphoranes of types RPX4 and R2PX3 can be obtained by halogenation of the appropriate alkyl phosphonous dihalide or dialkylphosphinous halide (Figures 6.4 and 6.5). 

Other methods which have been employed include the reduction of phosphonous dihalides (6.613) and the thermal decomposition of 7-phosphanorbomenes (6.614). 

Polyphosphines can be made by reduction of a phosphonous dihalide with a metal such as Li, Na, Mg or Hg, or with lithium aluminium hydride (6.680). They are also obtained on heating a phosphonous dihalide with tributyl phosphine (6.681), or triethyl stibine (6.682), or simply heating a phosphonous difluoride in a sealed tube (6.515). 

Phospholenes generally have an envelope-shaped conformation (6.884). The most versatile method for the synthesis of phospholenes is the McCormack cycloaddition reaction using a diene and a phosphonous dihalide or a phosphorus trihalide [63,64]. 

Phosphonamidous chlorides and bromides may be made by redistribution in mixtures of phosphonous dihalide and diamide, which readily takes place on mixing. 

Thiohalides of the type RP(S)X2 and R2P(S)X can be made by heating sulphur with the corresponding phosphonous or phosphinous halides. Phosphonothioic (thiophosphonic) halides can be obtained by the action of hydrogen sulphide on tetrachlorophosphoranes (9.425), or phosphonous halide-aluminium trichloride complex (Chapter 6), or P4SJ0 on the corresponding phosphonic dihalide (9.426), or by reaction (9.427) in which PSCI3 acts as a sulphur donor. Monophenyl phosphine and thionyl chloride produce phenyl phosphonothionic dichloride, which can also be obtained by thermal isomerisation (9.428). 

Phosphonothious acids may exist in equilibrium with the two phosphinothioic acids. The diesters can be made by reacting alcohols or thiols with an appropriate chlorophosphonite, in the presence of a base to remove hydrogen chloride (9.467, 9.468). A cyclic phosphonothionic ester can be obtained from phosphonic dihalides (9.528). 

Phosphine copolymers can be obtained by heating primary phosphines with non-conjugated dienes (12.173), or condensing them with diisocyanates (12.174), or by reacting aryl phosphonous dihalides with certain aromatic hydrocarbons (12.175). 

As might therefore be imagined (correctly), substituted phosphonous dihalides (e.g., dibromophenylphosphine, the product of Equation 10.70) can also react with Grignard reagents to produce unsymmetrical alkaryl-substituted phosphines (Equation 10.74). This reaction, like those of Grignard reactions in general, is usually exothermic and is preformed at low temperature and under nitrogen (to avoid the production of phosphine oxides). 

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