Hexachlorocyclotriphosphazene

Phosphazene polymers are normally made in a two-step process. First, hexachlorocyclotriphosphazene [940-71 -6J, trimer (1), is polymerized in bulk to poly(dichlorophosphazene) [26085-02-9], chloropolymer (2). The chloropolymer is then dissolved and reprecipitated to remove unreacted trimer. After redissolving, nucleophilic substitution on (2) with alkyl or aryloxides provides the desired product (3). 

Hexachlorocyclotriphosphazene (cycHc trimer) is a respiratory irritant. Nausea has also been noted on exposure (10). Intravenous and intraperitoneal toxicity measurements were made on mice. The highest nonlethal dose (LDq) was measured as 20 mg/kg (11). Linear chloropolymer is also beUeved to be toxic (10). Upon organic substitution, the high molecular weight linear polymers have been shown to be inert. Rat implants of eight different polyphosphazene homopolymers indicated low levels of tissue toxicity (12). EZ has been found to be reasonably compatible with blood (13), and has lower hpid absorption than fiuorosihcone. 

The conventional route to prepare I generally involves a high temperature melt polymerization of hexachlorocyclotriphosphazene, or trimer (IV). Recent studies have demonstrated the effectiveness of various acids and organometalllcs as catalysts for the polymerization of IV (8). Alternate routes for the preparation of chloro-polymer which do not involve the ring opening polymerization of trimer have been reported in the patent literature (9. 10). These routes involve a condensation polymerization process and may prove to be of technological importance for the preparation of low to moderate molecular weight polyphosphazenes. 

The first pyrrolylphosphazenes were apparently prepared by McBee and coworkers in 1960, and although the work was never documented in the chemical literature, hexakis-(pyrrolyl)cyclotriphosphazene (1) and octakis-(pyrrolyl)cyclotetraphosphazene were described in a Technical Report of the Defense Technical Information Center.19 Compound 1 was reported to be produced in 26% yield from the interaction of hexachlorocyclotriphosphazene [(NPC 2)3] with excess potassium pyrrolide in refluxing benzene over a 24 hour period. Lithium pyrrolide and pyrrolyl magnesium bromide were found to be unsatisfactory reagents for the preparation of 1. 

Tris-spiro compounds have been generated from hexachlorocyclotriphosphazene by substitution with dihydroxyby-pyridine derivatives (Equation 31) <1999IC5457>. Treatment of hexachlorocyclotriphosphazene with 2equiv of biphenol or binaphthol yields only the / >-compounds 25 and 176. Enantiomerically pure cyclotriphosphazenes were generated from the (R)- or (Tl-forms of binaphthol (Equation 32) <1999EJI1673>. 

Octachlorocyclotetraphoshazene 177 reacts with the sodium salt of 2,2 -methylenebis(4,6-di-/ -butylphenol) to give the 2,2-spiro product 28. A similar substitiution product 27 is formed when 177 is reacted with 1 equiv of N,N -diisopropylpropane-1,3-diamine 178. Reaction of 177 with two equivalents of 178 gave the novel 2,2,6,6-dispiro derivative 179 (Scheme 26). Reaction of hexachlorocyclotriphosphazene with two equivalents of 178 gave the monospiro derivative 126 (X = C1) <1999JCD891>. The tetra-spiro cyclic cyclophosphazene 181 is the major product of the thermolysis of the azide 180 (Equation 33) <2003ICC394>. 

WClg, and vanadium-based initiators (Eq. 53), and the thermal polymerization of hexachlorocyclotriphosphazene (Eq. 54). (Ringopening polymerizations of ethylene and propylene oxides,... 

The polymerization of hexachlorocyclotriphosphazene (I) has been the subject of numerous investigations (9,10). 

Hexachlorocyclotriphosphazene, 19 55 Hexachloroethane, 6 269 Hexachloromelamine, 23 111 Hexachlorophene, bioremediation substrate, 3 773-776 Hexachlorotitanates, 25 53 Hexacosanoic acid, physical properties, 5 30t... 

Thermal polymerization of hexachlorocyclotriphosphazene (LXXXIII) (also referred to as phosphonitrilic chloride) yields poly(dichlorophosphazene) (LXXXIV) (IUPAC poly[nitrilo (dichloro-Ls-phosphanetriyl)] or catena-poly[(dichlorophosphorus)- j,-nitrido]) [Allcock, 1976, 1986, 2002 Allcock and Connolly, 1985 Archer, 2001 De Jaeger and Gleria, 1998 Liu and Stannett, 1990 Majumdar et al., 1989, 1990 Manners, 1996 Potts et al., 1989 Scopelianos and Allcock, 1987 Sennett et al., 1986],... 

Hexachlorocyclotriphosphazene continued) hydrolysis, 21 57, 58 reaction with catechol, 21 60 with diols, 21 60... 

A second reason of interest in cyclophosphazenes has stemmed from the facile ring opening polymerization of the hexachlorocyclotriphosphazene, N3P3CI6, to the linear macromolecule [NPCl2]x [4, 5] (Eq. 1). 

Freshly sublimed hexachlorocyclotriphosphazene (17 g) was placed into a dry Pyrex tube and sealed under vacuum and then heated to 225°C for 1 hour and then at 250°C for 16 hours. The tube was cooled to ambient temperature, broken open, and the contents dissolved in a minimum amount of anhydrous toluene. The product was isolated as a colorless rubbery material after precipitation in an excess hexane. 

Hexachlorocyclotriphosphazene (3.19) is prepared on an industrial scale by the interaction of phosphorus pentachloride with ammonium chloride in an organic solvent such as chlorobenzene. This compound, after careful purification and protection from moisture, is heated in the molten state at temperatures between 210 and 250 °C to induce polymerization.15-18 The mechanism of this reaction is discussed in a later section. Here it is sufficient to note that the process can also be applied, with minor variations, to cyclic phosphazo-phosphazenes (3.22a, 3.23), to cyclic fluorophosphazenes (3.24,3.25), and to cyclic carbo- (3.26), thio- (3.27), and thionyl (3.28) -phosphazenes. 

Hexachlorocyclotriphosphazene (or simply trimer) can be thermally polymerized in bulk or solution at 200-270°C producing hydrolytically unstable poly-dichlorophosphazene (or simply chloropolymer). 

The reactions of hexachlorocyclotriphosphazene (I) with a variety of Grignard reagents (RMgCl where R = Me, Et, n-Pr, ni-Bu, -Pr, Jt-Bu, Ph) were investigated. It was found that these reactions did not lead to initial clevage of the phosphazene ring, but led exclusively to the formation of two well defined types of products, both of which contained intact phosphazene rings as shown in Scheme I. 

However, this reverse line of synthesis constituted in early 1982 a tricky task. Indeed at that time, although the reactions of N3P3Cl(j with monofunctional amines had been extensively investigated 20-25 >, those of hexachlorocyclotriphosphazene with difunctional reagents were less well documented 2t>). 

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