Names | |
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IUPAC name 2,2,4,4,6,6-Hexachloro-1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine | |
Other names
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Identifiers | |
3D model (JSmol) | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.012.160 |
EC Number |
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PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
P3N3Cl6 | |
Molar mass | 347.64 g·mol−1 |
Appearance | colourless solid |
Density | 1.98 g/mL at 25 °C |
Melting point | 112 to 114 °C (234 to 237 °F; 385 to 387 K) |
Boiling point | decomposes (above 167 °C) |
60 °C at 0.05 Torr | |
decomposes | |
Solubility in CCl4 | 24.5 wt % (20 °C) 35.6 wt % (40 °C) 39.2 wt % (60 °C) |
Solubility in cyclohexane | 22.3 wt % (20 °C) 36.8 wt % (40 °C) 53.7 wt % (60 °C) |
Solubility in xylene | 27.7 wt % (20 °C) 38.9 wt % (40 °C) 50.7 wt % (60 °C) |
−149×10−6 cm3/mol | |
Refractive index (nD) | 1.62 (589 nm) |
Structure | |
orthorhombic | |
62 (Pnma, D16 2h) | |
D3h | |
a = 13.87 Å, b = 12.83 Å, c = 6.09 Å | |
Formula units (Z) | 4 |
chair (slightly ruffled) | |
0 D | |
Thermochemistry | |
Std enthalpy of formation (ΔfH⦵298) | −812.4 kJ/mol |
Enthalpy of vaporization (ΔfHvap) | 55.2 kJ/mol |
Enthalpy of sublimation (ΔfHsublim) | 76.2 kJ/mol |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards | mild irritant |
GHS labelling: | |
Danger | |
H314 | |
P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501 | |
Flash point | Non-flammable |
Related compounds | |
Related compounds | Hexafluorophosphazene |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Hexachlorophosphazene is an inorganic compound with the formula (NPCl2)3. The molecule has a cyclic, unsaturated backbone consisting of alternating phosphorus and nitrogen centers, and can be viewed as a trimer of the hypothetical compound N≡PCl2. Its classification as a phosphazene highlights its relationship to benzene. [1] There is large academic interest in the compound relating to the phosphorus-nitrogen bonding and phosphorus reactivity. [2] [3]
Occasionally, commercial or suggested practical applications have been reported, too, utilising hexachlorophosphazene as a precursor chemical. [2] [4] Derivatives of noted interest include the hexalkoxyphosphazene lubricants obtained from nucleophilic substitution of hexachlorophosphazene with alkoxides, [4] or chemically resistant inorganic polymers with desirable thermal and mechanical properties known as polyphosphazenes produced from the polymerisation of hexachlorophosphazene. [2] [4]
Hexachlorophosphazene has a P3N3 core with six equivalent P–N bonds, for which the adjacent P–N distances are 157 pm. [1] [2] [5] This is characteristically shorter than the ca. 177 pm P–N bonds in the valence saturated phosphazane analogues. [3]
The molecule possesses D3h symmetry, and each phosphorus center is tetrahedral with a Cl–P–Cl angle of 101°. [5]
The P3N3 ring in hexachlorophosphazene deviates from planarity and is slightly ruffled (see chair conformation). [2] By contrast, the P3N3 ring in the related hexafluorophosphazene species is completely planar. [2]
31P-NMR spectroscopy is the usual method for assaying hexachlorophosphazine and its reactions. [6] [7] [8] Hexachlorophosphazine exhibits a single resonance at 20.6 ppm as all P environments are chemically equivalent. [7] [8]
In it IR spectrum, the 1370 and 1218 cm−1 vibrational bands are assigned to νP–N stretches. [7] [8] Other bands are found at 860 and 500–600 cm−1, respectively assigned to ring and νP–Cl. [8]
Hexachlorophosphazine and many of its derivatives have been characterized by single crystal X-ray crystallography. [2] [5]
Cyclophosphazenes such as hexachlorophosphazene are distinguished by notable stability and equal P–N bond lengths which, in many such cyclic molecules, would imply delocalization or even aromaticity. To account for these features, early bonding models starting from the mid-1950s invoked a delocalised π system arising from the overlap of N 2p and P 3d orbitals. [2] [3]
Starting from the late 1980s, more modern calculations and the lack of spectroscopic evidence reveal that the P 3d contribution is negligible, invalidating the earlier hypothesis. [3] Instead, a charge separated model is generally accepted. [1] [3]
According to this description, the P–N bond is viewed as a very polarised one (between notional P+ and N−), with sufficient ionic character to account for most of the bond strength. [1] [3]
The rest (~15%) of the bond strength may be attributed to a negative hyperconjugation interaction: the N lone pairs can donate some electron density into π-accepting σ* molecular orbitals on the P. [3]
The synthesis of hexachlorophosphazene was first reported by von Liebig in 1834. In that report he describes experiments conducted with Wöhler. [9] They found that phosphorus pentachloride and ammonia react exothermically to yield a new substance that could be washed with cold water to remove the ammonium chloride coproduct. The new compound contained P, N, and Cl, on the basis of elemental analysis. It was sensitive toward hydrolysis by hot water. [2]
Modern syntheses are based on the developments by Schenk and Römer who used ammonium chloride in place of ammonia and inert chlorinated solvents. By replacing ammonia with ammonium chloride allows the reaction to proceed without a strong exotherm associated with the NH3/PCl5 reaction. Typical chlorocarbon solvents are 1,1,2,2-tetrachloroethane or chlorobenzene, which tolerate the hydrogen chloride side product. Since ammonium chloride is insoluble in chlorinated solvents, workup is facilitated. [10] [11] For the reaction under such conditions, the following stoichiometry applies:
where n can usually take values of 2 (the dimer tetrachlorodiphosphazene), 3 (the trimer hexachlorotriphosphazene), and 4 (the tetramer octachlorotetraphosphazene). [12]
Purification by sublimation gives mainly the trimer and tetramer. Slow vacuum sublimation at approximately 60 °C affords the pure trimer free of the tetramer. [6] Reaction conditions such as temperature may also be tuned to maximise the yield of the trimer at the expense of the other possible products; nonetheless, commercial samples of hexachlorophosphazene usually contain appreciable amounts of octachlorotetraphosphazene, even up to 40%. [6]
The mechanism of the above reaction has not been resolved, but it has been suggested that PCl5 is found in its ionic form [PCl4]+[PCl6]− and the reaction proceeds via nucleophilic attack of [PCl4]+ by NH3 (from [NH4]Cl dissociation). [2] Elimination of HCl (the major side product) creates a reactive nucleophilic intermediate
which through further attack of [PCl4]+ and subsequent HCl elimination, creates a growing acyclic intermediate
until an eventual intramolecular attack leads to the formation of one of the cyclic oligomers. [2]
Hexachlorophosphazene reacts readily with alkali metal alkoxides and amides. [1] [2]
The nucleophilic polysubstitution of chloride by alkoxide proceeds via displacement of chloride at separate phosphorus centers: [1]
The observed regioselectivity is due to the combined steric effects and oxygen lone pair π-backdonation (which deactivates already substituted P atoms). [1] [2]
Heating hexachlorophosphazene to ca. 250 °C induces polymerisation. [1] [2] [4] [6] The tetramer also polymerises in this manner, although more slowly. [4] The conversion is a type of ring-opening polymerisation (ROP). [6] [7] The ROP mechanism is found to be catalysed by Lewis acids, but is overall not very well understood. [7] Prolonged heating of the polymer at higher temperatures (ca. 350 °C) will cause depolymerisation. [2]
The structure of the inorganic chloropolymer product (polydichlorophosphazene) comprises a linear –(N=P(−Cl)2−)n chain, where n ~ 15000. [2] [4] It was first observed in the late 19th century and its form after chain cross-linking has been called "inorganic rubber" due to its elastomeric behaviour. [4]
This polydichlorophosphazene product is the starting material for a wide class of polymeric compounds, collectively known as polyphosphazenes. Substitution of the chloride groups by other nucleophilic groups, especially alkoxides as laid out above, yields numerous characterised derivatives. [2] [4] [6]
The nitrogen centres of hexachlorophosphazene are weakly basic, and this Lewis base behaviour has been suggested to play a role in the polymerisation mechanism. [7] Specifically, hexachlorophosphazene has been reported to form adducts of various stoichiometries with Lewis acids AlCl3, AlBr3, GaCl3, SO3, TaCl5, VOCl3, but no isolable product with BCl3. [7]
Among these, the best structurally characterised are the 1:1 adducts with aluminium trichloride or with gallium trichloride; they are found with the Al/Ga atom bound to a N and assume a more prominently distorted chair conformation compared to the free hexachlorophosphazene. [7] The adducts also exhibit fluxional behaviour in solution for temperatures down to −60 °C, which can be monitored with 15N and 31P-NMR. [7]
Hexachlorophosphazene has also found applications in research by enabling aromatic coupling reactions between pyridine and either N,N-dialkylanilines or indole, resulting in 4,4'-substituted phenylpyridine derivatives, postulated to go through a cyclophosphazene pyridinium salt intermediate. [6]
The compound may also be used as a peptide coupling reagent for the synthesis of oligopeptides in chloroform, though for this application the tetramer octachlorotetraphosphazene usually proves more effective. [6]
Both the trimer and tetramer in hydrocarbon solutions photochemically react forming clear liquids identified as alkyl-substituted derivatives (NPCl2−xRx)n, where n = 3, 4. [6] Such reactions proceed under prolonged UVC (mercury arc) illumination without affecting the PnNn rings. Solid films of the trimer and tetramer will not undergo any chemical change under such irradiation conditions. [6]
The hexalkoxyphosphazenes (especially the aryloxy species), resulting from the nucleophilic hexasubstitution of the hexachlorophosphazene P atoms, are valued for their high thermal and chemical stability and their low glass transition temperature. [4] Certain hexalkoxyphosphazenes (such as the hexa-phenoxy derivative) have been put to commercial use as fireproof materials and high temperature lubricants. [4]
Polyphosphazenes obtained from polymerised hexachlorophosphazene (polydichlorophosphazene) have gathered attention within the field of inorganic polymers and probed investigations on the properties of elastomeric and thermoplastic derivatives. [2] [4] Some of them appear promising for future applications as fibre- or membrane-forming high performance materials, since they combine transparency, backbone flexibility, tunable hydrophilicity or hydrophobicity, and various other desirable properties. [4]
Current commercial applications for polyphosphazene rubber components are in O-rings, fuel lines and shock absorbers, where the polyphosphazenes confer fire resistance, imperviousness to oils and flexibility even at very low temperatures. [2]
In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.
Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as “tickle” or “tickle 4”, as a phonetic representation of the symbols of its molecular formula.
In chemistry, the term phosphonium describes polyatomic cations with the chemical formula PR+
4. These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions.
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides/oxychlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.
Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic and reacts readily with water to release hydrogen chloride.
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to PPh3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a ligand for transition metal complexes, including ones that serve as catalysts in organometallic chemistry. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.
Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.
Tetrasulfur tetranitride is an inorganic compound with the formula S4N4. This gold-poppy coloured solid is the most important binary sulfur nitride, which are compounds that contain only the elements sulfur and nitrogen. It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding.
Phosphoryl chloride is a colourless liquid with the formula POCl3. It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide. It is mainly used to make phosphate esters such as tricresyl phosphate.
Nucleophilic acyl substitution describes a class of substitution reactions involving nucleophiles and acyl compounds. In this type of reaction, a nucleophile – such as an alcohol, amine, or enolate – displaces the leaving group of an acyl derivative – such as an acid halide, anhydride, or ester. The resulting product is a carbonyl-containing compound in which the nucleophile has taken the place of the leaving group present in the original acyl derivative. Because acyl derivatives react with a wide variety of nucleophiles, and because the product can depend on the particular type of acyl derivative and nucleophile involved, nucleophilic acyl substitution reactions can be used to synthesize a variety of different products.
Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.
Lithium amide or lithium azanide is an inorganic compound with the chemical formula LiNH2. It is a white solid with a tetragonal crystal structure. Lithium amide can be made by treating lithium metal with liquid ammonia:
In inorganic chemistry, sulfonyl halide groups occur when a sulfonyl functional group is singly bonded to a halogen atom. They have the general formula RSO2X, where X is a halogen. The stability of sulfonyl halides decreases in the order fluorides > chlorides > bromides > iodides, all four types being well known. The sulfonyl chlorides and fluorides are of dominant importance in this series.
Phosphazenes refer to classes of organophosphorus compounds featuring phosphorus(V) with a double bond between P and N. One class of phosphazenes have the formula R−N=P(−NR2)3. These phosphazenes are also known as iminophosphoranes and phosphine imides. They are superbases. Another class of compounds called phosphazenes are represented with the formula (−N=P 2−)n, where X = halogen, alkoxy group, amide and other organyl groups. One example is hexachlorocyclotriphosphazene (−N=P 2−)3. Bis(triphenylphosphine)iminium chloride [Ph3P=N=PPh3]+Cl−is also referred to as a phosphazene, where Ph = phenyl group. This article focuses on those phosphazenes with the formula R−N=P(−NR2)3.
Organophosphines are organophosphorus compounds with the formula PRnH3−n, where R is an organic substituent. These compounds can be classified according to the value of n: primary phosphines (n = 1), secondary phosphines (n = 2), tertiary phosphines (n = 3). All adopt pyramidal structures. Organophosphines are generally colorless, lipophilic liquids or solids. The parent of the organophosphines is phosphine (PH3).
Thiophosphoryl chloride is an inorganic compound with the chemical formula PSCl3. It is a colorless pungent smelling liquid that fumes in air. It is synthesized from phosphorus chloride and used to thiophosphorylate organic compounds, such as to produce insecticides.
Cyclodiphosphazanes are saturated four membered P2N2 ring systems and one of the major classes of cyclic phosphazene compounds. Bis(chloro)cyclodiphosphazanes, (cis-[ClP(μ-NR)]2) are important starting compounds for synthesizing a variety of cyclodiphosphazane derivatives by nucleophilic substitution reactions; are prepared by reaction of phosphorus trichloride (PCl3) with a primary amine (RNH2) or amine hydrochlorides (RNH3Cl).
In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula AOmXn, where X is a halogen. Known oxohalides have fluorine (F), chlorine (Cl), bromine (Br), and/or iodine (I) in their molecules. The element A may be a main group element, a transition element, a rare earth element or an actinide. The term oxohalide, or oxyhalide, may also refer to minerals and other crystalline substances with the same overall chemical formula, but having an ionic structure.
Triphosphorus pentanitride is an inorganic compound with the chemical formula P3N5. Containing only phosphorus and nitrogen, this material is classified as a binary nitride. While it has been investigated for various applications this has not led to any significant industrial uses. It is a white solid, although samples often appear colored owing to impurities.
Vinylphosphonic acid is an organophosphorus compound with the formula C2H3PO3H2. It is a colorless, low-melting solid, although commercial samples are often yellowish viscous liquids. It is used to prepare adhesives. As in other phosphonic acids, the phosphorus center is tetrahedral, being bonded to an organic group (vinyl in this case), two OH groups, and an oxygen.