Phosphonium

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Phosphonium ion Phosphonium-2D.svg
Phosphonium ion
Structure of PH 4, the parent phosphonium cation. Phosphonium-3D-balls.png
Structure of PH
4, the parent phosphonium cation.

In chemistry, the term phosphonium (more obscurely: phosphinium) describes polyatomic cations with the chemical formula PR+
4 (where R is a hydrogen or an alkyl, aryl, or halide group). These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions. [1]

Contents

Types of phosphonium cations

Protonated phosphines

The parent phosphonium is PH+
4 as found in the iodide salt, phosphonium iodide. Salts of the parent PH+
4 are rarely encountered, but this ion is an intermediate in the preparation of the industrially useful tetrakis(hydroxymethyl)phosphonium chloride:

PH3 + HCl + 4 CH2O → P(CH
2OH)+
4Cl−

Many organophosphonium salts are produced by protonation of primary, secondary, and tertiary phosphines:

PR3 + H+ → HPR+
3

The basicity of phosphines follows the usual trends, with R = alkyl being more basic than R = aryl. [2]

Tetraorganophosphonium cations

The most common phosphonium compounds have four organic substituents attached to phosphorus. The quaternary phosphonium cations include tetraphenylphosphonium, (C6H5)4P+ and tetramethylphosphonium P(CH
3)+
4.

Tetramethylphosphonium bromide Me4PBr.png
Tetramethylphosphonium bromide
Structure of solid "phosphorus pentachloride", illustrating its autoionization to tetrachlorophosphonium. EntryWithCollCode76731.png
Structure of solid "phosphorus pentachloride", illustrating its autoionization to tetrachlorophosphonium.

Quaternary phosphonium cations (PR+
4) are produced by alkylation of organophosphines. [3] For example, the reaction of triphenylphosphine with methyl bromide gives methyltriphenylphosphonium bromide:

PPh3 + CH3Br → [CH3PPh3]+Br−

The methyl group in such phosphonium salts is mildly acidic, with a pKa estimated to be near 15: [5]

[CH3PPh3]+ + base → CH2=PPh3 + [Hbase]+

This deprotonation reaction gives Wittig reagents. [6]

Solid phosphorus pentachloride is an ionic compound, formulated PCl+
4PCl−
6, that is, a salt containing the tetrachlorophosphonium cation. [7] [8] Dilute solutions dissociate according to the following equilibrium:

PCl5⇌PCl+
4 + Cl−

Triphenylphosphine dichloride (Ph3PCl2) exists both as the pentacoordinate phosphorane and as the chlorotriphenylphosphonium chloride, depending on the medium. [9] The situation is similar to that of PCl5. It is an ionic compound (PPh3Cl)+Cl− in polar solutions and a molecular species with trigonal bipyramidal molecular geometry in apolar solution. [10]

Alkoxyphosphonium salts: Arbuzov reaction

The Michaelis–Arbuzov reaction is the chemical reaction of a trivalent phosphorus ester with an alkyl halide to form a pentavalent phosphorus species and another alkyl halide. Commonly, the phosphorus substrate is a phosphite ester (P(OR)3) and the alkylating agent is an alkyl iodide. [11]

The mechanism of the Michaelis-Arbuzov reaction Michaelis-Arbuzov Reaction Mechanism.png
The mechanism of the Michaelis–Arbuzov reaction

Uses

Textile finishes

Tetrakis(hydroxymethyl)phosphonium chloride is used in production of textiles. Tetrakis(hydroxymethyl)phosphonium chloride.png
Tetrakis(hydroxymethyl)phosphonium chloride is used in production of textiles.

Tetrakis(hydroxymethyl)phosphonium chloride has industrial importance in the production of crease-resistant and flame-retardant finishes on cotton textiles and other cellulosic fabrics. [12] [13] A flame-retardant finish can be prepared from THPC by the Proban Process, [14] in which THPC is treated with urea. The urea condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to phosphine oxide as the result of this reaction. [15]

Phase-transfer catalysts and precipitating agents

Organic phosphonium cations are lipophilic and can be useful in phase transfer catalysis, much like quaternary ammonium salts. Salts or inorganic anions and tetraphenylphosphonium (PPh+
4) are soluble in polar organic solvents. One example is the perrhenate (PPh4[ReO4]). [16]

Reagents for organic synthesis

Wittig reagents are used in organic synthesis. They are derived from phosphonium salts. A strong base such as butyllithium or sodium amide is required for the deprotonation:

[Ph3P+CH2R]X− + C4H9Li → Ph3P=CHR + LiX + C4H10

One of the simplest ylides is methylenetriphenylphosphorane (Ph3P=CH2). [6]

The compounds Ph3PX2 (X = Cl, Br) are used in the Kirsanov reaction. [17] The Kinnear–Perren reaction is used to prepare alkylphosphonyl dichlorides (RP(O)Cl2) and esters (RP(O)(OR′)2). A key intermediate are alkyltrichlorophosphonium salts, obtained by the alkylation of phosphorus trichloride: [18]

RCl + PCl3 + AlCl3 → [RPCl3]+AlCl−
4

Ammonia production for "green hydrogen"

The main industrial procedure for the production of ammonia today is the thermal Haber-Bosch process, which generally uses fossil gas as a source of hydrogen, which is then combined with nitrogen to produce ammonia. In 2021, Professor Doug MacFarlane and collaborators Alexandr Simonov and Bryan Suryanto of Monash University devised a method of producing green ammonia that has the potential to make Haber-Bosch plants obsolete. [19] Their process is similar to the electrolysis approach for producing hydrogen. While working with local company Verdant, which wanted to make bleach from saltwater by electrolysis, Suryanto discovered that a tetraalkyl phosphonium salt allowed the efficient production of ammonia at room temperature. [20]

See also

Related Research Articles

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.

<span class="mw-page-title-main">Phosphorus pentachloride</span> Chemical compound

Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, 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.

<span class="mw-page-title-main">Phosphorus trichloride</span> Chemical compound

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.

<span class="mw-page-title-main">Triphenylphosphine</span> Chemical compound

Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.

<span class="mw-page-title-main">Michaelis–Arbuzov reaction</span>

The Michaelis–Arbuzov reaction is the chemical reaction of a trivalent phosphorus ester with an alkyl halide to form a pentavalent phosphorus species and another alkyl halide. The picture below shows the most common types of substrates undergoing the Arbuzov reaction; phosphite esters (1) react to form phosphonates (2), phosphonites (3) react to form phosphinates (4) and phosphinites (5) react to form phosphine oxides (6).

<span class="mw-page-title-main">Rhodium(III) chloride</span> Chemical compound

Rhodium(III) chloride refers to inorganic compounds with the formula RhCl3(H2O)n, where n varies from 0 to 3. These are diamagnetic solids featuring octahedral Rh(III) centres. Depending on the value of n, the material is either a dense brown solid or a soluble reddish salt. The soluble trihydrated (n = 3) salt is widely used to prepare compounds used in homogeneous catalysis, notably for the industrial production of acetic acid and hydroformylation.

<span class="mw-page-title-main">Palladium(II) chloride</span> Chemical compound

Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value in organic synthesis. It is prepared by the reaction of chlorine with palladium metal at high temperatures.

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.

<span class="mw-page-title-main">Phosphine oxide</span> Class of chemical compounds

Phosphine oxides are phosphorus compounds with the formula OPX3. When X = alkyl or aryl, these are organophosphine oxides. Triphenylphosphine oxide is an example. An inorganic phosphine oxide is phosphoryl chloride (POCl3).

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).

<span class="mw-page-title-main">Tetraphenylphosphonium chloride</span> Chemical compound

Tetraphenylphosphonium chloride is the chemical compound with the formula (C6H5)4PCl, abbreviated Ph4PCl or PPh4Cl. Tetraphenylphosphonium and especially tetraphenylarsonium salts were formerly of interest in gravimetric analysis of perchlorate and related oxyanions. This colourless salt is used to generate lipophilic salts from inorganic and organometallic anions. Thus, Ph4P+ is useful as a phase-transfer catalyst, again because it allows inorganic anions to dissolve in organic solvents.

<span class="mw-page-title-main">Diphenylphosphine</span> Chemical compound

Diphenylphosphine, also known as diphenylphosphane, is an organophosphorus compound with the formula (C6H5)2PH. This foul-smelling, colorless liquid is easily oxidized in air. It is a precursor to organophosphorus ligands for use as catalysts.

<span class="mw-page-title-main">Tetrakis(hydroxymethyl)phosphonium chloride</span> Chemical compound

Tetrakis(hydroxymethyl)phosphonium chloride (THPC) is an organophosphorus compound with the chemical formula [P(CH2OH)4]Cl. The cation P(CH2OH)4+ is four-coordinate, as is typical for phosphonium salts. THPC has applications as a precursor to fire-retardant materials, as well as a microbiocide in commercial and industrial water systems.

<span class="mw-page-title-main">1,3-Bis(diphenylphosphino)propane</span> Chemical compound

1,3-Bis(diphenylphosphino)propane (dppp) is an organophosphorus compound with the formula Ph2P(CH2)3PPh2. The compound is a white solid that is soluble in organic solvents. It is slightly air-sensitive, degrading in air to the phosphine oxide. It is classified as a diphosphine ligand in coordination chemistry and homogeneous catalysis.

<span class="mw-page-title-main">Dimethylphenylphosphine</span> Chemical compound

Dimethylphenylphosphine is an organophosphorus compound with a formula P(C6H5)(CH3)2. The phosphorus is connected to a phenyl group and two methyl groups, making it the simplest aromatic alkylphosphine. It is colorless air sensitive liquid. It is a member of series (CH3)3-n(C6H5)2P that also includes n = 0, n = 2, and n = 3 that are often employed as ligands in metal phosphine complexes.

Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts.

<span class="mw-page-title-main">Metal-phosphine complex</span>

A metal-phosphine complex is a coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).

In organophosphorus chemistry, an aminophosphine is a compound with the formula R3−nP(NR2)n where R = H or an organic substituent, and n = 0, 1, 2. At one extreme, the parent H2PNH2 is lightly studied and fragile, but at the other extreme tris(dimethylamino)phosphine (P(NMe2)3) is commonly available. Intermediate members are known, such as Ph2PN(H)Ph. These compounds are typically colorless and reactive toward oxygen. They have pyramidal geometry at phosphorus.

<span class="mw-page-title-main">Phosphonium iodide</span> Chemical compound

Phosphonium iodide is a chemical compound with the formula PH
4I. It is an example of a salt containing an unsubstituted phosphonium cation. Phosphonium iodide is commonly used as storage for phosphine and as a reagent for substituting phosphorus into organic molecules.

Hydroxymethylation is a chemical reaction that installs the CH2OH group. The transformation can be implemented in many ways and applies to both industrial and biochemical processes.

References

  1. ↑ Corbridge, D. E. C. (1995). Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology (5th ed.). Amsterdam: Elsevier. ISBN   978-0-444-89307-9.
  2. ↑ Li, T.; Lough, A. J.; Morris, R. H. (2007). "An Acidity Scale of Tetrafluoroborate Salts of Phosphonium and Iron Hydride Compounds in [D2]Dichloromethane". Chem. Eur. J. 13 (13): 3796–3803. doi:10.1002/chem.200601484. PMID   17245785.
  3. 1 2 H.-F. Klein (1978). "Trimethylphosphonium Methylide (Trimethyl Methylenephosphorane)". Inorganic Syntheses. Inorganic Syntheses. Vol. 18. pp. 138–140. doi:10.1002/9780470132494.ch23. ISBN   9780470132494.
  4. ↑ Finch, A.; Fitch, A.N.; Gates, P.N. (1993). "Crystal and Molecular structure of a metastable modification of phosphorus pentachloride". Journal of the Chemical Society, Chemical Communications (11): 957–958. doi:10.1039/c39930000957.
  5. ↑ Ling-Chung, Sim; Sales, Keith D.; Utley, James H. P. (1990). "Measurement of pKa Values for Phosphonium Salts via the Kinetics of Proton Transfer to an Electrogenerated Base". Journal of the Chemical Society, Chemical Communications (9): 662. doi:10.1039/C39900000662.
  6. 1 2 Wittig; Schoellkopf, U. (1960). "Methylenecyclohexane". Organic Syntheses. 40: 66. doi:10.15227/orgsyn.040.0066.. Describes Ph3P=CH2.
  7. ↑ Holleman, A. F.; Wiber, E.; Wiberg, N. (2001). Inorganic Chemistry. Academic Press. ISBN   978-0-12-352651-9.
  8. ↑ Suter, R. W.; Knachel, H. C.; Petro, V. P.; Howatson, J. H. & Shore, S. G. (1978). "Nature of Phosphorus(V) Chloride in Ionizing and Nonionizing Solvents". Journal of the American Chemical Society . 95 (5): 1474–1479. doi:10.1021/ja00786a021.
  9. ↑ S. M. Godfrey; C. A. McAuliffe; R. G. Pritchard; J. M. Sheffield (1996). "An X-ray crystallorgraphic study of the reagent Ph3PCl2; not charge-transfer, R3P–Cl–Cl, trigonal bipyramidal or [R3PCl]Cl but an unusual dinuclear ionic species, [Ph3PCl+⋯Cl–⋯+CIPPh3]Cl containing long Cl–Cl contacts". Chemical Communications (22): 2521–2522. doi:10.1039/CC9960002521.
  10. ↑ Jennings, EV; Nikitin, K; Ortin, Y; Gilheany, DG (2014). "Degenerate Nucleophilic Substitution in Phosphonium Salts". J. Am. Chem. Soc. 136 (46): 16217–16226. doi:10.1021/ja507433g. PMID   25384344.
  11. ↑ Bhattacharya, A. K.; Thyagarajan, G. (1981). "Michaelis–Arbuzov rearrangement". Chem. Rev. 81 (4): 415–430. doi:10.1021/cr00044a004.
  12. ↑ Weil, Edward D.; Levchik, Sergei V. (2008). "Flame Retardants in Commercial Use or Development for Textiles". J. Fire Sci. 26 (3): 243–281. doi:10.1177/0734904108089485. S2CID   98355305.
  13. ↑ Svara, Jürgen; Weferling, Norbert ; Hofmann, Thomas. Phosphorus Compounds, Organic. Ullmann's Encyclopedia of Industrial Chemistry. John Wiley & Sons, Inc., 2008 doi : 10.1002/14356007.a19_545.pub2
  14. ↑ "Frequently asked questions: What is the PROBAN® process?". Rhodia Proban. Archived from the original on December 7, 2012. Retrieved February 25, 2013.
  15. ↑ Reeves, Wilson A.; Guthrie, John D. (1956). "Intermediate for Flame-Resistant Polymers-Reactions of Tetrakis(hydroxymethyl)phosphonium Chloride". Industrial and Engineering Chemistry . 48 (1): 64–67. doi:10.1021/ie50553a021.
  16. ↑ Dilworth, J. R.; Hussain, W.; Hutson, A. J.; Jones, C. J.; McQuillan, F. S. (1996). "Tetrahalo Oxorhenate Anions". Inorganic Syntheses. Inorganic Syntheses. Vol. XXXI. pp. 257–262. doi:10.1002/9780470132623.ch42. ISBN   9780470132623.
  17. ↑ Studies in Organophosphorus Chemistry. I. Conversion of Alcohols and Phenols to Halides by Tertiary Phosphine Dihalides G. A. Wiley, R. L. Hershkowitz, B. M. Rein, B. C. Chung J. Am. Chem. Soc., 1964, 86 (5), pp 964–965 doi : 10.1021/ja01059a073
  18. ↑ Svara, J.; Weferling, N.; Hofmann, T. "Phosphorus Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_545.pub2.
  19. ↑ Breakthrough brings green ammonia production closer to reality
  20. ↑ Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle
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