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 Gravimetric analysis describes a set of methods used in analytical chemistry for the quantitative determination of an analyte (the ion being analyzed) based on its mass. The principle of this type of analysis is that once an ion's mass has been ...

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. ...

and related oxyanions. This colourless

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

is used to generate lipophilic salts from inorganic and organometallic

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s. Thus, Ph₄P⁺ is useful as a

phase-transfer catalyst In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of heterogeneous catalysis. Ionic reac ...

, again because it allows inorganic anions to dissolve in

organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

Structure and basic properties

The cation is tetrahedral. PPh₄Cl crystallises as the anhydrous salt, which is normal item of commerce, as well as a monohydrate and a dihydrate. In

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

, salts are of interest as they often crystallise easily. The rigidity of the phenyl groups facilitates packing and elevates the

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

relative to alkyl-based

quaternary ammonium salt In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cation ...

s. Also, since these salts are soluble in organic media, a wide range of solvents can be employed for their crystallisation.

Preparation

PPh₄Cl and many analogous compounds can be prepared by the reaction of

chlorobenzene Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

with

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...

catalysed by nickel salts: :PhCl + PPh₃ → Ph₄PCl The compound was originally prepared as the corresponding bromide salt (CAS No. 2751-90-8), which in turn was synthesized by passing dry oxygen through the reaction of

phenylmagnesium bromide Phenylmagnesium bromide, with the simplified formula , is a magnesium-containing organometallic compound. It is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide is a Grignard reagent. It is ...

and

. The synthesis probably proceeds via the reaction of the

Grignard reagent A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . ...

with triphenylphosphine oxide. :PhMgBr + Ph₃PO → Ph₄POMgBr :Ph₄POMgBr + HBr → Ph₄PBr + "Mg(OH)Br"

Use in synthesis

Tetraphenylphosphonium salts of inorganic or metalloorganic anions are often sought because they are easily crystallized. They also tend to be soluble in polar organic solvents such as

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile ( hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

and

dimethylformamide Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the majo ...

. Examples include the

perrhenate The perrhenate ion is the anion with the formula , or a compound containing this ion. The perrhenate anion is tetrahedral, being similar in size and shape to perchlorate and the valence isoelectronic permanganate. The perrhenate anion is stable ove ...

(PPh₄ eO₄ and various

thiomolybdate Tetrathiomolybdate, also spelled tiomolibdate (USAN), is the anion of the following salts: * Ammonium tetrathiomolybdate, a building block in bioinorganic chemistry * Bis-choline tetrathiomolybdate Tiomolibdic acid (trade name Decuprate) is a c ...

s. Complexes of

maleonitriledithiolate Sodium maleonitriledithiolate is the chemical compound described by the formula Na2S2C2(CN)2. The name refers to the cis compound, structurally related to maleonitrile ((CHCN)2). Maleonitriledithiolate is often abbreviated mnt. It is a "dithiole ...

are also isolated as their PPh₄⁺ salts.

References

{{reflist Chlorides Quaternary phosphonium compounds Phenyl compounds