Tetrakis(hydroxymethyl)phosphonium chloride (THPC) is an

organophosphorus compound Organophosphorus compounds 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 in ...

with the chemical formula (CH₂OH)₄l. The cation P(CH₂OH)₄⁺ is four-coordinate, as is typical for

phosphonium salt In polyatomic cations with the chemical formula (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. Types of phosphonium c ...

s. THPC has applications as a precursor to fire-retardant materials,Svara, Jürgen; Weferling, Norbert ; Hofmann, Thomas. Phosphorus Compounds, Organic. Ullmann's Encyclopedia of Industrial Chemistry. John Wiley & Sons, Inc, 2008 as well as a microbiocide in commercial and industrial water systems.

Synthesis and reactions

THPC can be synthesized with high yield by treating

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

with

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

in the presence of

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

. :PH₃ + 4 H₂C=O + HCl → (CH₂OH)₄l THPC converts to tris(hydroxymethyl)phosphine upon treatment with aqueous

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

: : (CH₂OH)₄l + NaOH → P(CH₂OH)₃ + H₂O + H₂C=O + NaCl

Application in textiles

THPC has industrial importance in the production of crease-resistant and

flame-retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...

finishes on cotton textiles and other cellulosic fabrics. A flame-retardant finish can be prepared from THPC by the Proban Process, in which THPC is treated with urea. The

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to phosphine oxide as the result of this reaction. : (CH₂OH)₄l + NH₂CONH₂ → (HOCH₂)₂POCH₂NHCONH₂ + HCl + HCHO + H₂ + H₂O This reaction proceeds rapidly, forming insoluble high molecular weight polymers. The resulting product is applied to the fabrics in a "pad-dry process." This treated material is then treated with ammonia and ammonia hydroxide to produce fibers that are flame-retardant. THPC can condense with many other types of monomers in addition to urea. These monomers include amines, phenols, and polybasic acids and anhydrides.

Tris(hydroxymethyl)phosphine and its uses

Tris(hydroxymethyl)phosphine, which is derived from tetrakis(hydroxymethyl)phosphonium chloride, is an intermediate in the preparation of the water-soluble ligand 1,3,5-triaza-7-phosphaadamantane (PTA). This conversion is achieved by treating

hexamethylenetetramine Hexamethylenetetramine, also known as methenamine, hexamine, or urotropin, is a heterocyclic organic compound with the formula (CH2)6N4. This white crystalline compound is highly soluble in water and polar organic solvents. It has a cage-like s ...

with formaldehyde and tris(hydroxymethyl)phosphine. Tris(hydroxymethyl)phosphine can also be used to synthesize the heterocycle, N-boc-3-pyrroline by ring-closing metathesis using

Grubbs' catalyst Grubbs catalysts are a series of transition metal carbene complexes used as catalysts for olefin metathesis. They are named after Robert H. Grubbs, the chemist who supervised their synthesis. Several generations of the catalyst have been develo ...

(bis(tricyclohexylphosphine)benzylidineruthenium dichloride). N-Boc-diallylamine is treated with Grubbs' catalyst, followed by tris(hydroxymethyl)phosphine. The carbon-carbon double bonds undergo ring closure, releasing ethene gas, resulting in N-boc-3-pyrroline. The hydroxymethyl groups on THPC undergo replacement reactions when THPC is treated with α,β-unsaturated nitrile, acid, amide, and epoxides. For example, base induces condensation between THPC and acrylamide with displacement of the hydroxymethyl groups. (Z = CONH₂) : (CH₂OH)₄l + NaOH + 3CH₂=CHZ → P(CH₂CH₂Z)₃ + 4CH₂O + H₂O + NaCl Similar reactions occur when THPC is treated with

acrylic acid Acrylic acid (IUPAC: propenoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a ...

; only one hydroxymethyl group is displaced, however.

References

{{reflist Quaternary phosphonium compounds