Tetrakis(hydroxymethyl)phosphonium chloride (THPC) is an

organophosphorus compound 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 hydrocarbo ...

with the chemical formula (CH₂OH)₄l. It is a white water-soluble salt with applications as a precursor to fire-retardant materials and as a microbiocide in commercial and industrial water systems.

Synthesis, structure 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 an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

in the presence of

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

. :PH₃ + 4 H₂C=O + HCl → (CH₂OH)₄l The cation P(CH₂OH)₄⁺ features four-coordinate phosphorus, as is typical for

phosphonium salt In chemistry, the term phosphonium (more obscurely: phosphinium) describes polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, organyl or halogen group). These cations have tetrahedral structures. The salt ...

s. 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 . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

: : (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 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 called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to

phosphine oxide Phosphine oxide is the inorganic compound with the formula H3PO. Although stable as a dilute gas, liquid or solid samples are unstable. Unlike many other compounds of the type POxHy, H3PO is rarely discussed and is not even mentioned in major so ...

as the result of this reaction. : (CH₂OH)₄l + NH₂CONH₂ → (HOCH₂)₂P(O)CH₂NHC(O)NH₂ + 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.

References

{{reflist Quaternary phosphonium compounds Flame retardants Organophosphorus compounds