Tetrakis(hydroxymethyl)phosphonium chloride

Tetrakis(hydroxymethyl)phosphonium chloride (THPC) is an organophosphorus compound with the chemical formula [P(CH₂OH)₄]Cl. It is a white water-soluble salt with applications as a precursor to fire-retardant materials^[1] and as a microbiocide in commercial and industrial water systems.

Tetrakis(hydroxymethyl)­phosphonium chloride

Names
Preferred IUPAC name Tetrakis(hydroxymethyl)phosphonium chloride
Other names Tetrahydroxymethylphosphonium chloride, THPC
Identifiers
CAS Number	124-64-1 Y
ChEMBL	ChEMBL2131547
ChemSpider	29038 Y
ECHA InfoCard	100.004.280
EC Number	204-707-7
PubChem CID	31298
RTECS number	TA2450000
UNII	58WB2XCF8I Y
UN number	2810
CompTox Dashboard (EPA)	DTXSID5021330
Properties
Chemical formula	C4H12ClO4P
Molar mass	190.56 g·mol−1
Appearance	white solid
Density	1.341 g/cm3
Melting point	150 °C (302 °F; 423 K)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H302, H311, H312, H314, H315, H330, H334, H411
Precautionary statements	P260, P261, P264, P270, P271, P273, P280, P284, P285, P301+P310, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P304+P341, P305+P351+P338, P310, P312, P320, P321, P322, P330, P332+P313, P342+P311, P361, P362, P363, P391, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis, structure and reactions

THPC can be synthesized with high yield by treating phosphine with formaldehyde in the presence of hydrochloric acid.^[1]

PH₃ + 4 H₂C=O + HCl → [P(CH₂OH)₄]Cl

The cation P(CH₂OH)₄⁺ features four-coordinate phosphorus, as is typical for phosphonium salts.

THPC converts to tris(hydroxymethyl)phosphine upon treatment with aqueous sodium hydroxide:^[2]

[P(CH₂OH)₄]Cl + 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.^{[3] [4]} A flame-retardant finish can be prepared from THPC by the Proban Process,^[5] 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.^[6]

[P(CH₂OH)₄]Cl + 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.