7803-51-2 Usage
Chemical Description
Phosphine is a colorless gas with a pungent odor that is used in the semiconductor industry.
Uses
Used in Organic Preparations:
Phosphine is used as a reagent in a variety of organic preparations and in the preparation of phosphonium halides.
Used in Semiconductor Industry:
Phosphine is used as a doping agent for n-type semiconductors, and as a pure gas in the manufacture of light-emitting diodes.
Used in Fumigation:
Phosphine is used as a fumigant at low concentrations for grain, and is the most widely used fumigant for insect control in durable commodities throughout the world. It is increasingly used as a treatment to replace methyl bromide, especially because of its low cost, fast dispersion in the air, and low residues.
Used in Storage Buildings and Transit:
Phosphine can be used in a variety of storage buildings, during transit (e.g., in ship holds) or in plastic sheet enclosures for insect control.
Used in Electronic Components:
Phosphine occurs in the waste gases from plants manufacturing semiconductors and thin-film photovoltaic cells, and is used as a doping agent for electronic components.
Challenges and Solutions:
Phosphine has a few drawbacks, such as slow activity, rapid increase in insect resistance, flammability at higher concentrations (>900 ppm), and corrosion of copper, silver, and gold. The understanding of phosphine resistance mechanisms, improved monitoring tactics, and management of resistance are priorities in tackling the problem. The other problems like corrosion and flammability can be limited by using the combination of heat (30–36℃), carbon dioxide (3–7%), and phosphine at 80–100 ppm, while achieving complete insect control.
Production Methods
Phosphine, also known as phosphorated hydrogen or hydrogen
phosphide (PH3), has no direct commercial use. However,
it may be generated from aluminum or zinc phosphide
and water for grain fumigation. It may be present in phosphorus
as a polymer or generated at low rates under alkaline
conditions and at a temperature of 85C. The generation of
acetylene from calcium carbide containing calcium phosphide
as an impurity and metal processing procedures in
which phosphides are formed are the most frequent sources
of industrial hygiene problems with phosphine.
Preparation
Phosphine, unlike ammonia, is not made by direct union of elements. However, phosphine is prepared from other phosphorus compounds by several methods. Phosphine can be prepared by alkaline hydrolysis of white phosphorus. Thus, a strong aqueous solution of caustic potash when boiled with white phosphorus yields hypophosphite with liberation of phosphine: P4 + 3KOH + 3H2O → 3KH2PO2 + PH3↑ Caustic soda or barium hydroxide can be used instead of caustic potash. The apparatus should be free from air. Either hydrogen or natural gas may be passed through the generator to purge out all residual oxygen out from the flask to prevent any explosion. A small amount of diphosphine, P2H4 also is produced in the reaction. The latter inflames spontaneously in air. Diphosphine, which is an unstable liquid at 20°C, may be removed by condensation in a tube immersed in a freezing mixture; or by passing through concentrated hydrochloric acid; or slowly by photochemical decomposition by exposing to light. Phosphine also is prepared by reduction of a solution of phosphorus trichloride with lithium aluminum hydride in dry ether under warm conditions. The solution of the latter is added from a dropping funnel to phosphorus trichloride solution in dry ether placed in a water bath. 4 PCl3 + 3LiAlH4 → 3 LiCl + 3AlCl3 + 4PH3↑ The flask is connected to a reflux condenser to condense down solvent ether back into the flask. Phosphine is collected over water as a moist gas. Dry phosphine may alternatively be condensed in a U-tube placed in freezing mixture. Phosphine may be produced by mixing a solution of phosphonium iodide with potassium hydroxide: PH4I + KOH → KI + H2O + PH3↑ Another preparation method involves treating metallic phosphide with dilute acids: Ca3P2 + 6HCl → 3CaCl2 + 2PH3↑ This method was applied earlier to produce floating signal flares at sea. Floating cans of calcium phosphide were punctuated to admit sea water to generate phosphine, which ignited spontaneously to emit flares. The flares could not be extinguished by wind or water.
Air & Water Reactions
Highly flammable. Usually ignites spontaneously in air. Burns with a luminous flame [Merck 11th ed. 1989]. Insoluble in water.
Reactivity Profile
Phosphine is a reducing agent. Ignites spontaneously in air when pure [Sidgwick, 1950, p. 729]. Liquefied Phosphine can be detonated [Rust, 1948, p. 301]. Ignites or reacts violently with boron trichloride, dichlorine oxide, halogens (bromine, chlorine, iodine), metal nitrates, nitrogen oxides, nitric acid, nitrous acid, nitrogen trichloride [Bretherick, 5th ed., 1995, p. 1562]. Forms explosive mixtures with even small amounts of oxygen. Autoignites at low pressures [Fisher, E. O. et al., Angew. Chem., 1968, 7, p. 136].
Hazard
Phosphine is a highly toxic and flammable gas. Acute effects are irritation, tightness of chest, painful breathing, and lung damage. High concentration can be fatal. A fire hazard.
Health Hazard
Phosphine is a super- toxic gas with a probable oral lethal dose of 5 mg/kg or 7 drops for a 150 pound person. An air concentration of 3 ppm is safe for long term exposure, 500 ppm is lethal in 30 minutes, and a concentration of 1,000 ppm is lethal after a few breaths.
Health Hazard
Phosphine is a highly poisonous gas. The symptoms of its acute toxic effectsin humans can be respiratory passage irritation, cough, tightness of chest, painful breathing, a feeling of coldness, and stupor. Inhalation of high concentrations of phosphine in air can cause lung damage, convulsion, coma, and death. In addition to damaging the respiratory system, exposure to this compound can cause nausea, vomiting, diarrhea, and depression of the central nervous system. Exposure to a concentration of 1000 ppm in air for 5 minutes can be fatal to humans (NIOSH 1986). LC50 value, inhalation (rats): 11 ppm (15.3 mg/m3)/4 hChronic exposure is likely to cause phosphorus poisoning. Nutritional and toxicological studies indicated that ingestion of a phosphine-fumigated diet by rats for 2 years did not cause marked modification of growth, feed intake, functional behavior, or the incidence or type of tumors (Cabrol Telle et al. 1985).
Fire Hazard
Phosphine can explode with powerful oxidizers. The gas is heavier than air and may travel along the ground to an ignition source. Container may explode in heat of fire. When heated to decomposition, Phosphine emits highly toxic fumes of phosphorus oxides. Reacts violently with: air; boron trichloride; bromine; chlorine; chlorine monoxide; nitric acid; nitric oxide; nitrous oxide; nitrogen trioxide; silver nitrate; nitrous acid; mercuric nitrate; nitrogen trichloride; oxygen; and (potassium plus ammonia). Stable up to 131F. May become unstable at high temperatures.
Flammability and Explosibility
Highlyflammable
Trade name
ECO2 FUME TM?; VAPORPH3OS?
Safety Profile
A poison by inhalation. A very toxic gas whose effects are not completely understood. The chef effects are central nervous system depression and lung irritation. There may be pulmonary edema, dilation of the heart, and hyperemia of the visceral organs. Inhalation can cause coma and convulsions leading to death within 48 hours. However, most cases recover without after-effects. Chronic poisoning, characterized by anemia, bronchitis, gastrointestinal disturbances, and visual, speech, and motor disturbances, may result from continued exposure to very low concentrations.Very dangerous fire hazard by spontaneous chemical reaction. Moderately explosive when exposed to flame. Explosive reaction with dichlorine oxide, silver nitrate, concentrated nitric acid, nitrogen trichloride, oxygen. Reacts with mercury(Ⅱ) nitrate to form an explosive product. Ignition or violent reaction with air, boron trichloride, Br2, Cl2, aqueous halogen solutions, iodine, metal nitrates, NOx NCh, NO3, N20, HN02, K + NH3, oxidants. The organic derivatives of phosphine (phosphines) react vigorously with halogens. To fight fire, use CO2, dry chemical, or water spray. Dangerous; when heated to decomposition it emits highly toxic fumes of POx. Used as a fumigant, doping agent for electronic components, and in chemical synthesis
Potential Exposure
Phosphine is used as a fumigant; in the semiconductor industry, as a doping agent for electronic components to introduce phosphorus into silicon crystals; in chemical synthesis; used as a polymerization initiator; as an intermediate for some flame retardants. Also, exposures may occur when acid or water comes in contact with metallic phosphides (aluminum phosphide, calcium phosphide). These two phosphides are used as insecticides or rodenticides for grain, and phosphine is generated during grain fumigation. When phosphine toxicity is suspected, but phosphine exposure is not obvious, one should suspect transdermal contamination and/or ingestion of phosphides. Phosphine may also evolve during the generation of acetylene from impure calcium carbide, as well as during metal shaving; sulfuric acid tank cleaning; rustproofing, ferrosilicon, phosphoric acid; and yellow phosphorus explosive handling.
Physiological effects
Phosphine is a highly toxic gas that can cause
death from delayed pulmonary edema or from tissue anoxia secondary to interference with
tissue respiration. Phosphine is both an irritant
and a general systemic poison. Its action is
similar to that of hydrogen sulfide.
Symptoms of irritation include lacrimation,
substernal chest pain and chest tightness, shortness of breath, a slight cough, and cyanosis.
Nonlethal exposures can result in symptoms
referable to the gastrointestinal tract and the
nervous system. Abdominal symptoms include
nausea, vomiting, severe epigastric pain, and
diarrhea. Neurologic symptoms include vertigo,headache, restlessness, intentional tremor, lack
of muscular coordination, double vision,
drowsiness, and a decreased sensation in the
extremities. Death in humans has occurred after
exposures as low as 8 ppm for 1-2 hours.
Additional acute toxic symptoms involve cardiac abnormalities, liver dysfunction, and kidney inflammation. Agitated psychotic behavior
can occur.
ACGIH recommends a Threshold Limit
Value-Time-Weighted Average (TLV-TWA)
of 0.3 ppm (0.42 mg/m3) for phosphine. The
TLV-TWA is the time-weighted average concentration for a normal 8-hour workday and a
40-hour workweek, to which nearly all workers
may be repeatedly exposed, day after day, without adverse effect. ACGIH also recommends a
Threshold Limit Value-Short Term Exposure
Limit (TLV-STEL) of 1 ppm (1.4 mg/m3) for
phosphine. The TLV-STEL is the IS-minute
TWA exposure that should not be exceeded at
any time during a workday even if the 8-hour
TWA is within the TLV-TWA. Exposures
above the TLV- TWA up to the STEL should
not be longer than 15 minutes and should not
occur more than 4 times per day. There should
be at least 60 minutes between successive exposures in this range.
OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL)
of 0.3 ppm (0.4 mg/m3) for phosphine. TWAPEL is the exposure limit that shall not be exceeded by the 8-hour TWA in any 8-hour work
shift of a 40-hour workweek.
Environmental Fate
Because of its very high vapor pressure, phosphine exists in air
as a gas and volatilizes from water and surface soil. At high
concentrations, the vapors may spontaneously combust in air.
Atmospheric phosphine may be degraded by photochemically
produced hydroxyl radicals with an expected half-life of less
than 1 day. Phosphine can bind to subsurface soils and is
degraded quickly. The chemical does not accumulate in the
food chain.
storage
Since phosphine is an extremely toxic and
flammable gas, appropriate precautions must be
taken in its storage and handling. Store and use
phosphine and phosphine mixtures only in ventilated gas cabinets, exhaust hoods, or highly
ventilated rooms that supply a large volume of
forced air ventilation. Explosion-proof forced
draft gas cabinets or fume hoods are recommended. Use piping and equipment adequately
designed to withstand the pressures to be encountered.
Since phosphine may form explosive mixtures
with air, keep it away from heat and all ignition
sources such as flames and sparks. All lines,
connections, equipment, etc. must be thoroughly
checked for leaks and grounded prior to use.
Only use spark-proof tools and explosion-proof
equipment. The compatibility with plastics and
elastomers should be confirmed.
For basic safety information on the handling
of compressed gas cylinders, refer to CGA P-I,
Safe Handling of Compressed Gases in Containers.
Shipping
UN2199 Phosphine, Hazard Class: 2.3; Labels: 2.3-Poisonous gas, 2.1-Flammable gas, Inhalation Hazard Zone A. Cylinders must be transported in a secure upright position, in a well -ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner.
Purification Methods
PH3 is best purified in a gas line (in a vacuum) in an efficient fume cupboard. It is spontaneously flammable, has a strong odour of decayed fish and is POISONOUS. The gas is distilled through solid KOH towers (two), through a Dry ice-acetone trap (-78o, to remove H2O, and P2H4 which spontaneously ignites with O2), then through two liquid N2 traps (-196o), followed by distillation into a -126o trap (Dry ice-methylcyclohexane slush), allowed to warm in the gas line and then sealed in ampoules preferably under N2. IR: max 2327 (m), 1121 (m) and 900 (m) cm-1 . [Klement in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 525-530 1963, Gokhale & Jolly Inorg Synth IX 56 1967.] PH3 has also been absorbed into a solution of cuprous chloride in hydrochloric acid (when CuCl.PH3 is formed). PH3 gas is released when the solution is heated, and the gas is purified by passage through KOH pellets and then over P2O5. Its solubility is 0.26mL/1 mL of H2O at 20o, and a crystalline hydrate is formed on releasing the pressure on an aqueous solution.
Toxicity evaluation
Phosphine toxicity occurs in insects, rodents, and humans via
a common mechanism of respiratory inhibition. The chemical
is a noncompetitive inhibitor of cytochrome oxidase in mitochondria.
Human case reports and animal studies have shown
that phosphine also inhibits the activity of catalase and
cholinesterase, decreases glutathione content, and reacts with
hemoglobin. Overall, the studies show oxidative stress as the
mechanism of phosphine toxicity.
Incompatibilities
Phosphine reacts with acids, air, copper, moisture, oxidizers, oxygen, chlorine, nitrogen oxides; metal nitrates; halogens, halogenated hydrocarbons; copper and many other substances, causing fire and explosion hazard. Extremely explosive; may ignite spontaneously on contact with air at (or about) 100C. Attacks many metals. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine,fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong acids, amines, ammonia, ethylene oxide, metal nitrates, nitrous acid, phosgene, strong bases.
Waste Disposal
Return refillable compressed gas cylinders to supplier. Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers. Must be disposed properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office. Controlled discharges of Phosphine may be passed through 10% NAOH solution in a scrubbing tower. The product may be discharged to a sewer.
GRADES AVAILABLE
Phosphine is supplied in a number of grades,
primarily as electronic grade, with a purity of
99.999 percent on a hydrogen-free basis.An MOCVD grade is also offered with a purity of 99.9998 percent.
Check Digit Verification of cas no
The CAS Registry Mumber 7803-51-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,8,0 and 3 respectively; the second part has 2 digits, 5 and 1 respectively.
Calculate Digit Verification of CAS Registry Number 7803-51:
(6*7)+(5*8)+(4*0)+(3*3)+(2*5)+(1*1)=102
102 % 10 = 2
So 7803-51-2 is a valid CAS Registry Number.
InChI:InChI=1/H3P/h1H3
7803-51-2Relevant articles and documents
Kinetics of phosphine hydroxymethylation with formaldehyde
Grekov,Novakov
, p. 358 - 366 (2006)
The kinetics of phosphine hydroxymethylation with formaldehyde is studied. In the absence of a catalyst, phosphine reacts slowly with formaldehyde under normal conditions. Taken separately, amines, hydrochloric acid, and nickel chloride have a low catalytic activity, but the addition of a primary aliphatic amine to nickel chloride effectively increases the hydroxymethylation rate. A probable reaction mechanism is suggested. MAIK Nauka/ Interperiodica 2006.
Phosphine synthesis via cathodic reduction of molten white phosphorus
Vorotyntsev,Mochalov,Balabanov
, p. 1289 - 1293 (2005)
Cathodic reduction of molten phosphorus in an acid electrolyte with the formation of phosphine is studied. The results demonstrate that the process can be accelerated by sonication, which increases the current density corresponding to phosphine synthesis by a factor of 5, up to 1 A/cm2. It is shown that the electrochemical synthesis of phosphine is due to charge transport across the phosphorus film on the cathode. The optimized electrochemical synthesis conditions are described.
Electrolytic formation of phosphine from red phosphorus in aqueous solutions
Shalashova,Smirnov,Nikolashin,Turygin,Khudenko,Brekhovskikh,Fedorov,Tomilov
, p. 236 - 241 (2006)
Data are presented on the current-voltage behavior of red phosphorus suspensions at gold, platinum, lead, and cadmium cathodes in a 1.0 M Na 2CO3 solution. In experiments with a red phosphorus suspension in alkaline solutions, the fo
REACTION OF SODIUM WITH IONIC CONDUCTORS CONTAINING P-O BONDS AT ELEVATED TEMPERATURES.
Tennenhouse,Crosbie
, p. 204 - 207 (1984)
Sodium phosphate and a series of compounds containing Na, Zr, Si, P, and O were found to react with sodium at 380 degree C. The reaction products formed phosphine on hydrolysis. On the basis of these reactions and some thermodynamic calculations, it is not likely that any materials containing P-O bonds will be stable to sodium at the temperatures required for the Na-S battery or Na heat engine operation.
2,4,6-Tri(hydroxy)-1,3,5-triphosphinine, P3C3(OH)3: The Phosphorus Analogue of Cyanuric Acid
Suter, Riccardo,Mei, Yanbo,Baker, Matthew,Benk?, Zoltan,Li, Zhongshu,Grützmacher, Hansj?rg
, p. 1356 - 1360 (2017)
Cyanuric acid (C3H3N3O3) is widely used as cross-linker in basic polymers (often in combination with other crosslinking agents like melamine) but also finds application in more sophisticated materials such as in supramolecular assemblies and molecular sheets. The unknown phosphorus analogue of cyanuric acid, P3C3(OH)3, may become an equally useful building block for phosphorus-based polymers or materials which have unique properties. Herein we describe a straightforward synthesis of 2,4,6-tri(hydroxy)-1,3,5-triphosphinine and its derivatives P3C3(OR)3which have been applied as strong π-acceptor η6-ligands in piano stool Mo(CO)3complexes.
Organoactinide Phosphine/Phosphite Coordination Chemistry. Facile Hydride-Induced Dealkoxylation and the Formation of Actinide Phosphinidene Complexes
Duttera, Michael R.,Day, Victor W.,Marks, Tobin J.
, p. 2907 - 2912 (1984)
This contribution reports a study of the reaction of the organoactinide hydrides (Cp'2MH2)2 (Cp'=η5-(CH3)5C5, M=Th,U) with trimethyl phosphite.Quantitative transposition of hydryde and methoxide ligands occurs to yield the corresponding Cp'2M(OCH3)2 complexes (synthesized independently from Cp'2MCl2 and NaOCH3) and the phosphinidene-bridged methoxy complexes 2PH.The reaction is considerably more rapid for M=U than for M=Th.The new compounds were characterized by elemental analysis, 1H and 31P NMR, infrared spectroscopy, magnetic susceptibility, and D2O hydrolysis.The molecular structure of 2PH has been determined by single-crystal X-ray diffraction techniques.It crystallizes in the monoclinic space group P2/n with a=13.926(3) Angstroem, b=10.765(3) Angstroem, c=15.282(4) Angstroem, β=107.63(2) deg, and Z=2.Full-matrix least-squares refinement of the structural parameters for the 24 independent anisotropic non-hydrogen atoms has converged to R1 (unweighted, based on F) = 0.041 for 1677 independent absorption-corrected reflections having 2ΘMoKα3?(I).The 2PH molecule has C2 symmetry, with the μ-PH2- ligand lying on a crystallographic twofold axis.The coordination geometry about each uranium ion is of the typical pseudotetrahedral Cp'2M(X)Y type, with U-P=2.743(1) Angstroem, U-O=2.046(14) Angstroem, U-P-U=157.7(2) deg, and U-O-C(methyl)=178(1) deg.Evidence is presented that other >P-OR linkages react in a similar manner.
Expedient Route to Chalcogenophosphinates with Glucose Moieties via Todd-Atherton-Like Coupling between Secondary Phosphine Chalcogenides and Diacetone- d -Glucose in the CCl4/Et3N System
Volkov, Pavel A.,Ivanova, Nina I.,Gusarova, Nina K.,Sukhov, Boris G.,Khrapova, Kseniya O.,Zelenkov, Lev E.,Smirnov, Vladimir I.,Borodina, Tatyana N.,Vakul'Skaya, Tamara I.,Khutsishvili, Spartak S.,Trofimov, Boris A.
, p. 329 - 334 (2015)
Secondary phosphine chalcogenides react with diacetone-d-glucose (DAG) in the system CCl4/Et3N (70°C, 4-24 h) to afford DAG chalcogenophosphinates in up to 79% yield, thus paving a short way to optically active chalcogenophosphinates with glucose moieties. As an example, a mild regioselective hydrolysis (70 °C, aqueous MeCOOH) of DAG bis(2-phenylethyl)selenophosphinate) obtained leads to monoacetone-d-glucose bis(2-phenylethyl)selenophosphinate.
Intrinsic Barriers to Proton Exchange between Transition-Metal Centers: Application of a Weak-Interaction Model
Creutz, Carol,Sutin, Norman
, p. 2418 - 2427 (1988)
A weak-interaction model for proton self-exchange between transition-metal centers is considered.The rate constant obtained from the Fermi golden-rule expression of radiationless transition theory is a product of terms for assembling acid and base reactants at the correct orientation and distance, a classical reaction frequency, an electron-proton reaction probability, and classical nuclear factors deriving from the requirement for reorganization of ancillary ligands and solvent modes.It is found that such a model yields calculated rate constants and activation parameters in reasonable agreement with the experimental data, provided that the fluxionality of certain metal centers is taken into account.
Photocatalytic Arylation of P4 and PH3: Reaction Development Through Mechanistic Insight
Cammarata, Jose,Gschwind, Ruth M.,Lennert, Ulrich,Rothfelder, Robin,Scott, Daniel J.,Streitferdt, Verena,Wolf, Robert,Zeitler, Kirsten
supporting information, p. 24650 - 24658 (2021/10/14)
Detailed 31P{1H} NMR spectroscopic investigations provide deeper insight into the complex, multi-step mechanisms involved in the recently reported photocatalytic arylation of white phosphorus (P4). Specifically, these studies have identified a number of previously unrecognized side products, which arise from an unexpected non-innocent behavior of the commonly employed terminal reductant Et3N. The different rate of formation of these products explains discrepancies in the performance of the two most effective catalysts, [Ir(dtbbpy)(ppy)2][PF6] (dtbbpy=4,4′-di-tert-butyl-2,2′-bipyridine) and 3DPAFIPN. Inspired by the observation of PH3 as a minor intermediate, we have developed the first catalytic procedure for the arylation of this key industrial compound. Similar to P4 arylation, this method affords valuable triarylphosphines or tetraarylphosphonium salts depending on the steric profile of the aryl substituents.
Synthesis of monophosphines directly from white phosphorus
Scott, Daniel J.,Cammarata, Jose,Schimpf, Maximilian,Wolf, Robert
, p. 458 - 464 (2021/04/09)
Monophosphorus compounds are of enormous industrial importance due to the crucial roles they play in applications such as pharmaceuticals, photoinitiators and ligands for catalysis, among many others. White phosphorus (P4) is the key starting material for the preparation of all such chemicals. However, current production depends on indirect and inefficient, multi-step procedures. Here, we report a simple, effective ‘one-pot’ synthesis of a wide range of organic and inorganic monophosphorus species directly from P4. Reduction of P4 using tri-n-butyltin hydride and subsequent treatment with various electrophiles affords compounds that are of key importance for the chemical industry, and it requires only mild conditions and inexpensive, easily handled reagents. Crucially, we also demonstrate facile and efficient recycling and ultimately catalytic use of the tributyltin reagent, thereby avoiding the formation of substantial Sn-containing waste. Accessible, industrially relevant products include the fumigant PH3, the reducing agent hypophosphorous acid and the flame-retardant precursor tetrakis(hydroxymethyl)phosphonium chloride. [Figure not available: see fulltext.]
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