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HuagongsheHuagongshe Chemistry Print Report · For research reference only
HCID 8472Generated: October 23, 2026

Trimethyl phosphite

P(OMe)3 · P(OCH3)3 · PHOSPHOROUS ACID TRIMETHYL ESTER · Trimethoxyphosphine · METHYL PHOSPHITE · TrimethyPhosphite · AURORA KA-1230 · Trimethylfosfit

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Trimethyl phosphite molecular structure

Identifiers & Physical Properties

CAS No.121-45-9
Molecular formulaC3H9O3P
Average molar mass124.08 g/mol
Monoisotopic mass124.02893078 g/mol
SMILESCOP(OC)OC
InChIKeyCYTQBVOFDCPGCX-UHFFFAOYSA-N
PubChem CID8472
ChEMBLCHEMBL3186364
ChEBICHEBI:183313
EC No.204-471-5
DTXSIDDTXSID4026979

Chemical & Physical Properties

XLogP0.1
Topological polar surface area27.7
Hydrogen bond donors0
Hydrogen bond acceptors3
Rotatable bonds3
Heavy atoms7
Formal charge0
Complexity31.7
Chemical classesOther Classes -> Phosphite CompoundsFlammable agents - 3rd degree
SpringerMaterials PropertiesSchoenflies notation
OdorIrritating, pungent, oily, pyridine-like odorDistinctive, pungent odor.Powerful, sickly odor
Density1.046 at 68 °F (USCG, 1999) - Denser than waterwill sink1.0518 g/cu cm at 20 °CRelative density (water = 1): 1.11.046 @25 °C1.052 g/mL at 25 °C(lit.)
Color/FormColorless liquid
SolubilityReacts with water (NIOSH, 2024)Reacts (hydrolyzes) with waterVery soluble in ethanol, etherSoluble in hexane, benzene, acetone, carbon tetrachloride, and keroseneSolubility in water: reactionChloroform, DMSO (Sparingly)Hydrolyzes with water.
Flash point82 °F (USCG, 1999)28 °C (82 °F) - closed cup130 °F (54 °C) (open cup)23 °C c.c.
Boiling point232 °F at 760 mmHg (USCG, 1999)110 °C111.5 °C111-112 °C(lit.)
DecompositionHazardous decomposition products formed under fire conditions - Carbon oxides, oxides of phosphorus.... When heated to decomposition can emit highly toxic fumes of /phosphorus oxides/.
Melting point-108 °F (USCG, 1999)-78 °C−78 °C(lit.)
Vapor density4.3 (Air = 1)Relative vapor density (air = 1): 4.34.3 (vs air)
Odor thresholdOdor Threshold Low: 0.001 [ppm]Odor threshold (tested by means of a laboratory test panel) are on the order of 0.1 ppb.
Vapor pressure17 mm Hg ( 20 °C)
Refractive indexn20/D 1.408(lit.)
Storage conditions2-8°C
Physical stateLiquid
ColorColorless
Specific gravity1.052
Explosive limits5.2-61.2%(V)
SensitivityAir & Moisture Sensitive
Hydrolytic Sensitivity4: no reaction with water under neutral conditions
BRN956570
Henry's law constant9.0×10-1 mol/(m3Pa) at 25℃, HSDB (2015)
Exposure limitsTLV-TWA 10 mg/m3 (2 ppm) (ACGIH).
StabilityMoisture Sensitive
InChI1S/C3H9O3P/c1-4-7(5-2)6-3/h1-3H3
InChIKeyCYTQBVOFDCPGCX-UHFFFAOYSA-N
SMILESP(OC)(OC)OC
CAS DataBase Reference121-45-9(CAS DataBase Reference)
FDA UNII26Q0321ZDG
NIST Chemistry ReferencePhosphorous acid, trimethyl ester(121-45-9)
EPA Substance Registry SystemTrimethyl phosphite (121-45-9)
UNSPSC Code12352108
NACRESNA.22
GHS pictogramGHS02
Signal wordWarning
GHS hazard statementsH226
GHS precautionary statementsP210-P233-P240-P241-P242-P243-P280-P303+P361+P353-P370+P378-P403+P235-P501
Target organsRespiratory system
Hazard symbolsXn,T,F,Xi
Risk statements (R)10-22-36/37/38-41-37/38-65-48/23/24/25-11-46-45-67-66-36
Safety statements (S)26-39-62-45-16-53
Occupational exposure band (OEB)B
Occupational exposure limit (OEL)TWA: 2 ppm (10 mg/m3)
UN transport numberUN 2329
Water hazard class (WGK)1
RTECS numberTH1400000
F10-13-21
Autoignition temperature250 °C
TSCA inventory statusTSCA listed
Customs code2920 23 00
Hazard class3Acute Tox. 4 OralEye Irrit. 2Flam. Liq. 3Skin Irrit. 2STOT SE 3
Packing groupIII
Storage class3 - Flammable liquids
Hazardous substances data121-45-9(Hazardous Substances Data)
ToxicityLD50 orally in Rabbit: 1600 mg/kg LD50 dermal Rabbit 2600 mg/kg
REACH registrationsActive
Limited quantities5.0 L (1.3 gallons) (liquid)
Excepted quantitiesMax Inner Pack (30g or 30ml) and Max Outer Pack (1Kg or 1L)

Safety & Regulations

GHS classificationDangerH226 (99.6%): Flammable liquid and vapor [Warning Flammable liquids]P203, P210, P233, P240, P241, P242, P243, P261, P264, P264+P265, P270, P271, P280, P301+P317, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P305+P354+P338, P317, P318, P319, P321, P330, P332+P317, P337+P317, P362+P364, P370+P378, P403+P233, P403+P235, P405, and P501 (click each P-code to see the statement)Aggregated GHS information provided per 236 reports by companies from 15 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.H226: Flammable liquid and vapor [Warning Flammable liquids]
Regulatory informationChemical: Phosphorous acid, trimethyl esterPhosphorous acid, trimethyl ester is listed on the EPA's Chemical Data Reporting (CDR) system. Manufacturers and importers of Phosphorous acid, trimethyl ester are required to report information about their production and use of this chemical to the EPA under the Toxic Substances Control Act (TSCA). (40 eCFR Part 711)Status: Active Update: 22-03-2018 https://echa.europa.eu/registration-dossier/-/registered-dossier/13214Phosphorous acid, trimethyl ester: HSNO Approval: HSR001231 Approved with controlsThe New Jersey Worker and Community Right to Know Act requires public and private employers to provide information about hazardous substances at their workplaces. (N.J.S.A. 34:5A-1 et. seq.)
Other safety informationIMAP assessments - Phosphorous acid, trimethyl ester: Human health tier II assessment
DOT labelFlammable Liquid
Fire hazardsSpecial Hazards of Combustion Products: Toxic fumes of POx. (USCG, 1999)· HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames.Flammable. Gives off irritating or toxic fumes (or gases) in a fire. Above 23 °C explosive vapour/air mixtures may be formed.
Fire potentialFlammable liquid when exposed to heat, flame, or oxidizers.
Health hazardsSymptoms of exposure may include burning sensation, coughing, wheezing, laryngitis, shortness of breath, headache, nausea, and vomiting. (USCG, 1999)· May cause toxic effects if inhaled or absorbed through skin.
Hazards summaryCorrosive to skin[Quick CPC] Liquid causes second or third degree burns after short contact. [CHRIS] Dose dependent cataract formation occurs in rats exposed to concentrations above 100 ppm. Lung inflammation occurs in animals exposed at 600 ppm. Human subjects complain of objectionable odor above 20 ppm. No adverse health effects were found in 179 employees exposed regularly to 0.3 to 8 ppm. [ACGIH] A severe skin, eye, and respiratory tract irritant[ICSC]
DOT ID and guide2329 130
Reactive groupSulfonates, Phosphonates, and Thiophosphonates, Organic
UN classificationUN Hazard Class: 3UN Pack Group: III
Special ReportsOrganization for the Prohibition of Chemical WeaponsConvention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and Their Destruction. The Chemical Weapons Convention (CWC) is an international treaty which bans the development, production, stockpiling, and transfer or use of chemical weapons. The Convention mandates the destruction and prohibition of chemical weapons and related facilities and provides for restrictions on international trade in toxic chemicals and precursors.[Available from, as of November 12, 2008: http://www.opcw.org]
Reactivity AlertsHighly Flammable
Fire fightingExcerpt from ERG Guide 130 [Flammable Liquids (Water-Immiscible / Noxious)]:Use foam, carbon dioxide, powder. In case of fire: keep drums, etc., cool by spraying with water. NO direct contact with water.
First aid measuresFresh air, rest.Rinse and then wash skin with water and soap.First rinse with plenty of water for several minutes (remove contact lenses if easily possible), then refer for medical attention.Rinse mouth.
Accidental release measures· CALL 911. Then call emergency response telephone number on shipping paper. If shipping paper not available or no answer, refer to appropriate telephone number listed on the inside back cover.· ELIMINATE all ignition sources (no smoking, flares, sparks or flames) from immediate area.
First aidExcerpt from NIOSH Pocket Guide for Trimethyl phosphite:General First Aid:(General first aid procedures)
Safe storageFireproof. Separated from oxidants and strong bases.
Exposure control and personal protection· Wear positive pressure self-contained breathing apparatus (SCBA).
Fire fighting proceduresSuitable extinguishing media: Dry powder.Advice for firefighters: Wear self-contained breathing apparatus for firefighting if necessary.To fight fire, use water, foam, fog, /carbon dioxide/.
Storage conditionsKeep container tightly closed in a dry and well-ventilated place. Containers which are opened must be carefully resealed and kept upright to prevent leakage. Never allow product to get in contact with water during storage. Storage class (TRGS 510): Flammable liquids.
Cleanup methodsACCIDENTAL RELEASE MEASURES: Personal precautions, protective equipment and emergency procedures: Use personal protective equipment. Avoid breathing vapors, mist or gas. Ensure adequate ventilation. Remove all sources of ignition. Evacuate personnel to safe areas. Beware of vapors accumulating to form explosive concentrations. Vapors can accumulate in low areas. Environmental precautions: Prevent further leakage or spillage if safe to do so. Do not let product enter drains. Methods and materials for containment and cleaning up: Contain spillage, and then collect with an electrically protected vacuum cleaner or by wet-brushing and place in container for disposal according to local regulations. Do not flush with water.
Nonfire spill responseExcerpt from ERG Guide 130 [Flammable Liquids (Water-Immiscible / Noxious)]:
Disposal methodsSRP: Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air qualitypotential migration in air, soil or watereffects on animal, aquatic and plant lifeand conformance with environmental and public health regulations. If it is possible or reasonable use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity or environmental contamination.SRP: Wastewater from contaminant suppression, cleaning of protective clothing/equipment, or contaminated sites should be contained and evaluated for subject chemical or decomposition product concentrations. Concentrations shall be lower than applicable environmental discharge or disposal criteria. Alternatively, pretreatment and/or discharge to a permitted wastewater treatment facility is acceptable only after review by the governing authority and assurance that "pass through" violations will not occur. Due consideration shall be given to remediation worker exposure (inhalation, dermal and ingestion) as well as fate during treatment, transfer and disposal. If it is not practicable to manage the chemical in this fashion, it must be evaluated in accordance with EPA 40 CFR Part 261, specifically Subpart B, in order to determine the appropriate local, state and federal requirements for disposal.Product: Burn in a chemical incinerator equipped with an afterburner and scrubber but exert extra care in igniting as this material is highly flammable. Offer surplus and non-recyclable solutions to a licensed disposal company. Contact a licensed professional waste disposal service to dispose of this materialContaminated packaging: Dispose of as unused product.Principles and methods for destruction of chemical weapons: ... "Destruction of chemical weapons" means a process by which chemicals are converted in an essentially irreversible way to a form unsuitable for production of chemical weapons, and which in an irreversible manner renders munitions and other devices unusable as such. ... Each ... /nation/ shall determine how it shall destroy chemical weapons, except that the following processes may not be used: dumping in any body of water, land burial or open-pit burning. It shall destroy chemical weapons only at specifically designated and appropriately designed and equipped facilities. ... Each ... /nation/ shall ensure that its chemical weapons destruction facilities are constructed and operated in a manner to ensure the destruction of the chemical weaponsand that the destruction process can be verified under the provisions of this Convention.
Spillage disposalPersonal protection: self-contained breathing apparatus. Collect leaking and spilled liquid in sealable containers as far as possible.
Target organsEyes, skin, respiratory system, reproductive systemRespiratory system
Environmental fateTERRESTRIAL FATE: Trimethyl phosphite hydrolyzes rapidly in the presence of water(1,2) and therefore, adsorption to soil, volatilization from moist soil surfaces, and biodegradation are not expected to be important fate processes(SRC). The hydrolysis rate of trimethyl phosphite is expected to be similar to the hydrolysis rate of triethyl phosphite(SRC). In acid solution (pH=4) triethyl phosphite hydrolyzes immediately forming diethyl phosphite and ethanol(3). At pH 7, triethyl phosphite hydrolyzes completely within 20 minutesafter 3 hours 89.3% diethyl phosphite and 10.7% monoethyl phosphite are formed(3). At pH 9, the half-life of triethyl phosphite in water is approximately 5.1 hours70% of the substance remains unhydrolyzed after 3 hours(3). Trimethyl phosphite is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 24 mm Hg at 25 °C(4). Dimethyl phosphite, an hydrolysis product of trimethyl phosphite, reached 48% of its theoretical BOD in 4 weeks in the Japanese MITI test indicating it is inherently biodegradable, but not readily biodegradable(1).AQUATIC FATE: Trimethyl phosphite hydrolyzes rapidly in the presence of water(1,2) and therefore, adsorption to sediment, volatilization from water surfaces, bioconcentration and biodegradation are not expected to be important fate processes(SRC). Trimethyl phosphite hydrolyzes in water to form dimethyl phosphite and methanol(1,2). The hydrolysis rate of trimethyl phosphite is expected to be similar to the hydrolysis rate of triethyl phosphite(SRC). In acid solution (pH=4) triethyl phosphite hydrolyzes immediately forming diethyl phosphite and ethanol(3). At pH 7, triethyl phosphite hydrolyzes completely within 20 minutes70% of the substance remains unhydrolyzed after 3 hours(3). Dimethyl phosphite, an hydrolysis product of trimethyl phosphite, reached 48% of its theoretical BOD in 4 weeks in the Japanese MITI test indicating it is inherently biodegradable, but not readily biodegradable(1).ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), trimethyl phosphite, which has a vapor pressure of 24 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase trimethyl phosphite is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC)the half-life for this reaction in air is estimated to be 33 minutes(SRC), calculated from its rate constant of 7.1X10-10 cu cm/molecule-sec at 25 °C(3). Trimethyl phosphite does not absorb at wavelengths >290 nm(4) and therefore is not expected to be susceptible to direct photolysis by sunlight(SRC).
Adverse effectsDermatotoxin - Skin burns.
Exposure routesThe substance can be absorbed into the body through the skin and by ingestion.inhalation, ingestion, skin and/or eye contact
Toxicity summaryIDENTIFICATION AND USE: Trimethyl phosphite (TMP) is a colorless liquid. It is used primarily as an intermediate in the manufacture of pesticides. It is also used as a fireproofing agent in the production of textiles, as an intermediate in the production of flame-retardant polymers for polyurethane foams, and as a catalyst. HUMAN EXPOSURE AND TOXICITY: Examination of 179 employees involved in manufacturing of TMP failed to reveal any indications of ocular changes or other adverse effects on worker health associated with occupational exposure to trimethyl phosphite. It is only moderately toxic by oral ingestion and an irritant to eyes, skin and upper respiratory system. ANIMAL STUDIES: Topical application of trimethyl phosphite produced moderately severe but persistent irritation on rabbit skin. Instillation of undiluted trimethyl phosphite into the rabbit eye caused severe ocular irritation and swelling, which lasted for several days. No permanent damage to the eye could be detected. Marked mortality (> 70%) /was demonstrated/ among rats exposed at 600 ppm, 6 hours/day, 5 days/week for 4 weeks. Ten percent of the rats exposed at 300 ppm also died. Gross histological evidence of lung inflammation was observed in the animals exposed at 600 ppm, but no such changes occurred in those subjected to 300 or 100 ppm. Clinical signs of ocular irritation occurred in the animals exposed at 100 ppm or higher concentrations. Severe cataract developed in the 600 ppm exposure group, and mild cataracts from 300 ppm100 ppm exposures caused mild, reversible "striate opacities" of the lenses of a few animals. TMP was administered by gavage to pregnant rats at rates of 16, 49, or 164 mg/kg/day, on gestation Days 6 through 15. Acetyl salicylic acid (250 mg/kg/day) was also administered to a group of rats as a positive control. Teratologic evaluation revealed gross fetal abnormalities, skeletal defects, and soft tissue defects at a dose rate of 164 mg/kg/day of trimethyl phosphite, but not at the two lesser rates. An increased frequency of fetal resorption was also observed at 164 mg/kg/day. Trimethyl phosphite was genotoxic in three separate mouse lymphoma assays, either with or without microsomal activation. Trimethyl phosphite was also positive in a battery of Drosophila melanogaster mutagenicity assays and in a bacterial DNA damage/repair suspension assay using various strains of Escherichia coli and Salmonella typhimurium. Trimethyl phosphite failed to show evidence for genetic toxicity in Salmonella and Saccharomyces strains, in a cell transformation assay, in a bacterial DNA repair assay (Escherichia coli, Salmonella typhimurium) or in two Salmonella/mammalian-microsome preincubation assays.
Signs and SymptomsCough. Sore throat.Redness. Pain.irritation eyes, skin, upper respiratory systemdermatitisIn Animals: teratogenic effects
Ongoing Test StatusEPA has released the Interactive Chemical Safety for Sustainability (iCSS) Dashboard. The iCSS Dashboard provides an interactive tool to explore rapid, automated (or in vitro high-throughput) chemical screening data generated by the Toxicity Forecaster (ToxCast) project and the federal Toxicity Testing in the 21st century (Tox21) collaboration. /The title compound was tested by ToxCast and/or Tox21 assays/[USEPAICSS Dashboard ApplicationAvailable from, as of July 7, 2016: http://actor.epa.gov/dashboard/]
ICSC Environmental DataEnvironmental effects from the substance have not been investigated adequately.
Soil Adsorption/MobilityAdsorption to soils or suspended solids and sediment in water is not expected to be an important fate process(SRC) because trimethyl phosphite reacts (hydrolyzes) in water(1).
TSCA Test SubmissionsThe ability of 1,3-dioxolane to induce morphological transformation in the C3H/10T 1/2 mouse cell line (Cell Transformation Assay) without metabolic activation was evaluated. Based on preliminary toxicity tests (exposure time=24 hrs), 1,3-dioxolane was tested at 10 concentrations between 1.0-20,000 ul/ml, with cell survival ranging from 100% to 66%. 1,3-Dioxolane exhibited a weak transformation potential using this test system.Teratogenicity was evaluated in pregnant female BLU:(SD)BR albino rats (25/group) orally exposed by gavage to trimethyl phosphite at dose levels of 0, 16, 49 or 164 mg/kg/day on gestation days (GD) 6-15. Surviving animals were sacrificed on GD 20. Significant differences were observed between treated and control animals in the following (high-dose group unless otherwise noted): decreased body weight minus gravid uterine weight, increased incidence of morphological abnormalities in soft tissues and skeletal system and gross abnormalities (including widening of cal sutures, increased incidence of abnormalities, primarily partial ossification of the long bones, along with anomalies of several sternebrae and vertebrae, and all treated groups exhibited increased incidence of dams with fetuses afflicted with teratologic effects of any kind. No significant differences were observed between treated and control animals in the following: maternal mortality, pharmacological examination, food consumption or body weight, live fetuses/dam, average fetal weight, numbers of live litters, implantation sites, resorptions, and dead fetuses.The mutagenicity of trimethyl phosphite was evaluated in Salmonella tester strains TA98, TA100, TA1535, TA1537 and TA1538 (Ames Test) and in Saccharomyces cerevisiae strain D4, both in the presence and absence of added metabolic activation by Aroclor-induced rat liver S9 fraction. Based on preliminary toxicity determinations, trimethyl phosphite, diluted with DMSO, was tested at concentrations up to 5.0ul/plate using the plate incorporation technique. Trimethyl phosphite did not cause a positive response in any of the tester strains with or without metabolic activation.The mutagenicity of trimethyl phosphite was evaluated in the germ cells of Drosophila melanogaster by inhalation exposure employing the Y chromosome loss test, dominant lethal test, bithorax test of levels and sex-linked recessive lethal test. Based on preliminary toxicity determinations, trimethyl phosphite, was administered at 10mM to male flies and then mated. Trimethyl phosphite cause a significant increase in genetic damage in the treated Drosophila under the experimental conditions used. Also employed was the white-ivory mosaic test, which did not produce a positive response.For more TSCA Test Submissions (Complete) data for TRIMETHYL PHOSPHITE (10 total), please visit the HSDB record page.
Human Toxicity Excerpts/EPIDEMIOLOGY STUDIES/ Analyses of workplace air /from a plant engaged in the manufacture of trimethyl phosphite revealed concentrations averaging up to 8 ppm in 1969 and 1971. More thorough studies in this and another facility in 1979 indicated average exposures generally between 0.3 and 4 ppm, with occasional values as high as 15 ppm. Examination of 179 employees in these plants failed to reveal any indications of ocular changes or other adverse effects on worker health associated with occupational exposure to trimethyl phosphite./OTHER TOXICITY INFORMATION/ It is only moderately toxic by oral ingestion and an irritant to eyes, skin and upper respiratory system. No information of chronic toxicity of vapors. Exposure of workers during its manufacture and handling may involve low-level inhalation of vapors.
Artificial Pollution SourcesTrimethyl phosphite's production and use as an intermediate, especially for production of pesticides(1), as a fireproofing agent in the production of textiles, as an intermediate in production of flame-retardant polymers for polyurethane foams, and as a catalyst(2) may result in its release to the environment through various waste streams(SRC).
DHS Chemicals of Interest (COI)Trimethyl phosphite80220Chemical Weapons/Chemical Weapons Precursors chemical material that, if stolen or diverted, can be converted into weapons using simple chemistry, equipment, or techniques.
F10-13-21
Occupational exposure band (OEB)B
Occupational exposure limit (OEL)TWA: 2 ppm (10 mg/m3)
Water hazard class (WGK)1
TSCA inventory statusTSCA listed
RTECS numberTH1400000
UN transport numberUN 2329
Customs code2920 23 00
ToxicityLD50 orally in Rabbit: 1600 mg/kg LD50 dermal Rabbit 2600 mg/kg
Risk statements (R)10-22-36/37/38-41-37/38-65-48/23/24/25-11-46-45-67-66-36
Signal wordWarning
GHS pictogramGHS02
Hazard symbolsXn,T,F,Xi
Safety statements (S)26-39-62-45-16-53
Hazard class3Acute Tox. 4 OralEye Irrit. 2Flam. Liq. 3Skin Irrit. 2STOT SE 3
Storage class3 - Flammable liquids
Packing groupIII
GHS hazard statementsH226
Limited quantities5.0 L (1.3 gallons) (liquid)
Excepted quantitiesMax Inner Pack (30g or 30ml) and Max Outer Pack (1Kg or 1L)
REACH registrationsActive
Autoignition temperature250 °C
GHS precautionary statementsP210-P233-P240-P241-P242-P243-P280-P303+P361+P353-P370+P378-P403+P235-P501
Hazardous substances data121-45-9(Hazardous Substances Data)

Applications & Uses

Uses

Trimethyl phosphite has been used primarily as an intermediate in the manufacture of pesticides and the synthesis of organophosphate insecticides. It is also used as a fire retardants in the production of textiles, as an intermediate in the production of flame-retardant polymers for polyurethane foams, and as a catalyst.

General Description

Trimethyl phosphite appears as a clear colorless liquid with a strong foul odor. Flash point 99°F. Denser than water and insoluble in water. Vapors heavier than air. It is used in making pesticides, flame retardants and organophosphorous additives.