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CHEMINFO Record Number: 107
CCOHS Chemical Name: Phosphorus pentoxide

Diphosphorus pentoxide
Phosphoric acid anhydride
Phosphoric anhydride
Phosphoric oxide
Phosphoric pentoxide
Phosphorus(V) oxide
Phosphorus pentaoxide
Anhydride phosphorique

Chemical Name French: Pentoxyde de phosphore
Chemical Name Spanish: Pentóxido de fósforo
CAS Registry Number: 1314-56-3
UN/NA Number(s): 1807
RTECS Number(s): TH3945000
EU EINECS/ELINCS Number: 215-236-1
Chemical Family: Phosphorus and compounds / inorganic phosphorus compound / inorganic acid anhydride / phosphorus oxide
Molecular Formula: O5-P2 / O10-P4
Structural Formula: Bridged cyclic structure, with each P atom surrounded by 4 O atoms.


Appearance and Odour:
White crystals or powder; odourless or a slight phosphorus-like odour; deliquescent (readily absorbs moisture from air to form phosphoric acid).(6-9)

Odour Threshold:
Not available.

Warning Properties:
Insufficient information for evaluation.

Phosphorus pentoxide solid and vapour consist of the dimeric form which is actually called tetraphosphorus decaoxide (P4O10).(6,7) However, phosphorous pentoxide is generally referred to by its empirical formula, P205. Phosphorus pentoxide is available in technical and reagent grades, which are both typically greater than 99% pure. They may contain small amounts of phosphorus trioxide, and very small amounts of other lower oxides, arsenic, iron, heavy metals (e.g. lead) and fluorine.(6,7)

Uses and Occurrences:
Phosphorus pentoxide is used as a drying agent for materials with which it does not react; for absorption of moisture in vacuum systems; as a dehydrating agent; as a condensing agent in organic synthesis; for the manufacture of phosphorus oxychloride and metaphosphoric acid; as an intermediate in the synthesis of phosphate esters; as a catalyst in the air-blowing of asphalt; in the production of ammonium polyphosphate for fireproofing; and in sugar refining.(6,7,8)


White crystals or powder; odourless or a slight phosphorus-like odour. Deliquescent. Will not burn. Corrosive vapours or fumes may be formed in a fire. Reacts violently with water, producing orthophosphoric acid. The heat generated may be sufficient to ignite flammable and combustible materials. Orthophosphoric acid may produce flammable and explosive hydrogen gas upon contact with common metals. CORROSIVE to the eyes, skin, nose, throat and upper respiratory tract. Can cause blindness and permanent scarring.


Effects of Short-Term (Acute) Exposure

Phosphorus pentoxide dust reacts readily with moisture in the air and in the respiratory tract to form corrosive orthophosphoric acid, which will irritate the nose, throat, and upper respiratory tract, based on limited human evidence.
Exposure to 3.6-11.3 mg/m3 phosphorus pentoxide caused coughing among unaccustomed workers, but was tolerable. Exposure to 50-100 mg/m3 was intolerable to employees unaccustomed to exposure.(1)

Skin Contact:
The dust can react with moisture in the air and on the skin to form orthophosphoric acid, which can cause corrosive injury including severe burns.(2) Permanent scarring may result.

Eye Contact:
Phosphorus pentoxide dust reacts vigorously with moisture in the eyes to form orthophosphoric acid, which can cause severe burns and permanent eye damage, including blindness.(3,4)

Ingestion can probably cause burns to the mouth, throat and stomach, due to the formation of orthophosphoric acid. In severe cases, death may result, based on information for orthophosphoric acid. There is one case report which describes a death due to ingestion of an unspecified amount of phosphorus pentoxide.(3, unconfirmed) Ingestion is not a typical route of occupational exposure.

Effects of Long-Term (Chronic) Exposure

There is no human or animal information available.


There is no human or animal information available.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has no listing for this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
There is no human or animal information available.

Reproductive Toxicity:
There is no human or animal information available.

There is no information available.

Toxicologically Synergistic Materials:
There is no information available.

Potential for Accumulation:
Phosphorus pentoxide reacts with water in the body to form orthophosphoric acid, which enters the phosphate pool. Inorganic phosphate ion is naturally found in the body. It is excreted mainly in the urine.


If symptoms are experienced, remove source of contamination or move victim to fresh air. Obtain medical attention immediately.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. Quickly and gently, blot or brush away excess chemical. Remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). Flush contaminated area with lukewarm, gently flowing water for at least 20-30 minutes, by the clock. If irritation persists, repeat flushing. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Transport victim to an emergency care facility immediately. Discard contaminated clothing, shoes and leather goods.

Eye Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. Quickly and gently blot or brush away excess chemical. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for at least 20-30 minutes, by the clock, while holding the eyelid(s) open. Neutral saline may be used as soon as it is available. DO NOT INTERRUPT FLUSHING. If necessary, keep the emergency vehicle waiting. Take care not to rinse contaminated water into the non-affected eye or onto the face. If irritation persists, repeat flushing. Quickly transport victim to an emergency care facility.

NEVER give anything by mouth if victim is rapidly losing consciousness, or is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water to dilute material in stomach. If milk is available, it may be administered AFTER the water has been given. If vomiting occurs naturally, repeat administration of the water. Quickly transport victim to an emergency facility.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its condition of use in the workplace.


Flash Point:
Not combustible (does not burn).

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not applicable

Sensitivity to Mechanical Impact:
Not sensitive. Stable compound.

Sensitivity to Static Charge:
Probably will not accumulate static charge. Not combustible and therefore not sensitive to static discharge.

Electrical Conductivity:
Not available.

Combustion and Thermal Decomposition Products:
Phosphorus oxides.

Fire Hazard Summary:
Phosphorus pentoxide does not burn. It reacts violently with water and readily with moisture in the air. The heat generated may be sufficient to ignite flammable and combustible materials. The reaction with water produces orthophosphoric acid, which in contact with common metals may produce flammable and explosive hydrogen gas. Corrosive vapours or fumes may be formed in a fire.

Extinguishing Media:
This material does not burn. Use extinguishing media appropriate for the surrounding fire.

Extinguishing Media to be Avoided:
DO NOT use water or water-based extinguishers since phosphorus pentoxide reacts with water. If water is used, use very large quantities to absorb the heat of reaction and to dilute the acid formed.

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind.
Phosphorus pentoxide does not burn or support combustion. If a fire occurs in an area where phosphorus pentoxide containers are used or stored, isolate materials not involved in the fire and protect personnel. Move containers from fire area if it can be done without risk. Otherwise, fire-exposed containers should be cooled by application of hose streams and this should begin as soon as possible (within the first several minutes) and should concentrate on any unwetted portions of the container. Apply water from as far a distance as possible. When phosphorus pentoxide comes in contact with water, sufficient heat may be generated to ignite flammable and combustible materials. Therefore, avoid getting water inside containers.
If water is used to fight fires involving phosphorus pentoxide, use very large quantities of water to absorb the heat of the reaction between phosphorus pentoxide and water.

Protection of Fire Fighters:
Phosphorus pentoxide is a skin contact and inhalation hazard. Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective equipment (Bunker Gear) will not provide adequate protection. Chemical protective clothing (e.g. chemical splash suit and positive pressure self-contained breathing apparatus (NIOSH approved or equivalent) may be necessary.


NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


Molecular Weight: 141.95 (monomer); 283.90 (dimer)

Conversion Factor:
Not applicable at normal temperatures.

Physical State: Solid
Melting Point: 340 deg C (644 deg F) (11)
Boiling Point: Sublimes at 360 deg C (680 deg F) (7,11)
Relative Density (Specific Gravity): 2.30 (11,12); 2.39 (9,13) (water = 1)
Solubility in Water: Very soluble. Reacts violently with water to form orthophosphoric acid, with the generation of heat.(6,12)
Solubility in Other Liquids: Soluble in sulfuric acid; insoluble in acetone and ammonia.(11,13) Reacts with ethanol with the generation of heat.(12)
Coefficient of Oil/Water Distribution (Partition Coefficient): Not applicable (reacts with water).
pH Value: Forms orthophosphoric acid, a strong acid, when dissolved in water.
Vapour Density: Not applicable.
Vapour Pressure: Essentially zero at normal temperatures; 0.133 kPa (1 mm Hg) at 384 deg C (solid; stable form) (13); 0.133 kPa (1 mm Hg) at 189 deg C (metastable form) (13)
Saturation Vapour Concentration: Not applicable.
Evaporation Rate: Not available. Very low at normal temperatures.


Normally stable at room temperature. It reacts vigorously with the moisture in the air and violently with water to form orthophosphoric acid.(6,14)

Hazardous Polymerization:
Does not occur.

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

WATER - reacts violently with the generation of heat to form orthophosphoric acid.(6,14)
WOOD, COTTON, PAPER and STRAW - reacts violently with substances which can give off moisture, with the risk of ignition.(15)
METALS (e.g. ferrous metals, aluminum or zinc) - forms flammable and potentially explosive hydrogen gas in the presence of moisture.
STRONG OXIDIZING AGENTS (e.g. bromine pentafluoride, chlorine trifluoride, oxygen difluoride or hydrogen peroxide) - react violently, ignition often occurring.(9,14,16)
INORGANIC BASES (e.g. calcium oxide or sodium oxide) - react violently if warmed or moistened.(9,14,16)
FORMIC ACID - reaction causes rapid evolution of carbon monoxide.(9,16)
ALKALI or ALKALINE EARTH METALS - reaction with calcium is explosive when heated; reaction with warm sodium and potassium is incandescent (glowing hot).(9,14 16)
HYDROGEN FLUORIDE - react vigorously below 20 deg C.(9,14,16)
AMMONIA, PERCHLORIC ACID in CHLOROFORM, or METHYL HYDROPEROXIDE - reacts vigorously and may explode.(14,16)
SODIUM CARBONATE - the anhydrous reaction of the mixture may be initiated by strong local heating and can generate relatively high temperatures.(14,16)
PROPARGYL ALCOHOL - may result in fire.(9,14,16)

Hazardous Decomposition Products:
Orthophosphoric acid.

Conditions to Avoid:
Water, humid conditions, high temperatures.

Corrosivity to Metals:
Not corrosive to the common metals when dry.(17) Corrosive to metals, such as steel, cast iron, copper and its alloys, and aluminum, in the presence of moisture because orthophosphoric acid is formed.(17,18)


LC50 (rat): 304 mg/m3 (4-hour exposure) (phosphorus pentoxide smoke); cited as 1217 mg/m3 (1-hour exposure) (5)
LC50 (mouse): 68 mg/m3 (4-hour exposure) (phosphorus pentoxide smoke); cited as 271 mg/m3 (1-hour exposure) (5)
LC50 (rabbit): 422 mg/m3 (4-hour exposure) (phosphorus pentoxide smoke); cited as 1689 mg/m3 (1-hour exposure) (5)
LC50 (guinea pig): 15 mg/m3 (4-hour exposure) (phosphorus pentoxide smoke); cited as 61 mg/m3 (1-hour exposure) (5)
The phosphorus pentoxide smoke was generated by burning red phosphorus in an air stream. This experimental method is not relevant to workplace exposures to phosphorus pentoxide.


Selected Bibliography:
(1) Emergency response planning guideline for phosphorus pentoxide. American Industrial Hygiene Association (AIHA), 1988
(2) Beliles, R.P. et al. Phosphorus, selenium, tellurium and sulfur: phosphorus compounds. In: Patty's industrial hygiene and toxicology. 4th ed. Edited by G.D. Clayton et al. Vol. II. Toxicology. Part A. John Wiley & Sons, 1993. p. 785, 787-788
(3) Gosselin, R.E. et al. Clinical toxicology of commercial products. 5th ed. Williams & Wilkins, 1984. p. II-101
(4) Grant, W. M., et al. Toxicology of the Eye. 4th ed. Charles C. Thomas, 1993. p. 1158
(5) Ballantyne, B. Acute inhalation toxicity of phosphorus pentoxide smoke. Abstract. Toxicologist. Vol. 1 (1981). p. 140
(6) Fee, D.C., et al. Phosphorus compounds: phosphorus oxides. In: Kirk-Othmer encyclopedia of chemical technology. 4th ed. Vol. 18. John Wiley & Sons, 1996. p. 769-772
(7) Betterman, G., et al. Phosphorus compounds, inorganic. Ullmann's encyclopedia of industrial chemistry. 5th completely revised ed. Vol. A 19. VCH Verlagsgesellschaft, 1991. p. 527-529
(8) US National Library of Medicine. Phosphorus pentoxide. Last revision date: 1998-92-27. In: Hazardous Substances Data Bank (HSDB). CHEMpendium. [CD-ROM]. Canadian Centre for Occupational Health and Safety (CCOHS). Also available at: <>
(9) The Sigma-Aldrich library of chemical safety data. Ed. II. Vol. 2. Sigma-Aldrich Corporation, 1988. p. 2824C
(10) Emergency response planning guidelines. AIHA Journal. Vol. 56, no. 3, 1995. p. 297
(11) Dean, J.A. Lange's handbook of chemistry. 14th ed. McGraw- Hill, Inc., 1992. p. 3.43
(12) Budavari, S, ed. The Merck index: an encyclopedia of chemicals, drugs, and biologicals. 12th ed. Merck and Co., Inc., 1996
(13) Weast, R.C., ed. Handbook of chemistry and physics. 66th ed. CRC Press, 1985-1986. p. B-122, D-194
(14) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 491
(15) Chemical safety sheets: working safely with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 711
(16) Urben, P.G., ed. Bretherick's handbook of reactive chemical hazards. 5th ed. Vol. 1. Butterworth-Heinemann, Ltd., 1995. p. 1781-1782
(17) Corrosion data survey: metals section. 6th ed. National Association of Corrosion Engineers, 1985. p. 96-8 to 97-8, 96-11 to 97-11
(18) Pohanish, R.P., et al. Rapid guide to chemical incompatibilities. Van Nostrand Reinhold, 1997. p. 661
(19) European Economic Community. Commission Directive 93/72/EEC. Sept. 1, 1993
(20) Occupational Safety and Health Administration (OSHA). Phosphorus Pentoxide. In: OSHA Chemical Sampling Information. Available at: <>

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 2003-09-12

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