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Selenium dioxide

Physical Properties Preparation Reactions Toxicity
Selenium dioxide
Selenium dioxide structure
Chemical Name:
Selenium dioxide
Molecular Formula:
Formula Weight:
MOL File:

Selenium dioxide Properties

Melting point:
315 °C (subl.)(lit.)
Boiling point:
684.9 °C(lit.)
4.81 g/mL at 25 °C(lit.)
vapor pressure 
1 mm Hg ( 157 °C)
refractive index 
nD20 <1.76
Flash point:
storage temp. 
Store below +30°C.
H2O: soluble
Specific Gravity
2 (10g/l, H2O, 20℃)
Water Solubility 
38.4 g/100 mL (14 ºC)
315 ºC
Stable. Incompatible with organic materials, strong acids, ammonia, nitric acid, halogen acids. Protect from moisture.
CAS DataBase Reference
7446-08-4(CAS DataBase Reference)
NIST Chemistry Reference
Selenium dioxide(7446-08-4)
EPA Substance Registry System
Selenium oxide (SeO2)(7446-08-4)
  • Risk and Safety Statements
  • Hazard and Precautionary Statements (GHS)
Hazard Codes  T,N,Xn
Risk Statements  36/38-50/53-33-23/25-51/53-20/22
Safety Statements  26-61-60-45-28A-20/21-28
RIDADR  UN 3440 6.1/PG 3
WGK Germany  2
RTECS  VS8575000
HS Code  2811 29 90
HazardClass  6.1
PackingGroup  II
Hazardous Substances Data 7446-08-4(Hazardous Substances Data)
Toxicity LD50 orally in Rabbit: 68.1 mg/kg
Signal word: Danger
Hazard statements:
Code Hazard statements Hazard class Category Signal word Pictogram P-Codes
H301 Toxic if swalloed Acute toxicity,oral Category 3 Danger P264, P270, P301+P310, P321, P330,P405, P501
H302 Harmful if swallowed Acute toxicity,oral Category 4 Warning P264, P270, P301+P312, P330, P501
H331 Toxic if inhaled Acute toxicity,inhalation Category 3 Danger P261, P271, P304+P340, P311, P321,P403+P233, P405, P501
H373 May cause damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure Category 2 Warning P260, P314, P501
H400 Very toxic to aquatic life Hazardous to the aquatic environment, acute hazard Category 1 Warning P273, P391, P501
H410 Very toxic to aquatic life with long lasting effects Hazardous to the aquatic environment, long-term hazard Category 1 Warning P273, P391, P501
Precautionary statements:
P260 Do not breathe dust/fume/gas/mist/vapours/spray.
P261 Avoid breathing dust/fume/gas/mist/vapours/spray.
P273 Avoid release to the environment.
P311 Call a POISON CENTER or doctor/physician.
P301+P310 IF SWALLOWED: Immediately call a POISON CENTER or doctor/physician.
P304+P340 IF INHALED: Remove victim to fresh air and Keep at rest in a position comfortable for breathing.
P405 Store locked up.
P501 Dispose of contents/container to..…

Selenium dioxide price More Price(23)

Manufacturer Product number Product description CAS number Packaging Price Updated Buy
Sigma-Aldrich 200107 Selenium dioxide ≥99.9% trace metals basis 7446-08-4 5g $37.7 2018-11-20 Buy
Sigma-Aldrich 200107 Selenium dioxide ≥99.9% trace metals basis 7446-08-4 25g $127 2018-11-20 Buy
Alfa Aesar 010854 Selenium(IV) oxide, Puratronic?, 99.999% (metals basis) 7446-08-4 5g $60.7 2018-11-16 Buy
Alfa Aesar 010854 Selenium(IV) oxide, Puratronic?, 99.999% (metals basis) 7446-08-4 25g $229 2018-11-16 Buy
Strem Chemicals 93-3405 Selenium(IV) oxide (99.999%-Se) PURATREM 7446-08-4 25g $233 2018-11-13 Buy

Selenium dioxide Chemical Properties,Uses,Production

Physical Properties

White tetragonal crystals; acidic taste; leaves a burning sensation; density 3.95 g/cm3; sublimes at 315°C forming greenish yellow vapors with a sour and pungent odor; melts at 340 to 350°C; vapor pressure 12.5 torr at 70°C; soluble in water, 38.4 g/100mL at 14°C; highly soluble in hot water 82.5 g/100mL at 65°C; soluble in benzene; moderately soluble in ethanol and acetone 6.7 and 4.4g/100mL solvent, respectively, at 15°C; sparingly soluble in acetic acid (1.11g/100mL at 14°C).


Selenium dioxide is obtained by burning selenium metal in oxygen:
Se + O2 → SeO2
Selenium also forms a trioxide, SeO3. In excess oxygen the product mixture may contain both dioxide and trioxide. The trioxide is unstable.
Selenium dioxide may be prepared by heating selenium with oxygen and nitrogen dioxide. Presence of excess oxygen would oxidize nitrogen dioxide to pentoxide, instead converting selenium dioxide to trioxide:
2Se + 3O2 + 4NO2 → 2SeO2 + 2N2O5
Selenium dioxide also may be produced by oxidation of selenium by nitric acid. The overall reaction may be written as follows:
Se + 2HNO3 → SeO2 + H2O + NO2 + NO


Selenium dioxide is reduced to selenium metal when heated with carbon and other reducing agents.
When heated with ammonia, selenium dioxide forms selenium, nitrogen and water:
3SeO2 + NH3 → 3Se + 2N2 + 6H2O
Ammonia reacts with selenium dissolved in ethanol to form ammonium ethyl selenite, NH4(C2H5)SeO3.
Reaction with nitric acid forms selenic acid:
Se + 2HNO3 → H2SeO4 + 2NO
Selenium dioxide is reduced by hydrazine to black amorphous selenium:
SeO2 + N2H4 → Se + N2 + 2H2O
Hydroxylamine hydrochloride reduces selenium dioxide to reddish-brown amorphous selenium:
SeO2 + 4NH2OH•HCl → Se + 2N2 + 6H2O + 4HCl
The dioxide rapidly absorbs hydrogen halides, forming selenium oxyhalides:
SeO2 + HBr → SeOBr2 + H2O
Reaction with thionyl chloride yields selenium oxychloride:
SeO2 + SOCl2 → SeOCl2 + SO2


The compound is toxic by ingestion. Symptoms of the poisoning effects of selenium dioxide are similar to those of selenium metal. Selenium dioxide vapors are highly irritating to eyes, nose and respiratory tract.

Chemical Properties

Yellowish white to reddish powder or crystals. It is soluble in water and hygroscopic and absorbs moisture or water from the air. Selenium oxide is incompatible with strong oxidising agents, reducing agents, strong acids, ammonia, organics, and phosphorus trichloride.

Chemical Properties

Selenium dioxide is white to slightly reddish crystalline solid or yellow liquid which forms a yellowgreen vapor. It has a sour and pungent odor. Odor threshold in air50.0002 milligram per cubic meter.


In the manufacture of other selenium compounds; as a reagent for alkaloids; as oxidizing agent: L. F. Fieser, M. Fieser, Reagents for Organic Chemistry vol. 1 (New York, Wiley, 1967) p 992.

General Description

A white or creamy-white volatile lustrous crystal or crystalline powder with a pungent sour smell. Melting point 340 deg C. Density 3.954 g / cm3 . Toxic by ingestion and inhalation.

Air & Water Reactions

In presence of water will corrode most metals [USCG, 1999]. Readily soluble in water forming selenious (selenous) acid.

Reactivity Profile

Inorganic oxidizing agents, such as Selenium dioxide , react with reducing agents to generate heat and products that may be flammable, combustible, or otherwise reactive. Selenium dioxide reacts with water, particularly hot water, to give selenious (selenous) acid, a weak acid that is corrosive. Stable to light and heat. Rapidly absorbs dry hydrogen fluoride, hydrogen chloride, hydrogen bromide to form the corresponding selenium oxohalide. A good oxidizing agent. Reacts oxidatively with ammonia to form dinitrogen gas and selenium [Merck]. Oxidizes many organic substances.


Toxic by inhalation, ingestion, and skin absorption.

Health Hazard

Absorption of selenium may be demonstrated by presence of the element in the urine and by a garlic-like odor of the breath. Inhalation of dust can cause bronchial spasms, symptoms of asphyxiation, and pneumonitis. Acute symptoms of ingestion include sternal pain, cough, nausea, pallor, coated tongue, gastrointestinal disorders, nervousness, and conjunctivitis. Contact with eyes causes irritation.

Fire Hazard

Special Hazards of Combustion Products: Sublimes and forms toxic vapors when heated in fire.

Potential Exposure

Selenium dioxide is used in the manufacture of selenium compounds, a reagent for alkaloids; an oxidizing agent; in paint and ink pigments; in metal “blueing” and etching; as a chemical catalyst; in photographic toners; in electric and photoelectric components; and others.

First aid

Move victim to fresh air. Call 911 or emergency medical service. Give artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. Administer oxygen if breathing is difficult. Remove and isolate contaminated clothing and shoes. In case of contact with substance, immediately flush skin or eyes with running water for at least 20 minutes. For minor skin contact, avoid spreading material on unaffected skin. Keep victim warm and quiet. Effects of exposure (inhalation, ingestion, or skin contact) to substance may be delayed. Ensure that medical personnel are aware of the material(s) involved and take precautions to protect themselves. Medical observation is recommended for 24 to 48 hours after breathing overexposure, as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consider administering a drug or other inhalation therapy.


UN3283Selenium compound, solid, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous material, Technical Name Required.

Purification Methods

Purify it by sublimation at 315o, or by solution in HNO3, precipitation of selenium which, after standing for several hours or boiling, is filtered off, then re-oxidised by HNO3 and cautiously evaporated to dryness below 200o. The dioxide is dissolved in H2O and again evaporated to dryness. In H2O it forms selenious acid (see selenious acid above). Its solubility in H2O is 70%w/w at 20o, and it is soluble in EtOH. [Waitkins & Clark Chem Rev 36 235 1945, Fehér in Handbook of Preparative Inorganic Chemistry (Ed Brauer) Academic Press Vol I p 421 1963.]


Selenium dioxide is and inorganic oxidizer; reacts, possibly violently, with reducing agents such as hydrides, nitrides, alkali metals, and sulfides. Contact with strong acids may cause release of toxic hydrogen selenide gas. Water solution is a medium-strong acid (selenious acid). Rapidly absorbs dry hydrogen fluoride, hydrogen bromide, hydrogen chloride, to form corresponding selenium oxohalides. Reacts with many substances producing toxic selenium vapors. Attacks many metals in presence of water.

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform to EPA regulations governing storage, transportation, treatment, and waste disposal.

Selenium dioxide Preparation Products And Raw materials

Raw materials

Preparation Products

Selenium dioxide Suppliers

Global( 196)Suppliers
Supplier Tel Fax Email Country ProdList Advantage
Mainchem Co., Ltd.
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Chemwill Asia Co.,Ltd.
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Hubei Jusheng Technology Co.,Ltd.
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Haihang Industry Co.,Ltd
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Alfa Aesar 400-610-6006; 021-67582000
021-67582001/03/05 China 30273 84
Changsha Halin Chemical Technology Co., Ltd. 18229709969,13787155389
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Shanghai QianYan Bio-technology Co., Ltd 400-887-6760 China 9967 55
Nanjing Huang Tai Pharmaceutical Technology Co. Ltd. 18551845925QQ3569572487
025-58803650 China 1855 58
Shanghai Wei Nie Chemical Technology Co., Ltd. 13046668259 CHINA 53 58

Selenium dioxide Spectrum

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