Selenium dioxide Property

Melting point:

315 °C (subl.)(lit.)

Boiling point:

684.9 °C(lit.)

Density 

4.81 g/mL at 25 °C(lit.)

vapor pressure 

1 mm Hg ( 157 °C)

refractive index 

nD20 <1.76

Flash point:

315°C

storage temp. 

Store below +30°C.

solubility 

H₂O: soluble

form 

powder

color 

white

Specific Gravity

3.95

PH

2 (10g/l, H2O, 20℃)

Water Solubility 

38.4 g/100 mL (14 ºC)

Sublimation 

315 ºC

Merck 

14,8434

Exposure limits

ACGIH: TWA 0.2 mg/m3
NIOSH: IDLH 1 mg/m3; TWA 0.2 mg/m3

Stability:

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 dioxide (7446-08-4)

Safety

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

F 

3

TSCA 

Yes

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

Hazard and Precautionary Statements (GHS)

Symbol(GHS)

Signal word

Danger

Hazard statements

H373May cause damage to organs through prolonged or repeated exposure

H410Very toxic to aquatic life with long lasting effects

Precautionary statements

P273Avoid release to the environment.

P314Get medical advice/attention if you feel unwell.

Selenium dioxide Chemical Properties,Usage,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).

Preparation

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

Reactions

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

Toxicity

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

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.

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.

Uses

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.

Uses

Selenium dioxide (SeO2) is used as an oxidizing agent, as a catalyst, and as an antioxidant for lubricating oils and grease.

Uses

It is used in the manufacture of other selenium compounds. Selenium dioxide is an oxidizing agent mostly used in the allylic oxidation of alkenes to produce allylic alcohols. It is used in creating colorless glass and toner in photographic developing.

Production Methods

While selenium dioxide, SeO2, can be produced by direct reaction of the element with oxygen activated by passage through HNO3, the compound is easily made by heating selenious acid, H2SeO3. Selenium dioxide sublimes at 315–317 °C (599–603 °F), and is readily reduced by SO2 to elemental selenium.

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.

Hazard

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.

Flammability and Explosibility

Non flammable

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.

Shipping

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.]

Incompatibilities

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.