Selenium dioxide

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.

The Uses of Selenium dioxide

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

The Uses of Selenium dioxide

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.

The Uses of Selenium dioxide

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.