Натрий бромид

Химические свойства

Sodiumbromide, NaBr,is a white, hygroscopic, crystalline solid with a bitter, saline taste.It is water soluble,with a melting point of 758°C (1400 OF). Sodium bromide is used in medicine as a sedative and in photography in the preparation of silver bromide emulsion on photographic plates or films.

Физические свойства

White crystalline powder or granules; saline and slight bitter taste; cubic structure; density 3.20 g/cm³; melts at 747° C; vaporizes at 1,390°C; vapor pressure 1 torr at 806°C and 5 torr at 903°; highly soluble in methanol, 16.7 g/100mL.
The dihydrate is a white crystalline solid; density 2.18 g/cm³; decomposes at 36°C; soluble in water; sparingly soluble in methanol.

Вхождение

Sodium bromide occurs in seawater at an average concentration of 0.008%. It also is found naturally in some salt deposits. It is used in photography for preparing light-sensitive silver bromide emulsions. The salt also is used as a bleaching and disinfecting agent for water treatement in swimming pools, health spas, and hot tubs. Other uses are as a catalyst for partial oxidation of hydrocarbons, for increasing density of aqueous drillng fluids for oil wells, as an electrolyte component in sodium-halogen batteries, as a brominating agent in organic synthesis, in preparing bromide salts, and as a laboratory reagent. Sodium bromide is used in medicine as a sedative and hypnotic.

Использование

Sodium Bromide is a high-tonnage chemical and one of the most important of the bromide salts (NaBr2). High-purity grades are required in the formulation of silver bromide emulsions for photography. The compound, usually in combination with hypochlorites, is used as a bleach, notably for cellulosics. The production of sodium bromide simply involves the neutralization of HBr with NaOH or with sodium carbonate or bicarbonate.

Определение

ChEBI: Sodium bromide is an inorganic sodium salt having bromide as the counterion. It is a bromide salt and an inorganic sodium salt. It is used in photographic processingand in analytical chemistry.

Подготовка

Sodium bromide can be prepared by several methods. Pure salt can be made by neutralizing sodium hydroxide or sodium carbonate with hydrobromic acid. The solution is evaporated for crystallization:NaOH + HBr → NaBr + H₂O NaCO₃ + HBr → NaBr + CO₂ + H₂O
Sodium bromide can be made by passing bromine through an aqueous solution of sodium hydroxide or carbonate in the presence of a reducing agent, such as ammonia, hydrazine, activated charcoal, or Fe₂₊ ion. A typical method involves adding iron to bromine water to form ferrosoferric bromide, Fe[FeBr₅]. This double salt is dissolved in excess water followed by addition of sodium carbonate. The product mixture is filtered and the filtrate is evaporated to crystallize sodium bromide. The overall reaction may be written as follows: 3Fe + 4Br₂ + 4Na₂CO₃ → 8NaBr + FeCO₃ + Fe₂(CO₃)₃
Another method involves adding excess bromine to a solution of sodium hydroxide. This forms sodium bromide and bromate. The product solution is evapoated to dryness. The bromate is reduced to bromide by heating with carbon: 3Br₂ + 2NaOH + H₂O → NaBr + NaBrO₃ + 4HBr.

Общее описание

Sodium bromide is a brominating agent mainly used in organic synthetic reactions as a bromide source.

Опасность

Toxic by inhalation and ingestion.

Профиль безопасности

Moderately toxic by ingestion. Experimental reproductive effects. Incompatible with acids, alkaloidal and heavy-metal salts. When heated to decomposition it emits toxic fumes of Brand NazO. See also BROMIDES.

Методы очистки

Crystallise the bromide from water (0.86mL/g) between 50o and 0o, and dry it at 140o under vacuum (this purification may not eliminate chloride ion).

Несовместимости

Sodium bromide is compatible with most non-metallic materials of construction such as polypropylene, polyethylene, fiberglass reinforced plastic (FRP), cellulose, cloth, coatings, rubbers, etc. Metals can also be used provided the sodium bromide is kept dry. If the sodium bromide becomes wet, steel will suffer general corrosion and stainless steels and aluminum will suffer pitting attack. The rates of attack will depend upon the amount of oxygen present but in general will not be rapid.