Sodium bromide
Inorganic salt: NaBr
From Wikipedia, the free encyclopedia
Sodium bromide is an inorganic compound with the formula NaBr. It is a high-melting white, crystalline solid that resembles sodium chloride. It is a widely used source of the bromide ion and has many applications.[7]
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| IUPAC name
Sodium bromide | |
| Identifiers | |
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| ECHA InfoCard | 100.028.727 |
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CompTox Dashboard (EPA) |
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| Properties | |
| NaBr | |
| Molar mass | 102.894 g·molâ1 |
| Appearance | White powder, hygroscopic |
| Density | 3.21 g/cm3 (anhydrous) 2.18 g/cm3 (dihydrate) |
| Melting point | 747 °C (1,377 °F; 1,020 K) (anhydrous) 36 °C (97 °F; 309 K) (dihydrate) decomposes[1] |
| Boiling point | 1,390 °C (2,530 °F; 1,660 K)[1] |
| 71.35 g/100 mL (â20 °C) 79.52 g/100 mL (0 °C) 94.32 g/100 mL (25 °C)[2] 104.9 g/100 mL (40 °C) 116.2 g/100 mL (100 °C)[3] | |
| Solubility | Soluble in alcohol, liquid ammonia, pyridine, hydrazine, SO2 Insoluble in acetone, acetonitrile[2] |
| Solubility in methanol | 17.3 g/100 g (0 °C) 16.8 g/100 g (20 °C) 16.1 g/100 g (40 °C) 15.3 g/100 g (60 °C)[2] |
| Solubility in ethanol | 2.45 g/100 g (0 °C) 2.32 g/100 g (20 °C) 2.29 g/100 g (30 °C) 2.35 g/100 g (70 °C)[2] |
| Solubility in formic acid | 19.3 g/100 g (18 °C) 19.4 g/100 g (25 °C)[2] |
| Solubility in glycerol | 38.7 g/100 g (20 °C)[2] |
| Solubility in dimethylformamide | 3.2 g/100 g (10.3 °C)[2] |
| Vapor pressure | 1 torr (806 °C) 5 torr (903 °C)[1] |
| â41.0·10â6 cm3/mol | |
| Thermal conductivity | 5.6 W/(m·K) (150 K)[4] |
Refractive index (nD) |
1.6428 (24 °C) nKrF = 1.8467 (24 °C) nHeâNe = 1.6389 (24 °C)[5] |
| Viscosity | 1.42 cP (762 °C) 1.08 cP (857 °C) 0.96 cP (937 °C)[2] |
| Structure | |
| Cubic | |
| Thermochemistry | |
Heat capacity (C) |
51.4 J/(mol·K)[2] |
Std molar entropy (S⦵298) |
86.82 J/(mol·K)[2] |
Std enthalpy of formation (ÎfH⦵298) |
â361.41 kJ/mol[2] |
Gibbs free energy (ÎfG⦵) |
â349.3 kJ/mol[2] |
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| NFPA 704 (fire diamond) | |
| Flash point | 800 °C (1,470 °F; 1,070 K) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
3500 mg/kg (rats, oral) |
| Safety data sheet (SDS) | External MSDS |
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Other anions |
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Other cations |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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In repeated doses it is toxic to humans, leading to bromism, which may include symptoms such as skin rashes, drowsiness, nausea, and hallucinations.[8]
Synthesis, structure, reactions
NaBr crystallizes in the same cubic motif as NaCl, NaF and NaI. The anhydrous salt crystallizes above 50.7 °C.[7] Dihydrate salt (NaBr·2H2O) crystallize out of water solution below 50.7 °C.[9]
NaBr is produced by treating sodium hydroxide with hydrogen bromide.
Sodium bromide can be used as a source of the chemical element bromine. This can be accomplished by treating an aqueous solution of NaBr with chlorine gas:
- 2 NaBr + Cl2 â Br2 + 2 NaCl
Applications
Sodium bromide is the most useful inorganic bromide in industry.[7] It is also used as a catalyst in TEMPO-mediated oxidation reactions.[10]
Medicine
Also known as Sedoneural,[11] sodium bromide has been used as a hypnotic, anticonvulsant, and sedative in medicine, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries. Its action is due to the bromide ion, and for this reason potassium bromide is equally effective. In 1975, bromides were removed from drugs in the U.S. such as Bromo-Seltzer due to toxicity.[12]
Preparation of other bromine compounds
Sodium bromide is widely used for the preparation of other bromides in organic synthesis and other areas. It is a source of the bromide nucleophile to convert alkyl chlorides to more reactive alkyl bromides by the Finkelstein reaction:
- NaBr + RCl â RBr + NaCl (R = alkyl)
Once a large need in photography, but now shrinking, the photosensitive salt silver bromide is prepared using NaBr.
Disinfectant
Sodium bromide is used in conjunction with chlorine as a disinfectant for hot tubs and swimming pools.[13]
Petroleum industry
Because of its high solubility in water (943.2 g/L or 9.16 mol/L, at 25 °C) sodium bromide is used to prepare dense drilling fluids used in oil wells to compensate a possible overpressure arising in the fluid column and to counteract the associated trend to blow out. The presence of the sodium cation also causes the bentonite added to the drilling fluid to swell, while the high ionic strength induces bentonite flocculation.[14]
Safety
NaBr has a very low toxicity with an oral LD50 estimated at 3.5 g/kg for rats.[6] However, this is a single-dose value. Bromide ions are a cumulative toxin with a relatively long biological half-life (in excess of a week in humans): see potassium bromide.
