Chemical elements
  Arsenic
      Occurrence
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    Chemical Properties
      Aluminium Arsenide
      Antimony Arsenides
      Barium Arsenide
      Bismuth Arsenides
      Cadmium Arsenides
      Calcium Arsenide
      Cerium Arsenide
      Chromium Arsenides
      Cobalt Arsenides
      Copper Arsenides
      Gold Arsenides
      Iridium Arsenide
      Iron Arsenides
      Lead Arsenides
      Lithium Arsenide
      Magnesium Arsenide
      Manganese Arsenides
      Mercury Arsenides
      Molybdenum Arsenide
      Nickel Arsenides
      Niobium Arsenide
      Palladium Di-arsenide
      Platinum Arsenides
      Potassium Arsenides
      Rhodium Arsenide
      Ruthenium Arsenide
      Silver Arsenides
      Sodium Arsenide
      Strontium Arsenide
      Thallium Arsenide
      Tin Arsenides
      Tungsten Arsenide
      Uranium Arsenide
      Zinc Arsenides
      Arsenic Subhydride
      Arsenic Monohydride
      Arsenic Trihydride
      Arsenic Trifluoride
      Arsenic Pentafluoride
      Arsenic Nitrosyl Hexafluoride
      Arsenic Trichloride
      Arsenic Oxychloride
      Arsenic Pentachloride
      Arsenic Tribromide
      Arsenic Oxybromide
      Arsenic Moniodide
      Arsenic Diiodide
      Arsenic Triiodide
      Arsenic Pentiodide
      Arsenic Suboxide
      Arsenious Oxide
      Aluminium Arsenite
      Ammonium Arsenites
      Antimony Arsenite
      Barium Arsenites
      Beryllium Arsenite
      Bismuth Arsenite
      Cadmium Arsenites
      Calcium Arsenites
      Chromic Arsenite
      Cobalt Arsenites
      Copper Arsenites
      Gold Arsenites
      Iron Arsenites
      Lead Arsenites
      Lithium Arsenite
      Magnesium Arsenites
      Manganese Arsenites
      Mercury Arsenites
      Nickel Arsenites
      Palladium Pyroarsenite
      Platinum Arsenites
      Potassium Arsenites
      Arsenites of Rare Earth Metals
      Rubidium Metarsenite
      Silver Arsenites
      Sodium Arsenites
      Strontium Arsenites
      Thallous Orthoarsenite
      Tin Arsenites
      Titanyl Tetrarsenite
      Tungsto-arsenites
      Uranyl Metarsenite
      Zinc Arsenites
      Zirconium Arsenite
      Arsenic Tetroxide
      Arsenic Pentoxide
      Aluminium Arsenates
      Ammonium Arsenates
      Barium Arsenates
      Beryllium Arsenates
      Bismuth Arsenates
      Cadmium Arsenates
      Caesium Arsenate
      Calcium Arsenates
      Chromium Arsenates
      Cobalt Arsenates
      Copper Arsenates
      Hydroxylamine Orthoarsenate
      Iron Arsenates
      Lead Arsenates
      Lithium Arsenates
      Magnesium Arsenates
      Manganese Arsenates
      Mercury Arsenates
      Molybdenum Arsenates
      Nickel Arsenates
      Palladium Arsenate
      Platinic Arsenate
      Potassium Arsenates
      Rare Earth Metals Arsenates
      Rhodium Arsenate
      Rubidium Arsenates
      Silver Arsenates
      Sodium Arsenates
      Strontium Arsenates
      Thallium Arsenates
      Thorium Arsenates
      Tin Arsenates
      Titanyl Arsenate
      Tungsto-arsenic Acids
      Uranium Arsenates
      Vanado-arsenates
      Zinc Arsenates
      Zirconium Arsenates
      Perarsenates
      Arsenic and Sulphur
      Arsenic Subsulphide
      Tetrarsenic Trisulphide
      Arsenic Disulphide
      Arsenic Trisulphide
      Arsenic Pentasulphide
      Thioarsenates
      Ammonium Thioarsenates
      Antimony Thioarsenate
      Barium Thioarsenates
      Beryllium Thioarsenate
      Bismuth Thioarsenate
      Cadmium Thioarsenates
      Calcium Thioarsenates
      Cerium Thioarsenates
      Chromium Thioarsenate
      Cobalt Thioarsenate
      Copper Thioarsenates
      Gold Thioarsenates
      Iron Thioarsenates
      Lead Thioarsenates
      Lithium Thioarsenates
      Magnesium Thioarsenates
      Manganese Thioarsenates
      Mercury Thioarsenates
      Molybdenum Thioarsenates
      Nickel Thioarsenates
      Platinic Thioarsenate
      Potassium Thioarsenates
      Silver Thioarsenates
      Sodium Thioarsenates
      Strontium Thioarsenates
      Thallium Orthothioarsenate
      Tin Thioarsenates
      Uranyl Thioarsenate
      Yttrium Thioarsenate
      Zinc Thioarsenates
      Zirconium Thioarsenate
      Trioxythioarsenic Acid
      Dioxydithioarsenic Acid
      Oxytrithioarsenic Acid
      Arsenic Monosulphatotrioxide
      Arsenic Disulphatotrioxide
      Arsenic Trisulphatotrioxide
      Arsenic Tetrasulphatotrioxide
      Arsenic Hexasulphatotrioxide
      Arsenic Octasulphatotrioxide
      Complex salts of Sulphato-compounds of Arsenic
      Arsenic Nitride
      Arsenic Imide
      Arsenic Amide
      Arsenic Phosphides
      Arsenic oxyphosphides
      Arsenic Phosphate
      Arsenic Thiophosphate
      Arsenic Tricarbide
      Arsenic Pentasilicide
      Boron Arsenate
    Detection of Arsenic
    Estimation of Arsenic
    Physiological Properties
    PDB 1b92-1ihu
    PDB 1ii0-1tnd
    PDB 1tql-2hmh
    PDB 2hx2-2xnq
    PDB 2xod-3htw
    PDB 3hzf-3od5
    PDB 3ouu-9nse

Arsenic Tribromide, AsBr3






Arsenic Tribromide, AsBr3, was first obtained in 1828 by Serullas, who added dry powdered arsenic in small quantities to bromine contained in a glass retort until no further action occurred. On contact with the bromine the arsenic inflamed brilliantly, and on distillation of the product, arsenic tribromide condensed in the receiver in the form of prismatic crystals. A more convenient method is to pass bromine vapour over an excess of arsenic contained in a hard glass tube. By repeated distillation of the product, very pure arsenic tribromide may be obtained.

The bromide may also be prepared (1) by adding arsenic powder to a mixture of carbon disulphide and bromine (2:1 by weight) and agitating the liquid until decolorised; on evaporation, crystals of the bromide remain; (2) by heating a mixture of arsenious oxide, potassium bromide and acetic acid at 100° C.; (3) by heating a mixture of arsenious oxide and sulphur in a current of bromine vapour.


Physical Properties of Arsenic Tribromide

Arsenic tribromide is a solid at ordinary temperatures, crystallising in beautiful colourless rhombic prisms which possess a feebly aromatic odour and are stable in dry air. In the presence of moisture slight fuming occurs. The crystals melt sharply at 31° C. The density at 15° C. is 3.66; after fusion and resolidification, the product has density 3.54 at 25° C. The density of the liquid at various temperatures may be obtained from the expression

D4θ = 3.3972 – 0.002822(θ - 25) + 0.00000248(θ - 25)2

The surface tension, a, and molecular surface energy, μ, of the liquid at various temperatures have been found to be:

t, °C49.674.590.0121.0149.6165.0179.7
σ, dynes per cm.49.646.644.841.038.237.036.1
μ, ergs per sq. cm.1029.5980.5947.8884.1835.6815.6801.6
The parachor is 253.5


The molecular volume at the ordinary temperature is 111 c.c., and the ratio of this value to the sum of the atomic volumes of the constituent elements is 1.21. From measurements of density and coefficient of expansion at -194° C. the molecular volume at 0° Abs. has been calculated to be 76.1. The molecular weight determined by ebullioscopic and cryoscopic methods with bromine as solvent agrees with the formula AsBr3. The solution in bromine is a non-conductor of electricity; on the other hand, the solution in liquid sulphur dioxide is a conductor, the equivalent conductivity of 1 mole of AsBr3 in 101.4 and 925.3 litres of the solvent being respectively 0.249 and 2.347. The solution in liquid hydrogen sulphide also conducts electricity. Arsenic tribromide itself may be used as a solvent in molecular weight determinations; the cryoscopic constant has been given values ranging from 189 to 206. It behaves similarly to arsenic trichloride in forming mixed halides with halides of the elements of Groups IV and V. The ionising power of arsenic tribromide is somewhat less than that of the trichloride. The liquid boils at 221° C. (760 mm.); at lower pressures the following temperatures have been observed: 109° C. (20 mm.), 92° C. (14 mm.).

The heat of fusion is 8.93 calories per gram. The heat of formation is:

As(cryst.) + 3Br(liq.) = AsBr3(cryst.) + 45,500 calories

The following values for the refractive index for sodium, lithium and thallium light, respectively, have been obtained:

Temperature, ° C.nNanLinTl
241.7849 1.77161.7983
301.78151.76781.7939


The value for the electron polarisation, is 41.97, and the stable form of the molecule is a three-sided pyramid. The dipole moment is 1.66×10-18 e.s.u. The dielectric constant at 20° C. is 3.4, and at 35° C. 9.3.

Arsenic tribromide dissolves in many organic liquids, such as carbon disulphide, methylene iodide and benzene; in the last named the decomposition voltage is 0.50 volt. In solutions in diethyl ether the electrical conductance at 18° C. rapidly increases with increase in the bromide concentration up to 95 per cent., after which it quickly falls to the value for the pure bromide. For high concentrations the temperature coefficient is positive, but decreases with falling concentration and for concentrations below 75 per cent, is negative. This effect does not appear to be due to interaction between solvent and solute; if the molecular conductivity is calculated with reference to the bromide as electrolyte, the conductivity-concentration curve shows two maxima, but if the ether is taken as the electrolyte a normal curve results. For solutions in methylethyl ether1 the specific conductivity and its temperature coefficient are at a maximum for solutions containing the two components in equimolecular proportions, indicating the formation of the compound AsBr3.CH3OC2H5. The solution of arsenic tribromide in anisole is non-conducting. The tribromide also dissolves in boron bromide and in phosphoryl chloride.

Arsenic tribromide is itself a good solvent for certain halides. The following freezing points and densities at 15° C. of saturated solutions have been determined:

Solute.Freezing Point, °C.Density.
SbBr3473.685
SbI3403.720
ZnI3153.73


Arsenic triiodide also dissolves, the saturated solution at 15° C. having density 3.661. Other soluble halides are potassium bromide, anhydrous ferric and aluminium chlorides and tetramethyl ammonium iodide; but the iodides of rubidium, cadmium, manganese and cobalt, also mercuric and stannic iodides, and cobalt and stannic bromides, are insoluble or only very slightly soluble in arsenic tribromide. The liquid also dissolves phosphoryl bromide and, very slightly, ammonium thiocyanate. In the mixed solutions of halides, the components may react chemically, but such is not always the case; for example, with antimony tribromide a continuous series of solid solutions is formed.

Chemical Properties of Arsenic Tribromide

Arsenic tribromide reacts with water in small quantity to form the oxybromide, AsOBr; in larger quantity arsenious and hydrobromic acids are formed. One part of the tribromide dissolves in three parts of boiling water, and on cooling the solution deposits crystals of arsenious oxide. The tribromide is less soluble in aqueous hydrobromic acid. It dissolves in bromine, but does not combine. Oxygen reacts with arsenic tribromide vapour at red heat to form arsenious oxide, arsenic oxybromide, AsOBr, and free bromine. Hydrogen sulphide passed over the tribromide at 150° C. yields the bromosulphide, AsSBr (m.pt. 118° C.). Ammonia gas is absorbed by arsenic tribromide to yield a pale yellow solid of composition AsBr3.3NH3; if the bromide is in benzene solution the product, according to Landau, is a white precipitate of composition 2AsBr3.7NH3. The latter can be crystallised from hot absolute alcohol; it is soluble in cold water, but the solution decomposes on warming, as also does the dry ammine, losing ammonia. The pale yellow triammino-compound also decomposes on heating yielding, at 300° C., nitrogen, ammonium bromide and arsenic. Organic amines react similarly with arsenic tribromide. Phosphine yields hydrogen bromide and arsenic phosphide, AsP.

Carbon tetrachloride is partially transformed into the bromide by prolonged heating with arsenic tribromide at 150° to 200° C. Acetylene, in the presence of aluminium chloride or bromide as catalyst, forms the bromovinylarsines (CHBr:CH)AsBr2 and (CHBr:CH)2AsBr, and with an increased quantity of the catalyst (CHBr:CH)3As. When a mixture of arsenic tribromide and cyanogen bromide is slowly heated in an autoclave to 180° C. and then cooled and kept for an hour at 120° C., the additive compound AsBr3.2BrCN is formed. It is decomposed when heated above 190° C.

Certain compounds with metals and metallic salts have been described. Thus, by heating finely divided silver or copper with arsenic tribromide in a sealed tube, substances of composition 3Ag.AsBr3 and 7Cu.2AsBr3 have been isolated, the latter probably containing uncombined copper in solid solution. Similar products are obtained by the action of arsenic vapour on silver bromide or cuprous bromide at 500° C. Double decomposition reactions occur when arsenic tribromide is heated with stannic iodide or germanium iodide, the reactions being complete. Sodium azide reacts with the tribromide in acetone or methyl alcohol solution to form a white compound of composition Na8[AsBr3(N3)8]. Rubidium and caesium salts of composition 3RbBr.2AsBr3 and 3CsBr.2AsBr3 have been obtained in the form of trigonal crystals by a method analogous to that used for the corresponding chlorides.
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