Interhalogen Compounds And Their Properties

Interhalogen compounds are formed from two different halogens. These compounds resemble the halogens themselves in both their physical and chemical properties. Principal differences show up in their electronegativities. This is clearly shown by the polar compound IC1, which has a boiling point almost 40° C above that of bromine, although both have the same molecular weights. Interhalogens have bond energies that are lower than halogens and therefore in most cases they are more reactive. These properties impart special germicidal characteristics to these compounds. The principal germicidal compound of this group is bromine chloride. At equilibrium, BrCl is a fuming dark red liquid below 5° C. It exists as a solid only at relatively low temperatures. Liquid BrCl can be vaporized and metered as a vapor in equipment similar to that used for chlorine.

BrCl is prepared by the addition of equivalent amounts of chlorine to bromine until the solution has increased in weight by 44.3 percent: The reaction is as follows:

BrCl can be prepared by the reaction in the gas phase or in aqueous hydrochloric acid solution. In the laboratory, BrCl is prepared by oxidizing bromide salt in a solution containing hydrochloric acid.

BrCl exists in equilibrium with bromine and chlorine in both gas and liquid phases. Table 5 lists various physical properties of BrCl. Due to the polarity of BrCl, it shows greater solubility than bromine in polar solvents. In water, it has a solubility of 8.5 gms per 100 gms of water at 20o C (that is, 2.5 times the solubility of bromine; 11 times that of chlorine). Bromine chloride's solubility in water is increased greatly by adding chloride ions to form the complex chlorobromate ion, BrCl,.

Table 5. Physical Properties of BrCl.

Molecular weight


Melting point (°C)


Boiling point (°C)


Density (g/cc), 200 C


Heat of fusion (cal/g)


Heat of vaporization (cal/g)


Heat formation (kcal/mole)


Heat capacity (cal./deg. mole, 298° K)


Entropy (cal./deg. mole, 298° K)


Dipole moment


Electrical conductivity (dm"1 cm"1)


Degree of dissociation (%, vapor 25° C)




Various organic and inorganic species that act as reducing agents react with and destroy free halogen residuals during interaction with microorganisms (see Figure 2.13 for examples of competitive reactions). Competitive reactions depend on the reactivity of the chemical species, temperature, contact time, and pH. The quality of the effluent and the method of adding the disinfectant also help determine the specific reaction pathways. Bromine chloride is about 40 percent dissociated into bromine and chlorine in most solvents. Because of its high reactivity and fast equilibrium, BrCl often generates products that result almost entirely from it. This is illustrated by the disinfectant products shown in Figure 5. The major portion of the BrCl is eventually reduced to inorganic bromides and chlorides, with the exception of addition and substitution reactions with organic constituents.

Interhalogen Compound

Figure 5. Reactions in wastewater disinfection.

It should be noted that although BrCl is mainly a brominating agent that is competitive with bromine, its chemical reactivity makes its action similar to that of chlorine (that is, disinfection, oxidation, and a bleaching agent). BrCl hydrolyzes exclusively to hypobromous acid, and if any hydrobromic acid (HBr) is formed by hydrolysis of the dissociated bromine, it quickly oxidizes to hydrobromous acid via hypochlorous acid.

Since hypohalous acid is a much more active disinfectant than the hypohalite ion, the effect of pH on ionization becomes important. Hypobromous acid has a lower ionization value than hypochlorous acid and this contributes to the higher disinfectant activity of BrCl compared with chlorine.

Bromine chloride also undergoes very specific reactions with ammonia and with organics. Monobromamine and dibromamine are the major products formed from reactions between BrCl and ammonia. These are unstable compounds in most conventional wastewater treatment plant effluents. In comparing the activities of bromarnine versus chloramines, the effects of ammonia and high pH tend to improve the bromarnine performance whereas the chloramine activity is reduced significantly. The reaction of ammonia with either BrCl or chlorine to form the halamine is very fast and generally goes to completion. As such, the presence of ammonia is essential to the disinfectant properties. Most sewage effluents typically have high ammonia concentrations in the range of 5 - 20 ppm. For such samples, the predominant bromine species (pH at 7 to 8) monobromamine and dibromamine are approximately equally distributed.

There are a large number of organics that undergo disinfection during the purification process. There are unfortunately a number of undesirable byproducts and side reactions which occur with some of them. One is the reaction between chlorine and phenol, producing chlorophenols, which are suspected carcinogens. Chlorophenols have obnoxious tastes and are toxic to aquatic life even at very low concentrations. Brominated phenolic products which are formed in the chlorobromination of wastewater are generally more readily degraded and often less offensive than their chlorinated counterparts.

The major organic reactions of BrCl consist of electrophilic brominations of aromatic compounds. Many aromatic compounds do not react in aqueous solution unless the reaction involves activated aromatic compounds (an example being phenol). Bromine chloride undergoes free-radical reactions more readily than bromine.

Metal ions in their reduced state also undergo reactions with BrCl. Examples include iron and manganese.

Wastewater occasionally contains hydrogen sulfide and nitrites. These contribute to higher halogen demands. Many of these reactions reduce halogens to halide salts.

Bromine chloride's reactivity with metals is not as great as that of bromine; however, it is comparable to chlorine. Dry BrCl is typically two orders of magnitude less reactive with metals than dry bromine. Most BrCI is less corrosive than bromine. Like chlorine, BrCl is stored and shipped in steel containers. Also, Kynar and Viton plastics and [email protected] are preferred over polyvinyl chloride (PVC) when BrCl is in the liquid or vapor states.

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  • natsnet
    How are Interhalogen compounds formed?
    3 years ago
  • rasmus
    How are interhalogen compounds prepared?
    3 years ago
  • noora
    Do interhalogen compounds have low boiling points?
    3 years ago
  • leonie
    What is interhalogens compounds. How are they prepared?
    3 years ago
  • calan
    What are inter halogen compounds with examples?
    3 years ago
  • dennis
    Is interhalogen compound are soluble in water?
    3 years ago
    Why are boiling point of interhalogen higher than halogens?
    2 years ago
  • cotman
    What are the importance of interhalogen compound?
    2 years ago
    What are the importants of interhalogen?
    6 months ago

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