Halogenation 64--------------------------, with bromine vapor/solution

Several patents describe solvent-free bulk-phase halogenation (67—69). Dry soHd butyl mbber is fed into a specially designed extmder reactor and contacted with chlorine or bromine vapor. The by-product HCl or HBr ate vented directly without a separate neutralization step. Halogenated butyl mbbers produced are essentially comparable in composition and properties to commercial products made by the solution process. 

The solubility of chlorine per 100 cc. of water at 20° is 1.85 g. that of bromine is 3.58 g. and that of iodine 0.28 g. Both chlorine and bromine form crystalline hydrates, C12-8H20 and BrjTOHjO. They are stable only at low temperatures (0-9°). The increased solubility of bromine in potassium bromide solution is ascribed to the formation of KBr if such solutions are saturated with bromine, the vapor pressure of the latter is the same as that of a water solution saturated with bromine. However, the halogen can be removed completely by extraction with carbon disulfide or by a stream of air the KBra must be stable only in the presence of free bromine. The solubility of iodine in water is increased by potassium iodide to 1.4 g. per 100 cc. and in ethanol a 20% solution can be formed. 

Analogous to chlorine, bromine or iodine form stable halogen-carbon complexes, with the maximum amount fixed at about 773 K. The mechanism of bromine incorporation varies depending on the physical form of bromine (vapors or aqueous solution). When bromine is present in aqueous solution, bromine occupies unsaturated sites on the carbon surface, whereas in reaction with vapor, partial substitution for hydrogen also takes place. The former reaction is used as a measure of surface unsaturation [147,153,154]. The driving force for a partial substitution of hydrogen by bromine is inaccessibility of the small pores to the large bromine molecule. 

Halogens react with the metal at elevated temperatures. Fluorine reacts with ruthenium at 300°C forming colorless vapors of pentafluoride, RuFs, which at ordinary temperatures converts to a green solid. Chlorine combines with the metal at 450°C to form black trichloride, RuCF, which is insoluble in water. Ru metal at ambient temperature is attacked by chlorine water, bromine water, or alcoholic solution of iodine. 

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