Hydrogen, reaction with bromine chlorine

Addition reactions with bromine, chlorine, hydrogen bromide or hydrogen chloride are very vigorous and may be explosive if uncontrolled. 

The next more complicated system which yields laboratory flames is that of hydrogen-halogens. In practice, flames can be obtained from hydrogen mixed with bromine, chlorine, or fluorine. No hydrogen-iodine flame has been observed. These systems are identical in their chemistry and the failure to realize a hydrogen-iodine flame is connected with the dominance of the direct molecular reaction over the atom-catalyzed reaction which characterizes the other flames. This occurs because of the low reactivity of the iodine atom. 

Bromine, like chlorine, also undergoes a photochemical chain reaction with hydrogen. The reaction with bromine, however, evolves less energy and is not explosive. 

Photochlorination of tetrachloroethylene, observed by Faraday, yields hexachloroethane [67-72-1]. Reaction with aluminum bromide at 100°C forms a mixture of bromotrichloroethane and dibromodichloroethane [75-81-0] (6). Reaction with bromine results in an equiUbrium mixture of tetrabromoethylene [79-28-7] and tetrachloroethylene. Tetrachloroethylene reacts with a mixture of hydrogen fluoride and chlorine at 225—400°C in the presence of zirconium fluoride catalyst to yield l,2,2-trichloro-l,l,2-trifluoroethane [76-13-1] (CFG 113) (7). 

Undoubtedly, the best method for the production of pure anhydrous lanthanide trihalides involves direct reaction of the elements. However, suitable reaction vessels, of molybdenum, tungsten, or tantalum, have to be employed silica containers result in oxohalides (27). Trichlorides have been produced by reacting metal with chlorine (28), methyl chloride (28), or hydrogen chloride (28-31). Of the tribromides, only that of scandium has been prepared by direct reaction with bromine (32). The triiodides have been prepared by reacting the metal with iodine (27, 29, 31, 33-41) or with ammonium iodide (42). 

EXPLOSION and FIRE CONCERNS highly flammable liquid NFPA rating Health 2, Flammability 4, Reactivity 2 oxidizes readily in air to unstable peroxides that may explode spontaneously condensation reaction with acid anhydrides, alcohols, ketones, and phenols can be violent combination with bromine, chlorine, fluorine, or iodine can be violent reaction of anhydrous ammonia, hydrogen cyanide, or hydrogen sulfide can be violent use carbon dioxide, dry chemical powder, or appropriate foam for firefighting purposes. 

EXPLOSION and FIRE CONCERNS a highly flammable liquid NFPA rating Health 2, Flammability 2, Reactivity 1 vapors form explosive mixtures with air, explosive reactions with bromine pentafluoride, chromium trioxide, hydrogen peroxide, potassium permanganate, sodium peroxide ignites on contact with pot issium-tert-butoxide incompatible or reacts violently with acetaldehyde, acetic anhydride, chromic acid, nitric acid, ammonium nitrate, chlorine trifluoride, (nitric acid + acetone), perchloric acid, potassium hydroxide, sodium hydroxide, xylene use water spray, dry chemical, foam, or carbon dioxide for firefighting purposes. 

Ketones containing an enolizable hydrogen can be halogenated at the a position (the carbon adjacent to the carbonyl) with bromine, chlorine, NBS, or NCS. The reaction probably proceeds via addition of X2 to the enol form of the carbonyl (secs. 9.2.A, 9.8.A). Elimination of HX from the addition product generates an other enol, which tautomerizes to the a-haloketone. Reaction of cyclohexanone with bromine, for example, would give 2-bromocyclohexanone (174) and a similar reaction with NCS (173) would give 2-chloro-cyclohexanone (172). 

In other words, the reaction of 146 with bromine leads to >99% of a single product, 64, with <1% of the second product 1150, despite the fact that there are only one tertiary hydrogen and nine primary hydrogen atoms. Where the reaction with chlorine gave a mixture, the reaction with bromine gives essentially one product. This means that radical chlorination is unselective, but radical bro-mination is selective, making radical bromination a more useful reaction. 

Bromination of methane is exothermic but less exothermic than chlorination The value calculated from bond dissociation energies is AH° = -30 kJ Al though bromination of methane is energetically fa vorable economic considerations cause most of the methyl bromide prepared commercially to be made from methanol by reaction with hydrogen bromide... 

The reaction with fluorine occurs spontaneously and explosively, even in the dark at low temperatures. This hydrogen—fluorine reaction is of interest in rocket propellant systems (99—102) (see Explosives and propellants, propellants). The reactions with chlorine and bromine are radical-chain reactions initiated by heat or radiation (103—105). The hydrogen-iodine reaction can be carried out thermally or catalyticaHy (106). 

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