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For example, consider radical bromination of toluene: [5] bromination of toluene with hydrobromic acid and hydrogen peroxide in water. This reaction takes place on water instead of an organic solvent and the bromine is obtained from oxidation of hydrobromic acid with hydrogen peroxide. An incandescent light bulb suffices to radicalize.
Bromotoluenes are aryl bromides based on toluene in which at least one aromatic hydrogen atom is replaced with a bromine atom. They have the general formula C 7 H 8–n Br n, where n = 1–5 is the number of bromine atoms.
Together with other isomers, 4-nitrotoluene is prepared by nitration of toluene, [4] commonly using titanium(IV) nitrate. [5] It undergoes the reactions typical for nitrobenzene derivatives, e.g. hydrogenation gives p-toluidine. Oxidation of the methyl substituent of 4-nitrotoluene has been extensively investigated.
Bromination is more selective than chlorination because the reaction is less exothermic. Illustrative of the bromination of an alkene is the route to the anesthetic halothane from trichloroethylene: [6] Iodination and bromination can be effected by the addition of iodine and bromine to alkenes.
In 1967 the group of George A. Olah obtained NMR spectra of tetramethylethylenebromonium ions by dissolving 2,3-dibromo-2,3-dimethylbutane in magic acid at −60 °C. [5] The spectrum for the corresponding fluorine compound on the other hand was consistent with a rapidly equilibrating pair of β-fluorocarbocations.
The mechanism for bromination of benzene. The mechanism for iodination is slightly different: iodine (I 2) is treated with an oxidizing agent such as nitric acid to obtain the electrophilic iodine ("I +", probably IONO 2). Other conditions for iodination include I 2, HIO 3, H 2 SO 4, and N-iodosuccinimide, H 2 SO 4.
Benzyl bromide is used in organic synthesis for the introduction of the benzyl groups when the less expensive benzyl chloride is insufficiently reactive. [6] [7] Benzylations are often achieved in the presence of catalytic amounts of sodium iodide, which generates the more reactive benzyl iodide in situ. [3]
Bromine monofluoride in ethanol readily leads to the monobromination of the aromatic compounds PhX (para-bromination occurs for X = Me, Bu t, OMe, Br; meta-bromination occurs for the deactivating X = –CO 2 Et, –CHO, –NO 2); this is due to heterolytic fission of the Br–F bond, leading to rapid electrophilic bromination by Br +. [4]