Bromide catalysis

Bromide ndIodide. The spectrophotometric determination of trace bromide concentration is based on the bromide catalysis of iodine oxidation to iodate by permanganate in acidic solution. Iodide can also be measured spectrophotometricaHy by selective oxidation to iodine by potassium peroxymonosulfate (KHSO ). The iodine reacts with colorless leucocrystal violet to produce the highly colored leucocrystal violet dye. Greater than 200 mg/L of chloride interferes with the color development. Trace concentrations of iodide are determined by its abiUty to cataly2e ceric ion reduction by arsenous acid. The reduction reaction is stopped at a specific time by the addition of ferrous ammonium sulfate. The ferrous ion is oxidi2ed to ferric ion, which then reacts with thiocyanate to produce a deep red complex. 

Preparation by oxidising tris(phenanthroline)cobalt(III) tetrafluoroborate with nitric acid in sulfuric acid with potassium bromide catalysis is potentially explosive. See Nitric acid... 

Generalizing the known data and established experimental peculiarities of the action of the cobalt bromide catalyst, we have to emphasize the following advantages of cobalt bromide catalysis ... 

The protected propargylamines 224 (R = H, CH2C02Me or CH2CH2C02Me) react with aqueous formaldehyde under copper bromide catalysis to yield the allene derivatives 225. Deprotection with ethereal hydrogen chloride affords the free amines218. 

It is known that the oxidation of alkyl-substituted aromatic hydrocarbons in acetic acid on metal bromide catalysis follows the one-electron transfer mechanism (Sheldon and Kochi 1981). The rate-determining stage is the one-electron transfer from the substrate to the metal ion in the highest oxidation state (Digurov et al. 1986). As a result, an unstable cation-radical is formed that... 

The easily available 1-bromo-l-seleno alkene, by treatment with sodium phenyl tellurolate under bis(bipyridine)nickel (11) bromide catalysis, furnishes the corresponding telluro(seleno)ketene acetal. " ... 

Competition between Homolytic and Heterolytic Catalytic Decompositions of Hydroperoxides Reactions of Transition Metals with Free Radicals Reactions of Transition Metal Ions with Dioxygen Catalytic Oxidation of Ketones Cobalt Bromide Catalysis Oscillating Oxidation Reactions... 

In this paper we hope to clarify the features of cobalt bromide catalysis using various hydrocarbons and a neutral bromide as sodium bromide at low temperatures and at moderate concentrations of cobalt. 

Effect on the Oxidation of Polymers. In the cobalt bromide catalysis, the steric hindrance to the intramolecular hydrogen abstraction in the autoxidation of polymers is expected to be reduced remarkably. 

The perben/oate ester decomposes under copped I) bromide catalysis into a hen/oate anion and a terr-hutoxy radical. This radical abstracts a hydrogen atom at an allylic position... 

Perbenzoic acid fcrf-butjl ester (51) is the source — under copper I) bromide catalysis —of a benzoate anion (52) and radical 53. Radical 53 subsequently abstracts a hydrogen atom selective ) from the 11 -position of 55 in a homolytic bond cleavage to give a buta diene system with opening of the cyclopropane ring.Jn... 

Zinc bromide catalysis effects a similar aminomethylation of silyl sulfides and phosphites (equation 11). ... 

The example studied in most detail is the bromination of 5a 3 ketones (i). The product from monobromination in acetic acid, with hydrogen bromide catalysis, is the sa-bromoketone (2). This appeared to contravene the principle [113] that stereoelectronic control favours the formation of the axial bromoketone, especially when kinetically-controlled bromination of the enol acetate (3 was found to give the same product [136]. Detailed experimental and theoretical investigations have established that the stereoelectronic preference for axial attack is fulfilled, by the molecule adopting a boat or flexible conformation (5) of ring A during attack by bromine, and changing later into the chair conformation (6)... 

The oxidation of alkylaromatic hydrocarbons proceeds particularly easily in the presence of both cobalt and bromide ions (a so-called cobalt-bromide catalysis ). Carboxylic acids are the final products of the reaction. For example, terephthalic acid is selectively formed from p-xylene, the whole process being used in the industrial production of the acid [Ik, 19]. Despite the large number of works on cobalt-bromide catalysis, its mechanism has long remained speculative. 

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