Bromination metal ions

Impurities in bromine may be deterrnined quantitatively (54). Weighing the residue after evaporation of a bromine sample yields the total nonvolatile matter. After removing the bromine, chloride ion may be deterrnined by titration with mercuric nitrate, and iodide ion by titration with thiosulfate water and organic compounds may be detected by infrared spectroscopy sulfur may be deterrnined turbidimetricaHy as barium sulfate and heavy metals may be deterrnined colorimetricaHy after conversion to sulfides. 

In the CeSI (115) and NdSBr (334) type of structure, bromine and iodine are coordinated to five metal ions (four of the same layer, and one of the opposite layer) and four halogen ions of the double layer. In the SmSI type (335), iodine is coordinated to three metal ions of a [LS] layer and three other iodine ions of the double layer. In the FeOCl type of compound, such as ErSCl (355) and LuSBr (85), the halogen is surrounded by a polyhedron formed by six sulfur and four halogenide ions. 

The beauty of bromide-mediated oxidations is that they combine mechanistic complexity with practical simplicity and, hence, utility. They involve an intricate array of electron transfer steps in which bromine atoms function as go-betweens in transfering the oxidizing power of peroxidic intermediates, via redox metal ions, to the substrate. Because the finer mechanistic details of these elegant processes have often not been fully appreciated we feel that their full synthetic potential has not yet been realized. Hence, we envision further practical applications in the future. 

Nucleophilic substitution reactions, to which the aromatic rings are activated by the presence of the carbonyl groups, are commonly used in the elaboration of the anthraquinone nucleus, particularly for the introduction of hydroxy and amino groups. Commonly these substitution reactions are catalysed by either boric acid or by transition metal ions. As an example, amino and hydroxy groups may be introduced into the anthraquinone system by nucleophilic displacement of sulfonic acid groups. Another example of an industrially useful nucleophilic substitution is the reaction of l-amino-4-bromoanthraquinone-2-sulfonic acid (bromamine acid) (76) with aromatic amines, as shown in Scheme 4.5, to give a series of useful water-soluble blue dyes. The displacement of bromine in these reactions is catalysed markedly by the presence of copper(n) ions. 

Bromination of Beta Keto Esters. The work of K. A. Pedersen on the bromination of beta keto esters in the presence of copper(II) and other divalent metal ions provides several examples of reactions proceeding via complexes (29), The complexes provide an alternative and much more rapid route for the bromination reaction. These reactions are accelerated by bases which take up a proton from the beta keto esters. For such substrates, e.g. ethyl acetoacetate, the general expression for the pseudo first order rate constant in the presence of copper has the form ... 

Another reaction in which the cleavage of a carbon-hydrogen bond is important is the bromination of ketones. In the bromination of ethyl acetoacetate and 2-carboethoxycyclopentanone, it was shown that multivalent cations are catalysts. In the latter reaction, cupric, nickelous, lanthanum, zinc, plumbous, manganous, cadmium, magnesium, and calcium ions were effective (45). One can interpret the effect of the metal ion in terms of its catalysis of the proton transfer from the ester to a base, whether the reaction is carried out in dilute hydrochloric acid solution (acid-catalyzed bromination) or in acetate buffer (base-catalyzed bromination). 

Y. Kamiya illustrates the influence on catalytic activity of the form of the catalyst. Thus, in the cobalt-catalyzed oxidation of hydrocarbons in acetic acid solution, introduction of bromide ions increases the activity of the catalyst, especially when the metal ion concentration is fairly high. The presence of bromides also results in a marked increase in the proportion of carbonyl compounds among the products and it is believed that these are formed as a result of a propagation step in which bromine-containing cobaltous ions react with alkylperoxy radicals. 

Neutral square coplanar complexes of divalent transition metal ions and monoanionic chelate or dianionic tetrachelate ligands have been widely studied. Columnar stack structures are common but electrical conductivities in the metal atom chain direction are very low and the temperature dependence is that of a semiconductor or insulator. However, many of these compounds have been shown to undergo partial oxidation when heated with iodine or sometimes bromine. The resulting crystals exhibit high conductivities occasionally with a metallic-type temperature dependence. The electron transport mechanism may be located either on predominantly metal orbitals, predominantly ligand re-orbitals and occasionally on both metal and ligand orbitals. Recent review articles deal with the structures and properties of this class of compound in detail.89 90 12... 

The Lewis acidity of a particular metal ion will be primarily a function of the charge density on the metal centre. Complexes of Cu11, Zn11 and Co111 should therefore display properties intermediate between those of the free ligand and its conjugate acid. Early measurements on the bromination of aniline, the anilinium ion and coordinated aniline provide a good illustration of this point (Table 1). Since this reaction is an electrophilic substitution, protonation and metal... 

Solid-supported reagents which have found utility include Nafion-scandium Lewis acid catalyst (allyl additions to aldehydes) [62], HOBt (medium-ring lactamization) [63], EDC (preparation of active esters) [64], and thiazolium hydrotribromide (brominations) [65], A review has also appeared describing the use of supported reagents in separation science, primarily for the selective sequestration of metal ions [66],... 

The four-electron change necessary for the quantitative conversion to nitrogen occurs only within certain limits of pH, concentration and temperature. Chlorine, bromine, iodine and iodates bring about this reaction quantitatively at pH 7. Dissolved molecular oxygen oxidises aqueous hydrazine to nitrogen in a series of stages, so hydrazine is an effective deoxidant for boiler-water. Several metal ions, particularly copper, catalyse the reaction. 

Perfluoroalkyl anions can, in principle, be generated by the same methods as "normal alkyl or aryl anions - either by deprotonation of a suitable CH-acidic precursor by a strong base or by reductive halogen (usually iodine or bromine) metal exchange (Scheme 2.109). Another method - unique to the "perfluoro world -is addition of fluoride ions or other anions to perfluoroolefins. 

For those proteins containing metal ions or metal clusters, such as Fe, Ni, and Cu, the MAD experiment can be carried out directly on the native protein crystals without the need of seleno-derivatives. Crystals containing heavy atoms incorporated via chemical modification or by soaking (McPherson, 1982) can also be used for MAD experiments. Finally, Dauter et al. (2000) has shown that ordered bromine in the protein s solvation shell could provide MAD phasing information. 

Aqueous extractions of bromide and chloride ions were done at various temperatures ranging from 120- to 250°C. This was done to verify the thermal stability of brominated resins in aqueous medium at elevated temperatures. The total level of alkali metal ions and NH4+ combined was nearly an order of magnitude lower than either bromide or chloride this indicated that the halides were mostly derived from organic sources. Arrhenius plots of bromide... 

Original B-Z reaction where metal ion catalyzed organic substrate is brominated by enolization and bromide is liberated when the organic bromate reacts with the oxidized form of the catalyst, [See G G]. 

Other examples of electrophilic substitution reactions catalyzed by metal ions through mechanisms involving the promotion of proton loss and stabilization of enol forms of reactants include the bromination of /3-diketones ... 

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