Halide ion sources

Platinum is not attacked by any of the mineral acids, but does dissolve in aqua regia, an HCl HNO3 mixture. The nitric acid provides the oxidizing power and the HCl provides the chloro ligands that stabilize Pt in solution. The metal is also attacked by fused alkalis, by fused sodium peroxide and, at red heat, by chlorine and fluorine, especially in the presence of NaCl or other halide ion sources. 

It is not difficult to incorporate this observation into the general mechanisms for hydrogen halide additions. These products are formed as the result of solvent competing with halide as the nucleophilic component of the addition reaction. Solvent addition can occur via the concerted mechanism or through a carbonium ion mechanism. Added halide salts can serve as a halide ion source, which increases the likelihood of capture of the carbonium ion intermediate by halide ion. The effect of halide salts can be detected kinetically. For example, the presence of tetramethylam-monium chloride increases the rate of addition of hydrogen chloride to cyclohexene. Similarly, lithium bromide increases the rate of addition of hydrogen bromide to cyclopentene." ... 

Anti stereochemistry can be explained by a mechanism in which the alkene interacts simultaneously with the proton-donating hydrogen halide and with a source of halide ion, either a second molecule of hydrogen halide or a free halide ion. The anti stereochemistry is consistent with the expectation that the attack of halide ion would be from the opposite... 

In Table 40 the values for the cesium salts show that, if a zero value or a positive value of the activity /l-cocflicient is used, approximate agreement with experiment can be obtained only by introducing a value of a that is smaller than the lattice spacing in the crystal- an impossibly small value. Figure 74 indicates that this situation may have arisen because a mutual attraction between the Cs+ ion and the halide ion is superimposed on their electrostatic attraction. We may tentatively look for the source of this additional attraction in the situation depicted in Fig. 69. 

Coulter C, JTG Hamilton, WC McRoberts, L Kulakov, MJ Larkin, DB Harper (1999) Halomethane bisulfite/halide ion methyltransferase, an unusual corrinoid enzyme of environmental significance isolated from an aerobic methylotroph using chloromethane as the sole carbon source. Appl Environ Microbiol 65 4301-4312. 

Megagraft 1000, the calcium phosphate bioceramic, is synthesized by chemical reaction between calcium and phosphate ion sources (6-9). This synthesis is done by taking the mixture of a calcium and a phosphate source and heating it to a temperature below the starting melting point for an extended period of time. The calcium source can be from calcium phosphates, calcium hydroxide, calcium halides,... 

Hu and Truhlar (1995) also found the same source and temperature dependence for the secondary a-deuterium KIE in a theoretical investigation of the secondary a-deuterium KIEs for three halide ion-methyl halide SN2 reactions (7). 

The liquid-membrane electrode is another important type of ion-selective electrode. The internal filling solution contains a source of the ion under investigation, i.e. one for which the ion exchanger is specific, while also containing a halide ion to allow the reference electrode to function. The physico-chemical behaviour of the ISE is very similar to that of the fluoride electrode, except that ise and the selectivity are dictated by the porosity of a membrane rather than by movement through a solid-state crystal. 

This last electrochemical process is carried out in an undivided electrolysis cell fitted with a sacrificial magnesium anode and a nickel foam as cathode. The reaction is conducted in dimethylformamide in the presence of both NiBr2(bpy) as the catalyst and dried ZnBr2 (1.1 molar equivalents with respect to bromothiophene), which is used both as supporting electrolyte and as a zinc(II) ion source. The other conditions are the same as those described in the section concerning the aromatic halides. The yield of 3-thienylzinc bromide was roughly 80%, as determined by GC analysis after treatment with iodide (equation 34). 

A variety of phosphorus-coutaining reagents have been employed in sugar chemistry in the direct SN2 replacement of hydroxy groups mainly by halide ions [35], Most of these reagents used a combination of triphenylphosphine with an electrophilic halogen source such as /V-halosuccinimide [36,37], carbon tetrahalides [38-41], and more recently, tri-haloimidazole or iodine and imidazole [42-45] or related reagents [46J. The Mitsunobu... 

Carbene precursors are compounds that have or acquire good leaving groups (e.g., halide ions). Thus, halogen compounds frequently are carbene sources. Trihalomethanes are the oldest known sources of dihalocarbenes but there are other methods for generating carbenes, and some of these are listed for reference in Table 14-2 (see also Section 14-10C). There is a question as to whether a free carbene actually is formed in some of these reactions, particularly those involving metals, but for our purposes we will classify them as routes to carbenes or carbenelike species. 

Coulter C, Hamilton JTG, McRoberts WC, Kulakov L, Larkin MJ, Harper DB (1999) Halomethane Bisulfide/Halide Ion Methyltransferase, an Unusual Corrinoid Enzyme of Environmental Significance Isolated from an Aerobic Methyltroph Using Chloromethane as the Sole Carbon Source. Appl Environ Microbiol 65 4301... 

Most other peroxidases are Fe-heme-containing systems, which function as two-electron redox catalysts (Scheme 8). Dihydrogen peroxide oxidizes the Fe-heme moiety by two electrons, forming Compound 1 (a heme + FeIV=0 species) [97], Compound 1 oxidizes the halide ion, forming the active halogenating species. This mechanism cannot be operative in V-BrPO because the vanadium is already in its highest accessible oxidation state. Moreover, native V-BrPO does not oxidize bromide without an acceptable peroxide source. However, it should... 

Under an atmospheric pressure of carbon monoxide, aryl- and alkenylsilanes undergo a carbonylative coupling reaction with aryl and alkenyl halides [44,45]. The optimized conditions for arylsilanes involve the use of N,M-dimethyl-2-imidazolidinone (DMI) as a solvent and KF as a fluoride ion source (Eq. 38), whereas alkenylsilanes prefer THF and TBAF (Eq. 39). 

In view of these results a study of the reaction of t-butyl chloride,which should act as an Ion source,with methylcyclopentane which should be an effective hydride donor was undertaken. The reaction was followed manometrlcally by observing the pressure generated after the halide was added to a stirring emulsion of methylcyclopentane and 96 percent H2SO (14). 

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