Halogens, elemental bromination

Halogenation (Section 11 12) Free radical halo genation of alkylbenzenes is highly selective for substitution at the benzylic position In the exam pie shown elemental bromine was used Alterna Lively N bromosuccinimide is a convenient re agent for benzylic bromination... 

All six possible diatomic compounds between F, Cl, Br and I are known. Indeed, ICl was first made (independently) by J. L. Gay Lussac and H. Davy in 1813-4 soon after the isolation of the parent halogens themselves, and its existence led J. von Liebig to miss the discovery of the new element bromine, which has similar properties (p. 794). The compounds vary considerably in thermal stability CIF is extremely robust ICl and IBr are moderately stable and can be obtained in very pure crystalline form at room temperature BrCl readily dissociates reversibly into its... 

Principles and Characteristics Combustion analysis is used primarily to determine C, H, N, O, S, P, and halogens in a variety of organic and inorganic materials (gas, liquid or solid) at trace to per cent level, e.g. for the determination of organic-bound halogens in epoxy moulding resins, halogenated hydrocarbons, brominated resins, phosphorous in flame-retardant materials, etc. Sample quantities are dependent upon the concentration level of the analyte. A precise assay can usually be obtained with a few mg of material. Combustions are performed under controlled conditions, usually in the presence of catalysts. Oxidative combustions are most common. The element of interest is converted into a reaction product, which is then determined by techniques such as GC, IC, ion-selective electrode, titrime-try, or colorimetric measurement. Various combustion techniques are commonly used. 

Cadmium(II) bromide Cd + 2Br " —> CdBr. This compound is used in photography, engraving, and lithography. The other halogen elements also combine with cadmium in a similar ionic reaction as with bromine. 

Bromine.—Of the three halogens, chlorine, bromine, and iodine, bromine has the least eventful history. Its elemental nature and its relation to chlorine and iodine were recognized from the very first. While studying the mother-liquid which remains after the crystallization of salt from the water of the salt-marshes of Montpellier, A. J. Balard was attracted by the intense yellow coloration developed when chlorine water is added to the liquid. A. J. Balard digested the yellow liquid with ether decanted off the supernatant ethereal soln. and treated this with potassium hydroxide. The colour was destroyed. The residue resembled potassium chloride but unlike the chloride, when heated with manganese dioxide and sulphuric acid it furnished red fumes which condensed to a dark brown liquid with an unpleasant smell. 

The halogen elements are converted into the corresponding hydracids by sulphurous acid, the change being reversible in the case of bromine and especially with iodine ... 

All the halogen elements combine with tellurium. The powdered crystalline form is inflamed by fluorine in the cold 1 and by warm chlorine, the product in the latter case being the tetrachloride.2 With bromine the product is the dibromide, whilst iodine reacts only at a higher temperature, giving a tetra-iodide. Hydrogen chloride does not affect the element. 

Hydrogen telluride is very sensitive towards the halogen elements. It not only readily reduces chlorine, bromine and iodine to the corresponding hydracids with simultaneous liberation of tellurium (which in the case of chlorine can further pass easily into the tetrachloride), but it also reduces solutions of such salts as ferric chloride and mercuric chloride to the lower chlorides, tellurium being precipitated. It also reduces tellurium chlorides, the only products being hydrogen chloride and tellurium. 

By using displacement reactions it is possible to deduce the order of reactivity of the halogens. Discuss this statement with reference to the elements bromine, iodine and chlorine only. 

Elements having similar electron orbital configurations tend to display similar properties. Because of the way the periodic table is organized, elements that tend to behave the same way can be found in the vertical columns. For instance, the halogen elements, near the right edge of the table, combine in the same ways with other elements. Thus, chlorine, bromine, and fluorine readily form compounds with sodium, calcium, and other similar elements. 

Halides are compounds that include one of the halogen elements fluorine, chlorine, bromine, or iodine. The simplest halides are combinations of one element, such as sodium (Na), with a halogen element, such as chlorine (Cl). Complex halides combine two or more elements with a halogen, and some contain water. Some halides are economically important minerals, such as halite (common salt), fluorite (fluorine), and chlorargyrite (silver ore). 

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