Bromides and Iodides

Natural waters contain only very low concentrations of bromide and iodide ions. Higher concentrations may occur in mineral waters, natural salt brines and in certain industrial wastewaters in most cases they are accompanied by a very large excess of chloride ions. 

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Wadsd I 1968 Heats of vaporization of organic compounds II. Chlorides, bromides and iodides Acta Chem. Scand. 22 2438... 

Lithium bromide and iodide probably have some degree of covalenc> but this does not affect the general conclusion. 

The lower members in Group II form essentially ionic halides, with magnesium having intermediate properties, and both magnesium bromide and iodide dissolve in organic solvents. 

Bromides and iodides Soluble in Insoluble in organic solvents... 

Chlorides, bromides and iodides Covalent when anhydrous. Soluble in Soluble in water ... 

A number of bromides and iodides are known but there are no sulphur iodides. 

Chlorine has a lower electrode potential and electronegativity than fluorine but will displace bromine and iodine from aqueous solutions of bromide and iodide ions respectively ... 

While the chloride, bromide and iodide are insoluble in water, the fluoride, AgF, is very soluble. 

The Alkyl Halides. Ethyl bromide and iodide (see below) are typical alkyl halides. Compounds of this class are of very great importance in synthetic work, owing to the reactivity of the halogen atom. This is illustrated by the following reactions ... 

Methyl iodide, ethyl bromide and iodide, higher alpihatic halides chloroform, iodoform, carbon tetrachloride chlorobenzene, bromobenzene, iodobenzene benzyl chloride. 

Principle. An organic compound which contains chlorine is mixed with sodium peroxide and ignited in a closed metal bomb. The chlorine is thus converted to sodium chloride, and after acidification the chloride is estimated by the Volhard volumetric method. Bromine and iodine, when constituents of organic compounds similarly treated, are converted largely into sodium bromate and iodate respectively these ions are therefore subsequently reduced by hydrazine to bromide and iodide ions, and estimated as before. 

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

Nickel-allyl complexes prepared from Ni(CO)4 and allyl bromides are useful for the ole-fination of alkyl bromides and iodides (E.J. Corey, 1967 B A.P. Kozikowski, 1976). The reaction has also been extended to the synthesis of macrocycles (E.J. Corey, 1967 C, 1972A). 

Aryl and vinylic bromides and iodides react with the least substituted and most electrophilic carbon atoms of activated olefins, e.g., styrenes, allylic alcohols, a,p-unsaturated esters and nitriles. 

Another method for the hydrogenoiysis of aryl bromides and iodides is to use MeONa[696], The removal of chlorine and bromine from benzene rings is possible with MeOH under basic conditions by use of dippp as a ligand[697]. The reduction is explained by the formation of the phenylpalladium methoxide 812, which undergoes elimination of /i-hydrogen to form benzene, and MeOH is oxidized to formaldehyde. Based on this mechanistic consideration, reaction of alcohols with aryl halides has another application. For example, cyclohex-anol (813) is oxidized smoothly to cyclohexanone with bromobenzene under basic conditions[698]. 

Density Alkyl fluorides and chlorides are less dense and alkyl bromides and iodides more dense than water... 

Although acyl fluorides bromides and iodides are all known classes of organic com pounds they are encountered far less frequently than are acyl chlorides Acyl chlorides will be the only acyl halides discussed m this chapter... 

Acid chlorides —COCI Saturated 1815-1790 Acid fluorides higher, bromides and iodides... 

Nitryl chloride Ammonia, sulfur trioxide, tin(IV) bromide and iodide... 

Selectivity Due to the chemical nature of the precipitation process, precipitants are usually not selective for a single analyte. For example, silver is not a selective precipitant for chloride because it also forms precipitates with bromide and iodide. Consequently, interferents are often a serious problem that must be considered if accurate results are to be obtained. 

Mono-, di-, and trivalent bromides and iodides may be made by methods similar to the chlorides. The lower valence salts also disproportionate in water. Indium trifluoride [7783-52-0] InF., is sparingly soluble in water. It forms an ammonium double salt, SNH F TnF. [15273-84-4] which decomposes on heating to indium nitride [25617-98-5] InN. 

Lithium Halides. Lithium haHde stabiHty decreases with increasing atomic weight of the halogen atom. Hence, the solubiHty increases from the sparingly soluble Hthium fluoride to the very soluble bromide and iodide salts. The low melting points of Hthium haHdes are advantageous for fluxes in many appHcations. 

Ammonium chloride [12125-02-9] NH Q, ammonium bromide [12124-97-9] NH Br, and ammonium iodide [12027-06-4] NH I, are crystalline, ionic compounds of formula wts 53.49, 97.94, and 144.94, respectively. Their densities d systematically foUow the increase in formula weight 1.53, 2.40, and 2.52. AH three exist in two crystal modifications (10) the chloride, bromide, and iodide have the CsQ stmcture below temperatures of 184.5, 137.8, and — 17.6°C, respectively each reversibly transforms to the NaQ. stmcture at higher temperatures. 

Other Reactions. Primary amyl alcohols can be halogenated to the corresponding chlorides by reaction with hydrogen chloride in hexamethylphosphoramide (87). Neopentyl chloride [753-89-9] is formed without contamination by rearrangement products. A convenient method for preparing / f/-amyl bromide and iodide involves reaction of / f/-amyl alcohol with hydrobromic or hydroiodic acid in the presence of Li or Ca haUde (88). The metal haUdes increase the yields (85 —95%) and product purity. 

Only three simple silver salts, ie, the fluoride, nitrate, and perchlorate, are soluble to the extent of at least one mole per Hter. Silver acetate, chlorate, nitrite, and sulfate are considered to be moderately soluble. AH other silver salts are, at most, spatingly soluble the sulfide is one of the most iasoluble salts known. SHver(I) also forms stable complexes with excess ammonia, cyanide, thiosulfate, and the haUdes. Complex formation often results ia the solubilization of otherwise iasoluble salts. Silver bromide and iodide are colored, although the respective ions are colorless. This is considered to be evidence of the partially covalent nature of these salts. 

Halide Complexes. Silver hahdes form soluble complex ions, AgX and AgX , with excess chloride, bromide, and iodide. The relative stabihty of these complexes is 1 > Br > Cl. Complex formation affects solubihty greatiy. The solubihty of silver chloride in 1 A/ HCl is 100 times greater than in pure water. 

Strontium Halides. Strontium haUdes are made by the reactions of strontium carbonate with the appropriate mineral acids. They are used primarily in medicines as replacements for other bromides and iodides. 

Bromides and Iodides. Anhydrous ThBr [13453 9-1] and Thl [7790 9-0] have been prepared in a similar fashion as the chloride, ie,... 

Comparable with the chloride system, complex ions of the form M2 ThX3] (A =Br [44490-064], M = (CH3) N, (C2H3) N X = I [44490-18-8], M = (C2H3) N, (CH3)3C3H3N) are known where the metal center is octahedral. Additional information on thorium bromides and iodides can be found in the hterature (81). 

Physica.1 Properties. Physical properties of some typical diorganotin compounds are shown in Table 6. The diorganotin chlorides, bromides, and iodides are soluble in many organic solvents and, except for dimethyltin dichloride, are insoluble in water. 

Many organic hahdes, especially alkyl bromides and iodides, react direcdy with tin metal at elevated temperatures (>150° C). Methyl chloride reacts with molten tin metal, giving good yields of dimethyl tin dichloride, which is an important intermediate in the manufacture of dimethyl tin-ha sed PVC stabilizers. The presence of catalytic metallic impurities, eg, copper and zinc, is necessary to achieve optimum yields (108) ... 

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