Iodine halides

Iodine Halides and Polyhalides. Iodine forms six weU-defined compounds with the other haUdes (115,116). These compounds are readily formed by direct reaction of the two halogens (117). 

From calorimetric studies of enthalpy of formation of complexes with I2 or iodine halides, the donor ability of some O-donors is ranked as Ph2CO < Ph2SO < Ph3PO < Ph2SeO < PhjAsO.37... 

In the case of aromatic bodies the temperature has an important influence on the part of the molecules the chlorine or bromine will attack in the cold in the presence of carriers, the halogen enters the nucleus, while at the boiling point the side chain is attacked. The carriers most frequently used are iron, aluminium-mercury couple, iodine, halides of phosphorus, antimony, iron, aluminium, sulphur or pyridine. The halogen is always more active in sunlight, or in ultra-violet light. 

Solutions of alkali metal and ammonium iodides in liquid iodine are good conductors of electricity, comparable to fused salts and aqueous solutions of strong acids. The liquid is therefore a polar solvent of considerable ionizing power, whereas its own electrical conductivity suggests that it is appreciably ionized, probably into I+ and I"3 (triodide). Iodine resembles water in this respect. The metal iodides and polyiodides are bases, whereas the iodine halides are acids. 

Polyhalide compounds are formed between iodine or iodine halides and other halide salts. The formulas of some of these compounds are Rbl3... 

Other iodine halides are iodine monobromide [7789-33-5], IBr, iodine tribromide [7789-58-4], IBr3, iodine pentafluoride [7783-66-6], IF5, and iodine heptafluoride [16921 -96-3], IF7. 

In the early 1950s Anderson315,317 used bromine, or bromine and iodine halides in the presence of iron powder (i.e. FeX3 formed in situ) to cleave the C—Ge bond. 

It is probable that similar complexes are formed when iodine and the iodine halides are intercalated into graphite. In this case, two subspectra are seen (Table 6), suggesting that the I2 molecule is bound through only one atom. The parameters are very similar to those for the cr-complexes discussed below (Table 7). It seems likely that the structure of the Qo—12 complex is similar, although other possibilities have also been considered28. 

Bis[pentafluorophenyl] tellurium tetrafluoride is very reactive and fluori nates organic solvents such as diethyl ether, methanol, acetonitrile, dimethyl sulfoxide, and nitromethane4.The products obtained by the addition of iodine or iodine halides to... 

Popov Al, Rygg RH (1957) Studies on the chemistry of halogens and of polyhalides. XI. Molecular complexes of pyridine, 2-picoline and 2,6-lutidine with iodine and iodine halides. J Am Chem Soc 79 4622-4625... 

Chlorine also forms BrCl (see bromine halides) and ICl and ICI3 (see iodine chlorides). See also inierhalogen compounds. 

These values indicate a rapid fall in thermal stability of the halide from fluorine to iodine, and hydrogen iodide is an endothermic compound. If we now examine the various enthalpy changes involved. we find the following values (in kJ) ... 

Chlorine, bromine and iodine form halic(V) acids but only iodic(V) acid, HIO3, can be isolated. Solutions of the chloric) V) and bromic) V) acids can be prepared by the addition of dilute sulphuric acid to barium chlorate(V) and bromate(V) respectively, and then filtering (cf. the preparation of hydrogen peroxide). These two acids can also be prepared by decomposing the corresponding halic(I) acids, but in this case the halide ion is also present in the solution. 

The iodine atom in iodobenzene (unlike that in the corresponding aliphatic compounds) is very resistant to the action of alkalis, potassium cyanide, silver nitrite, etc. This firm attachment of the iodine atom to the benzene ring is typical of aromatic halides generally, although in suitably substituted nitio-compounds, such as chloro-2,4-dinitrobenzene, the halogen atom does possess an increased reactivity (p. 262). 

To determine which halogen is present, take 1-2 ml. of the filtrate from the sodium fusion, and add dilute sulphuric acid until just acid to litmus. Add about 1 ml. of benzene and then about 1 ml. of chlorine water and shake. A yellowish-brown colour in the benzene indicates bromine, and a violet colour iodine. If neither colour appears, the halogen is chlorine. The result may be confirmed by testing the solubility of the silver halide (free from cyanide) in dilute ammonia solution silver chloride is readily soluble, whereas the bromide dissolves with difficulty, and the iodide not at all. 

A newer and equally effective way of swapping azides with halides (bromines or iodines) is in the use of phase transfer catalysts [68]. Strike wouldn t expect an underground chemist to purchase the exotic catalyst Aliquat 336 which the investigators in this reference used to get yields approaching 100% but an alternative catalyst of... 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

Sulfenylation of indoles can be carried out with sulfenyl halides[7], disulfides[7-9] or with A -methylthiomorpholine[10]. With disulfides the indoles are converted to lithium[8] or zinc[9] salts prior to sulfenylation. Thiophenols and iodine convert indoles to 3-(arylthio)indoles[l 1]. 

The order of alkyl halide reactivity in nucleophilic substitutions is the same as their order m eliminations Iodine has the weakest bond to carbon and iodide is the best leaving group Alkyl iodides are several times more reactive than alkyl bromides and from 50 to 100 times more reactive than alkyl chlorides Fluorine has the strongest bond to car bon and fluonde is the poorest leaving group Alkyl fluorides are rarely used as sub states m nucleophilic substitution because they are several thousand times less reactive than alkyl chlorides... 

Lithium Iodide. Lithium iodide [10377-51 -2/, Lil, is the most difficult lithium halide to prepare and has few appHcations. Aqueous solutions of the salt can be prepared by carehil neutralization of hydroiodic acid with lithium carbonate or lithium hydroxide. Concentration of the aqueous solution leads successively to the trihydrate [7790-22-9] dihydrate [17023-25-5] and monohydrate [17023-24 ] which melt congmendy at 75, 79, and 130°C, respectively. The anhydrous salt can be obtained by carehil removal of water under vacuum, but because of the strong tendency to oxidize and eliminate iodine which occurs on heating the salt ia air, it is often prepared from reactions of lithium metal or lithium hydride with iodine ia organic solvents. The salt is extremely soluble ia water (62.6 wt % at 25°C) (59) and the solutions have extremely low vapor pressures (60). Lithium iodide is used as an electrolyte ia selected lithium battery appHcations, where it is formed in situ from reaction of lithium metal with iodine. It can also be a component of low melting molten salts and as a catalyst ia aldol condensations. 

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