Exchange of Halogen

Exchange of halogen in alkyl halides (see also Makosza). 

A peripheral substitution of phthalocyanines can be achieved via exchange of halogen atoms in halogenated phthalocyanines with alkali alkoxide340 or thiolate341. 

There is no value available for LEL and two flashpoint values, which lead to flashpoints of 79 ( cc ) and 87 a flashpoint oc. S = 5.071 (group 2) is obtained for the group, which is consistent with the Hass table that indicates that the group of this substance is the same as the one resulting from an exchange of halogens for hydrogen atoms. 

In the case where X = Cl, exchange of halogen with KI leads to H3GeCH2I278. Mercuric chloride in THF can be used to introduce chlorine into germanium trihydrides279 with a functional group in the aliphatic chain (Scheme 24). Finally, y-hydroxygermylenes are produced. 

Formation of C—C links in the anthraquinone molecule, especially substitutions with aryl moieties, proceed via copper-catalyzed nucleophilic exchange of halogenated anthraquinone compounds. These methods include dimerization of 1 -aminoanthraquinone. 

Studies of Equilibria and Shift Reagents.—N.m.r. studies of the exchange of halogen in boron trihalide adducts of trimethylphosphine, its oxide, and sulphide,49 and exchange of chloro- and methoxy-groups between methylphosphino and methyl-silyl or -germyl moieties,80 have been reported. The rates of ionization of phosphoranes... 

The exchange of halogen for fluorine with sulfur tetrafluoride, due to the high temperatures generally required, is of limited use. Carbon tetrachloride and carbon tetrabromide react with sulfur tetrafluoride at 225-325 C to give mixtures of halofluoromethanes, while hexachloro-ethane under similar conditions gives l,1.2,2-tetrachloro-l,2-difluoroethane (59%) as the main product.191... 

Some examples of routine exchange of halogens with fluorine in halogenated carboxylates are given in Table 1. 

Further studies are needed to find mild reaction conditions for exchange of halogen atoms in monohalogeno heterocycles under PTC conditions. 

An example of rapid exchange of substituents in a simple system is shown in Fig. 7 for an equilibrated mixture of CH3PC12 and CH3PBr2 (184). As the temperature is decreased, the rate of exchange of halogen atoms diminishes, thus sharpening the individual proton NMR signals. 

Exchange of halogen with hydrogen atoms on aluminum is also quite rapid since solutions of aluminum hydride and aluminum chloride readily form hydridoaluminum halides 302). The ether and trialkylamine addition compounds disproportionate upon distillation or sublimation 10, 306). 

Extreme nonrandom behavior was observed for the exchange of halogens with dimethylamino groups. A kinetic study of the latter exchange revealed that equilibrium is reached in a series of consecutive reactions of different rates. Alkoxyl-dimethylamino exchanges are, for all practical purposes, random exchanges. 

The following examples illustrate the displacement of halogen by oxygen-, sulfur-, or nitrogen-containing substituents and the exchange of halogen ... 

Exchange of halogen could then proceed either through a four-center transition state (which, however, requires one boron atom to be five-coordinate) ... 

Covalent hahdes can be prepared by various synthetic routes. The simplest are direct reactions of elemental halogens (equation 9), or hydrogen halides with elements (equation 10) or oxides (equation 11). In other processes, the oxides are reacted with a halogen halide in the presence of carbon to combine with the oxygen (equation 12) or other reactive carbon-halides (equation 13). Exchange of halogens can also take place (equations 14 16). Anhydrous halides can also be obtained by dehydration of metal halide hydrates, using reactants such as thionyl halide, which react with the hydrated water (equation 17). 

The exchange of halogen for the amino group is important in the formation of other polyfunctional compounds, particularly the amino acids. In several of these transformations with aqueous or liquid ammonia, it has been shown that the presence of ammonium salts minimizes the formation of secondary and tertiary aminesExcellent directions for the synthesis of a-amino acids (C,-C ) from a-halo acids and ammonia are given. The methods have been reviewed. Long-chain amino acids are prepared by this and other procedures. ... 

Labelling of organic compounds with " I is performed by exchange of halogen atoms or by iodination. Decay of Xc in the presence of organic compounds also leads to formation of labelled compounds (recoil labelling). 

For exchange of halogen with nitrogen-, oxygen- or sulfur-containing functional groups, see also ref 297 and Houben-Weyl, Vol. 6/3. p 79. 

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