Halogenation special

Oxyfluorides are the most stable of the oxyhalides, and the stability decreases with increasing atomic weight of the halogen. Special methods are used in the preparation of oxyfluorides, while the other oxyhalides can be prepared by general reactions, such as the partial hydrolysis of the pentahalides, or the oxidation of the trihalides. The compounds fume in the air and readily undergo further hydrolysis giving hydrogen halides and oxyaeids of phosphorus. 

The major types are the trihalides (EX3), the pentahalides (EX5), and the dielement tetrahalides (E2X4). We shall discuss them in that order. All trihalides except PF3 are best obtained by direct halogenation, keeping the element in excess, whereas the pentahalides may all be prepared by reaction of the elements with excess halogen. Special methods are used for E2X4 compounds. 

After the usual sections on the history of the discoveries of and the application of the network to the halogens, special sections on (1) the oxoacids and their salts and (2) the interhalogens follow. The section on reactions and compounds of practical importance comes next and finally the selected topic in depth, which concerns the threat posed by chlorofluorocarbons to the ozone layer. 

The main synthetic fluids used as special lubricants are esters, polyglycols, silicones, halogenated hydrocarbons and polyphenyl ethers. 

Cobalt is a bluish silvery metal, exhibits ferromagnetism, and can exist in more than one crystal form it is used in alloys for special purposes. Chemically it is somewhat similar to iron when heated in air it gives the oxides C03O4 and CoO, but it is less readily attacked by dilute acids. With halogens, the cobalt(II) halides are formed, except that with fluorine the (III) fluoride, C0F3, is obtained. 

Principle. This is essentially a small-scale modification of the macro piethod described on p. 416, the substance being completely oxidised in a sealed tube with fuming nitric acid in the presence of silver nitrate, the halogen being thus converted into silver halide. The collection and weighing of the silver halide require special techniques on the semi-micro scale. 

This method cannot be applied to polynitro amines, since these are so weakly basic that they can be diazotised only under special conditions in strongly acidic solutions. In such cases use may, however, be made of the mobility oonfared upon halogen atoms by the presence of nitro groups in the orlko and para positions. Thus the valuable reagent 2 4-dinitrophenylhydrazine is readily prepared by the condensation of 2 4-dinitrochlorobenzene with hydrazine ... 

One of the virtues of the Fischer indole synthesis is that it can frequently be used to prepare indoles having functionalized substituents. This versatility extends beyond the range of very stable substituents such as alkoxy and halogens and includes esters, amides and hydroxy substituents. Table 7.3 gives some examples. These include cases of introduction of 3-acetic acid, 3-acetamide, 3-(2-aminoethyl)- and 3-(2-hydroxyethyl)- side-chains, all of which are of special importance in the preparation of biologically active indole derivatives. Entry 11 is an efficient synthesis of the non-steroidal anti-inflammatory drug indomethacin. A noteworthy feature of the reaction is the... 

The reactivity of the halogens decreases m the order F2 > CI2 > Br2 > I2 Fluo rme is an extremely aggressive oxidizing agent and its reaction with alkanes is strongly exothermic and difficult to control Direct fluonnation of alkanes requires special equip ment and techniques is not a reaction of general applicability and will not be discussed further... 

Equipment should be carefiiUy and completely degreased and passivated with low concentrations of fluorine or the gaseous halogen fluoride before use. Special care should be taken that valves are completely disassembled and each part carefiiUy cleaned. 

Using supercritical water is not without its drawbacks, two of which are the high pressures and temperatures involved. Another difficulty is the extreme corrosive nature of water at supercritical conditions. If halogenated organics are treated, special alloy reactors are requited. 

Several patents describe solvent-free bulk-phase halogenation (67—69). Dry soHd butyl mbber is fed into a specially designed extmder reactor and contacted with chlorine or bromine vapor. The by-product HCl or HBr ate vented directly without a separate neutralization step. Halogenated butyl mbbers produced are essentially comparable in composition and properties to commercial products made by the solution process. 

A special bath for high speed plafing of strip steel usiag all halogens was iatroduced ia 1942 (134). 

In looking for the mechanism, many intermediates are assumed. Some of these are stable molecules in pure form but very active in reacting systems. Other intermediates are in very low concentration and can be identified only by special analytical methods, like mass spectrometry (the atomic species of hydrogen and halogens, for example). These are at times referred to as active centers. Others are in transition states that the reacting cheimicals form with atoms or radicals these rarely can be isolated. In heterogeneous catalytic reaction, the absorbed reactant can... 

Not to be Used Water, foam, carbon dioxide, or halogenated hydrocarbons Special Hazards of Combustion Products No data Behavior in Fire Reacts violently with water, forming flammable and explosive hydrogen gas. This product may spontaneously ignite in air Ignition Temperature No data Electrical Hazard Not pertinent Burning Rate Not pertinent. 

Generally, the addition of chlonne or bromine to tnfluoroacetonitrile leads to a mixture of partially halogenated imines, amines and azo alkanes [270, 271] In special cases, such as the HgF2-mediated addition of bromine, N,N dihaloper-fluoro-2-alkylamines can be obtained in good yields [272]... 

Few of the many other inorganic compounds of Ge, Sn and Pb call for special comment. Many pseudo-halogen derivatives of Sn, Pb and Pb have been reported, e.g. cyanides, azides, isocyanates, isothiocyanates, isoselenocyanates and alkoxides. ... 

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