Nitrogen Iodine process

Zirconium, too, is produced commercially by the Kroll process, but the van Arkel-de Boer process is also useful when it is especially important to remove all oxygen and nitrogen. In this latter method the crude zirconium is heated in an evacuated vessel with a little iodine, to a temperature of about 200° C when Zrl4 volatilizes. A tungsten or zirconium filament is simultaneously electrically heated to about 1300°C. This decomposes the Zrl4 and pure zirconium is deposited on the filament. As the deposit grows the current is steadily increased so as to maintain the temperatures. The method is applicable to many metals by judicious adjustment of the temperatures. Zirconium has a high corrosion resistance and in certain chemical plants is preferred to alternatives such as stainless... 

It has been suggested that the initial formation of iodine on addition of iodide to a diazonium salt solution is caused by oxidation of the iodide by excess nitrite from the preceding diazotization. Packer and Taylor (1985) demonstrated that, if urea was added as a nitrite scavenger (see Sec. 2.1) to a diazotization solution, that solution produced iodine much more rapidly than a portion of the same diazonium salt solution not containing urea, but eventually the latter reaction too appeared to follow the same course. This confirms the role of excess nitrite, and suggests that the iodo-de-diazoniation steps only occur in the presence of iodine or triiodide (I -). The same authors also found that iodo-de-diazoniation is much slower under nitrogen. All these observations are consistent with radical-chain processes, but not with a heterolytic iodo-de-diazoniation. 

In one of J. S. Stas processes, the iodine was dissolved in a soln. of potassium iodide. The soln. was diluted with water until a precipitate began to form, and then three-fourths of the amount of water required to precipitate all the iodine were added. The separated iodine was washed free from potassium iodide by decantation, the crystals, after draining, were dried over calcium nitrate in vacuo, and then distilled twice from barium oxide. In another process, J. S. Stas purified the iodine by first treating the iodide with ammonia which converts about 95 per cent, of it into the explosive nitrogen iodide. The washed nitrogen iodide decomposes quietly when warmed with an excess of water. J. S. Stas thus describes the procedure ... 

Chemically, proteins are distinguished from other body substances in that all proteins contain nitrogen. Some contain sulfur, phosphorus, iron, iodine, cobalt, and other elements, some of which are generally not thought of as components of the life process, but which nevertheless do play extremely important roles (e.g., as catalysts), even if present only in very minute quantities. 

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