Thiocyanates naturally occurring

III.b.1.1. Anion inhibitors. Perchlorate, periodate, pertechnetate and thiocyanate (a naturally occurring goitrogen) are classified as iodide pump inhibitors, antagonizing iodide transport through competitive inhibition. This effect can be overcome by large dose of iodides. Perchlorate is used to block reuptake of iodide in cases of amiodarone induced hyperthyroidism and for the perchlorate discharge test . 

It was the first naturally occurring crown ether, and the earliest for which the antibiotic activity could be traced to its ionophoric properties (4). The actins give one-to-one complexes with many alkali and alkaline earth metal ions, with nonactin showing selectivity in the order NH4+ > K+ = Rb+ > Cs+ > Na+ > Ba2+ (5). The first X-ray crystal structure of an ionophore-metal complex was obtained from the nonactin-potassium thiocyanate complex (6). The potassium is bound by coordination to all four tetrahydrofuran oxygens and to the four ester carbonyl oxygens, which creates overall a "tennis ball seam" conformation to the carbon framework as it wraps around the metal. 

Most LWR fuel rod cladding is made of Zircaloy (and its derivatives), which is an alloy of primarily zirconium and tin. Other alloying elements include niobium, iron, chromium, and nickel. Zircaloy was chosen because it has a very low cross section for thermal neutrons. Naturally occurring zirconium contains about l%-5% hafnium. The hafnium must be removed because it has a very high thermal neutron cross section and is often used in making control rods for reactors. The separation process used in the United States is a liquid-liquid extraction process. It is based on the difference in solubility of the metal thiocyanates in methyl isobutyl ketone. In Europe, a process known as extractive distillation is used to purify zirconium. This method employs a separation solvent that interacts differently with the zirconium and hafnium, causing their relative volatilities to change. This enables them to be separated by a normal distillation process. The separated zirconium is then alloyed with the required constituents. 

Excessive accumulation of side-reaction products in the solution, such as thiosulfates and thiocyanates, is prevented by naturally occurring losses. Since these solution losses also entail continuous loss of catalyst, periodic additions of the catalytic compound ate required. Operating results from two Perox plants are shown in Table 9-9 (Pippig, 1933 Anon., 1937A Brommer and Luhr, 1936). 

The blue color of 83 has been observed in numerous experiments. For example, a brilliant blue color occurs if a potassium thiocyanate melt is heated to temperatures above 300 °C [132] or if eutectic melts of LiCl-KCl (containing some sulfide) are in contact with elemental sulfur [132, 133], if aqueous sodium tetrasulfide is heated to temperatures above 100 °C [134], if alkali polysulfides are dissolved in boiling ethanol or in polar aprotic solvents (see above), or if borate glasses are doped with elemental sulfur [132]. In most of these cases mixtures of much 83 and little 82 will have been present demonstrating the ubiquitous nature of these radicals [12]. 

Releases of thiocyanate to soil result from anthropogenic and natural sources. Anthropogenic releases occur primarily from direct application in herbicidal formulations (e.g., amitrol-T, a mixture of ammonium thiocyanate and amino-1,2,4-triazole) and from disposal as byproducts from industrial processes. Nonanthropogenic sources include damaged or decaying tissues of plants from the family Brassica (e.g., mustard, rape) (Brown and Morra 1993). Thiocyanate has been detected in soil samples collected at 2 of the 8 hazardous waste sites, and in sediment samples at 3 of the 8 hazardous waste sites where thiocyanate has been detected in some medium (HazDat 1996). The HazDat information used includes data from both NPL and other Superfund sites. 

The primary route of exposure to thiocyanates for the general population appears to be from ingestion of foods in which thiocyanate occurs naturally (e.g., cabbage, kale, spinach, kohlrabi). Estimates of the thiocyanate concentration in the total diet of an adult in the United States were not located in the available literature however, these would be expected to be quite low. Exposure to cyanide also is a source of thiocyanate exposure because thiocyanate is a major metabolite of cyanide in the human body. 

Solvent extraction has proved to be the most effective method for the separation of zirconium and hafnium, which invariably occur in nature in close association, owing to their almost identical chemical properties. These metals have found considerable use in the nuclear-power industry on account of their unusually high (hafnium) and low (zirconium) neutron-capture cross-sections. It is evident that the mutual separation of the two metals must be of a high degree to make them suitable for such applications. Two different solvent-extraction processes are known to be used on a commercial scale in one process, zirconium is selectively extracted from nitrate media into TBP in the second process, hafnium is selectively extracted from thiocyanate solutions into methyl isobutyl ketone (MIBK). 

The reaction of the acid chloride phenylhydrazone (11) with base gives the nitrile-imine 1,3-dipolar compound (12) which reacts with potassium thiocyanate to give the A2-thiadiazo-line (13 Scheme 1). Thus the cycloaddition occurs at the C=S and not the C=N bond. This regioselectivity can be explained in terms of the frontier orbital treatment. Due to the electron rich nature of the thiocyanate anion, its reaction with (12) is expected to be controlled by the LUMO and HOMO of (12) and the thiocyanate respectively. As the HOMO of the thiocyanate anion has the larger orbital coefficient on the sulfur atom, it can be concluded that the larger orbital coefficient in the LUMO of (12) is on the carbon atom. This is also in agreement with other dipolar cycloadditions (82H( 19)57). 

Cobalt Monosulphide, Cobaltous Sulphide, CoS, occurs in nature as the mineral syepoorite or jaipurite. The mineral has been prepared artificially by fusing cobalt sulphate with barium sulphide and sodium chloride.8 The monosulphide is also obtained by heating a solution of cobalt sulphite9 to 200° C., or a mixture of solutions of cobalt salts with ammonium thiocyanate to 180° C., in either case in sealed tubes,10 and by heating cobalt sulphate and carbon to the temperature of the electric arc.11... 

The important part of cyanide is the same, whether it is derived from salts, prussic acid, hydrogen cyanide, or released from kernels. It is written by chemists as CN , which means that it is the cyanide ion. When cyanide is absorbed into the body from the stomach, some will exist in this form in the blood and be transported to the liver, where it can be detoxified by an enzyme that converts it into something less toxic, thiocyanate. This is then excreted into the urine. Humans and other animals have probably evolved this mechanism to protect them from the various cyanide-containing plants that occur naturally If the amount taken is too much for the system, the victim suffers poisoning which can be lethal. 

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