Mercurial salts observational studies

The mechanism of mercuration is shown in Scheme 2. In the first step, the mercury salt forms a Jt-complex with the aromatic substrate [15, 16]. In 1982, Lau, Huffman, and Kochi [17] reported the first isolation and full characterization (including X-ray molecular and crystal structure) of such an intermediate, a complex of hexamethylbenzene with Hg(TFA)2. The X-ray structure revealed a Hg2( -TFA)i framework with a molecule of C6Me6 -coordinated to each of the Hg atoms. Analogous Jt-complexes have also been observed and studied by Dean and co-workers [18] and more recently by Barron s [19] and Gabbai s [20] groups. The Jt-complex intermediate can rearrange to the ej-complcx (a Wheland intermediate) directly, or sometimes via electron transfer, to produce a radical ion pair which then collapses (Scheme 2) [21,22]. 

A variety of effects have been observed in animals treated with toxic doses, but some of these, such as renal damage and anorexia, have not been observed in humans exposed to high doses. The primary tissues of concern in humans are the nervous system and particularly the developing brain, and these have been the main reason for the wide range of epidemiologial studies. Methylmercury passes about ten times more readily through the placenta than other mercury compounds. The dermal absorption of methylmercury is similar to that of inorganic mercury salts. 

These observations subsequently led to studies on Koenigs-Knorr-type glycosylations employing promotion by mercury salts and silver triflate. The studies were based on product composition rather than on kinetics.69... 

The iodine atom in the monoiodide may be replaced by other groups and, by reaction with silver salts, for example, As(CF3)2CN (b.p. 89 5°) and As(CFg)2SCN (b.p. 116—118°) are readily prepared. Reaction of the monoiodide with mercury gives the cacodyl As2(CF3)4 (b.p. 106 to 107°), while with mercuric oxide the oxide As2(CF3)40 (b.p. 95—97°) is formed. The chemistry of these substances has not yet been studied in detail, but it is noteworthy that hydrolysis of the perfluorocacodyl gives both fluoroform and fluoride, which parallels the observations made on the diphosphine. 

Model reactions have contributed significantly to our understanding of biological processes. Both pyridoxal phosphate (vitamin B6) and Bi2-coenzymes have proved useful in mechanism studies. Methyl transfer reactions to various metals are of environmental significance. In 1968 it was shown that methylcobalamin could transfer a methyl carbanion to mercury(II) salts in aqueous solutions. Recent research on interaction between B12-coenzymes and platinum salts has shown that charged Ptn salts labilize the Co—-C bond. Secondly, the B12-coenzymes are unstable in the presence of platinum salts this observation correlates with the fact that patients who have received cw-platin develop pernicious anemia. 

The base-catalyzed conversion of 5-alkyl-substituted isothiazolium salts 88 (R = Me, R = Et) to 2,3-dihydrothio-phene derivatives 329 occurs in basic conditions via intermediates 328. The distribution of diastereomers 329 is dependent on the base and aryl substituent <1997SUL35>. Similar behavior was observed in the case of 88 (R = R =-(0112)4-) <1996JPG424>. The condensation of 5-Me-substituted isothiazolium salts 88 with a second molecule of a different isothiazolium salts affords haA -thia-Eh-diazapentalenes 330. In this way, macrocyclic ethers 332 were prepared from 331 and their complexation behavior toward sodium(l), silver(l), and mercury(n) studied <2001PS(170)29>. 

Lead, like mercury, causes neurological diseases. The organolead compounds are more toxic than mineral lead salts, since they are non-polar, lipid-soluble, and more readily cross the blood-brain barrier. This disease is related to mental retardation is children, lower performance on I.Q. tests, and hyperactivity. Severe exposure in adults causes irritability, sleeplessness, and irrational behavior. Some have gone as far as to blame anti-social behavior and criminality on sub-clinical Pb poisoning. A correlation between Pb in blood and Pb in air, dust and soils has been observed in many studies. The U.S. Centers for Disease Control has proclaimed a goal of reducing blood lead contents in children below 10 jag/lOOmL. 

It will be useful to emphasize the practical aspects of the problem which are twofold the solution side and the metal side. On the solution side at the interphase, a level of impurities which does not interfere with dl measurements over the time scale of a mercury-drop lifetime, which is 4 s, could completely hinder observations of significant current-potential curves [i( )] or meaningful differential capacity-potential curves [C(E)] at a solid metal electrode which will stay 2, 3, or 4 h in the same solution. Not only must the water, salts, and glassware be kept clean, but also the gas used to remove oxygen and the tubing for the gas. Of course, conditions are less drastic for studies of strong adsorption than in the case of no adsorption also bacteria develop less in acid solutions than in neutral ones (which cannot be kept uncontaminated more than one or two days). This aspect will not be discussed in this chapter. 

The most serious defect in the system, especially in its usefulness in the laboratory, is that similar elements are sometimes in remote positions, while dissimilar elements are brought close together. These difficulties are most pronounced in qualitative analysis, in which the solubilities of salts are of prime importance. As illustrations of this defect it may be observed that copper and mercury, silver and thallium, barium and lead, have many similar properties which are not suggested by their positions ixi the table. On the other hand we might expect gold and caesium, rubidium aud silver, and manganese and chlorine to resemble each other much more closely than they do. It is obvious, however, that no table could possibly show all the resemblances and contrasts of each dement, and a, detailed study of each of these elements justifies in a measure its usual position in the table. 

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