Halogens in organic combination

Application of the oxygen-flask combustion method to the determination of fluorine in organic combination has now been made by a number of workers. The fluoride in solution after combustion may be determined by thorium nitrate titration or colorimetrically as the alizarin complexan chelate or with a chloranilate (see Halogen Acids and Salts, p. 302). A method based upon the alizarin complexan chelate is given in Appendix IV. 

There is only one simple anion commonly found in soil, and that is chloride (Cl ). Chloride is an essential nutrient for plants but is typically present in sufficiently high concentrations that deficiencies are never observed. If other halogens are present, they will also be present as simple anions. Most soils do contain small amounts of bromide as the second most common simple anion. In some cases, significant levels of fluoride and iodide may be present, although this is rare. These anions are generally soluble in water and tend to exist as the simple anion. However, they can combine with other components and exist as other species. For instance, halogens are present in organic compounds such as solvents, insecticides, and herbicides, which can be soil contaminants. There are also other nonionic species of these elements that may be present [20],... 

Selenium resembles sulphur in its variations in valency, compounds being known in which the element is definitely bivalent, quadrivalent and sexavalent, respectively. The tendency to quadrivalency, however, is greater than in the case of sulphur, and the compounds formed in which this valency is exhibited are relatively more stable in the case of selenium than in the case of sulphur.5 Thus, whilst the bivalent selenium in organic selenides readily combines with a molecular proportion of chlorine or other halogen,5 sexavalent selenium in the selenates is easily reduced to the quadrivalent selenious condition. As with sulphur, it has been possible to demonstrate that in quadrivalent selenium the four valencies are disposed in three dimensions of space, since substances of the type... 

All four mercury (n) halides are known, and their properties are hsted in Table 5. All can be prepared by the direct combination of the appropriate halogen with mercury metal. Except for the fluoride, which has bonds that are predominantly ionic in character, they are characterized by relatively low-melting and boiling points and display surprising solubility in organic solvents such as acetone. Their coordination chemistry has been reviewed. A summary of the structural features of the crystalline mercury(II) halides is given in Table 6. 

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