Astatine identification

Astatine - the atomic number is 85 and the chemical symbol is At. The name derives from the Greek astatos for unstable since it is an unstable element. It was first thought to have been discovered in nature in 1931 and was named alabamine. When it was determined that there are no stable nuclides of this element in nature, that claim was discarded. It was later shown that astatine had been synthesized by the physicists Dale R. Corson, K. R. Mackenzie and Emilio Segre at the University of California lab in Berkeley, California in 1940 who bombarded bismuth with alpha particles, in the reaction Bi ( He, 2n ) "At. Independently, a claim about finding some x-ray lines of astatine was the basis for claiming discovery of an element helvetium, which was made in Bern, Switzerland. However, the very short half-life precluded any chemical separation and identification. The longest half-life associated with this unstable element is 8.1 hour °At. 

Identification and quantitation of the three main astatine isotopes, ° At, °At, and At, can be achieved by the appropriate measurement of a-, y-, or X-ray activity. X-rays and y-rays can be counted conveniently by well-type crystal counters, whereas a-counting requires that astatine samples be measured as infinitely thin or thick preparations. Astatine-211 can be measured by counting its 79- to 92-keV Po K-L,M,NX-rays, and, importantly, discriminated from At and ° At by their y-emissions (245, 1180 195, 545, and 782 keV, respectively). Identification and aspects of counting other astatine isotopes have been briefly discussed elsewhere (6,110). 

Normal physicoorganic methods used for the formal identification of organic compounds are not applicable to organic astatine chemistry. The mass quantities required for the characterization of compounds by UV, NMR, and IR spectroscopy are in the region 10 -10" g molar concentrations of 10 preclude the application of such techniques. Mass spectrometry has not yet been developed to operate at such a concentration, except under special laboratory conditions (4). 

Astatine, 6 207-223, 31 43-88 as astatate ion, 6 219-220 as astatide ion, properties of, 6 217-218 biochemical compounds of, 6 222 biochemical fate, 31 78 biological behavior, 6 222 31 77-78 biomedical applications, 31 79-83 therapeutic studies, 31 80-81 chemical properties of, 6 216 diatomic, 31 50 distallation, 31 47-48 elementary, 6 218-219 embryotoxicity, 31 78 extraction techniques, 31 47 identification, 31 49 in intermediate oxidation state, 6 219 iodide, 6 218-219 isotopes, 31 43-49 decay, 31 44 half-lives, 31 44 decay and half-lives of, 6 210 experimental methods for, 6 213-216 production and measurement of, 6 209-216... 

The decade that has elapsed since the previous survey on the organic chemistry of astatine was published in this series1 has seen a considerable increase of knowledge. The most important results that have been achieved are those concerning the preparation and identification of astatine-labelled organic compounds utilizable for biomedical purposes and those from studying their chemical and biochemical properties. Much less has been... 

It might be of interest to recall here the time-of-flight MS investigation by Appelman and coworkers14 from the sixties which allowed direct identification of the At+ ion—among other astatine species—owing to the extreme sensitivity of the method. 

The combination of triphenylphosphine with esters of trihaloacetic acids provides a reagent system for the stereo- and regio-selective conversion of alcohols into alkyl halides.The bromine-triphenylphosphine adduct has been used at low temperatures (-50 C in dichloromethane) for the removal of the tetrahydropyranyl protecting group from tetrahydropyranyl ethers derived from secondary and tertiary alcohols.The reactions of tertiary phosphines (and other trivalent phosphorus compounds) with iodine in aprotic solvents have received further study, a range of species being identified.The first reported study of the reactions of trivalent phosphorus compounds with monopositive astatine has led to the identification of stable complexes with triphenylphosphine, trioctylphosphine, and triethylphosphite. 

These related elements will carry the traces of radium from the solution, and it is by methods such as this that the chemical identification of technetium, promethium, astatine, and francium were made. 

Certain predicted volatility characteristics of elements 116,117, and 118 (eka-polonium, eka-astatine, and eka-radon) or their compounds may offer advantages for chemical identification this, of course, is especially true for element 118. The chemical properties of element 116 should be determined by extrapolation from polonium, and thus it should be stable in the ii state with a less stable IV state. 

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