Chlorine radioactive isotopes

The halogens will be restricted to chlorine, bromine and iodine since fluorine, as the most electronegative element, does not function as the central atom in a complex and astatine has only short-lived, radioactive isotopes, so that very little of its coordination chemistry has been investigated.2 ... 

It is evident from Table 1 that certain limiting factors exist. For example, experiments with bromine-82 are limited to a duration of about one week because of the short half-life. At the other end of the scale, experiments with stable carbon-13 are limited to dilutions of less than x 500. Even with radioactive isotopes the maximum specific activity available may limit dilution though not to the same extent. Thus, chlorine-36 can stand dilutions up to x 107 but tritium can improve on this to a factor of x 1012. 

Madelmont and Veyre have reported the preparation of (206) from cyanuric chloride (75MI22002). The compound is valuable in the dynamic exploration of the lymphatic system, when it is prepared using radioactive isotopes of iodine. 2,4-Dichloro-l,3,5-triazines containing a secondary amino group with a vinylic substituent have promise in binding dental resins to biological tissues. The chlorines react with the dentine tooth enamel whilst the vinyl moiety bonds to the resin (75GEP2630745). 

After a new (and unusual) mechanism, such as the benzyne mechanism for nucleophilic aromatic substitution, is proposed, experiments are usually designed to test that mechanism. A classic experiment supporting the benzyne mechanism used a radioactive carbon label. Examination of the mechanism shown in Figure 17.6 shows that the carbon bonded to the leaving chlorine and the carbon ortho to it become equivalent in the benzyne intermediate. Consider what would happen if the carbon bonded to the chlorine were a radioactive isotope of carbon (l4C) rather than the normal isotope of carbon (I2C). If we follow the position of the radioactive carbon label through the mechanism of Figure 17.6, we find that the label should be equally distributed between the carbon attached to the amino group in the product and the carbon ortho to it. 

Chlorine-36 is an isotope that can be measured by specialized laboratories and its sample collection in the field is simple. It is a radioactive isotope with a half-life of 3 x 105 years, making it useful for groundwater age determinations in the range of 105-106 years. 

Chlorine has two stable isotopes, Cl and Cl, and one radioactive isotope, C1 (half-life = 0.301 Ma). The stable isotopic composition of chloride in geologic materials is reported in the conventional del notation as S Cl. Seawater, which is used as the isotopic standard, has a S Cl of 0%c. Most natural waters have S Cl values between —l%o and +l%o. However, values of —8%c have been measured in marine pore waters. Minerals in which chloride substitutes for OH at high temperatures have S Cl values as high as 7%c (Banks et al., 2000). 

Sixteen radioactive isotopes of chlorine are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive. 

One radioactive isotope of chlorine is used in research. That isotope is chlorine-36. This isotope is used because compounds of chlorine occur so commonly in everyday life. The behavior of these compounds can be studied if chlorine-36 is used as a tracer. A tracer is an isotope whose presence in a material can be traced (followed) easily. 

Most elements occur naturally as a mixture of isotopes, differing from one another by the number of neutrons present in the nucleus. Natural carbon comprises a mixture of mainly and (98.9 and 1.1% respectively) with a trace of the radioactive isotope Chlorine has isotopes Cl (75.77%) and Cl (24.23%). Thus any mass spectrum will demonstrate a number of molecular ions due to the isotopomers present. Most data systems have programs which allow the input of a molecular formula which generates a theoretical isotopic distribution. This can then be compared with the actual spectrum obtained (Fig. 5.16). It may be necessary to add or subtract a proton from the inputted formula, hydrogen contains 0.015% deuterium. 

Non-radioactive elements can be converted into radioactive isotopes by neutron bombardment in a reactor, cyclotron or van de Graaff generator they can then be detected by radiometric methods. Phosphorus-, sulphur- and chlorine-containing compounds for example, have been detected on paper chromatograms in this way. In order to determine traces of a compound quantitatively, known amounts of it are irradiated on the same chromatogram. 

A clue to this puzzle comes from an isotopic labeling experiment. Chlorobenzene can be prepared such that the carbon bearing the chlorine atom is C, a radioactive isotope of carbon. The position of the isotopic label (indicated with an asterisk) can then be tracked before and after the reaction. 

A solution to the question of the mechanism of these reactions was provided by John D Roberts m 1953 on the basis of an imaginative experiment Roberts prepared a sample of chlorobenzene m which one of the carbons the one bearing the chlorine was the radioactive mass 14 isotope of carbon Reaction with potassium amide m liquid... 

Naturally occurring isotopes of any element are present in unequal amounts. For example, chlorine exists in two isotopic forms, one with 17 protons and 18 neutrons ( Cl) and the other with 17 protons and 20 neutrons ( Cl). The isotopes are not radioactive, and they occur, respectively, in a ratio of nearly 3 1. In a mass spectrum, any compound containing one chlorine atom will have two different molecular masses (m/z values). For example, methyl chloride (CH3CI) has masses of 15 (for the CH3) plus 35 (total = 50) for one isotope of chlorine and 15 plus 37 (total = 52) for the other isotope. Since the isotopes occur in the ratio of 3 1, molecular ions of methyl chloride will show two molecular-mass peaks at m/z values of 50 and 52, with the heights of the peaks in the ratio of 3 1 (Figure 46.4). 

Crystallisation was one of the earliest methods used for separation of radioactive microcomponents from a mass of inert material. Uranium X, a thorium isotope, is readily concentrated in good yield in the mother liquors of crystallisation of uranyl nitrate (11), (33), (108). A similar method has been used to separate sulphur-35 [produced by the (n, p) reaction on chlorine-35] from pile irradiated sodium ot potassium chloride (54), (133). Advantage is taken of the low solubility of the target materials in concentrated ice-cold hydrochloric acid, when the sulphur-35 as sulphate remains in the mother-liquors. Subsequent purification of the sulphur-35 from small amounts of phosphorus-32 produced by the (n, a) reaction on the chlorine is, of course, required. Other examples are the precipitation of barium chloride containing barium-1 from concentrated hydrochloric acid solution, leaving the daughter product, carrier-free caesium-131, in solution (21) and a similar separation of calcium-45 from added barium carrier has been used (60). 

ISOTOPES There are a total of 25 isotopes of chlorine. Of these, only two are stable and contribute to the natural abundance on Earth as follows Cl-35 = 75.77% and Cl-37 = 24.23%. All the other 23 isotopes are produced artificially, are radioactive, and have half-lives ranging from 20 nanoseconds to 3.01 x 10+ years. 

Chlorine has three isotopes in nature 35C1—common and stable 36C1—very rare and radioactive, with a 301,000-year half-life and 37C1—less common and stable. Chlorine-36 concentrations are commonly expressed in units of 107 atoms/1 of water. The measurement is performed in specialized laboratories with dedicated accelerators. Measurements can be done on 1-1 water samples. 

Several chlorine isotopes exist with mass numbers ranging between 32 and 40. The two stable isotopes are Cl and Cl with natural abundances of 75.77% and 24.23% respectively, while the others are radioactive. Bromine also has two stable isotopes, Br and Br, with natural abundances of 50.69% and 49.31% respectively, while the others are radioactive. Iodine has only one stable isotope, and numerous radioactive ones are known. Astatine is known only as its radioisotope see Radioactive Decay). 

The deuterium isotope effect in the photo-induced chlorine atom exchange reaction with HCl has been investigated by Klein et over the range 30-150 °C by using the competition for chlorine atoms between D2 and DCl (or HCl). The exchange reactions were labeled with radioactive C1. Known mixtures of Cl2, D2, and DCl (or HCl) were irradiated followed by measurement of the residual D2 as well as the activity of the DCl. From this data the rate of the isotope exchange reaction could be determined with respect to the rate of chlorination of deuterium. The results are listed in Table 12 for the reactions... 

A second software feature capitalizes on the fact that many potential drug candidates contain atoms that are not naturally occurring in the body and which possess unique isotopic patterns. In particular, chlorine and bromine atoms give unique and distinctive mass spectral signals. The computer can evaluate the sample dataset and find any chromatographic peaks that contain these characteristic isotopic patterns. An example of how these software routines can simplify a complex chromatogram is shown in Fig. 2. This compound contained a tritium label, so the top trace (A) shows peaks corresponding to radioactive metabolites. The second... 

Astatine is a member of the halogen family, elements in Group 17 (VlIA) of the periodic table. It is one of the rarest elements in the universe. Scientists believe that no more than 25 grams exist on Earth s surface. All isotopes of astatine are radioactive and decay into other elements. For this reason, the element s properties are difficult to study. What is known is that it has properties similar to those of the other halogens—fluorine, chlorine, bromine, and iodine. Because it is so rare, it has essentially... 

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