Tritium containing compounds

OtherApphca.tlons. Many appHcations of adsorption involving radioactive compounds simply parallel similar appHcations involving the same compounds in nonradio active forms, eg, radioactive carbon-14, or deuterium- or tritium-containing versions of CO2, H2O, hydrocarbons. For example, molecular sieve 2eohtes are commonly employed for these separations, just as for the corresponding nonradio active uses. 

In these examples labeling is said to be specific in that only one position in the compound contains radioactive nuclides. Alternatively, labeling may be general when all positions are labeled, which oft is the case for tritium-labeled compounds (cf. 15.6.2). 

Deuterium (and tritium) labelled compounds are not only useful for mechanistic studies but valuable information concerning both ground state and excited state properties of molecules has been obtained by the use of compounds containing isotopes of hydrogen. 

Tritium (Table 10.1) occurs in the upper atmosphere and is formed naturally by reaction 10.5, involving neutrons arriving from outer space. Tritium (see Section 3.8) was first obtained synthetically by the bombardment of deuterium-containing compounds with fast neutrons, but is now prepared from lithium deuteride, LiF or Mg/Li enriched in fLi (equation 10.6). 

Non-volatile tritium-labelled compounds have been produced, but the degree of polymerization has been found to be not very high since the intermediate carbocations participate also in other reactions which lead to shortening of the chain length (equation 132). Reaction 132c seems to be the most probable. No simple saturated aliphatic hydrocarbon has been formed in the system C H3 — CH2=CH2 . In a mixture consisting of C H3, CH2—CH2 and H2O no n-alcohols containing more than two carbon atoms have been detected. This means that the isomerization of the carbocations formed is a faster process than their reactions with water or with ethylene. The reaction... 

Both deuterium and tritium can be incorporated into a variety of hydrogen-containing compounds and used to follow (or trac the course of reactions involving these compounds. For example, one can follow the rate of absorption and excretion of water in the body by using small amounts of D2O. Some D2O is almost immediately... 

Electron Capture Detector In the electron capture detector (ECD), a beta emitter such as tritium or 63Ni is used to ionize the carrier gas. Electrons from the ionization migrate to the anode and produce a steady current. If the GC effluent contains a compound that can capture electrons, the current is reduced because the resulting negative ions move more slowly than electrons. Thus, the signal measured is the loss of electrical current. The ECD is very sensitive to materials that readily capture electrons. These materials frequently have unsaturation and electronegative substituents. Because the ECD is sensitive to water, the carrier gas must be dry. 

The extra mass associated with these labeled atoms may cause compounds containing deuterium or tritium atoms to react more slowly than compounds with ordinary hydrogen atoms. 

Useful labelled compounds containing deuterium or tritium normally require the isotopic hydrogen to be attached to carbon, so the acid-base equilibrium will require cleavage of a C-H bond, where acid... 

For reviews of compounds where chirality is due to the presence of deuterium or tritium, see Barth Djcrassi Tetrahedron 1981, 24, 4123-4142 Arigoni Eliel Top. Stereochem. 1969, 4, 127-243 Verbit Prog. Phys. Org. Chem. 1970,7,51-127. For a review of compounds containing chiral methyl groups, see Floss Tsai Woodard Top. Stereochem. 1984, 75, 253-321. 

When a 2 -Cl or -F analog of UDP was used in place of the substrate an irreversible side reaction occurred by which Cl or F, inorganic pyrophosphate, and uracil were released 349 When one of these enzyme-activated inhibitors containing 3H in the 3 position was tested, the tritium was shifted to the 2 position with loss of Cl and formation of a reactive 3 -carbonyl compound (Eq. 16-24) that can undergo P elimination at each end to give an unsaturated ketone which inactivates the enzyme. This suggested that the Fe-tyrosyl radical abstracts an electron (through a... 

By Reduction of Unsaturated Precursors The method of choice for labeling with tritium is the reduction of a suitable unsaturated precursor (containing a double bond, carbonyl group, etc.) with carrier-free tritium gas or tritiated metal hydrides. The major limitation of this method is the availability of a suitable unsaturated precursor of the desired compound. It is essential to carry out the synthesis in a non-hydroxylic solvent (dioxane, ethyl acetate, etc.). Reductions carried out in alcohol or water will lead to almost complete exchange of the tritium gas with the solvent. 

In the 18 years since its discovery, Wilkinson s catalyst has been used to hydrogenate all kinds of unsaturated compounds and great efforts have been made to develop other phosphorus ligand-containing catalysts of both rhodium and other metals. This in turn has led to catalytically active complexes which do not contain phosphorus. In Table 1 the hydrogenation of various unsaturated compounds catalysed by [RhCl(PPh3)3] is summarized. In some cases the addition of deuterium and tritium to the substrate was investigated.84,95,101,102... 

III. SYNTHESIS AND USES OF COMPOUNDS CONTAINING C=C, C=0 OR CN GROUPS LABELLED WITH TRITIUM... 

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