Tritiated Hydrocarbons

The decay-induced unimolecular fragmentation of tritiated hydrocarbons was studied by several authors with mass spectrometric techniques. The results of the investigation carried out by Snell and Pleasonton (1958b) on monotritiated methane are shown in Table 5. The... 

The experimental procedures were adapted to allow the application of a number of physical and chemical techniques, including the use of radical scavengers, ionic interceptors, deuteriated reagents, pressure-dependence studies, competition kinetics, etc. A serious problem, already encountered in the study of the carbonium ions directly formed from the decay of tritiated hydrocarbons (vide supra), arises from the possibility that radiolytic processes, promoted by the j8-radiation of... 

Large isotope effects have also been observed by Antonovskii and Berezin (1960) in the reaction of acetyl peroxide with tritiated hydrocarbons. At 85°C the values k jk - = 6-0 and = 12-1 were found for benzene-f and toluene-< higher isotope effects were measured for the methylation of aliphatic hydrocarbons. Measurements at three temperatures (55°, 70°, 85°), showed that the isotope effect is due to both activation energy and entropy terms. 

These tritiated hydrocarbons, needed to study hydrocarbon utilization by microorganisms, have been prepared by simultaneous Kolbe electrolysis of mixtures of T-labelled... 

The gas-phase reactions of HeT with bicyclo[2.1.0]pentane, bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane (41) have been investigated and the formation of tritiated hydrocarbons retaining the bicyclic structure of the starting substrate has been observed. This finding indicates that the gaseous bicycloalkylium ions are formed via exothermic trition transfer from the HeT to the bicyclic substrate (equation 107). Due to the... 

In another experiment tritiated adamantane diazirine fixed to the hydrocarbon core of a membrane gave rise to carbene insertion into the catalytic subunit of ATP-ase. After protolytic degradation adjacent areas of the original structure became evident (80JBC(255)860). 

Kinetic studies with caesium cyclohexylamide have also been performed593. For reaction of tritiated benzene, the kinetic order was one in both hydrocarbon and caesium cyclohexylamide ion-pair (Table 180) and rate coefficients were... 

Tritiated or " C-tagged hydrocarbons (including tritium gas) can be measured by using a liquid scintillation counter or a gas proportional counter [1717,1718]. 

Experiments with rats given oral doses of tritiated food-grade mineral oil provide supporting evidence that the absorption of hydrocarbons in mineral oils is limited. Five hours after dosing with 0.66 mL/kg of tritiated mineral oil ("liquid petrolatum U.S.P."), -75% of the administered radioactivity remained in the alimentary tract, and only 3% of the administered radioactivity was accounted for by radioactivity in other parts of the rat carcass (Ebert et al. 1966). About 80% of the administered radioactivity was recovered in feces during the first 2 days after treatment, and over 90% of the radioactivity in the feces was in the form of mineral oil. These data are consistent with the hypothesis that ingested mineral oil was poorly absorbed. Neither biliary excretion nor enterohepatic circulation of mineral oils was measured in this study, and thus, any quantitative estimates of the extent of absorption based on these data should be viewed as tentative. 

Experiments with rats given oral or intraperitoneal doses of tritiated mineral oil (Liquid Petrolatum USP) indicate that orally administered hydrocarbons in mineral oil are predominately excreted rapidly, unchanged, and unabsorbed in the feces and that absorbed mineral oil is slowly excreted in the feces (presumably via biliary excretion) (Ebert et al. 1966). 

Direct Methods. The classical approach has been to prepare tritiated or carbon labeled analogs of the parent hydrocarbons which may then be used in animal or in vitro experiments. Tritiated compounds are generally easier to prepare, using exchange reactions on the parent hydrocarbon, than their 14C analogs and have higher specific activities. However, during the metabolism of such compounds, some of the tritium is released as tritiated water, either directly or... 

This tritiated water can become incorporated into the normal bases of DNA and may contribute significantly to the overall apparent binding levels measured in DNA (4). Such problems are circumvented in the case of 14C labeled hydrocarbons. Tritium labeled compounds can be prepared at sufficiently high specific activities (often 20-80 Ci/mmole) that fentomole amounts of adduct may be detected. 

An obvious pattern of the yields of the tritiated products formed from triton transfer to cyclopropane, cyclobutane, cyclopentane and cyclohexane, listed in Table 21, is represented by the regular increase of the HT yields with the molecular weight of the hydrocarbon, from 35% in c-CsHe to 75% in c-CgHi2- This finding was rationalized by assuming that the competition between triton transfer... 

It was proposed that the stabilized protonated cyclopropane can thermoneutrally transfer a proton to c-CsHg, according to reaction (58), which represents the source of the tritiated C3 hydrocarbons, namely propylene and cyclopropane, isolated with a yield of 6-7 and 19-2%, respectively ... 

Aliphatic EC>18-EC35 Fraction. Hydrocarbons in this fraction may be expected to be eliminated predominately in the feces, based on experiments with rats given oral or intraperitoneal doses of tritiated mineral oil. With oral exposure, 90% of administered radioactivity appeared rapidly (within 2 days) in the feces, predominately as unchanged mineral oil less than 10% of administered radioactivity appeared in the urine within 2 days of administration. With intraperitoneal exposure, radioactivity appeared more slowly in the feces (11% of administered radioactivity appeared in the feces within 8 days of dosing) urinary excretion of metabolites, within 8 days of dosing, represented about 8% of administered radioactivity (ATSDR 1997b). 

Site-specific tritium-labeled arenes. Taylor reports that tritium-labeled aromatics can be obtained by wetting dried ether with tritiated water, adding an aryl halide, cooling to -70°, and then adding n-butyllithium. Trimethylsilyl derivatives of aromatics can be prepared using trimethylchlorosilane in the same way. When the organometaUic intermediate is formed first and then treated with tritiated water, only the unlabeled hydrocarbon is obtained in some cases. Apparently, the cross-metalation reaction is faster than the reaction of -butyl-lithium with either water or trimethylchlorosilane. 

Before the war, using one of the earliest samples of tritium from the Radiation Laboratory c.t Berkeley, he found the rate of isomerization of n-butane to isobutane, over aluminum chloride promoted with water, was proportional to the rate of exchange of hydrogens between the hydrocarbon and a catalyst promoted with tritiated water. This observation may have been part of the stimulus for the more detailed studies with isotopic tracers of acid catalysis after the war. 

Formation of tritiated methane in both systems and the absence of C4H7 H hydrocarbons in the products indicate that production of methane involves the attack of He H on a methyl group of the substrate followed by fast dissociation of the methyl-tritiated intermediate (equation 84). The butenyl ions, C4H7, are transformed by hydride-ion abstraction from the substrate to butenes. Methane formation according to a... 

A small fraction of the ions receive in the j -transition sufficient excitation energy to cause isomerization and fragmentation of the parent molecule to tritiated C1-C5 hydrocarbons. The yields in the case of cyclopentane at 700torr have been MeT—1.6%, Et H3—0-4%, C2 H H—about 0.1%, n-Pr H—0.5%, n-Bu H—0.7%, [ H Jpent-l-ene—3.5%, combined yields of the tritiated products—6.7%. 

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